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  • 1. Alameldin, A.
    et al.
    El-Gabry, L. A.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Saha, Ranjan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    CFD analysis of suction and pressure side film cooling influence on vane aero performance in a transonic annular cascade2014Ingår i: Proceedings of the ASME Turbo Expo, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Operating at temperatures well above their melting point, gas turbines' components are subject to terribly high thermal stresses. In order to keep them intact and performing, different cooling techniques are implemented. One of these methods is film cooling. Film cooling implementation in vane cascades has a potential loss expense. Proper assessment of its impact on the vane performance has to be conducted. The CFD approach of modeling each hole and cooling tube autonomously is very computationally expensive. In the current work an assessment of a new, more computationally efficient CFD approach for modelling film cooling was conducted on a vane cascade operating in the transonic regime (M =0.89). The film cooling holes were represented by orifice boundary condition at the vane surface, omitting the need to model internal coolant plenum and cooling tubes mesh, resulting in 180% reduction in grid size and attributed computational cost interpreted in 300% saving in computation time. Uncooled, and film cooled with different configurations and at different blowing ratios (BR) simulations were performed and compared to experimental measurements. A good agreement was obtained for the exit flow angles, vorticity and aerodynamic loss for all the cases (uncooled and cooled). Pitch-averaged exit flow angle outside endwalls regions remains unchanged for all cooling configurations and blowing ratios. The aerodynamic loss was found to be more sensitive to increasing the blowing ratio on the suction side than on the pressure side. The proposed approach of coolant injection modeling is shown to yield reliable results, within the uncertainty of the measurements in most cases. Along with lower computational cost compared to conventional film cooling modeling approach, the new approach is recommended for further analysis for aero and thermal vane cascade flows.

  • 2.
    Baagherzadeh Hushmandi, Narmin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines2011Ingår i: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 133, nr 4, s. 041017-1-041017-12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A numerical and experimental study of partial admission in a low reaction two-stage axial air test turbine is performed in this paper. In order to model one part load configuration, corresponding to zero flow in one of the admission arcs, the inlet was blocked at one segmental arc, at the leading edge of the first stage guide vanes. Due to the unsymmetrical geometry, the full annulus of the turbine was modeled numerically. The computational domain contained the shroud and disk cavities. The full admission turbine configuration was also modeled for reference comparisons. Computed unsteady forces of the first stage rotor blades showed cyclic change both in magnitude and direction while moving around the circumference. Unsteady forces of first stage rotor blades were plotted in the frequency domain using Fourier analysis. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Unsteady forces of rotating blades in a partial admission turbine could cause unexpected failures in operation; therefore, knowledge about the frequency content of the unsteady force vector and the related amplitudes is vital to the design process of partial admission turbine blades. The pressure plots showed that the nonuniformity in the static pressure field decreases considerably downstream of the second stage's stator row, while the nonuniformity in the dynamic pressure field is still large. The numerical results between the first stage's stator and rotor rows showed that the leakage flow leaves the blade path down into the disk cavity in the admitted sector and re-enters downstream of the blocked channel. This process compensates for the sudden pressure drop downstream of the blockage but reduces the momentum of the main flow.

  • 3.
    Baagherzadeh Hushmandi, Narmin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Hu, Jiasen
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Numerical Investigation of Partial Admission Phenomena at Midspan of an Axial SteamTurbine2007Ingår i: Proceedings of 7th European Conference on Turbomachinery,Fluid Dynamics and Thermodynamics, 2007Konferensbidrag (Refereegranskat)
  • 4.
    Baagherzadeh Hushmandi, Narmin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Hu, Jiasen
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Numerical Study of Unsteady Flow Phenomena in a Partial Admission Axial Steam Turbine2008Ingår i: Proceedings of ASME Turbo EXPO 2008, New York: AMER SOC MECHANICAL ENGINEERS , 2008, s. 713-722Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a numerical investigation of unsteady flow phenomena in a two-stage partial admission axial steam turbine. Results from unsteady three-dimensional computations are analyzed and compared with the available experimental data. Partial admission in the present study is introduced into the model by blocking only one segmental arc of the inlet guide vanes. Blocking only one segment (which corresponds to the experimental setup) makes the model unsymmetrical; therefore it is necessary to model the whole annulus of the turbine. The first stage rotor blades experience large static pressure change on their surface while passing the blocked channel. The effect of blockage on the rotor blades' surface pressure can be seen few passages around the blocked channel. Strong changes of the blades' surface pressure impose large unsteady forces on the blades of first stage rotor row.

    The circumferential static pressure plots at different cross sections along the domain indicate how the non-uniformity propagates in the domain. A peak pressure drop is seen at the cross section downstream of the first stage stator row. At further downstream cross sections, the static pressure becomes more evenly distributed. Entropy generation is higher behind the blockage due to the strong mixing and other loss mechanisms involved with partial admission. Analysis of the entropy plots at different cross sections indicates that the peak entropy moves in a tangential direction while traveling to the downstream stages. Comparisons of the unsteady three-dimensional numerical results and the experimental measurement data show good agreement in tendency. However some differences are seen in the absolute values especially behind the blockage.

  • 5. Dahlqvist, Johan
    et al.
    Fridh, Jens
    A Hands-On Student Lab for the Relation Between Unsteady Aerodynamics and Structural Dynamics2016Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A small plate is excited with sound from a portable speaker. Strain gauges and a fast data acquisition unit are used to measure the variations in surface strain on the plate. This is the setup of a new student laboratory to combine theory and practice within unsteady aerodynamics and structural dynamics.

    To clearly visualize and offer important hands-on lessons for graduate students in a master’s program in aeromechanics, a lab facility has been put together for the participants to study the interaction between unsteady aerodynamics and structural dynamics.

    The facility was run the first time with students during spring this year, with successful results both in terms of measurements and learning outcomes.

  • 6.
    Dahlqvist, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Experimental flow and performance investigations of cavity purge flows in a high pressure turbine stage2015Ingår i: 11th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2015, European Conference on Turbomachinery (ETC) , 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    A high pressure turbine stage has been investigated from the aspect of flow and performance impact associated with cavity purge. Performance is referred to as the operating parameters of the turbine, mainly based on the continuous output torque monitoring. The flow parameters were studied through measurements featuring temperature and pressure throughout the flow path, as well as in the cavity. Purge and main flow velocities were quantified in the vane exit section, and degree of sealing based on purge-amount correlations and pressure readings. Results were related to turbine efficiency based on a simple correlation, and also entropy generation. Change of operating point was found to have a significant effect on degree of sealing, while the change of efficiency was found to be linear with respect to relative purge rate and independent of operating point.

