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  • 1.
    Baagherzadeh Hushmandi, Narmin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Effects of multiblocking and axial gap distance on performance of partial admission turbines: A numerical analysis2011In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 133, no 3, p. 031028-Article in journal (Refereed)
    Abstract [en]

    In this paper, the effects of axial gap distance between the first stage stator and rotor blades and multiblocking on aerodynamics and performance of partial admission turbines are analyzed numerically. The selected test case is a two stage axial steam turbine with low reaction blades operating with compressed air. The multiblocking effect is studied by blocking the inlet annulus of the turbine in a single arc and in two opposing blocked arcs, each having the same admission degree. The effect of axial gap distance between the first stage stator and rotor blades is studied while varying the axial gap by 20% compared with the design gap distance. Finally, full admission turbine is modeled numerically for comparison. Performance of various computational cases showed that the first stage efficiency of the two stage partial admission turbine with double blockage was better than that of the single blockage turbine; however, the extra mixing losses of the double blockage turbine caused the efficiency to deteriorate in the downstream stage. It was shown that the two stage partial admission turbine with smaller axial gap than the design value had better efficiency of the first stage due to lower main flow and leakage flow interactions; however, the efficiency at the second stage decreased faster compared with the other cases. Numerical computations showed that the parameters, which increased the axial force of the first stage rotor wheel for the partial admission turbine, were longer blocked arc, single blocked arc, and reduced axial gap distance between the first stage stator and rotor blades.

  • 2.
    Baagherzadeh Hushmandi, Narmin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fridh, Jens
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines2011In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 133, no 4, p. 041017-1-041017-12Article in journal (Refereed)
    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.
    Binder, Christian
    et al.
    Experimental Study on Pressure Losses in Circular Orifices for the Application in Internal Cooling Systems, Sweden.
    Kinell, Mats
    Utriainen, Esa
    Eriksson, Daniel
    Bahador, M.
    Kneer, J.
    Bauer, H.J.
    Experimental Study on Pressure Losses in Circular Orifices for the Application in Internal Cooling Systems2015In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 137Article in journal (Refereed)
    Abstract [en]

    The cooling air flow in a gas turbine is governed by the flow through its internal passages and controlled by restrictors such as circular orifices. If the cooling air flow is incorrectly controlled, the durability and mechanical integrity of the whole turbine may be affected. Consequently, a good understanding of the orifices in the internal passages is important. This study presents experimental results for a range of pressure ratios and length-to-diameter ratios common in gas turbines including even very small pressure ratios. Additionally, the chamfer depth at the inlet was also varied. The results of the chamfer depth variation confirmed its beneficial influence on decreasing pressure losses. Moreover, important effects were noted when varying more than one parameter at a time. Besides earlier mentioned hysteresis at the threshold of choking, new phenomena were observed, e.g. a rise of the discharge coefficient for certain pressure and length-to-diameter ratios. A correlation for the discharge coefficient was attained based on the new experimental data with a generally lower error than previous studies.

  • 4.
    Dahlqvist, Johan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fridh, Jens
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Experimental Investigation of Turbine Stage Flow Field and Performance at Varying Cavity Purge Rates and Operating Speeds2018In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 140, no 3, article id 031001Article in journal (Refereed)
    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.

  • 5. El-Gabry, Lamyaa
    et al.
    Saha, Ranjan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fridh, Jens
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Measurements of Hub Flow Interaction on Film Cooled Nozzle Guide Vane in Transonic Annular Cascade2015In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 137, no 8, article id 081004Article in journal (Refereed)
    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.

  • 6. Freund, Oliver
    et al.
    Bartelt, Michael
    Mittelbach, Marc
    Montgomery, Matthew
    Vogt, Damian M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Seume, Joerg R.
    Impact of the Flow on an Acoustic Excitation System for Aeroelastic Studies2013In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 135, no 3, p. 031033-Article in journal (Refereed)
    Abstract [en]

