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  • 1. Amos, I. G.
    et al.
    Jablonowski, T.
    Rossi, E.
    Vogt, Damian M.
    KTH, Superseded Departments, Energy Technology.
    Boncinelli, P.
    Design and off-design optimisation of highly loaded industrial gas turbine stages2004In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 24, no 12-nov, 1735-1744 p.Article in journal (Refereed)
    Abstract [en]

    A European collaborative project to investigate the design of advanced industrial gas turbine stages (DAIGTS) has now completed 30 months of a 36-month programme of work. The objectives of the project were to investigate advanced aerodynamic analysis of industrial gas turbine stages, off-design performance characteristics, prediction of aero-mechanical behaviour.This paper gives an overview of the technical progress made and includes a description of the rigs used in the study. Key results include the development of advanced CFD models to include cooling and real engine geometric features, off-design performance mapping of transonic industrial turbine stages and the development of a unique oscillating cascade rig.

  • 2.
    Andrinopoulos, Nikos
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Hu, Jiasen
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Design And Testing Of A Vibrating Test Object For Investigating Fluid-Structure Interaction2008In: PROCEEDINGS OF THE ASME TURBO EXPO 2008, VOL 5, PT A, NEW YORK: AMER SOC MECHANICAL ENGINEERS , 2008, 415-424 p.Conference paper (Refereed)
    Abstract [en]

    In this study the vibration properties of a deforming test object are presented. The test object is bump shaped and is integrated into the wall of a transonic wind tunnel. The purpose for using such a test object is to study, in a generic manner, the unsteady aerodynamic phenomena occurring due to the presence of a vibrating structure in the flow. The setup is part of an ongoing study to address the phenomena of fluid-structure interaction and shock-boundary layer interaction. The design objective for the test object is to assimilate a IF vibration mode at a given section of atypical compressor blade. Finite element (FE) analyses have been used to predict the frequency response of the test object prior to manufacturing. The design objectives have been verified experimentally by time-resolved laser measurements. It has been found that the FE predictions are in good agreement with experimental data. Furthermore it has been shown that the present test object allows for the achievement of the targeted vibration properties up to a frequency of 250Hz, corresponding to a reduced frequency above 0.8.

  • 3. Freund, O.
    et al.
    Bartelt, M.
    Mittelbach, M.
    Montgomery, M.
    Vogt, Damian M.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Seume, J. R.
    Impact of the flow on an acoustic excitation system for aeroelastic studies2012In: Proceedings of the ASME Turbo Expo, 2012, no PARTS A AND B, 1609-1620 p.Conference paper (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 non-contact 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 (AETR) 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.

  • 4.
    Fruth, Florian
    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.
    Bladh, R.
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Unsteady forcing vs. efficiency - The effect of clocking on a transonic industrial compressor2013In: ASME 2013 Fluids Engineering Division Summer Meeting: Volume 1A, Symposia: Advances in Fluids Engineering Education; Advances in Numerical Modeling for Turbomachinery Flow Optimization; Applications in CFD; Bio-Inspired Fluid Mechanics; CFD Verification a., ASME Press, 2013, V01AT02A010- p.Conference paper (Refereed)
    Abstract [en]

    A numerical investigation on the impact of clocking on the efficiency and the aerodynamic forcing of the first 1.5 stages of an industrial transonic compressor was conducted. Using unsteady 3D Navier-Stokes equations, seven clocking positions were calculated and analyzed. Efficiency changes due to clocking were up to 0.125%, whereas modal excitation changes up to 31.7%. However, no direct correlation between the parameters of efficiency, stimulus and modal excitation was found as reported by others. It was found that potential forced response risks can be reduced by clocking, resulting only in minor efficiency penalties. Assuming almost sinusoidal behavior of efficiency and stimulus changes, as found in this investigation, both parameters can be set into correlation by using an ellipse interpolation. Direct impact of design changes on efficiency and stimulus through clocking can be deducted from that graph and quick estimations about extrema be made using only 5-6 transient simulations. Results however also stress the importance of considering modal excitation when optimizing for aerodynamic forcing, for which the ellipse interpolation is not necessarily possible. Highest efficiency is achieved with the IGV wake impinging on the stator blade leading edge at mid-span. It was found however that this alone is not a sufficient criteria in case of inclined wakes, as wake impingement at different span positions leads to different efficiencies.

