| 1. |
- Gao, Yang, et al.
(författare)
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FORCED RESPONSE ANALYSIS OF A RADIAL TURBINE WITH DIFFERENT MODELLING METHODS
- 2019
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Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO. - : ASME Press.
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Konferensbidrag (refereegranskat)abstract
- Forced response analysis is a critical part in the radial turbine design process. It estimates the vibration mode and level due to aerodynamic excitations and then enables the analysis of high-cycle fatigue (HCF) to determine the life span of the turbine stage. Two key aspects of the forced response analysis are the determination of the aerodynamic forcing and damping which can be calculated from unsteady 3D computational fluid dynamics (CFD) simulations. These simulations are problematic due to the high level of complexity in the simulations (multi row, full annular, tip gap, etc.) and the consequent high-computational cost. The aim of this paper is to investigate and compare different CFD methods applied to the forced response analysis of a radial turbine. Full annular simulations are performed for the prediction of the excitation force. This method is taken as the baseline and is usually the most time-consuming one. One method of reducing the computational effort is to use Phase-lag periodic boundary conditions. A further reduction can be obtained by using a frequency-based method called nonlinear harmonic. For the prediction of aerodamping, the Phase-lag periodic boundary condition method is also available. Moreover, a frequency-based method called harmonic balance can further accelerate the aero-damping calculation. In this paper, these CFD methods will be applied to the simulations of an open-geometry radial turbine with a vaned volute. A comparison of unsteady results from different methods will be presented. These unsteady results will also be implemented to a tuned forced response analysis in order to directly compare the corresponding maximum blade vibration amplitudes.
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| 2. |
- Gezork, Tobias, et al.
(författare)
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A NEW VISUALIZATION METHOD FOR HARMONIC UNSTEADY FLOWS IN TURBOMACHINERY
- 2016
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Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO. - : AMER SOC MECHANICAL ENGINEERS.
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
- Gezork, Tobias, et al.
(författare)
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Applicability of quasi-3d blade design methods to profile shape optimization of turbine blades
- 2013
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Ingår i: Proc. ASME Turbo Expo. - 9780791855232
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Konferensbidrag (refereegranskat)abstract
- The performance of gas turbine airfoils is continually improved by creating advanced aerodynamic and thermal designs. Optimization methods are used to handle the increasing complexity of such a design. However, optimization is expensive when performed based on 3D CFD calculations. Therefore, an optimization strategy based on simpler, less expensive analysis methods is desirable. Oftentimes, a so-called quasi-3D (Q3D) approach is used, where 2D calculations are carried out on multiple, radially stacked meridional blade sections. This paper investigates the applicability of such an approach for optimization with regard to blade profile loss. Obviously, certain physical effects are neglected using this approach, leading to errors in the predicted blade performance. Still, optimization based on Q3D calculations might be possible if the error is consistent, i.e. not random. For this purpose, a design of experiment (DOE) was carried out to compare and correlate loss predictions from Q3D calculations and high-fidelity 3D CFD calculations for gas turbine blades. It is shown that the total pressure loss coefficients found with both the Q3D and 3D calculations correlate well (75-90%) to warrant the use of a Q3D method for profile shape optimization. Subsequently, an optimization is performed to demonstrate the applicability of the method.
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| 4. |
- Gezork, Tobias, et al.
(författare)
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Influence of gap detailing on calculated unsteady non-adjacent blade row aero-forcing in a transonic compressor stage
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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).
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| 5. |
- Gezork, Tobias, et al.
(författare)
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Influence of Gap Detailing on Calculated Unsteady Non-Adjacent Blade Row Aero-Forcing in a Transonic Compressor Stage
- 2020
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 142:11
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Tidskriftsartikel (refereegranskat)abstract
- 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 exciting forces are large and damping is insufficient. When numerically quantifying the forcing function by means of simulations, simplifications are typically made in the analysis to reduce complexity and computational cost. In this paper, we numerically investigate how the blade forcing function is influenced by the rotor tip gap flow and by flow across gaps in the upstream variable inlet guide vane row. Unsteady simulations are made using a test rig geometry where a forcing crossing with an excitation from a non-adjacent blade row had previously been measured. The effects of the gaps on the forcing function for the first torsion mode 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 an 80% increase in terms of forcing function amplitude comparing with a case without gaps).
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| 6. |
- Gezork, Tobias, et al.
(författare)
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Influence of tip shroud cavity detailing on turbine blade forcing calculations
- 2014
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Ingår i: ASME Turbo Expo 2014. - : ASME Press. - 9780791845776 ; , s. V07BT35A021-
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Konferensbidrag (refereegranskat)abstract
- Forced response in turbomachinery refers to the vibration of a component due to an excitation originating from another component. Obstacles, such as struts and blade rows in the upstream and downstream flow path of a turbomachine engine lead to engine order (EO) excitations. To be able to predict the severity of these excitations, both aerodynamic and structural calculations are performed. There is a risk of critical high cycle fatigue (HCF) failure when the force acts at a resonance frequency. Customarily, forcing calculations exclude detailing features, such as leakage flows. The current investigation uses a two stage subsonic model steam turbine configuration with shrouded rotor blades to demonstrate the influence of neglecting flow through seal cavities for blade forcing predictions. Upstream and downstream vanes are the excitation sources on the rotor blade. Calculation results are compared for a configuration including and excluding the tip shroud cavity. Computed data is compared to available pressure data from tests in the model turbine. The investigation shows for the first blade passing excitation at design point that the axial and circumferential rotor forcing change by +22%, respectively +4% when including the tip shroud cavity for the investigated configuration. The change in forcing arises from the interaction of the leakage flow with the main stream flow. For highly loaded designs this can be of importance if there is a critical excitation.