    The flow in turbomachines is highly unsteady. Effects like vortices, flow separation, and shocks are an inevitable part of the turbomachinery flow. Furthermore, high blade aspect ratios, aerodynamically highly loaded and thin profiles increase the blade sensitivity to vibrations. According to the importance of aeroelasticity in turbomachines, new strategies for experimental studies in rotating machines must be developed. A basic requirement for aeroelastic research in rotating machines is to be able to excite the rotor blades in a defined manner. Approaches for active blade excitation in running machines may be piezoelectric elements, magnetism, or acoustics. Contact-free excitation methods are preferred, since additional mistuning is brought into the investigated system otherwise. A very promising method for aeroelastic research is the noncontact acoustic excitation method. In this paper, investigations on the influence of an annular cascade flow on the blade vibration, excited by an acoustic excitation system, are presented for the first time. These investigations are carried out at the Aeroelastic Test Rig of the Royal Institute of Technology in Stockholm. By varying the excitation angle, the outlet Mach number, and the relative position of the excited blade to the excitation system, the influence of the flow on the acoustic excitation is quantified. The results show that there is a strong dependency of the excited vibration amplitude on the excitation angle if the outlet Mach number is increased, which implies that preferable excitation directions exist. Furthermore, it is shown that a benefit up to 23% in terms of excited vibration amplitude can be reached if the flow velocity is raised.

  • 7.
    Fridh, Jens
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Laumert, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Forced Response in Axial Turbines Under the Influence of Partial Admission2013In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 135, no 4, p. 041014-Article in journal (Refereed)
    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.

  • 8.
    Hellström, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Gutmark, Ephraim
    Department of Aerospace, Engineering and Engineering Mechanics, University of Cincinnati.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Large Eddy Simulation of the Unsteady Flow in a Radial Compressor Operating Near Surge2012In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 134, no 5, p. 051006-Article in journal (Refereed)
    Abstract [en]

    The flow in a centrifugal compressor has been computed using large eddy simulation (LES). The investigated geometry is that of a ported shroud compressor with a 10 blade impeller with an exducer diameter of 88 mm. The computational data compares favorably with measured data for the same compressor and operational point. For the considered operational point near surge, the flow field in the entire compressor stage is unsteady. Back-flow occurs in the diffuser, wheel, and the ported shroud channels resulting in back-flow at the walls in the inlet region of the compressor. In the diffuser and volute, the flow is highly unsteady with perturbations that are convected around the volute, affecting the flow field in most of the entire compressor. The mechanism driving this unsteadiness is assessed by flow visualizations, frequency analysis, and correlations of pressure and velocity data in order to gain a more comprehensive understanding of the mechanism leading to stall and surge.

  • 9. Jocker, M.
    et al.
    Hillion, F. X.
    Fransson, Torsten H.
    KTH, Superseded Departments, Energy Technology.
    Wahlen, U.
    Numerical unsteady flow analysis of a turbine stage with extremely large blade loads2002In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 124, no 3, p. 429-438Article in journal (Refereed)
    Abstract [en]

    This paper presents the detailed numerical analysis including parametric studies on the aerodynamic excitation mechanisms in a turbine stage due to the unsteady stator-rotor interaction, The work is part of the predesign study of a high-pressure subsonic turbine,for a rocket engine turbopump. The pressure level in such turbines can be remarkably high (in this case 54 MPa inlet total pressure). Hence, large unsteady rotor blade loads can be expected, which impose difficult design requirements, The parameter studies are performed at midspan with the numerical flow solver UNSFLO, a 2-D/Q3-D unsteady hybrid Euler/Navier-Stokes solver. Comparisons to 2-D and steady, 3-D results obtained with a fully viscous solver VOLSOL, are made. The investigated design parameters are the axial gap (similar to8-29 percent of rotor axial chord length) and the stator vane size and count (stator-rotor pitch ratio similar to1-2.75), For the nominal case the numerical solution is analyzed regarding the contributions of potential and vortical flow disturbances at the rotor inlet using rotor gust computations. It was found that gust calculations were not capable to capture the complexity of the detected excitation mechanisms, but the possibility to reduce excitations by enforcing cancellation of the vortical and potential effects has been elaborated. The potential excitation mechanism in the present turbine stage is found dominant compared to relatively small and local wake excitation effects. The parameter studies indicate design recommendations for the axial gap and the stator size regarding the unsteady rotor load.