  • 7.
    Dahlqvist, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Experimental Investigation of Turbine Stage Flow Field and Performance at Varying Cavity Purge Rates and Operating Speeds2018Ingår i: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 140, nr 3, artikel-id 031001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aspect of hub cavity purge has been investigated in a high-pressure axial lowreaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the cavities below the hub level from the hot main annulus flow. A fullscale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely, a high loading design case, and two high-speed points encompassing the peak efficiency. At each of these operating speeds, the amount of purge flow was varied from 0% to 2%. Observing the effect of the purge rate on measurement plane averaged parameters, a minor flow angle decrease and Mach number increase is seen for the low speed case, while maintaining near constant values for the higher operating speeds. The prominent effect due to purge is seen in the efficiency, showing a linear sensitivity to purge of 1.3%-points for every 1% of added purge flow for the investigated speeds. While spatial average values of flow angle and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible at higher span, with associated decreased turning. A radial efficiency distribution is utilized, showing negative impact through span heights from 15% to 70%. Pitchwise variation of investigated flow parameters is significantly influenced by purge flow, making this a parameter to include for instance when evaluating benefits of stator clocking positions.

  • 8.
    Dahlqvist, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    EXPERIMENTAL INVESTIGATION OF TURBINE STAGE FLOW FIELD AND PERFORMANCE AT VARYING CAVITY PURGE RATES AND OPERATING SPEEDS2016Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 2B, AMER SOC MECHANICAL ENGINEERS , 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    The aspect of hub cavity purge has been investigated in a high-pressure axial low-reaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the hot main annulus flow from cavities below the hub level. A full-scale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely a high loading case, the peak efficiency, and a high speed case. At each of these operating speeds, the amount of purge flow was varied across a very wide range of ejection rates. Observing the effect of the purge rate on measurement plane averaged parameters, a minor outlet swirl decrease is seen with increasing purge flow for each of the operating speeds while the Mach number is constant. The prominent effect due to purge is seen in the efficiency, showing a similar linear sensitivity to purge for the investigated speeds. An attempt is made to predict the efficiency loss with control volume analysis and entropy production. While spatial average values of swirl and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible in the tip region, and an associated decreased turning. A radial efficiency distribution is utilized, showing increased impact with increasing rotor speed.

  • 9.
    Dahlqvist, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Purge Flow Impact on Turbine Stage and Seal Performance at Varying Cavity Purge Rates and Operating SpeedIngår i: International Journal of Turbomachinery, Propulsion and Power, ISSN 2504-186XArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of the wheelspace cavity purge flow on a high-pressure axial low-reaction turbine stage is investigated. Both the flow's sealing ability and the performance impact associated with its injection are studied. Two operating speeds are tested, namely a high loading case and the peak efficiency, with purge flow rates covering a wide range. As the purge flow is injected upstream of the rotor, the sealing effectiveness is quantified both radially and tangentially close to the rim seal, where the tangential variation is used to identify the seal mixing region. Having passed the rotor blading, the purge flow distribution in the main annulus is quantified, showing an influence of operating speed. The purge flow core is localized to the trace of the vane wake, however somewhat migrated while passing through the blading. The combination of measurements shows that the impact on flow parameters cannot be used to determine the spanwise transport of the purge flow; hence two techniques are necessary to both judge the spanwise transport and impact on flow. With known sealing effectiveness, industry correlations may be adapted to make use of the variation of necessary purge rate to obtain a certain degree of effectiveness at a given operating point, and thereby optimize the efficiency. Also the distribution of the coolant in the main flow path may be used to optimize film cooling in that area.

  • 10.
    Dahlqvist, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    SEEDGAS INVESTIGATION OF TURBINE STAGE AND SEAL PERFORMANCE AT VARYING CAVITY PURGE RATES AND OPERATING SPEEDS2017Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2017, VOL 2A, AMER SOC MECHANICAL ENGINEERS , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    The topic of hub cavity purge is investigated in a high-pressure axial low-reaction turbine stage. Both the sealing ability of the purge flow and the performance impact associated with its injection into the main flow are studied. Three operating speeds are investigated, namely a high loading case, the peak efficiency, and a high speed case, and purge flow rates across a wide range. The operating points coincide with investigations previously reported, where the flow field and stage efficiency was quantified using pneumatic probes. Comparative measurements are also performed, varying a leakage flow through the rotor below the hub platform. The purge flow is now seeded with CO2 in order to measure its distribution throughout the stage, as it is injected into the wheelspace upstream of the rotor, allowing for quantification of the sealing effectiveness. This is done at a number of defined locations along the stator-side wall in the wheel space, resolving the radial variation through the cavity. Important radial variations of effectiveness are observed, confirming that the flow is in the regime of merged boundary layers, due to the narrow cavity, as compared to typical gas turbine operation with separated. boundary layers. The trends are found to be related to operating speed and platform leakage. With known sealing effectiveness, industry correlations may be adapted to make use of the variation of necessary purge rate to obtain a certain degree of sealing at a given operating point, and thereby optimize the efficiency. In addition to quantification of potential hot-gas ingestion, the paper initiates an investigation of the transport of the purge flow in the main annulus, through sampling on the hub, as well as area traverse downstream of the rotor. The amount of sealing gas leads to opportunity to quantify the cooling performance of the purge flow in the main annulus. Both the cooling performance in the main annulus and cavity are shown to be significantly influenced by the rotor leakage, while its effect on efficiency is minor.

  • 11.
    Dahlqvist, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten H
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    TEST TURBINE INSTRUMENTATION FOR CAVITY PURGE INVESTIGATIONS2014Ingår i: The XXII Symposium on Measuring Techniques in Turbomachinery, Lyon, 4-5 September 2014, 2014Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The upstream wheelspace of the KTH Test Turbine has been instrumented with the aim of investigating cavity flow phenomena, as well as cavity-main annulus interaction. Measurements include static pressure, unsteady pressure and temperature.The stage used is of high pressure steam turbine design. The trials include investigating the design point and also a high pressure, high speed operating point, assimilating gas turbine operation. At each point, varying amounts of purge flow are superposed and the influences on the measurements studied.Initial results show considerable dependence of both operating

  • 12. El-Gabry, Lamyaa
    et al.
    Saha, Ranjan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Measurements of Hub Flow Interaction on Film Cooled Nozzle Guide Vane in Transonic Annular Cascade2015Ingår i: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 137, nr 8, artikel-id 081004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental study has been performed in a transonic annular sector cascade of nozzle guide vanes (NGVs) to investigate the aerodynamic performance and the interaction between hub film cooling and mainstream flow. The focus of the study is on the endwalls, specifically the interaction between the hub film cooling and the mainstream. Carbon dioxide (CO2) has been supplied to the coolant holes to serve as tracer gas. Measurements of CO2 concentration downstream of the vane trailing edge (TE) can be used to visualize the mixing of the coolant flow with the mainstream. Flow field measurements are performed in the downstream plane with a five-hole probe to characterize the aerodynamics in the vane. Results are presented for the fully cooled and partially cooled vane (only hub cooling) configurations. Data presented at the downstream plane include concentration contour, axial vorticity, velocity vectors, and yaw and pitch angles. From these investigations, secondary flow structures such as the horseshoe vortex, passage vortex, can be identified and show the cooling flow significantly impacts the secondary flow and downstream flow field. The results suggest that there is a region on the pressure side (PS) of the vane TE where the coolant concentrations are very low suggesting that the cooling air introduced at the platform upstream of the leading edge (LE) does not reach the PS endwall, potentially creating a local hotspot.

