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  • 1. Fuhrer, C.
    et al.
    Grübel, M.
    Vogt, D. M.
    Petrie-Repar, Paul
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    The influence of non-equilibrium wet steam effects on the aeroelastic properties of a turbine blade row2016In: Proceedings of the ASME Turbo Expo, ASME Press, 2016Conference paper (Refereed)
    Abstract [en]

    Turbine blade flutter is a concern for the manufacturers o steam turbines. Typically, the length of last stage blades of larg steam turbines is over one meter. These long blades are susceptibl to flutter because of their low structural frequency an supersonic tip speeds with oblique shocks and their reflections Although steam condensation has usually occurred by the las stage, ideal gas is mostly assumed when performing flutter analysi for steam turbines The results of a flutter analysis of a 2D steam turbine tes case which examine the influence of non-equilibrium wet stea are presented. The geometry and flow conditions of the test cas are supposed to be similar to the flow near the tip in a stea turbine as this is where most of the unsteady aerodynamic wor contributing to flutter is done. The unsteady flow simulation required for the flutter analysis are performed by ANSYS CFX Three fluid models are examined: ideal gas, equilibrium we steam (EQS) and non-equilibrium wet steam (NES), of whic NES reflects the reality most Previous studies have shown that a good agreement betwee ideal gas and EQS simulations can be achieved if the prescribe ratio of specific heats is equal to the equilibrium polytropic inde of the wet steam flow through the turbine.

  • 2. Gao, Yang
    et al.
    Petrie-Repar, Paul
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Validation of meanline performance prediction method for radial and mixed flow turbine2018In: Institution of Mechanical Engineers - 13th International Conference on Turbochargers and Turbocharging 2018, Institution of Mechanical Engineers , 2018, p. 357-372Conference paper (Refereed)
    Abstract [en]

    This paper describes a meanline performance prediction method which is developed based on a preliminary design tool, namely TOPGEN. The newly proposed method extends the application of former tool to off-design conditions and mixed flow turbine. To achieve this goal, special treatments to incidence loss calculation of mixed flow turbine and throat flow prediction are developed. The method is validated against test data from open literature. The predicted results of radial turbine showed good agreement with test data on whole performance curve. For mixed flow turbine, different loss model combinations were investigated to give insights to mixed flow turbine prediction.

  • 3.
    Gezork, Tobias
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Petrie-Repar, Paul
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Influence of gap detailing on calculated unsteady non-adjacent blade row aero-forcing in a transonic compressor stageManuscript (preprint) (Other academic)
    Abstract [en]

    Resonant or close to resonant forced response excitation of compressor blades limits component life time, and can potentially lead to high cycle fatigue failure if the excitingforces are large and damping is insufficient. When numerically quantifying the forcing function by means of simulations,simplifications are typically made in the analysis to reducecomplexity and computational cost. In this paper we numerically investigate how the blade forcing function is influencedby the rotor tip gap flow and by flow across gaps in the upstream VIGV row. Unsteady simulations are made using a testrig geometry where a forcing crossing with an excitation froma non-adjacent blade row had previously been measured. Theeffects of the gaps on the forcing function for the first torsionmode are presented for both the non-adjacent blade row excitation (changes compared with a case without gaps indicating a 20% reduction) and an adjacent excitation (changes indicating an80% increase in terms of forcing function amplitude comparing with a case without gaps).

  • 4.
    Gezork, Tobias
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Petrie-Repar, Paul
    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 VISUALIZATION METHOD FOR HARMONIC UNSTEADY FLOWS IN TURBOMACHINERY2016In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 7B, AMER SOC MECHANICAL ENGINEERS , 2016Conference paper (Refereed)
    Abstract [en]

    Understanding unsteady flow processes is key in the analysis of challenging problems in turbomachinery design such as flutter and forced response. In this paper a new visualization method for harmonic unsteady flow is presented. The method illustrates the direction in which unsteady waves are traveling and transporting energy by the direct visualization of the propagating pressure waves in terms of field lines constructed from the wave group velocity. The group velocity is calculated from the unsteady flow solution by assuming that the local unsteady pressure perturbation of interest can be represented by a single harmonic unsteady wave. The applicability of the method is demonstrated for three test cases including a linear cascade of two-dimensional flat plates and a linear cascade of two-dimensional compressor blade profiles.