  • 10. Kielb, R.
    et al.
    Barter, J.
    Chernycheva, Olga
    KTH, Superseded Departments, Energy Technology.
    Fransson, Torsten H.
    KTH, Superseded Departments, Energy Technology.
    Flutter of low pressure turbine blades with cyclic symmetric modes: A preliminary design method2004In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 126, no 2, p. 306-309Article in journal (Refereed)
    Abstract [en]

    A current preliminary design method for flutter of low pressure turbine blades and vanes only requires knowledge of the reduced frequency and mode shape (real). However many low pressure turbine (LPT) blade designs include a tip shroud that mechanically connects the blades together in a structure exhibiting cyclic symmetry. A proper vibration analysis produces a frequency and complex mode shape that represents two real modes phase shifted by 90 deg. This paper describes an extension to the current design method to consider these complex mode shapes. As in the current method, baseline unsteady aerodynamic analyses must be performed for the three fundamental motions, two translations and a rotation. Unlike the current method work matrices must be saved for a range of reduced frequencies and interblade phase angles. These work matrices are used to generate the total work for the complex mode shape. Since it still only requires knowledge of the reduced frequency and mode shape (complex), this new method is still very quick and easy to use. Theory and an example application are presented.

  • 11.
    Laumert, Björn
    et al.
    KTH, Superseded Departments, Energy Technology.
    Mårtensson, H.
    Fransson, Torsten H.
    KTH, Superseded Departments, Energy Technology.
    Investigation of unsteady aerodynamic blade excitation mechanisms in a transonic turbine stage - Part I: Phenomenological identification and classification2002In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 124, no 3, p. 410-418Article in journal (Refereed)
    Abstract [en]

    Based on the results of time-dependent 3-D viscous computations the aerodynamic mechanisms that cause the unsteady pressure fluctuations on the vane and rotor blade surface of a high-pressure transonic turbine are identified and separately classified in a phenomenological manner. In order to be able to describe separately the influence of wake, potential and shock distortions on the blade surface pressure tit design operation conditions, the stator exit Mach number is increased as to enhance the shock distortions and lowered as to enhance potential anti wake distortions, In a comprehensive approach the observations from the off-design conditions are utilized to classify every major perturbation observed in the perturbation space-time maps tit design operation conditions. The spanwise variations caused by the inherent 3-D nature of the flow field and promoted by the 3-D shape of the rotor blade are addressed.

  • 12.
    Laumert, Björn
    et al.
    KTH, Superseded Departments, Energy Technology.
    Mårtensson, H.
    Fransson, Torsten H.
    KTH, Superseded Departments, Energy Technology.
    Investigation of unsteady aerodynamic blade excitation mechanisms in a transonic turbine stage - Part II: Analytical description and quantification2002In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 124, no 3, p. 419-428Article in journal (Refereed)
    Abstract [en]

    This paper presents a study of the blade pressure perturbation levels and the resulting blade forces in a high-pressure transonic turbine stage based on 3-D time dependent viscous computations. Globally, the blade pressure unsteadiness is quantified with the RMS of the pressure perturbations integrated in both time and along the blade surface. Operation point as well as spanwise variations are addressed. Locally, the relative strength of the pressure perturbation events on the vane and rotor blade surface is investigated. To obtain information about the relative strength of events related to the blade passing frequency and higher harmonics, the pressure field is Fourier decomposed in time at different radial positions along the blade arc-length. The amplitude peaks are then related to the pressure events in space-time maps. With the help of the observations and results from the blade pressure study, the radial variations of the unsteady blade force and torque acting on a constant span blade profile section are investigated. The connection between the first and second vane passing frequency pressure amplitudes on the rotor blade surface and the resulting force and the torque amplitudes for three selected blade modes was investigated in detail. In this investigation the pressure was integrated over defined rotor blade regions to quanti,, local force contributions. Spanwise as well as operation point variations are addressed.

  • 13.
    Lim, Shyang Maw
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Dahlkild, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Aerothermodynamics and Exergy Analysis in Radial Turbine With Heat Transfer2018In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 140, no 9, article id 091007Article in journal (Refereed)
    Abstract [en]

    This study was motivated by the difficulties to assess the aerothermodynamic effects of heat transfer on the performance of turbocharger turbine by only looking at the global performance parameters, and by the lack of efforts to quantify the physical mechanisms associated with heat transfer. In this study, we aimed to investigate the sensitivity of performance to heat loss, to quantify the aerothermodynamic mechanisms associated with heat transfer and to study the available energy utilization by a turbocharger turbine. Exergy analysis was performed based on the predicted three-dimensional flow field by detached eddy simulation (DES). Our study showed that at a specified mass flow rate, (1) pressure ratio drop is less sensitive to heat loss as compared to turbine power reduction, (2) turbine power drop due to heat loss is relatively insignificant as compared to the exergy lost via heat transfer and thermal irreversibilities, and (3) a single-stage turbine is not an effective machine to harvest all the available exhaust energy in the system.