  • 13. El-Gabry, Lamyaa
    et al.
    Saha, Ranjan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Measurements of Hub Flow Interaction on Film Cooled Nozzle Guide Vane in Transonic Annular Cascade2012Ingår i: Proceedings of the ASME Turbo Expo, ASME Press, 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    An experimental study has been performed in a transonic annular sector cascade of nozzle guide vanes to investigate the aerodynamic performance and the interaction between hub film cooling and mainstream flow. The focus of the study is on the endwalls, specifically the interaction between the hub film cooling and the mainstream. Carbon dioxide (CO2) has been supplied to the coolant holes to serve as tracer gas. Measurements of CO2 concentration downstream of the vane trailing edge can be used to visualize the mixing of the coolant flow with the mainstream.

    Flow field measurements are performed in the downstream plane with a 5-hole probe to characterize the aerodynamics in the vane. Results are presented for the fully cooled and partially cooled vane (only hub cooling) configurations. Data presented at the downstream plane include concentration contour, axial vorticity, velocity vectors, and yaw and pitch angles. From these investigations, secondary flow structures such as the horseshoe vortex, passage vortex, can be identified and show the cooling flow significantly impacts the secondary flow and downstream flow field. The results suggest that there is a region on the pressure side of the vane trailing edge where the coolant concentrations are very low suggesting that the cooling air introduced at the platform upstream of the leading edge does not reach the pressure side endwall, potentially creating a local hotspot.

  • 14.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Experimental Investigation of Performance, Flow Interactions and Rotor Forcing in Axial Partial Admission Turbines2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Denna sammanläggningsavhandling består av fyra artiklar och föregås av en sammanfattning med kompletterande bilagor. Kärnan av undersökningen är experimentell även om referenser och jämförelser med numeriska modeller förekommer där så bedöms lämpligt. Det första steget i en industriell ångturbin kallas reglersteg om partialpådrag tillämpas. Det används rutinmässigt i kraftvärmeanläggningar som ofta körs vid dellaster för att åstadkomma en hög dellastverkningsgrad och hög stegeffekt. Inloppsflödet delas in separata och individuellt strypreglerade pådragsbågar som leder till det första munstycksgittret. Ibland används partialpådrag i små turbiner för att undvika korta blad och på så sätt minska takläckage och ändväggsförlusternas inflytande på den totala förlusten. Det finns i huvudsak tre aerodynamiska/aeromekaniska egenheter som bör beaktas. Först det första är det speciella aerodynamiska förluster associerade till partialpådrag eller reglersteget: ventilations-, tömnings och fyllningsförluster. För det andra, om det är en flerstegsturbin påverkas också nedströms steg negativt av det asymmetriska flödet runt omkretsen som innefattar stora tryckvariationer och flödesvinkelvariationer. För det tredje är den aeromekaniska situationen speciell jämfört med ett fullpådraget steg. För partialpådrag existerar dynamiska krafter med snabba laständringar vid in och utpassering i pådragsbågen. Även om det existerar generella förklaringar i den öppna litteraturen angående förluster så har inte förlustmekanismerna utretts i samma omfattning jämfört med fullpådrag. Ingen generell förlustkorrelation finns. Utmattning på grund oförutsedda excitationsfrekvenser, underskattade kraftamplituder eller en kombination av båda orsakar reglerstegshaveri för ångturbinintressenter. De huvudsakliga målsättningarna med denna studie är att experimentellt utforska och bestämma prestanda och förluster för ett stort antal partialpådragskonfigurationer. Samt att genomföra en vibrationsanalys (relaterat till aerodynamiska kraftimpulser) utifrån mätdata från provturbinen avhandlad häri. Detta för att kartlägga de aeromekaniska förutsättningarna och om möjligt identifiera egenheter viktiga för konstruktion av reglersteg. Prestandamätningar rörande verkningsgradstrender och generella strömningsvariationer runt omkretsen bekräftar resultat från den öppna litteraturen och därmed demonstrerar dugligheten av den partialpådragskonfiguration som används i luftprovturbinen. Dessutom visar resultaten bland annat att reaktionsgraden varierar kraftigt runt omkretsen med stora variationer i rotorns utloppsvinkel inte enbart i anslutning till sektorändar utan långt in i pådragssektorn. Flödeskapacitetskoefficienten eller turbinkonstanten ökar med minskat pådrag och fyllningsprocessen genererar stora variationer i rotorns inloppsvinkel förknippade med höga förluster. Det är viktigt att beakta dellastförutsättningarna och verkningsgradsminskningen för nedströms steg. Genom att använda två pådragsbågar istället för en för ett givet pådrag av 52,4% minskar partialpådragsförlusterna för nedströmssteget med nästan 10 % vid designpunkten, härlett från mätningar. Samlade medelvärden från roterande instationära mätningar visar på en fördubbling av det relativa dynamiska trycket vid rotortömning jämfört med en opåverkad del av pådragsbågen. Vibrationsanalys (relaterat till aerodynamiska kraftimpulser) av mätdata avslöjar att partialpådrag orsakar en stor mängd kraftimpulser med låga varvtalsmultiplar, främst från ventilationen och påavlastningsprocesserna. För provturbinen så är det helt och hållet kombinationer mellan antalet rotorblad och dessa kraftimpulser som orsakar strömningspåverkade vibrationer. Ett möjligt tillvägagångssätt konstruktionsmässigt för att ändra kraftspektrumet är att ändra längförhållandet mellan pådragen och blockerad del.

  • 15.
    Fridh, Jens
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Bunkute, Birute
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fakhrai, Reza
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    An experimental study on partial admission in a two-stage axial air test turbine with numerical comparisons2004Ingår i: Proceedings of the ASME Turbo Expo 2004, Vienna, 2004, Vol. 5 B, s. 1285-1297Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents ongoing experimental aerodynamic and efficiency measurements on a cold flow two-stage axial air test turbine with low reaction steam turbine blades at different degrees of partial admission. The overall objectives of the work are to experimentally investigate and quantify the steady and unsteady aerodynamic losses induced by partial admission. The first results show that both the total-to-static turbine efficiency drops and that the efficiency peak appears at lower isentropic velocity ratios with lower degrees of admission. Detailed steady traverse measurements of the static wall pressures downstream of sector-ends show strong local variations. The pressure wake from the partial admission blockage moves almost axially through the turbine while the temperature wake is located in a tangential position that represents the position of a particle trace based on velocity triangles, in the direction of the rotor rotation. Comparisons with 2D compressible flow computations around the circumference demonstrate the importance of the radial flow component in these experiments.

  • 16.
    Fridh, Jens
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Andersson, Nils-Erik
    Siemens Industrial Turbomachinery AB.
    Magnusson, Peter
    Siemens Industrial Turbomachinery AB.
    REDUNDANT ROTATING MEASUREMENTS IN AN AXIAL COLD FLOW TEST TURBINE: Development and Procedure2006Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A rotating measurement system has been designed and commissioned for a cold flow test turbine and tested under the influence of partial admission. A shrouded turbine rotor of impulse design is equipped with miniature pressure transducers and strain gauges. This paper discusses the selected experimental design and procedure. Overall, the first test runs went well and necessary data were collected and could be evaluated accordingly. Encountered specific measurement technique problems are addressed where the importance of high redundancy is stressed. Results demonstrate one effect that imbedded sensor technology may encounter as regards of dynamic measurements and calibrations.