  • 5.
    Fruth, Florian
    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.
    Influence of the blade count ratio on aerodynamic forcing part II: High pressure transonic turbine2012In: Proceedings of the ASME Turbo Expo, New York: American Society of Mechanical Engineers , 2012, 1343-1354 p.Conference paper (Refereed)
    Abstract [en]

    The influence of the Blade Count Ratio (BCR) on the aerodynamic forcing of a transonic high pressure turbine has been investigated numerically. Main focus here was put on the change in unsteady aerodynamics, modal properties and the mode excitation. Using a scaling technique, six different transonic turbine stages with different numbers of scaled blades but maintained steady aerodynamics were generated and further analyzed. In the analysis a non-linear, time marching CFD solver was used and the unsteady, harmonic forces projected onto the mode shapes. For this transonic turbine the unsteady pressure at the rotor blade decreases in amplitude and spanwise distribution from low to high blade count ratios. In chordwise direction a local minimum for intermediate blade count ratios was found for the rotor and stator blades. Mode frequencies decreased monotonically with an increasing BCR. Significant mode changes for modes 5 and 6 of the different BCRs were captured  using the Modal Assurance Criteria. It was found that for these transonic turbines the blade count ratio and reduced frequency are amongst others key parameters for a reduction in aerodynamic forcing. Even though an almost monotonic trend was found for the stator blade excitation, the rotor blade excitation behaves highly non-monotonic. A maximum value in excitation potential was found close to reported blade count ratio values. Optimization of certain modes is possible but case dependent, due to the non-monotonic nature. Moreover it was found that for a minor increase in upstream blade count the mean unsteady forces on the rotor blades is reduced, but the mode excitation not necessarily has to decrease.

  • 6.
    Fruth, Florian
    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, Hans
    Volvo Aero. Researchers.
    Mayorca, Maria A.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    INFLUENCE OF THE BLADE COUNT RATIO ON AERODYNAMIC FORCING PART I: HIGHLY LOADED TRANSONIC COMPRESSOR2010Conference paper (Refereed)
    Abstract [en]

    The influence of the Blade Count Ratio (BCR) on the aerodynamic forcing of a highly transonic compressor has been investigated. The focus has been put on the unsteady aerodynamics as well as mode excitability and thus High Cycle Fatigue (HCF) risk. A number of compressor stages were investigated that differed in blade count of the stator blade row. Time-resolved aerodynamic forcing results were acquired using a non-linear CFD approach. The results were decomposed into frequency content and combined with modal properties of the various components. It is found that the BCR is a key parameter to reduce generalized force and consequently vibratory HCF stresses. Furthermore a potential in avoiding and/or alleviating potential resonant crossings in the Campbell diagram is reported. The dependency of these aspects from BCR is largely non-linear and for the first time discussed in detail on the basis of a transonic compressor stage.

  • 7.
    Glodic, Nenad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Bartelt, Michael
    Vogt, Damian
    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.
    Aeroelastic Properties of Combined Mode Shapes in an Oscillating LPT Cascade2009Conference paper (Refereed)
  • 8.
    Glodic, Nenad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    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.
    Experimental and numerical investigation of mistuned aerodynamic influence coefficients in an oscillating LPT cascade2012In: Proceedings of the ASME Turbo Expo, New York: American Society of Mechanical Engineers , 2012, 1355-1367 p.Conference paper (Refereed)
    Abstract [en]

    The effect of aerodynamic mistuning on the aerodynamic damping in an oscillating Low-Pressure Turbine (LPT) cascade is investigated. The considered aerodynamic mistuning is caused by blade-to-blade stagger angle variations. The study is carried out experimentally and numerically by employing the influence coefficient method. On the experimental side a sector cascade is used where one of the blades is made oscillating in three orthogonal modes. The unsteady blade surface pressure is acquired on the oscillating blade and two neighbour blades and reduced to aeroelastic stability data. By gradually de-staggering the oscillating blade, aerodynamically mistuned influence coefficients are acquired. On the numerical side full-scale time-marching RANS CFD simulations are performed using nominal and de-staggered blades. The study shows that variations in blade-to-blade stagger angle affect the aerodynamic influence coefficients and as a consequence overall aeroelastic stability. Whereas discrepancies are found in the exact prediction of mistimed influence coefficients compared to measured, the overall magnitude and trends are well captured.