  • 14.
    Mayorca, Maria Angelica
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian M.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Mårtensson, H.
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Prediction of Turbomachinery Aeroelastic Behavior From a Set of Representative Modes2013In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 135, no 1, p. 011032-Article in journal (Refereed)
    Abstract [en]

    A method is proposed for the determination of the aeroelastic behavior of a system responding to mode-shapes which are different from the tuned in vacuo ones, due to mistuning, mode family interaction, or any other source of mode-shape perturbation. The method is based on the generation of a data base of unsteady aerodynamic forces arising from the motion of arbitrary modes and uses least square approximations for the prediction of any responding mode. The use of a reduced order technique allows for mistuning analyses and is also applied for the selection of a limited number of arbitrary modes. The application of this method on a transonic compressor blade shows that the method captures the aeroelastic properties well in a wide frequency range. A discussion of the influence of the mode-shapes and frequency on the final stability response is also provided.

  • 15.
    Mayorca, María A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    De Andrade, Jesus A.
    Vogt, Damian M.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Mårtensson, Hans
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Effect of Scaling of Blade Row Sectors on the Prediction of Aerodynamic Forcing in a Highly Loaded Transonic Compressor Stage2011In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 133, no 2, p. 021013-Article in journal (Refereed)
    Abstract [en]

    An investigation of the sensitivity of a geometrical scaling technique on the blade forcing prediction and mode excitability has been performed. A stage of a transonic compressor is employed as a test object. A scaling ratio is defined, which indicates the amount of scaling from the original geometry. Different scaling ratios are selected and 3D Navier-Stokes unsteady calculations completed for each scaled configuration. A full-annulus calculation (nonscaled) is performed serving as reference. The quantity of interest is the generalized force, which gives a direct indication of the mode excitability. In order to capture both up- and downstream excitation effects, the mode excitability has been assessed on both rotor and stator blades. The results show that the first harmonic excitation can be predicted well for both up-and downstream excitations using moderate amounts of scaling. On the other hand, the predictions of second harmonic quantities do show a higher sensitivity to scaling for the investigated test case.

  • 16.
    Mayorca, María A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian M.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Mårtensson, H.
    A New Reduced Order Modeling for Stability and Forced Response Analysis of Aero-Coupled Blades Considering Various Mode Families2012In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 134, no 5, p. 051008-Article in journal (Refereed)
    Abstract [en]

    This paper presents the description and application of a new method for stability and forced response analyses of aerodynamically coupled blades considering the interaction of various mode families. The method, here referred as multimode least square, considers the unsteady forces due to the blade motion at different modes shape families and calculates the aerodynamic matrixes by means of a least square (L2) approximations. This approach permits the prediction of mode families' interaction with capabilities of structural, aerodynamic and force mistuning. A projection technique is implemented in order to reduce the computational domain. Application of the method on tuned and structural mistuned forced response and stability analyses is presented on a highly loaded transonic compressor blade. When considering structural mistuning the forced response amplitude magnification is highly affected by the change in aerodynamic damping due to mistuning. Analyses of structural mistuning without aerodynamic coupling might result in over-estimated or under-estimated response when the source of damping is mainly aerodynamic. The frequency split due to mistuning can cause that mode families' interact due to reducing their frequencies separation. The advantage of the present method is that the effect of mode family interaction on aerodynamic damping and forced response is captured not being restricted to single mode families.