  • 17.
    Fridh, Jens
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Laumert, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Forced Response in axial turbines under the influence of partial admission2012Ingår i: ASME Turbo Expo 2012 - Turbine Technical Conference and Exposition, Copenhagen, June 11-15, 2012: Volume 7, Issue PARTS A AND B, 2012, ASME Press, 2012, s. 1419-1429Konferensbidrag (Refereegranskat)
    Abstract [en]

    High cycle fatigue (HCF) due to unforeseen excitation frequencies or due to under predicted force magnitudes, or a combination of both causes control stage failures for steam turbine stakeholders. The objectives of this paper is to provide an extended design criteria toolbox and validation data for control stage design based on experimental data, with the aim to decrease HCF incidents for partial admission turbines. The upstream rotor in a two stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees stretching from 28.6% to 100% as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of first stator vanes by aerodynamically shaped filling blocks. Sweeps across a speed range from 50 to 105% of design speed are performed at constant turbine pressure ratio during simultaneous high speed acquisition. A forced response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low engine order forced responses because of the blockage, pumping, loading and unloading processes. Combinations of the number of rotor blades and low engine order excitations are the principal sources of forced response vibrations for the turbine studied herein. Altering the stator and/or rotor pitches will change the excitation pattern. A relation between the circumferential lengths of the admitted and non-admitted arcs that dictates the excitation forces is observed that may serve as a design parameter.

  • 18.
    Fridh, Jens
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Laumert, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Forced Response in Axial Turbines Under the Influence of Partial Admission2013Ingår i: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 135, nr 4, s. 041014-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High cycle fatigue (HCF) due to unforeseen excitation frequencies, underestimated force magnitudes, or a combination of both causes control-stage failures for steam turbine stakeholders. This paper provides an extended design criteria toolbox, as well as validation data, for control-stage design based on experimental data to reduce HCF incidents in partial-admission turbines. The upstream rotor in a two-stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees extend from 28.6% to 100%, as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of the first stator vanes with aerodynamically shaped filling blocks. Sweeps across a speed range of 50%-105% of design speed are performed at a constant turbine pressure ratio during simultaneous high-speed acquisition. A forced-response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low-engine-order forced responses because of the blockage, pumping, loading, and unloading processes. Combinations of the number of rotor blades and low-engine-order excitations are the principal sources of forced-response vibrations for the turbine studied here. Altering the stator and/or rotor pitches changes the excitation pattern. We observed that a relationship between the circumferential lengths of the admitted and nonadmitted arcs dictates the excitation forces and may serve as a design parameter.

  • 19.
    Fridh, Jens
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Wikström, Rolf
    Siemens Industrial Turbomachinery AB.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    DYNAMIC FEATURES OF PARTIAL ADMISSION: OUTCOMES FROM ROTATING MEASUREMENTS2007Ingår i: Euroturbo 7: Proceedings of the 7th European Conference on Turbomachinery, Fluid Dynamics and Thermodynamics, Athens: Local Conference Organising Committee , 2007, s. 451-462Konferensbidrag (Refereegranskat)
    Abstract [en]

    A system for rotating measurements has been designed and commissioned for a two-stage axial turbine of impulse design. Relative total pressure and strain gauge measurements in the rotating frame of reference have been performed during partial admission tests in this turbine. The overall project objectives are to determine unsteady aerodynamic losses related to admission sector-ends and rotor forcing functions. Some outcomes are presented and discussed herein. The unsteadiness in the measured relative total pressure is observed to be largest downstream of the suction side of the partial admission blockage where the high momentum fluid vividly interacts with the rotor. Strain gauge results show a high strain peak downstream of the suction side of the blockage. When reducing the shaft speed at constant pressure ratio, the dip in relative total pressure and the peak in tensile strain, that occur when a blade enters the blocked region, are shifted in the counter rotational direction. This is believed to reflect earlier emptying of the rotor blade channel. Furthermore, an increase of the flow capacity coefficient with a decrease of admission degree has been observed.

  • 20.
    Horwood, Joshua T. M.
    et al.
    Univ Bath, Dept Mech Engn, Bath, Avon, England..
    Hualca, Fabian P.
    Univ Bath, Dept Mech Engn, Bath, Avon, England..
    Wilson, Mike
    Univ Bath, Dept Mech Engn, Bath, Avon, England..
    Scobie, James A.
    Univ Bath, Dept Mech Engn, Bath, Avon, England..
    Sangan, Carl M.
    Univ Bath, Dept Mech Engn, Bath, Avon, England..
    Lock, Gary D.
    Univ Bath, Dept Mech Engn, Bath, Avon, England..
    Dahlqvist, Johan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi. KTH, Tidigare Institutioner (före 2005), Energiteknik.
    FLOW INSTABILITIES IN GAS TURBINE CHUTE SEALS2019Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2019, VOL 5B, ASME Press, 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    The ingress of hot annulus gas into stator-rotor cavities is an important topic to engine designers. Rim-seals reduce the pressurised purge required to protect highly-stressed components. This paper describes an experimental and computational study of flow through a turbine chute seal. The computations which include a 360 degrees domain - were undertaken using DLR TRACE's time-marching solver. The experiments used a low Reynolds number turbine rig operating with an engine-representative flow structure. The simulations provide an excellent prediction of cavity pressure and swirl, and good overall agreement of sealing effectiveness when compared to experiment. Computation of flow within the chute seal showed strong shear gradients which influence the pressure distribution and secondary-flow field near the blade leading edge. High levels of shear across the rim-seal promote the formation of large-scale structures at the wheel-space periphery; the number and speed of which were measured experimentally and captured, qualitatively and quantitatively, by computations. A comparison of computational domains ranging from 30 degrees to 360 degrees indicate that steady features of the flow are largely unaffected by sector size. However, differences in large-scale flow structures were pronounced with a 60 degrees sector and suggest that modelling an even number of blades in small sector simulations should be avoided.

  • 21.
    Mamaev, Boris
    et al.
    Siemens LLC Energy Oil & Gas Design Department, Russia.
    Saha, Ranjan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Aerodynamic investigation of turbine cooled vane block2015Ingår i: Thermal Engineering, ISSN 0040-6015, Vol. 62, nr 2, s. 97-102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The vane block (VB) has been investigated and it gives several important results related to test methods and calculation procedures. The vane block is characterized by a developed film and convective cooling system. Blowing tests demonstrate that there is a weak correlation between cooling type and energy loss. Superposition of these effects is true for the central part over VB height without secondary flows. Coolant discharge increases profile loss and it rises if coolant flow rate is increased. Discharge onto profile convex side through the trailing edge slot influences the most considerably. The discharge through perforation decreases the vane flow capacity and insufficiently influences onto the flow outlet angle, but the trailing edge discharge increases this angle according to loss and mixture flow rate growth. The secondary flows reduce the effect of coolant discharge, which insufficiently changes losses distribution at turbine blades tips and even decreases the secondary losses. The flow outlet angle rises significantly and we are able to calculate it only if we correct the ordinary flow model. In the area of secondary flows, the outlet angle varies insufficiently under any type of cooling. This area should be investigated additionally.