  • 9.
    Glodic, Nenad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    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 Tip Clearance Modelling in Predictions of Aeroelastic Response in an Oscillating LPT Cascade2012Conference paper (Refereed)
    Abstract [en]

    The present study investigates the influence of tip clearance modelling in predictions of the aeroelastic response in an oscillating Low-Pressure Turbine (LPT) cascade. The study was carried out through validation of different numerical models against experimental data. On the experimental side a sector cascade was used, where one of the blades was oscillated in axial bending mode. Unsteady pressure measurements were performed at several spanwise positions on the non-oscillating blades and at mid-span of the oscillating blade. On the numerical side full-scale time-marching RANS CFD simulations were performed employing models with and without tip clearance. The study showed that the model without tip clearance provides reliable result up to 70%. In the near-tip region difference induced due to the absence of tip clearance in the model amounts to about 25% of minimum stability value, relative to the nominal tip clearance model. It has also been shown that the resolution of the tip clearance mesh in spanwise direction of the gap might have a considerable impact of prediction accuracy. Imposed small variations in the tip clearance size have not led to substantial changes in predicted aeroelastic response of the cascade.

  • 10.
    Hosseini, Seyed Mohammad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fruth, Florian
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    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.
    Effect of Scaling of Blade Row Sectors on the Prediction of Aerodynamic Forcing in a Highly-Loaded Transonic Turbine Stage2012In: Proceedings of the ASME Turbo Expo 2011, Vol 6, Parts A And B, New York: American Society of Mechanical Engineers , 2012, 1297-1307 p.Conference paper (Refereed)
    Abstract [en]

    The viability of a scaling technique in prediction of forced response of the stator and rotor blades in a turbine stage has been examined. Accordingly the so called parameter, generalized force, is defined which describes the excitation of a modeshape due to the unsteady flow forces at a certain frequency. The capability of this method to accurately predict the generalized forces serves as the viability criterion. The scaling technique modifies the geometry to obtain an integer stator, rotor blade count ratio in an annulus section while maintaining steady aerodynamic similarity. A non-scaled configuration is set up to serve as the reference case. Further configurations with different scaling ratios are also generated for accuracy comparison. Unsteady forces are calculated through 3D Navier-Stokes simulations by VolSol, which is based on an explicit, time-marching. A general purpose finite element model of blades is also provided to enable modal analysis with the harmonic forces. The generalized forces of stator and rotor blades revealed high sensitivity towards modification of stator blades while acceptable accuracy was obtained by moderate modifications of the rotor blades for first harmonic forces. Moreover the influence of variable blade's structural characteristics proved to be remarkable.

  • 11.
    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, 011032- p.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.

  • 12.
    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, Hans
    VOLVO Aero Corporation.
    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 Modes2012In: Proceedings of the ASME Turbo Expo 2011, Vol 6, Parts And B / [ed] Presented by ASME International Gas Turbine Institute, Vancouver, Canada: American Society of Mechanical Engineers , 2012, 1449-1461 p.Conference paper (Refereed)
    Abstract [en]

    A method is proposed for the determination of the aeroelastic behavior of a system responding to mode-shapes different to 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 on a transonic compressor blade shows that the method captures well the aeroelastic properties in a wide frequency range. A discussion of the influence of the mode-shapes and frequency on the final stability response is also provided.

  • 13.
    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, 021013- p.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.

  • 14.
    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, 051008- p.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.

  • 15.
    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.
    Mårtensson, Hans
    VOLVO Aero Corporation, Trollhättan, Sweden.
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    A New Reduced Order Modeling for Stability and Forced Response Analysis of Aero-Coupled Blades Considering Various Mode Families2010In: Proceedings of ASME Turbo Expo 2010: Scottish Exhibition & Conference Centre / [ed] ASME 2010, Glasgow, UK: ASME 2010 , 2010, 1-10 p.Conference paper (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 MLS (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.

  • 16.
    Mayorca, María Angélica
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    De Andrade, Jesús A.
    Universidad Simon Bolivar - USB Laboratorio de Conversión de Energia Mecánica Sartenejas, Miranda, Venezuela.
    Vogt, Damian
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Mårtensson, Hans
    VOLVO Aero Corporation, Trollhättan, Sweden.
    Fransson, Torsten
    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 stage2009In: PROCEEDINGS OF THE ASME TURBO EXPO 2009, VOL 6, PTS A AND B, 2009, 535-546 p.Conference paper (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 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 (non-scaled) 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 first harmonic excitation can be predicted well for both up- and downstream excitation using moderate amount of scaling. On the other hand, the predictions of second harmonic quantities do show a higher sensitivity to scaling for the investigated test case.