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| 7. |
- Gezork, Tobias
(författare)
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The Influence of Flow Leakage Modelling on Turbomachinery Blade Forcing Predictions
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vibrations in turbomachinery engine components are undesirable as they put the structural integrity of the components at risk and can lead to failure during the lifetime of the turbomachinery engine. Vibrations arising from aerodynamic forces and stability of turbomachinery blades is assessed in the discipline of aeromechanics. Ultimately, aeromechanical considerations limit turbomachinery designs and impose constraints on innovative aerodynamic designs with highly loaded light-weight components. Besides, aeromechanical assessment of blade vibration is done at a late stage of the design process and the number of iterations in the design loop is limited. Aeromechanical calculations can have large uncertainties in the prediction accuracy, especially when made a-priori without test data or without comparable design experience to tune the analysis methods. Therefore, large safety margins are required in the design, given that only a small set of prototype engines of a chosen design can be manufactured for testing. This may result in unnecessarily conservative engines and inhibit efficient or cost-effective design.Accurate prediction methods together with a reliable estimate of the accuracy and sensitivity of the calculations will allow designers to push the limits and to design machines with highly efficient components. Efficiency directly translates into savings in terms of operational cost, capital cost as well as reductions in emissions when fuels are used.In the presented work the sensitivity of aerodynamic forcing to the geometry features of a tip gap, hub cavity, tip-shroud cavity and inlet guide vane partial gaps has been investigated by the means of URANS CFD computations. The results indicate that sensitivity is both feature and case dependent, and that the detailing features can significantly alter the aerodynamic forcing function. The work shows, that the features should be included in high-fidelity aerodynamic models used for aeromechanics and highlights the mechanisms in which the features affect the aeromechanic forcing.Investigations were performed for a subsonic model steam turbine configuration in 1.5 stage simulations, for a transonic turbine stage and for a 1.5 stage transonic research compressor in a 5 row investigation. Computations were performed using time domain simulations on scaled sectors of the blade rows. Results are analysed in terms of generalised modal force, and differences in the flow-field between the investigated detailing configurations are highlighted, marking the influence of the detailing features.
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| 8. |
- Gezork, Tobias, et al.
(författare)
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Unsteady blade force computation sensitivity in a transonic turbine to rotor tip gap, hub and shroud cavity model detail
- 2015
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Ingår i: Proceedings of the 14th International Symposium on Unsteady Aerodynamics, Aeroacoustics & Aeroelasticity of Turbomachines.
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Konferensbidrag (refereegranskat)abstract
- The influence of including geometric detailing features on blade forcing predicted by CFD calculations is investigated. Various features such as rotor tip gap, rotor tip shroud cavity with substantial leakage flow and large rotor upstream hub rim cavity are investigated. The test case is based on a single stage transonic test turbine rig in which the unsteady aerodynamics and blade forcing have previously been investigated numerically.Including the tip gap and the tip shroud leakage in the computational model resulted in an overall increase in unsteady forcing. The change in forcing is mainly due to a change in secondary flow structure, but also due to a change of the stage flow condition. Conversely, it is shown that including the hub cavity in the computational model, even without the presence of purge-flow, reduces the unsteady force. Lastly, even though there are changes in unsteady blade loading, the blade response amplitude is only changed marginally (maximum 7%) due to forcing variations alone.
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| 9. |
- Gutierrez, Mauricio, et al.
(författare)
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Forced response analysis of a transonic turbine using a free interface component mode synthesis method
- 2015
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Ingår i: 11th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2015. - : European Conference on Turbomachinery (ETC).
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Konferensbidrag (refereegranskat)abstract
- Assessing forced response is crucial during the design phase of turbomachines. Since the analyses are computationally expensive and time-consuming when using full models, Reduced Order Models (ROM) are utilized to decrease the number of Degrees Of Freedom (DOF) and consequently analysis time and cost. The ROM used in the current analysis belongs to the component mode synthesis (CMS) method with a free-interface approach known as Craig-Chang. A transonic high pressure turbine is investigated featuring large ranges of disk and blade dominated modes depending in the Nodal Diameter (ND). The free-interface approach will be assessed in the disk and blade dominated regions with a detailed study of the frequencies and mode shapes. In addition, a forced response analysis within the blade dominated region is evaluated in the paper. Moreover, a study of the amount of modes required in the basis for the reduced order transformation matrix is presented.
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| 10. |
- Pan, Minghao, et al.
(författare)
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Determination of aerodynamic damping at high reduced frequencies
- 2018
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Ingår i: Proceedings of the ASME Turbo Expo. - : ASME Press. - 9780791851159
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 11. |
- Qi, Di, et al.
(författare)
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Establishment of an open 3D steam turbine flutter test case
- 2017
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Ingår i: 12th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2017. - : European Turbomachinery Society.
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Konferensbidrag (refereegranskat)abstract
- This paper introduces an open three-dimensional (3D) flutter test case for steam turbines. The test case is fully described and initial results are presented. The steam turbine last stage blading geometry is taken from a test case originally presented by Durham University. The stage is representative of the aerodynamic characteristics of modern steam turbine blading. To the authors' knowledge, this is the first time that a steam turbine flutter test case is presented based on an open 3D realistic blade geometry. ANSYS CFX and LUFT (Linearized Unsteady Flow solver for Turbomachinery) were both applied to calculate inviscid and RANS steady and unsteady flow solutions. Plots of aerodynamic damping versus inter-blade phase angle and plots of the local work coefficient on the blade for critical cases are presented.
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