  • 22. Mamaev, Boris
    et al.
    Saha, Ranjan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    The influence of a special fillet between the endwall and airfoil at the leading edge on the performance of the turbine nozzle diaphragm2013Ingår i: Thermal Engineering, ISSN 0040-6015, Vol. 60, nr 3, s. 217-222Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is shown from the results of experimental investigations carried out on a nozzle diaphragm’s sector that an enlarged fillet at the vane leading edge does not have an essential effect on the flow and energy losses in the nozzle diaphragm

  • 23.
    Mironovs, A.
    et al.
    D un D Centrs.
    Doronkins, P.
    D un D Centrs.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    MODELING OF VARIABLE AERODYNAMIC FORCES IN TURBINE BASED ON EXPERIMENTAL DATA2009Ingår i: Proceedings of the 12th International Symposium on Unsteady Aerodynamics, Aeroacoustics & Aeroelasticity of Turbomachines ISUAAAT12 1-4 September 2009, Imperial College London, UK, Imperial College Press, 2009Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Effective methods of vibration diagnostics of a turbomachine’s flow duct are necessary for efficient condition based maintenance. Modern equipments provide extended opportunities for vibration measurements. However, there are few adequate models of high frequency vibration. A majority of the existing diagnostic techniques are limited within the low frequency range. This paper suggests the variable forces model intended for high frequency vibration diagnostics. For modeling of variable forces acting on the vane the test series are performed using a two-stage air test turbine. High frequency signals of total pressure and casing vibration are measured in order to investigate the airflow and vibration structure generated by the blades. Parameters of the blade wake are investigated and the wake’s dual nature is determined. Harmonic and random components of blade wakes are related to specific blade aerodynamic features as well as upstream airflow characteristics. Air duct failures are simulated with upstream static and rotating disturbances. The model of flow velocity oscillation, which acconts for both harmonic and random features of blade wakes is presented. Dynamic forces acting on a single vane are also modeled based on the model of blade wakes.

  • 24.
    Noor, Hina
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Genrup, Magnus
    Lund Univ, Dept Energy Sci, S-22100 Lund, Sweden..
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    INVESTIGATION OF ONE-DIMENSIONAL TURBINE DESIGN PARAMETERS WITH RELATION TO COOLING PARAMETERS FOR A HIGH PRESSURE INDUSTRIAL GAS TURBINE STAGE2011Ingår i: 9TH EUROPEAN CONFERENCE ON TURBOMACHINERY: FLUID DYNAMICS AND THERMODYNAMICS, VOLS I AND II / [ed] Sen, M Bois, G Manna, M Arts, T, EUROPEAN TURBOMACHINERY SOC-EUROTURBO , 2011, s. 557-568Konferensbidrag (Refereegranskat)
    Abstract [en]

    This parametric study describes the effects of design parameters on coolant consumption and performance loss of the first stage of a high pressure industrial gas turbine. The Lund University Axial Turbine (LUAX-T) tool is employed to develop a better coupling between design parameters, cooling air and aerodynamic losses. From the performed design study; a lower stage reaction degree decreases the rotor coolant requirement, mainly due to a resulting decrease in rotor inlet temperature. However, a low reaction degree increases the cooling losses for the vane, which is because of a direct proportion between the mixing losses and the local Mach number. Based on the performed calculations and loss predictions, a range of design parameters is recommended for first stage of a gas turbine, while considering the influence of this choice on the next stage. The loss calculated for the stator blade has been calibrated against existing experimental data.

  • 25.
    Noor, Hina
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Genrup, Magnus
    Department of Energy Sciences, Lund University, Sweden.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Investigation of one-dimensional turbine design parameters with relation to cooling parameters for high pressure industrial gas turbine stage2011Ingår i: The 9th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, 2011Konferensbidrag (Refereegranskat)
  • 26.
    Petrov, Miroslav
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Göransson, Åke
    Siemens Industrial Turbomachinery AB, Finspång.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    High-speed Steam Turbine Systems for Distributed Generation Applications2012Ingår i: Proceedings of the ASME 2012 Power Conference. Power 2012, ASME Press, 2012, s. 7-Konferensbidrag (Refereegranskat)
    Abstract [en]

    The efficiency of utilization of low-grade solid fuels of either renewable or fossil origin such as biomass, municipal or agricultural wastes, peat, lignite, etc. for distributed generation applications and combined heat and power (CHP) production at small scales can be improved by a simple technology shift. This study evaluates the technical feasibility of a compact power generation package comprising a small steam turbine directly coupled to a high-speed alternator delivering around 2 MW of electricity. Existing high-speed electrical generators at MW-scale are presented and reviewed, and a basic thermodynamic design and flow-path analysis of a steam turbine able to drive such a generator is attempted. Most importantly, the speed-controlled turbogenerator arrangement promises improved electrical efficiency especially at part-load (in off-design mode), compared to the typically low off-design performance of small-scale steam cycles using state-of-art fixed speed turbines. High-speed alternators with related power electronics are nowadays becoming increasingly available for the MW-size market. One such product – a commercial 2 MW permanent-magnet alternator running at 22,500 rpm – has been used as a reference for evaluating the behavior of a speed-controlled steam turbine as a prime mover. The specific turbine losses due to its comparatively small size remain serious. However, a low steam parameter approach suits well for converting, for example, heat-only boilers into CHP units, adding value by local electricity production at affordable costs. Steam superheat temperatures of around or less than 350 C (660 F) would keep the steam volumetric flow sufficiently high in order to restrain the turbine losses and allow for a cost-effective electricity production for enhanced utilization of locally-available solid fuels via steam cycles. Such a steam turbine is possible to manufacture and would deliver a promising performance despite its small size. The possibility for the turbine to be speed-controlled and its characteristics thereof have been evaluated by computer simulations using the in-house code AXIAL by courtesy of the Swedish branch of Siemens Industrial Turbomachinery, steam turbine division. Simulation results show that a reasonable improvement in part-load performance can be achieved for the high-rpm turbine-generator drivetrain: up to 30% better in the load spectrum down to 50% of nominal output, if compared with a fixed-speed arrangement of similar size and parameters.