  • 17.
    Mayorca, María Angélica
    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.
    Andersson, C.
    Mårtensson, Hans
    VOLVO Aero Corporation.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Uncertainty of forced response numerical predictions of an industrial blisk - Comparison with experiments2012In: Proceedings of the ASME Turbo Expo 2012: Volume 7, Issue PARTS A AND B, 2012, ASME Press, 2012, 1537-1548 p.Conference paper (Refereed)
    Abstract [en]

    Numerical methods, both Computational Fluid Dynamics (CFD) as well as Finite Elements (FE) methods, are widely used in industry with the purpose of predicting potential fatigue problems early in the design process. However, the uncertainty of such predictions is not clearly identified. The present paper presents the prediction of the vibration response of a rotor blisk part of 1 1/2 transonic compressor stage with comparison with experiments. Different uncertainty sources along the numerical aeromechanical chain are then identified. CFD solvers are employed for the prediction of both blade row interaction forces as well as the aerodynamic damping determination. Mistuning is assessed by the use of Reduced Order Modeling analyses and results compared with tip timing data. The peak amplitude response of a resonance mode of interest is determined for two different inlet conditions and thus the accuracy dependence on the excitation level is discussed. Results show that the largest uncertainties come from the unsteady aerodynamics, in which both aerodynamic damping and forcing estimations are critical. The structural dynamic models seem to capture the vibration response and mistuning effects well. Additionally, the challenges of tip timing data processing for detailed one-to-one validation of the tools are highlighted.

  • 18.
    Mayorca, María Angélica
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Mårtensson, Hans
    VOLVO Aero Corporation, Trollhättan, Sweden.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Numerical tool for prediction of aeromechanical phenomena in gas turbines2009In: 19th ISABE Conference / [ed] ISABE, Montreal: American Institute of Aeronautics and Astronautics Inc. , 2009, 1-11 p.Conference paper (Refereed)
    Abstract [en]

    A numerical tool for aeromechanic design is presented. The output of the tool is the fatigue risk of the critical blade obtained by the Haigh diagram, and stability curves for the stability analyses. The tool integrates results from commercial Computational Fluid Dynamics (CFD) and Finite Element (FE) solvers. It uses a Reduced Order Modeling (ROM) technique in order to account for mistuning effects in an efficient way. The description of the numerical tool and an overview of typical results are presented in this paper. The applicability of the tool in the industrial design process is discussed as well as the outlook of the targeted capabilities.

  • 19.
    Monaco, Lucio
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    Bergmans, J.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. KIC InnoEnergy S.E.,, Netherlands .
    A remotely operated aeroelastically unstable LPT cascade for turbomachinery aeromechanics education and training: Remote flutter lab2014In: Proceedings of the ASME Turbo Expo, 2014, Vol. 6Conference paper (Other academic)
    Abstract [en]

    The use of advanced pedagogical methodologies in connection with advanced use of modern information technology (ICT) for delivery enables new ways of communicating, of exchanging knowledge, and of learning that are gaining increasing relevance in our society. Remote laboratory exercises offer the possibility to enhance learning for students in different technical areas, especially to the ones not having physical access to laboratory facilities and thus spreading knowledge in a world-wide perspective. A new "Remote Flutter Laboratory" has been developed to introduce aeromechanics engineering students and professionals to aeroelastic phenomena in turbomachinery. The laboratory is world-wide unique in the sense that it allows global access for learners anywhere and anytime to a facility dedicated to what is both a complex and relevant area for gas turbine design and operation. The core of the system consists of an aeroelastically unstable turbine blade row that exhibits self-excited and self-sustained flutter at specific operating conditions. Steady and unsteady blade loading and motion data are simultaneously acquired on five neighboring suspended blades and the whole system allows for a distant-based operation and monitoring of the rig as well as for automatic data-retrieval. This paper focuses on the development of the "Remote Flutter Laboratory" exercise as a hands-on learning platform for online and distant-based education and training in turbomachinery aeromechanics enabling familiarization with the concept of critical reduced frequency and of flutter phenomena. This laboratory set-up can easily be used "as is" directly by any turbomachinery teacher in the world, free of charge and independent upon time and location with the intended learning outcomes as specified in the lab, but it can also very easily be adapted to other intended learning outcomes that a teacher might want to highlight in a specific course. As such it is also a base for a turbomachinery repository of advanced remote laboratories of global uniqueness and access. The present work documents also the pioneer implementation of the LabSocket System for the remote operation of a wind tunnel test facility from any Internet-enabled computer, tablet or smartphone with no end-user software or plug-in installation.