  • 5.
    Gutierrez, Mauricio
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Petrie-Repar, Paul
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Kielb, Robert E.
    Duke Univ, Dept Mech Engn, Durham, NC 27708 USA..
    Key, Nicole L.
    Purdue Univ, Sch Mech Engn, Zucrow Labs, Purdue, IN 47907 USA..
    A Mistuned Forced Response Analysis of an Embedded Compressor Blisk Using a Reduced-Order Model2019In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 141, no 3, article id 032505Article in journal (Refereed)
    Abstract [en]

    Accuracy when assessing mistuned forced response analyses is still a major concern. Since a fully coupled analysis is still very computational expensive, several simplifications and reduced-order models (ROMs) are carried out. The use of a reduction method, the assumptions and simplifications, generate different uncertainties that challenge the accuracy of the results. Experimental data are needed for validation and also to understand the propagation of these uncertainties. This paper shows a detailed mistuned forced response analysis of a compressor blisk. The blisk belongs to the Purdue Three-Stage (P3S) Compressor Research Facility. Two different stator-rotor-stator configurations of 38 and 44 upstream stator vanes are taken into consideration. Several loading conditions are analyzed at three different speed lines. A ROM known as subset nominal mode (SNM), has been used for all the analyses. This reduction takes as a basis a set of modes within a selected frequency spectrum. It can consider a complete family of modes to study the disk-blade modal interaction. A detailed comparison between the predicted and measured results has been performed, showing a good agreement for the high loading (HL) conditions.

  • 6.
    Gutierrez Salas, Mauricio
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Bladh, Ronnie
    Martensson, Hans
    Petrie-Repar, Paul
    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.
    Vogt, Damian M.
    Forced Response Analysis of a Mistuned, Compressor Blisk Comparing Three Different Reduced Order Model Approaches2017In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 139, no 6, article id 062501Article in journal (Refereed)
    Abstract [en]

    Accurate structural modeling of blisk mistuning is critical for the analysis of forced response in turbomachinery. Apart from intentional mistuning, mistuning can be due to the manufacturing tolerances, corrosion, foreign object damage, and in-service wear in general. It has been shown in past studies that mistuning can increase the risk of blade failure due to energy localization. For weak blade to blade coupling, this localization has been shown to be critical and higher amplitudes of vibration are expected in few blades. This paper presents a comparison of three reduced order models (ROMs) for the structural modeling of blisks. Two of the models assume cyclic symmetry, while the third model is free of this assumption. The performance of the reduced order models for cases with small and large amount of mistuning will be examined. The benefits and drawbacks of each reduction method will be discussed.

  • 7.
    Pan, Minghao
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Mårtensson, H.
    Petrie-Repar, Paul
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Sun, Tianrui
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Gezork, Tobias
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Determination of aerodynamic damping at high reduced frequencies2018In: Proceedings of the ASME Turbo Expo, ASME Press, 2018Conference paper (Refereed)
    Abstract [en]

    In turbomachines, forced response of blades is blade vibrations due to external aerodynamic excitations and it can lead to blade failures which can have fatal or severe economic consequences. The estimation of the level of vibration due to forced response is dependent on the determination of aerodynamic damping. The most critical cases for forced response occur at high reduced frequencies. This paper investigates the determination of aerodynamic damping at high reduced frequencies. The aerodynamic damping was calculated by a linearized Navier-Stokes flow solver with exact 3D non-reflecting boundary conditions. The method was validated using Standard Configuration 8, a two-dimensional flat plate. Good agreement with the reference data at reduced frequency 2.0 was achieved and grid converged solutions with reduced frequency up to 16.0 were obtained. It was concluded that at least 20 cells per wavelength is required. A 3D profile was also investigated: an aeroelastic turbine rig (AETR) which is a subsonic turbine case. In the AETR case, the first bending mode with reduced frequency 2.0 was studied. The 3D acoustic modes were calculated at the far-fields and the propagating amplitude was plotted as a function of circumferential mode index and radial order. This plot identified six acoustic resonance points which included two points corresponding to the first radial modes. The aerodynamic damping as a function of nodal diameter was also calculated and plotted. There were six distinct peaks which occurred in the damping curve and these peaks correspond to the six resonance points. This demonstrates for the first time that acoustic resonances due to higher order radial acoustic modes can affect the aerodynamic damping at high reduced frequencies.