  • 27.
    Petrov, Miroslav
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Göransson, Åke
    Fransson, Torsten H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    High-Speed Steam Turbine Systems For Small-Scale Power Generation Applications2012Ingår i: Proceedings of the 20th International Conference on Nuclear Engineering collocated with the ASME 2012 Power Conference: ICONE20-POWER2012, American Society of Mechanical Engineers ASME, ASME Press, 2012, s. 651-657Konferensbidrag (Refereegranskat)
    Abstract [en]

    Energy utilization from low-grade fuels of either fossil or renewable origin, or from medium-temperature heat sources such as solar, industrial waste heat, or small nuclear reactors, for small-scale power generation via steam cycles, can be reasonably enhanced by a simple technology shift. This study evaluates the technical feasibility of a compact power generation package comprising a steam turbine directly coupled to a high-speed alternator delivering around 8 - 12 MW of electrical power. Commercial or research-phase high-speed electrical generators at MW-scale are reviewed, and a basic thermodynamic design and flow-path analysis of a steam turbine able to drive such a generator is attempted. High-speed direct drives are winning new grounds due to their abilities to be speed-controlled and to avoid the gearbox otherwise typical for small system drivetrains. These two features may offer a reasonable advantage to conventional drives in terms of higher reliability and better economy. High-speed alternators with related power electronics are nowadays becoming increasingly available for the MW-size market. A generic 8 to 12 MW synchronous alternator running respectively at 15,000 to 10,000 rpm, have been used as a reference for evaluating the fundamental design of a directly coupled steam turbine prime mover. The moderate steam parameter concept suits well for converting mid-temperature thermal energy into electrical power with the help of low-tech steam cycles, allowing for distributed electricity production at reasonable costs and efficiency. Steam superheat temperatures below 350 degrees C (660 degrees F) at pressures of maximum 20 bar would keep the steam volumetric flow sufficiently high in order to restrain the turbine losses typical for small-scale turbines, while helping also with simpler certification and safety procedures and using primarily established technology and standard components. The proposed steam turbines designs and their characteristics thereof have been evaluated by computer simulations using the in-house code ProSteam and its sub-procedures AXIAL and VaxCalc, by courtesy of Siemens Industrial Turbomachinery and its steam turbine division located in Finspong, Sweden. The first results from this study show that high-speed steam turbines of the proposed size and type are possible to design and manufacture based on conventional components, and can be expected to deliver a very satisfactory performance at variable power output.

  • 28.
    Saha, Ranjan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Aerodynamic Investigation of External Cooling and Applicability of Superposition2015Ingår i: 11th EUROPEAN CONFERENCE ON TURBOMACHINERY FLUID DYNAMICS AND THERMODYNAMICS, EUROPEAN TURBOMACHINERY SOC-EUROTURBO , 2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    An experimental investigation of the overall external cooling on a cooled nozzle guide vanehas been conducted in a transonic annular sector cascade. The investigated vane is a typicaltransonic high pressure gas turbine vane, geometrically similar to a real engine component.The investigations are performed for various coolant-to-mainstream mass-flux ratios. Resultsindicate that the aerodynamic loss is influenced substantially with the change of the coolingflow. Area-averaged exit flow angles in midspan region are unaffected at moderate filmcoolant flows, for all cooling configurations except for trailing edge cooling. The trailing edgecooling decreases the turning in all investigated cases. Results lead to a conclusion that bothtrailing edge and suction side cooling have significant influence on the aerodynamic losswhereas the shower head cooling is less sensitive to the loss. Investigations with individualcooling features essentially lead to the applicability of the superposition technique regardingthe aerodynamic loss for film cooled vanes, which is this paper’s contribution to the researchfield. Results show that the superposition technique can be used for the profile loss but not forthe secondary loss.

  • 29. Saha, Ranjan
    et al.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Annerfeldt, Mats
    Aerodynamic implications of reduced vane count2015Ingår i: Proceedings of the ASME Turbo Expo, ASME Press, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    Given the shortage of fossil fuels and the growing greenhouse effect, one strive in modern gas turbines is to make maximum usage of the burnt fuel. By reducing the number of vanes or blades and thereby increasing the loading per vane (or blade) it is possible to spend less cooling air, which will have a positive impact on the combined cycle efficiency. It also reduces the number of components and usage of metal and thereby also the cost of the engine. These savings should be achieved without any efficiency deficit in aerodynamic efficiency. Based on the fact, aerodynamic investigations were performed to see the aerodynamic implications of reduced vane number in a transonic annular sector cascade. The number of new nozzle guide vane was reduced with 24% compared to a previous design with higher vane count. The investigated vanes were two typical high pressure gas turbine vanes. Results regarding the loading indicated an expected increase with the reduced vane case. The minimum static pressure at the suction side is lower and at an earlier location for the reduced vane case and therefore, an extension of the trailing edge deceleration zone is observed for the reduced vane case. Results regarding losses indicate that even though the losses produced per vane significantly increases for the reduced vane case, a comparison of mass averaged losses between the reduced vane case and previous vane case show similar spanwise loss distributions. Assessing results leads to a conclusion that the reduction of the number of vanes in the first stage seems to be a useful method to save cooling flow as well as material costs without any significant deficit in overall efficiency.

  • 30.
    Saha, Ranjan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Annerfeldt, Mats
    Aerodynamic Implication of Endwall and Profile Film Cooling in a Transonic Annular Cascade2013Ingår i: 21st ISABE Conference / [ed] ISABE, Busan, Korea, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    An experimental study is performed to observe the aerodynamic implications of endwall and profile film cooling on flow structures and aerodynamic losses. The investigated vane is a geometrically similar transonic nozzle guide vane with engine-representative cooling geometry. Furthermore, a new formulation of the cooling aerodynamic loss equation is presented and compared with the conventional methods. Results from a 5-hole pneumatic probe show that the film coolant significantly alters the secondary flow structure. The effect of different assumptions for the loss calculation is shown to significantly change the measured loss.

  • 31.
    Saha, Ranjan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Mamaev, Boris
    Annerfeldt, Mats
    Experimental studies of leading edge contouring influence on secondary losses in transonic turbines2012Ingår i: ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, ASME Press, 2012, s. 1109-1119Konferensbidrag (Refereegranskat)
    Abstract [en]

    An experimental study of the hub leading edge contouring using fillets is performed in an annular sector cascade to observe the influence of secondary flows and aerodynamic losses. The investigated vane is a three dimensional gas turbine guide vane (geometrically similar) with a mid-span aspect ratio of 0.46. The measurements are carried out on the leading edge fillet and baseline cases using pneumatic probes. Significant precautions have been taken to increase the accuracy of the measurements. The investigations are performed for a wide range of operating exit Mach numbers from 0.5 to 0.9 at a design inlet flow angle of 90°. Data presented include the loading, fields of total pressures, exit flow angles, radial flow angles, as well as profile and secondary losses. The vane has a small profile loss of approximately 2.5 % and secondary loss of about 1.1%. Contour plots of vorticity distributions and velocity vectors indicate there is a small influence of the vortex-structure in endwall regions when the leading edge fillet is used. Compared to the baseline case the loss for the filleted case is lower up to 13 % of span and higher from 13% to 20 % of the span for a reference condition with Mach no. of 0.9. For the filleted case, there is a small increase of turning up to 15 % of the span and then a small decrease up to 35 % of the span. Hence, there are no significant influences on the losses and turning for the filleted case. Results lead to the conclusion that one cannot expect a noticeable effect of leading edge contouring on the aerodynamic efficiency for the investigated 1st stage vane of a modern gas turbine.