  • 20.
    Monaco, Lucio
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    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.
    A new linear cascade test facility for use in engineering education2012Conference paper (Other academic)
    Abstract [en]

    A new low-speed air-operated linear cascade testfacility has been developed at the Heat and PowerTechnology Division at KTH, Sweden. The rig has fullyremote operability and is used as an educational tool forthe students in engineering courses on turbomachinery.Both on campus and distant students are involved inexperimental activities with the rig in the form oflaboratory exercises. The current setup allowsdetermination of profile losses through a low pressureturbine blade row at low subsonic flow conditions.The present paper contains a description of test rigdesign and its commissioning and introduces theconcepts for future applications of the facility ininvestigation of additional flow phenomena inturbomachinery. Findings of the first field experiencewith the linear cascade are here reported.

  • 21.
    Monaco, Lucio
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    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.
    Implementation of a remote pump laboratory exercise in the training of engineering students2012In: Proceedings of ASME Turbo Expo 2012 GT2012: Volume 3, 2012, ASME Press, 2012, 479-487 p.Conference paper (Refereed)
    Abstract [en]

    The use of laboratory exercises in the training of engineering students is of paramount importance to give the students the possibility to gain practical experience on real hardware and on real test data. Recent trends in the education of engineers at the Department of Energy Technology at KTH go towards an increasing share of distant-based education, which is put in place to educate students at different geographic locations, not only locally (such as for example with engineers in industry) but also internationally (i.e. with students in different countries). In order to provide the possibility to follow a course at a distance without compromising on learning objectives and learning quality, a number of remotely operated laboratory exercises have been developed and implemented in the engineering curriculum at the department. Among these, to mention the work carried out by Navarathna et al. [11] on a remotely operated linear cascade test facility. The present laboratory exercise is integrated in a course on turbomachinery and gives the students the possibility to interactively learn about the operation of pumps at various speeds, various mass flow rates, parallel operation and serial operation. Students access the laboratory exercise using a web-based interface, perform measurements and finally have test data sent to an initially specified email address for further analysis.

  • 22. Mårtensson, H.
    et al.
    Gunnsteinsson, Stefan Sturla
    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.
    Aeroelastic properties of closely spaced modes for a highly loaded transonic fan2008Conference paper (Refereed)
    Abstract [en]

    In the design of modem compressor blades of wide chord (low aspect ratio) type it is often hard to avoid having modes that are close to each other in frequency. Modes which are closely spaced can interact dynamically. Mistuning and localization of stresses are known problems with this. A potential problem with this is also the possibility of coalescence flutter of the modes. Even if the modes are frequency separated at zero rotational speed, the centrifugal stiffening may cause the modes to attract and even cross (or veer) at some rotational speed. In design, mode separation criteria are sometimes applied in order to minimize the risk of encountering unknown dynamic phenomena. This study is performed to better understand the dynamics of closely spaced modes with respect to risk for coalescence flutter. A reduced order aeroelastic system is then constructed that describes the interaction between the different modes. The aeroelastic couplings are then calculated for the 2 mode system. The method is general in terms of mode shapes and number of interacting modes. A parametrical study is performed in order to study how strongly the modes interact when the frequency separation is decreased and if there is a risk of destructive coalescence flutter. The investigation is performed on a high pressure ratio front stage fan blade. The tendency of the modes to interact depends on the strength of the coupling compared to the strength of the pure structural modes. The tendency towards instability was increased in cases where the stability margin was smaller of the single modes. The results can be considered to support a separation criterion of 2% for the lower. A re-evaluation should be considered if lighter blade material and increased loads are to be used.

  • 23. Mårtensson, H.
    et al.
    Vogt, Damian
    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.
    Assessment of a 3D Linear Flutter Prediction Tool using Sector Cascade Test Data2005In: Proceedings of the ASME Turbo Expo 2005, Vol 4, ASME Press, 2005, 613-623 p.Conference paper (Refereed)
    Abstract [en]

    An assessment and validation of a numerical prediction tool for flutter are made using new experimental data from experiments on turbine blades in a sector cascade. The 3D geometry is that of a low-pressure (LP) turbine blade with twist and a profile that changes along span in an annular sector cascade. The numerical model is a linear harmonic Euler equation solver. Rig results are obtained for the blade by oscillating I blade out of 7 in the annular sector cascade. The blade is oscillated in the rig using a mechanical type of actuator to control the mode. The mode shapes in the rig consist of torsion and bending modes around a pivot mechanism fixed inside the hub end wall. The frequencies obtained in the rig are in the range up to 219 Hz, or reduced frequency based on full chord k=0.5, which covers the range of useful reduced frequencies typically found in turbine designs. Under reference running conditions the unsteady pressure responses are found qualitatively in line with the experiment. The test case is shown to be challenging to the numerical tool in terms of effects of tip clearance as well as off-design effects. In order to improve results tip clearance modeling and inclusion of viscous terms are identified as key factors.

