Establishment of an open 3D steam turbine flutter test case

Qi, Dawei; Petrie-Repar, Paul; Gezork, Tobias; Sun, Tianrui

doi:10.29008/etc2017-315

Cited by 7 publications

(17 citation statements)

References 4 publications

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“…The systematic use of a few open geometries not only allows validating numerical methods, it also leads to a sum of works that are directly comparable, that provide a better understanding of the phenomena at stake, and that can be used utimately to extract design guidelines. Recently, the idea of using open test cases was also introduced in the fields of aerodynamics and flutter in steam turbines [33,34] and structural dynamics of blades with friction dampers [35]. This latter geometry responds to researchers' needs in nonlinear structural dynamics, but it is not applicable to the case of contact interactions, as a realistic blade geometry is necessary.…”

Section: Introductionmentioning

confidence: 99%

Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37

Piollet

Nyssen

Batailly

2019

Journal of Sound and Vibration

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Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37. Journal of Sound and Vibration, Elsevier, 2019, 460, pp.Abstract In order to improve the efficiency of aircraft engines, the reduction of clearances between blade tips and their surrounding casing is one avenue manufacturers consider to lower aerodynamic losses. This reduction increases the risk of blade tip/casing contact interactions under nominal operating conditions. Designers need tools to accurately predict subsequent nonlinear vibrations. Engineers and researchers have developed a variety of sophisticated numerical models to predict blades' responses. These models are related to distinct frameworks (time/frequency domain) and various solution algorithms (explicit/implicit time integration schemes, penalty/Lagrange multiplier contact treatment...) which calls for comparative analyses. However, published results are often limited for the sake of confidentiality thus preventing any detailed confrontation. While qualitative understanding can be gained from simplified academic models, full scale models are needed to predict complex interactions in a realistic manner. In this context, this paper proposes a benchmark featuring detailed simulations and analyses of a full 3D finite element model based on the open NASA rotor 37 compressor blade to facilitate reproducibility and collaboration across the research community. NASA rotor 37, a compressor stage widely used as a test case in aerodynamic simulations and validations, has the advantage of presenting a realistic blade geometry. The geometry of the blade is built from publicly available reports. The paper provides details on the geometry, the numerical model and the results to allow an easy use of this model across the fields of structural dynamics. Two contact scenarios are investigated: one with direct contact against the casing, and one with abradable material deposited on the casing to mitigate contact severity through wear. The nonlinear vibration response of the blade is simulated in the time domain. It is evidenced that the addition of the abradable material decreases the amplitude of vibration for most of the angular speeds investigated. However, new interactions appear for some angular speeds. The obtained results are consistent with previous simulations on industrial geometries. Based on works showing improved aerodynamic performances when the blade is tilted, a total of seven geometries are investigated: the reference blade, with a straight vertical stacking line similar to the original rotor 37, two forward-leaned blades, two backward-swept blades and two full forward chordwise swept blades. The sweep and lean variations are shown to have a dramatic impact on the vibration response: the backward sweep results in an increased blade's robustness to contact events and the full forward chordwise sweep in a reduced robustness, while the forward lean leads to a robustness similar to the reference blade. RésuméLa réduction des jeux au...

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Section: Introductionmentioning

confidence: 99%

Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37

Piollet

Nyssen

Batailly

2019

Journal of Sound and Vibration

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“…The rotor blade count was 65 with a blade length of 0.92 m. The rotational speed was 3000 min −1 . In this work, the rotor tip gap height was 2.1 mm (approximately 0.25% blade height), which was half the tip gap size in [6] but similar to the tip gap height of 2.3 mm that was used by Qi et al [7] and Sun et al [8].…”

Section: Test Casementioning

confidence: 78%

“…The boundary conditions for the configuration including stator and exhaust hood were taken from [7]. The stator inlet total pressure and temperature were set to 26.7 kPa and 339.5 K, respectively.…”

Section: Test Casementioning

confidence: 99%

“…In this study, the methods above were applied to the flutter analysis of an open access steam turbine [6] established by Qi et al [7] as an open flutter test case. We demonstrated the applicability of the approaches and compared the results to each other and to results obtained by Qi et al [7] and Sun et al [8] with other flow solvers. Note that Fuhrer and Vogt [9] also applied a variety of simulation approaches to predict the aerodynamic damping of this turbine rotor.…”

Section: Introductionmentioning

confidence: 99%

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Flutter Analysis of a Transonic Steam Turbine Blade with Frequency and Time-Domain Solvers

Frey

Ashcroft

Kersken

et al. 2019

IJTPP

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The aim of this study was to assess the capabilities of different simulation approaches to predict the flutter stability of a steam turbine rotor. The focus here was on linear and nonlinear frequency domain solvers in combination with the energy method, which is widely used for the prediction of flutter onset. Whereas a GMRES solver was used for the linear problem, the nonlinear methods employed a time-marching procedure. The solvers were applied to the flutter analysis of the first rotor bending mode of the open Durham Steam Turbine test case. This test case is representative of the last stage of modern industrial steam turbines. We compared our results to those published by other researchers in terms of aerodynamic damping and local work per cycle coefficients. Time-domain, harmonic balance, and time-linearised methods were compared to each other in terms of CPU efficiency and accuracy.

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“…TurboGrid uses a non 1:1 mesh interface to connect the meshes from the pressure and suction side in the tip clearance. The number of mesh nodes and layers used in the spanwise direction in the tip clearance after mesh independence verification [18] is also presented in Table 2. The average y-plus of the cell height on the walls was around 20 to meet the requirement of the automatic turbulence wall function.…”

Section: Steam Turbine Flutter Test Casementioning

confidence: 99%

Influence of the Tip Clearance on the Aeroelastic Characteristics of a Last Stage Steam Turbine

et al. 2019

Self Cite

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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.

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Establishment of an open 3D steam turbine flutter test case

Cited by 7 publications

References 4 publications

Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37

Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37

Flutter Analysis of a Transonic Steam Turbine Blade with Frequency and Time-Domain Solvers

Influence of the Tip Clearance on the Aeroelastic Characteristics of a Last Stage Steam Turbine

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