  • 32.
    Saha, Ranjan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Mamaev, Boris
    Siemens LLC Energy Oil & Gas Design Department, Russia.
    Annerfeldt, Mats
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Suction and Pressure Side Film Cooling Influence on Vane Aero Performance in a Transonic Annular Cascade2013Ingår i: Proceedings of the ASME Turbo Expo, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    An experimental study on a film cooled nozzle guide vane has been conducted in a transonic annular sector to observe the influence of suction and pressure side film cooling on aerodynamic performance. The investigated vane is a typical high pressure gas turbine vane, geometrically similar to a real engine component, operated at an exit reference Mach number of 0.89. The aerodynamic results using a five hole miniature probe are quantified and compared with the baseline case which is uncooled. Results lead to a conclusion that the aerodynamic loss is influenced substantially with the change of the cooling flow rate regardless the positions of the cooling rows. The aerodynamic loss is very sensitive to the blowing ratio and a value of blowing ratio higher than one leads to a considerable higher loss penalty. The suction side film cooling has larger influence on the aerodynamic loss compared to the pressure side film cooling. Pitch-averaged exit flow angles around midspan remain unaffected at moderate blowing ratio. The secondary loss decreases (greater decrease in the tip region compared to the hub region) with inserting cooling air for all cases compared to the uncooled case.

  • 33.
    Saha, Ranjan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Mamaev, Boris
    Annerfeldt, Mats
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Utriainen, Esa
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Shower Head and Trailing Edge Cooling Influence on Transonic Vane Aero Performance2014Ingår i: ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, ASME Press, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    An experimental investigation on a cooled nozzle guide vane has been conducted in an annular sector to quantify aerodynamic influences of shower head and trailing edge cooling. The investigated vane is a typical high pressure gas turbine vane, geometrically similar to a real engine component, operated at a reference exit Mach number of 0.89. The investigations have been performed for various coolant-to-mainstream mass-flux ratios. New loss equations are derived and implemented regarding coolant aerodynamic losses. Results lead to a conclusion that both trailing edge cooling and shower head film cooling increase the aerodynamic loss compared to an uncooled case. In addition, the trailing edge cooling has higher aerodynamic loss compared to the shower head cooling. Secondary losses decrease with inserting shower head film cooling compared to the uncooled case. The trailing edge cooling appears to have less impact on the secondary loss compared to the shower head cooling. Area-averaged exit flow angles around midspan increase for the trailing edge cooling.

  • 34.
    Saha, Ranjan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Mamaev, Boris
    Annerfeldt, Mats
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Utriainen, Esa
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Shower Head and Trailing Edge Cooling Influence on Transonic Vane Aero Performance2014Ingår i: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 136, nr 11, s. 111001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental investigation on a cooled nozzle guide vane (NGV) has been conducted in an annular sector to quantify aerodynamic influences of shower head (SH) and trailing edge (TE) cooling. The investigated vane is a typical high pressure gas turbine vane, geometrically similar to a real engine component, operated at a reference exit Mach number of 0.89. The investigations have been performed for various coolant-to-mainstream mass-flux ratios. New loss equations are derived and implemented regarding coolant aerodynamic losses. Results lead to a conclusion that both TE cooling and SH film cooling increase the aerodynamic loss compared to an uncooled case. In addition, the TE cooling has higher aerodynamic loss compared to the SH cooling. Secondary losses decrease with inserting SH film cooling compared to the uncooled case. The TE cooling appears to have less impact on the secondary loss compared to the SH cooling. Area-averaged exit flow angles around midspan increase for the TE cooling.

  • 35.
    Saha, Ranjan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Mamaev, Boris
    Siemens LLC Energy Oil & Gas Design Department, Russia.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Laumert, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Influence of Prehistory and Leading Edge Contouring on Aero Performance of a Three-Dimensional Nozzle Guide Vane2014Ingår i: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 136, nr 7, s. 071014-1-071014-10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments are conducted to investigate the effect of the prehistory in the aerodynamic performance of a three-dimensional nozzle guide vane with a hub leading edge contouring. The performance is determined with two pneumatic probes (five hole and three hole) concentrating mainly on the end wall. The investigated vane is a geometrically similar gas turbine vane for the first stage with a reference exit Mach number of 0.9. Results are compared for the baseline and filleted cases for a wide range of operating exit Mach numbers from 0.5 to 0.9. The presented data includes loading distributions, loss distributions, fields of exit flow angles, velocity vector, and vorticity contour, as well as mass-averaged loss coefficients. The results show an insignificant influence of the leading edge fillet on the performance of the vane. However, the prehistory (inlet condition) affects significantly in the secondary loss. Additionally, an oil visualization technique yields information about the streamlines on the solid vane surface, which allows identifying the locations of secondary flow vortices, stagnation line, and saddle point.

  • 36.
    Saha, Ranjan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Mamaev, Boris
    Siemens LLC Energy Oil & Gas Design Department, Rusia.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Laumert, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Influence of pre-history and leading edge contouring on aero-performance of a 3D nozzle guide vane2013Ingår i: Proceedings of the ASME Gas Turbine India Conference -2013- ; presented at ASME 2013 Gas Turbine India Conference, December 5-6, 2013, Bangalore, India, ASME Press, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Experiments are conducted to investigate the effect of the pre-history in the aerodynamic performance of a threedimensional nozzle guide vane with a hub leading edge contouring. The performance is determined with two pneumatic probes (5 hole and 3 hole) concentrating mainly on the endwall. The investigated vane is a geometrically similar gas turbine vane for the first stage with a reference exit Mach number of 0.9. Results are compared for the baseline and filleted cases for a wide range of operating exit Mach numbers from 0.5 to 0.9. The presented data includes loading distributions, loss distributions, fields of exit flow angles, velocity vector and vorticity contour, as well as, mass-averaged loss coefficients. The results show an insignificant influence of the leading edge fillet on the performance of the vane. However, the pre-history (inlet condition) affects significantly in the secondary loss. Additionally, an oil visualization technique yields information about the streamlines on the solid vane surface which allows identifying the locations of secondary flow vortices, stagnation line and saddle point.

  • 37.
    Salomon Popa, Marianne
    et al.
    KTH, Tidigare Institutioner, Energiteknik.
    Fridh, Jens
    KTH, Tidigare Institutioner, Energiteknik.
    Kessar, Alexandros
    KTH, Tidigare Institutioner, Energiteknik.
    Fransson, Torsten
    KTH, Tidigare Institutioner, Energiteknik.
    Gas turbine simulations in the computerized educational program CompEduHPT: Educational aspects2003Ingår i: American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI, 2003, Vol. 1, s. 733-739Konferensbidrag (Refereegranskat)
    Abstract [en]

    An overview of computerized educational program (CompEduHPT) which includes several simulations was presented. These simulations provide an alternative way to learn, based on discovery and experience. All the simulations were preceded with theory chapters, quizzes and preparatory tasks to enable fruitful exercises to be designed. Evaluations show that a computerized program including multiple ways of learning provides considerable support to the conventional student-teacher way of learning.