  • 24.
    Sanz Luengo, Antonio
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Schmitt, S.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Validation of linearized navier-stokes based flutter prediction tool part2: Quantification of the prediction accuracy on a turbine test case2012In: Proceedings of the ASME Turbo Expo 2012: Volume 7, Issue PARTS A AND B, 2012, ASME Press, 2012, no PARTS A AND B, 1581-1592 p.Conference paper (Refereed)
    Abstract [en]

    This is the second part of two papers describing the validation of a tool chain for flutter prediction. The first paper provides an overview of the numerical methods and their verification. The second paper presents the detailed validation of the tool chain on the basis of experimental data obtained from measurements of an annular cascade sector comprising 3D twisted turbine blades. Aeroelastic test data has been acquired in an isolated blade row consisting of seven free-standing low-pressure (LP) turbine blades. The middle blade has been oscillated in controlled manner in three orthogonal modes and at various frequencies while measuring the unsteady blade surface pressure on several blades. The data has been reduced to aerodynamic influence coefficients and finally recombined to travelling wave mode stability curves. By acquiring data at various spanwise positions, a basis for validating three-dimensional effects has been provided. The validation of the investigated flutter prediction tool has been performed in a detailed manner and on various levels, started from a critical reduced frequency over stability curves to local work coefficients. At the lowest level of condensation, the unsteady blade surface pressures have been compared. Correlation to test data is shown and discussed rigorously at these various levels giving a detailed assessment of the prediction accuracy of the investigated tool.

  • 25. Sundkvist, S. G.
    et al.
    Andersson, M.
    Gherman, B.
    Sveningsson, A.
    Vogt, Damian M. A.
    KTH, Superseded Departments, Energy Technology.
    On-going development and recent results of the research in the Swedish Gas Turbine Centre (GTC)2004In: Proc. ASME Turbo Expo, 2004, 261-268 p.Conference paper (Refereed)
    Abstract [en]

    This paper describes a way of co-operation between industries, universities and government that has proven to be very fruitful. The Swedish Gas Turbine Centre (GTC) is constituted as a research consortium between technical universities and gas turbine industry. The overall goal of the centre, that was founded in 1996 on a governmental initiative, is to build up a basis of knowledge at Swedish universities to support the industrial development in Sweden of gas turbines of the future with expected requirements on low emissions, high efficiencies, high availability, and low costs. Since the start the research has had a focus on high temperature components of gas turbines (combustion chamber and turbine). This is also reflected in the on-going development phase where the research program consists of four project areas: cooling technology, combustion technology, aeroelasticity, and life time prediction of hot components. The projects are aiming at developing design tools and calculation and verification methods within these fields. A total of eleven research students (among them one industrial PhD student) are active in the centre at present. Numerical analysis as well as experimental verification in test rigs are included. The program has so far produced eleven Licentiate of Engineering and five PhD. On-going activities and recent results of the research in the four research areas are presented: A new test rig for investigation of time-dependent pressures of three-dimensional features on a vibrating turbine blade at realistic Mach, Reynolds and Strouhal numbers and first experimental results. Results of numerical simulations of heat loads on turbine blades and vanes, especially platform cooling. First results of numerical investigations of combustion and thermo-acoustic instabilities in gas turbine chambers. Experimental investigation of crack propagation in gas turbine materials using the scanning electron microscope (SEM).

  • 26.
    Vogt, Damian
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Experimental Investigation of Three-Dimensional Mechanisms in Low-Pressure Turbine Flutter2005Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    The continuous trend in gas turbine design towards lighter, more powerful and more reliable engines on one side and use of alternative fuels on the other side renders flutter problems as one of the paramount challenges in engine design. Flutter denotes a self-excited and self-sustained aeroelastic instability phenomenon that can lead to material fatigue and eventually damage of structure in a short period of time unless properly damped. The design for flutter safety involves the prediction of unsteady aerodynamics as well as structural dynamics that is mostly based on in-house developed numerical tools. While high confidence has been gained on the structural side unanticipated flutter occurrences during engine design, testing and operation evidence a need for enhanced validation of aerodynamic models despite the degree of sophistication attained. The continuous development of these models can only be based on the deepened understanding of underlying physical mechanisms from test data.