  • 17.
    Navarathna, Nalin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fedulov, Vitali
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Martin, Andrew
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Web-Based, Interactive Laboratory Experiment in Turbomachine Aerodynamics2010In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 132, no 1, p. 011015-Article in journal (Refereed)
    Abstract [en]

    Remote laboratory exercises are gaining popularity due to advances in communication technologies along with the need to provide realistic yet flexible educational tools for tomorrow's engineers. Laboratory exercises in turbomachinery aerodynamics generally involve substantial equipment in both size and power, so the development of remotely controlled facilities has perhaps not occurred as quickly as in other fields. This paper presents an overview of a new interactive laboratory exercise involving aerodynamics in a linear cascade of stator blades. The laboratory facility consists of a high-speed fan that delivers a maximum of 2.5 kg/s of air to the cascade. Traversing pneumatic probes are used to determine pressure profiles at upstream and downstream locations, and loss coefficients are later computed. Newly added equipment includes cameras, stepper motors, and a data acquisition and control system for remote operation. This paper presents the laboratory facility in more detail and includes discussions related to user interface issues, the development of a virtual laboratory exercise as a complement to experiments, and comparative evaluation of virtual, remote, and local laboratory exercises.

  • 18. Rehill, B.
    et al.
    Walsh, E. J.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Zaki, T. A.
    McEligot, D. M.
    Identifying Turbulent Spots in Transitional Boundary Layers2012In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 135, no 1, p. 011019-Article in journal (Refereed)
    Abstract [en]

    An artificial turbulent spot is simulated in a zero free-stream turbulence base flow and a base flow with organized streaks. Six identification methods are used in order to isolate the turbulent spot from the surrounding nonturbulent fluid. These are (i) instantaneous wall-normal velocity v, (ii) instantaneous spanwise velocity w, (iii) instantaneous turbulent dissipation, (iv) lambda(2) criterion, (v) Q criterion, and (vi) gradient of the finite time Lyapunov exponent. All methods are effective in isolating the turbulent spot from the streaks. The robustness of each technique is determined from the sensitivity of the maximum spot dimensions to changes in threshold level. The Q criterion shows the least sensitivity for the zero free-stream turbulence case and the instantaneous turbulent dissipation technique is least sensitive in the organized streaks case. For both cases the v technique was the most sensitive to changes in threshold level.

  • 19.
    Saha, Ranjan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fridh, Jens
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    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 Performance2014In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 136, no 11, p. 111001-Article in journal (Refereed)
    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.

  • 20.
    Saha, Ranjan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Mamaev, Boris
    Siemens LLC Energy Oil & Gas Design Department, Russia.
    Fridh, Jens
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Laumert, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Influence of Prehistory and Leading Edge Contouring on Aero Performance of a Three-Dimensional Nozzle Guide Vane2014In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 136, no 7, p. 071014-1-071014-10Article in journal (Refereed)
    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.

  • 21.
    Siddique, Waseem
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    El-Gabry, Lamyaa
    American University in Cairo, Egypt.
    Shevchuk, Igor
    MBtech Group GmbH & Co. KGaA, Germany..
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Validation and Analysis of Numerical Results for a Two-Pass Trapezoidal Channel With Different Cooling Configurations of Trailing Edge2012In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 135, no 1, p. 011027-Article in journal (Refereed)
    Abstract [en]

    High inlet temperatures in a gas turbine lead to an increase in the thermal efficiency of the gas turbine. This results in the requirement of cooling of gas turbine blades/vanes. Internal cooling of the gas turbine blade/vanes with the help of two-pass channels is one of the effective methods to reduce the metal temperatures. In particular, the trailing edge of a turbine vane is a critical area, where effective cooling is required. The trailing edge can be modeled as a trapezoidal channel. This paper describes the numerical validation of the heat transfer and pressure drop in a trapezoidal channel with and without orthogonal ribs at the bottom surface. A new concept of ribbed trailing edge has been introduced in this paper which presents a numerical study of several trailing edge cooling configurations based on the placement of ribs at different walls. The baseline geometries are two-pass trapezoidal channels with and without orthogonal ribs at the bottom surface of the channel. Ribs induce secondary flow which results in enhancement of heat transfer; therefore, for enhancement of heat transfer at the trailing edge, ribs are placed at the trailing edge surface in three different configurations: first without ribs at the bottom surface, then ribs at the trailing edge surface in-line with the ribs at the bottom surface, and finally staggered ribs. Heat transfer and pressure drop is calculated at Reynolds number equal to 9400 for all configurations. Different turbulent models are used for the validation of the numerical results. For the smooth channel low-Re k-e model, realizable k-e model, the RNG k-ω model, low-Re k-ω model, and SST k-ω models are compared, whereas for ribbed channel, low-Re k-e model and SST k-ω models are compared. The results show that the low-Re k-e model, which predicts the heat transfer in outlet pass of the smooth channels with difference of +7%, underpredicts the heat transfer by -17% in case of ribbed channel compared to experimental data. Using the same turbulence model shows that the height of ribs used in the study is not suitable for inducing secondary flow. Also, the orthogonal rib does not strengthen the secondary flow rotational momentum. The comparison between the new designs for trailing edge shows that if pressure drop is acceptable, staggered arrangement is suitable for the outlet pass heat transfer. For the trailing edge wall, the thermal performance for the ribbed trailing edge only was found about 8% better than other configurations.