  • 38.
    Salomon Popa, Marianne
    et al.
    KTH, Tidigare Institutioner, Energiteknik.
    Fridh, Jens
    KTH, Tidigare Institutioner, Energiteknik.
    Kessar, Alexandros
    KTH, Tidigare Institutioner, Energiteknik.
    Fransson, Torsten
    KTH, Tidigare Institutioner, Energiteknik.
    Gas turbine simulations in the computerized educational program CompEduHPT: Three case studies2003Ingår i: American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI, 2003, Vol. 1, s. 741-748Konferensbidrag (Refereegranskat)
    Abstract [en]

    An overview of the Computerized Educational Program (CompEduHPT) which includes different simulations was presented. These simulations give the students an outlook of the different parameters that affect the performance based on the ideal and real approach of gas turbine calculations. The simulations show the students the different aspects, effects and results when a calculation is made considering a mixture of two ideal gases. They also show the improvements in the performance of the gas turbine depending on the various options available.

  • 39.
    Salomon Popa, Marianne
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Kessar, Alexandros
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Gas Turbine Simulations in the Computerized Educational Program CompEduHPT: Three Case Studies2005Ingår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919Artikel i tidskrift (Refereegranskat)
  • 40.
    Thantla, Sandhya
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Aspfors, Jonas
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Christiansen Erlandsson, Anders
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Characterization of an organic Rankine cycle system for waste heat recovery from heavy-duty engine coolant and exhaust2019Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    To meet the strict legislations imposed on carbon-dioxide emissions, organic Rankine cycle (ORC) waste heat recovery (WHR) technology is being extensively studied and applied in long haulage heavyduty (HD) truck engines. The focus of this paper isto characterize an ORC system of a HD long-haulage commercial truck engine that uses single and dual heat sources for WHR. The main objective of this work is to estimate the improvement in the system’s performance when the number of heat sources is increased. Two different WHR configurations: (i) integrated with the engine exhaust and (ii) integrated with both the engine coolant and the exhaust, are studied using the 1D simulation tool GT-Suite. Two types of scroll expanders, adopted from literature, are used in the ORC system configurations to analyze and compare their effect on the overall performance of the engine. Performance of the scroll expanders are generated from their semi-empirical models and R1233zD is used as the working fluid. With engine exhaust as the only heat source, both the expanders exhibit similar performance potentials at their optimum speeds. With two heat sources, fuel-saving is considerably improved, provided the coolant temperature is increased to 120°C and above. For the chosen conditions, expander A, at its optimum coolant temperature of 150oC, leads to around 5.7% fuel-saving; whereas, expander B, at its optimum coolant temperature of 130oC, leads to 5.5% fuel-saving. Further, this paper discusses the effect of expander speeds, expander volumes and superheating on the overall system efficiency.

  • 41. Thiyagarajan, Janakiraman
    et al.
    Halldorf, Erik
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    TRANSIENT THRUST FORCES ON A TWIN SCROLL TURBOCHARGER2017Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2017, VOL 8, AMER SOC MECHANICAL ENGINEERS , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    The bearing system of turbochargers used in trucks needs to be optimized in order to reduce the frictional losses. This helps in transmitting the exhaust energy more efficiently to the compressor wheel to increase boost pressure. Understanding the thrust loading on the axial bearing helps in optimal design of the bearing and the associated lubrication system. With the advent of twin scroll turbochargers, it is necessary to understand the thrust load behaviour at different operating conditions. This paper pioneers in studying the unsteady axial loads measured on a twin scroll turbocharger mounted on a 6 cylinder 13 litre diesel engine used in the truck industry along with the corresponding analytical predictions for varied engine speeds and loading conditions. Transient thrust forces were measured using a weakened bearing in the experimental approach along with transient pressure measurments on the turbocharger The axial bearing weakening required a design trade-off between flexibility and rigidity of the bearing. The results from the experimental and analytical methods provide better understanding of the characteristics of transient thrust forces that act on a turbocharger mounted on an engine of a heavy duty truck along with its design implications. The maximum normalized axial load measured and predicted were -90 N and -100 N, respectively.

  • 42.
    Vogt, Damian
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    CHARACTERIZATION AND FIRST APPLICATION OF A THIN-FILM ELECTRET UNSTEADY PRESSURE MEASUREMENT TECHNIQUE2008Ingår i: XIX Biannual Symposium on Measuring Techniques in Turbomachinery: Transonic and Supersonic Flow in Cascades and Turbomachines, Brussels: Von Karman Institute for Fluid Dynamics , 2008, s. 1-5Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A new thin-film electret unsteady pressure measurement technique for application in turbomachine aerodynamical experiments is under investigation. The technique is based on a layered sensor comprising a permanently polarized foil in the center. Changes in foil thickness due to variation in pressure result in a potential difference, which is used as measurement signal. The investigated technique presents a cost attractive alternative for unsteady pressure measurement instrumentation. Low signal levels however put severe requirements to acquisition and the treatment of the signals, especially when reducing the sensor area. First measurements have been performed with a 2.5x2.5mm sensor. The signals have been correlated to Kulite data and good agreement has been found. A characterization of the technique as well a description of the first tests in relevant flow is presented in the paper.

  • 43.
    Vogt, Damian
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Design and Construction of a New Modular Wind Tunnel System2006Konferensbidrag (Refereegranskat)
  • 44. Yasa, T.
    et al.
    Paniagua, G.
    Fridh, Jens
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Vogt, Damian
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Performance of a nozzle guide vane in subsonic and transonic regimes tested in an annular sector2010Ingår i: Proceedings of the ASME Turbo Expo 2010: Power for Land, Sea, and Air, 2010, Vol. 7, nr PARTS A, B, AND C, s. 1457-1467Konferensbidrag (Refereegranskat)
    Abstract [en]

    The understanding of shock interactions and mixing phenomena is crucial to design and analysis of advanced turbines. A nozzle guide vane (NGV) is experimentally investigated at subsonic and transonic off-design conditions (M2is of 0.6 and 0.95) in an annular sector at the Royal Institute of Technology (KTH). The effect of cooling ejection (3% of main stream mass flow rate) on the downstream flow field is also studied. The airfoil loading is monitored with pneumatic taps. The downstream pressure field is characterized at four different axial locations using a 5-hole probe and a total pressure probe that contains a single piezo-resistive transducer. The probe with a piezo resistive transducer is also used as a virtual 3-hole probe to measure the flow angle. The time-averaged yaw angle measured with the virtual 3-hole probe is in agreement with the 5-hole probe data. At subsonic conditions the wake causes a pressure loss of 7% of the upstream total pressure and covers 25% of the pitch whereas the pressure deficit is doubled in transonic operation. The coolant ejection results in an additional loss of 2% of the upstream total pressure. The flow speed does not have a significant effect on the wake width at 7% C ax. However, the low pressure region has different width at far downstream depending on the flow velocity. The fillet at the hub region has a significant effect on the secondary flow development. The frequency spectrums at the different conditions clearly reveal the shear layers. The results aim to help the characterization of mixing phenomena downstream of the NGV.

1 - 44 av 44
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