    As a matter of fact most flutter test cases treat the turbomachine flow in two-dimensional manner indicating that the problem is solved as plane representation at a certain radius rather than representing the complex annular geometry of a real engine. Such considerations do consequently not capture effects that are due to variations in the third dimension, i.e. in radial direction. In this light the present thesis has been formulated to study three-dimensional effects during flutter in the annular environment of a low-pressure turbine blade row and to describe the importance on prediction of flutter stability. The work has been conceived as compound experimental and computational work employing a new annular sector cascade test facility. The aeroelastic response phenomenon is studied in the influence coefficient domain having one blade oscillating in various three-dimensional rigid-body modes and measuring the unsteady response on several blades and at various radial positions. On the computational side a state-of-the-art industrial numerical prediction tool has been used that allowed for two-dimensional and three-dimensional linearized unsteady Euler analyses.

    The results suggest that considerable three-dimensional effects are present, which are harming prediction accuracy for flutter stability when employing a two-dimensional plane model. These effects are mainly apparent as radial gradient in unsteady response magnitude from tip to hub indicating that the sections closer to the hub experience higher aeroelastic response than their equivalent plane representatives. Other effects are due to turbomachinery-typical three-dimensional flow features such as hub endwall and tip leakage vortices, which considerably affect aeroelastic prediction accuracy. Both effects are of the same order of magnitude as effects of design parameters such as reduced frequency, flow velocity level and incidence. Although the overall behavior is captured fairly well when using two-dimensional simulations notable improvement has been demonstrated when modeling fully three-dimensional and including tip clearance.

  • 27.
    Vogt, Damian
    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).
    A New Turbine Cascade for Aeromechanical Testing2002Conference paper (Refereed)
  • 28.
    Vogt, Damian
    et al.
    KTH, Superseded Departments, Energy Technology.
    Fransson, Torsten
    KTH, Superseded Departments, Energy Technology.
    A Technique for Using Recessed-Mounted Pressure Transducers to Measure Unsteady Pressure2004Conference paper (Refereed)
  • 29.
    Vogt, Damian
    et al.
    KTH, Superseded Departments, Energy Technology.
    Fransson, Torsten
    KTH, Superseded Departments, Energy Technology.
    Effect of Blade Mode Shape on the Aeroelastic Stability of a LPT Cascade2004Conference paper (Refereed)
  • 30.
    Vogt, Damian
    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).
    Introducing the New Transonic Cascade Test Facility at KTH2002Conference paper (Refereed)
  • 31.
    Vogt, Damian
    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.
    Turbomachinery Aeroelasticity Analyses: Everyday Business or Exceptional Challenge?2011Conference paper (Refereed)
  • 32.
    Vogt, Damian
    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.
    CHARACTERIZATION AND FIRST APPLICATION OF A THIN-FILM ELECTRET UNSTEADY PRESSURE MEASUREMENT TECHNIQUE2008In: XIX Biannual Symposium on Measuring Techniques in Turbomachinery: Transonic and Supersonic Flow in Cascades and Turbomachines, Brussels: Von Karman Institute for Fluid Dynamics , 2008, 1-5 p.Conference paper (Other academic)
    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.

  • 33.
    Vogt, Damian
    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.
    Design and Construction of a New Modular Wind Tunnel System2006Conference paper (Refereed)
  • 34.
    Vogt, Damian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Glodic, Nenad
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    The Effect of Unsteady Aerodynamic Asymmetric Perturbations on the Mode Shape Sensitivity of an Oscillating LPT Cascade2009Conference paper (Refereed)
  • 35.
    Vogt, Damian M.
    et al.
    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.
    Experimental investigation of mode shape sensitivity of an oscillating low-pressure turbine cascade at design and off-design conditions2007In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 129, no 2, 530-541 p.Article in journal (Refereed)
    Abstract [en]

    The effect of negative incidence operation on mode shape sensitivity of an oscillating low-pressure turbine rotor blade row has been studied experimentally. An annular sector cascade has been employed in which the middle blade has been made oscillating in controlled three-dimensional rigid-body modes. Unsteady blade surface pressure data were acquired at midspan on the oscillating blade and two pairs of nonoscillating neighbor blades and reduced to aeroelastic stability data. The test program covered variations in reduced frequency, flow velocity, and inflow incidence; at each operating point, a set Of three orthogonal modes was tested such as to allow for generation of stability plots by mode recombination. At nominal incidence, it has been found that increasing reduced frequency has a stabilizing effect on all modes. The analysis of mode shape sensitivity yielded that the most stable modes are of bending type with axial to chordwise character whereas high sensitivity has been found for torsion-dominated modes. Negative incidence operation caused the flow to separate on the fore pressure side. This separation was found to have a destabilizing effect on bending modes of chordwise character, whereas an increase in stability could be noted for bending modes of edgewise character Variations of stability parameter with inflow incidence have hereby found being largely linear within the range of conditions tested. For torsion-dominated modes, the influence on aeroelastic stability was close to neutral.