  • 22.
    Sun, Tianrui
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. Beihang Univ, Sch Energy & Power Engn, Beijing 100191, Peoples R China..
    Petrie-Repar, Paul
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian M.
    Univ Stuttgart, ITSM Inst Thermal Turbomachinery, D-70569 Stuttgart, Germany.;Univ Stuttgart, Machinery Lab, D-70569 Stuttgart, Germany..
    Hou, Anping
    Beihang Univ, Sch Energy & Power Engn, Beijing 100191, Peoples R China..
    Detached-Eddy Simulation Applied to Aeroelastic Stability Analysis in a Last-Stage Steam Turbine Blade2019In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 141, no 9, article id 091002Article in journal (Refereed)
    Abstract [en]

    Blade flutter in the last stage is an important design consideration for the manufacturers of steam turbines. Therefore, the accurate prediction method for blade flutter is critical. Since the majority of aerodynamic work contributing to flutter is done near the blade tip, resolving the tip leakage flow can increase the accuracy of flutter predictions. The previous research has shown that the induced vortices in the tip region can have a significant influence on the flow field near the tip. The structure of induced vortices due to the tip leakage vortex cannot be resolved by unsteady Reynolds-averaged Navier-Stokes (URANS) simulations because of the high dissipation in turbulence models. To the best of author's knowledge, the influence of induced vortices on flutter characteristics has not been investigated. In this paper, the results of detached-eddy simulation (DES) and URANS flutter simulations of a realistic-scale last-stage steam turbine are presented, and the influence of induced vortices on the flutter stability has been investigated. Significant differences for the predicted aerodynamic work coefficient distribution on the blade surface, especially on the rear half of the blade suction side near the tip, are observed. At the least stable interblade phase angle (IBPA), the induced vortices show a destabilizing effect on the blade aeroelastic stability. The motion of induced vortices during blade oscillation is dependent on the blade amplitude, and hence, the aerodynamic damping is also dependent on the blade vibration amplitude. In conclusion, the induced vortices can influence the predicted flutter characteristics of the steam turbine test case.

  • 23.
    Tian, Simeng
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Petrie-Repar, Paul
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Glodic, Nenad
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Sun, Tianrui
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    CFD-Aided Design of a Transonic Aeroelastic Compressor Rig2019In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 141, no 10, article id 101003Article in journal (Refereed)
    Abstract [en]

    This paper presents the results of computational fluid dynamics (CFD)-aided design calculations of a transonic linear cascade wind tunnel. The purpose of the wind tunnel is to generate data for the validation of numerical methods employed to calculate aerodynamic damping for forced response cases in transonic compressors. It is common for transonic wind tunnels to use transonic walls (perforated walls with controlled suction) to adjust the transonic flow in the experiment. Unfortunately, perforated walls are difficult to model in CFD simulations, and they complicate the validation process. One of the goals of the new tunnel is not to use perforated walls. The main difficulty in the design of a transonic linear cascade is achieving periodic flow for the central blades due to shock reflections from the side walls and the sensitivity of transonic flow to small changes in geometry. Other design constraints are the maximum available mass flow of 4.5 kg/s and the minimum required blade thickness of 2 mm for instrumentation. The purpose of the current CFD simulations is to determine the optimum geometry (sidewalls, tailboards, and throttle) of the tunnel with the goal of achieving near periodic flow conditions for the central blade channels at the similar condition in a typical transonic compressor.

1 - 23 of 23
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