  • 8.
    Sun, Tianrui
    et al.
    Beihang Univ, Sch Energy & Power Engn, Beijing 100191, Peoples R China..
    Hou, Anping
    Beihang Univ, Sch Energy & Power Engn, Beijing 100191, Peoples R China..
    Zhang, Mingming
    Beijing Univ Technol, Coll Appl Sci, Beijing Inst Sci & Engn Comp, Beijing 100124, Peoples R China..
    Petrie-Repar, Paul
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Influence of the Tip Clearance on the Aeroelastic Characteristics of a Last Stage Steam Turbine2019In: Applied Sciences, E-ISSN 2076-3417, Vol. 9, no 6, article id 1213Article in journal (Refereed)
    Abstract [en]

    In this paper, the tip clearance effects on the aeroelastic stability of a last-stage steam turbine model are investigated. Most of the unsteady aerodynamic work contributing to flutter of the long blades of the last-stage of a steam turbine is done near the tip of the blade. The flow in this region is transonic and sensitive to geometric parameters such as the tip clearance height. The KTH Steam Turbine Flutter Test Case was chosen as the test case, which is an open geometry with similar parameters to modern free-standing last-stage steam turbines. The energy method based on 3D URANS simulation was applied to investigate the flutter characteristics of the rotor blade with five tip gap height varying from 0-5% of the chord length. The numerical results show that the global aerodynamic damping for the least stable inter-blade phase angle (IBPA) increases with the tip gap height. Three physical mechanisms are found to cause this phenomenon. The primary cause of the variation in total aerodynamic damping is the interaction between tip clearance vortex and the trailing edge shock from the adjacent blade. Another mechanism is the acceleration of the flow near the aft side of the suction surface in the tip region due to the well-developed tip leakage vortex when the tip clearance height is greater than 2.5% of chord. This causes a stabilizing effect at the least stable IBPA. The third mechanism is the oscillation of the tip leakage vortex due to the blade vibration. This has a negative influence on the aeroelastic stability.

  • 9.
    Sun, Tianrui
    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, Heat and Power Technology.
    Qi, Di
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Investigation of tip clearance flow effects on an open 3D steam turbine flutter test case2017In: Proceedings of the ASME Turbo Expo, American Society of Mechanical Engineers (ASME) , 2017Conference paper (Refereed)
    Abstract [en]

    Blade failure caused by flutter is a major problem in the last stage of modern steam turbines. It is because rotor at this stage always has a large scale in spanwise, which provides low structural frequency as well as supersonic tip speeds. Since most of the unsteady aerodynamic work is done in the tip region, transonic tip-leakage flow that influences the tip region flow could have a remarkable effect on the aerodynamic stability of rotor blades. However, few research had been done on the tipleakage flow influence on flutter characteristic based on fullscale steam turbine numerical models. In this paper, an open 3D steam turbine stage model designed by Durham University was applied, which was widely analyzed and representative for the last stage of modern industrial steam turbines. The average Mach number at the rotor outlet is 1.1. URANS simulation carried by both numerical software CFX and LUFT code is applied, and the two solvers show an agreement on steady and unsteady results. The numerical results indicate that the influence of tip leakage flow on blade stability is based on two types of flow mechanisms. Both mechanisms act on the suction side of near tip region. The first type of mechanism is produced by the reduction of passage shock near the leading edge, and the other type of mechanism at the rear of blade is caused by the interaction between tip leakage vortex and trailing edge shock of the neighbor blade. In conclusion, tip leakage flow has a significant influence on steam turbine flutter boundary prediction and requires further analysis in the future.

  • 10.
    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.

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