  • 36.
    Vogt, Damian M.
    et al.
    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.
    Experimental investigation of mode shape sensitivity of an oscillating LPT cascade at design and off-design conditions2006In: Proceedings of the ASME Turbo Expo 2006, Vol 5, Pts A and B, 2006, 1151-1163 p.Conference paper (Refereed)
    Abstract [en]

    The effect of negative incidence operation on mode shape sensitivity of an oscillating low pressure (LP) turbine rotor blade row has been studied experimentally. An annular sector cascade has been employed in which the middle blade has been made oscillating in controlled three-dimensional rigid-body modes. Unsteady blade surface pressure data were acquired at midspan on the oscillating blade and two pairs of non-oscillating neighbor blades and reduced to aeroelastic stability data. The test program covered variations in reduced frequency, flow velocity and inflow incidence; at each operating point a set of three orthogonal modes was tested such as to allow for generation of stability plots by mode recombination. At nominal incidence it has been found that increasing reduced frequency has a stabilizing effect on all modes. The analysis of mode shape sensitivity yielded that the most stable modes are of bending type with axial to chordwise character whereas high sensitivity has been found for torsiondominated modes. Negative incidence operation caused the flow to separate on the fore pressure side. This separation was found to have a destabilizing effect on bending modes of chordwise character whereas an increase in stability could be noticed for bending modes of edgewise character. Variations of stability parameter with inflow incidence have hereby found being largely linear within the range of conditions tested. For torsion-dominated modes the influence on aeroelastic stability was close to neutral.

  • 37.
    Vogt, Damian M.
    et al.
    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.
    Podcasting the whiteboard: - A new way of teaching engineers2012In: ASME Turbo Expo 2012: Turbine Technical Conference and Exposition: Volume 3: Cycle Innovations; Education; Electric Power; Fans and Blowers; Industrial and Cogeneration, ASME Press, 2012, 525-536 p.Conference paper (Refereed)
    Abstract [en]

    The education of engineers largely relies on traditional classroom teaching in which a teacher instructs a subject using a variety of techniques ranging from the traditional blackboard (nowadays also whiteboard), over overhead to computer-based presentations. In order to deepen knowledge and get hands-on experience, students are often given practical exercises or case studies to perform, be it individually or in group in the form of a seminar. It is experienced that black-(or white) board based lectures are having an advantage over overheads / slide shows as knowledge is built up instantaneously at a natural pace rather than confronting students with pages of prepared material. The present paper presents a new technique herein referred to as "podcasted whiteboard lectures" in which lectures are given in a traditional lecture hall setup but with having the teacher lecturing by means of an electronic whiteboard. A key advantage of this technique is that it can be recorded and made available to students afterwards, which is here done using podcasting. It is experienced that the technique is very efficient for maximizing the students' learning experience as one is given the possibility to follow a subject ubiquitous and at preferred pace. Another advantage is that animations and simulations can be integrated right into the lecture and into the same medium used for lecturing. The technique is thereby equally applicable to campus as well as distance-based teaching.

  • 38.
    Vogt, Damian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Mårtensson, H
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Direct Calculation of Aerodynamic Influence Coefficients Using a Commercial CFD Solver2007Conference paper (Refereed)
  • 39.
    Vogt, Damian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Mårtensson, H.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Experimental and Numerical Study of Unsteady Aerodynamics in an Oscillating Low-Pressure Turbine Cascade of Annular Sector Shape2006Conference paper (Refereed)
  • 40.
    Vogt, Damian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Mårtensson, H.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Validation of a Three-Dimensional Flutter Prediction Tool2005Conference paper (Refereed)
  • 41. Yasa, T.
    et al.
    Paniagua, G.
    Fridh, Jens
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Vogt, Damian
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Performance of a nozzle guide vane in subsonic and transonic regimes tested in an annular sector2010In: Proceedings of the ASME Turbo Expo 2010: Power for Land, Sea, and Air, 2010, Vol. 7, no PARTS A, B, AND C, 1457-1467 p.Conference paper (Refereed)
    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.

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