Prediction of the unsteady turbine trailing edge wake flow characteristics and comparison with experimental data

Vagnoli, Stefano; Verstraete, Tom; Mateos, B.; Sieverding, C. H.

doi:10.1177/0957650915592074

Cited by 14 publications

(31 citation statements)

References 18 publications

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“…12. A similar effect has been shown by Vagnoli et al (2015), due to a variation of the Mach number. To further investigate the difference of wave generation between the 60M and 213M grids, local probes named A and B are placed in the wake and on the blade surface of both grids as shown in Fig.…”

Section: Grid Effect: 60m-213msupporting

confidence: 80%

LES of the LS89 cascade: influence of inflow turbulence on the flow predictions

Segui

Gicquel

Duchaine

et al. 2017

European Conference on Turbomachinery Fluid Dynamics and Hermodynamics

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Free-stream turbulence preceding high-pressure turbine blades has a crucial impact on blade fields including the heat transfer on the wall. Many parameters characterize this turbulence; its intensity, length scales and physical spectrum are addressed in the study of various operating points of the LS89 configuration. Usually, operating points where weak turbulence is injected are well predicted for all fields by Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). The MUR235 operating point however, with an experimentally injected turbulence level of 6%, remains incorrectly predicted when imposing the experimental values in the simulations. Such difficulties raise many questions amongst which mesh size and turbulent kinetic energy spectrum are of specific importance for LES. Going away from synthetic turbulence injection by imposing a physical energy spectrum can help improving the prediction of heat transfer. From the present study, it seems that turbulent spots developing in a pre-transition region for higher levels of turbulence on the suction side are important features to capture for proper predictions. In parallel, typical structures of boundary layers such as streamwise oriented vortices have been observed and their existence conditions the heat transfer field on the blade wall. From this specific study, all of these physical processes are seen to be highly dependent on the turbulent specification and turbulent transition observed for the MUR235 case. Depending on these inflow specifications, a transitional boundary layer may be encountered upstream of the shock thus modifying the heat transfer profile.

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Section: Grid Effect: 60m-213msupporting

confidence: 80%

LES of the LS89 cascade: influence of inflow turbulence on the flow predictions

Segui

Gicquel

Duchaine

et al. 2017

European Conference on Turbomachinery Fluid Dynamics and Hermodynamics

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“…In the case of thick trailing edges, in addition to the mixing of fluid streams, the separated blade boundary layers at the trailing edge also contribute to the formation of vortices. When the vortices mix out, high rates of viscous shear occurs which is a major entropy generation mechanism [15].…”

Section: Resultsmentioning

confidence: 99%

Effect of trailing edge thickness on the performance of a helium turboexpander used in cryogenic refrigeration and liquefaction cycles

Sam

Ghosh

2017

IOP Conf. Ser.: Mater. Sci. Eng.

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View the article online for updates and enhancements. Related contentParametric studies on floating pad journal bearing for high speed cryogenic turboexpanders A Jain, M M Jadhav, S Karimulla et al. Abstract. Turboexpanders in cryogenic refrigeration and liquefaction cycles, which is of radial inflow configuration, constitute stationary and rotating components like nozzle, a rotating wheel and a diffuser. The relative motion between the stationary and rotating components and the interactions of secondary flows and vortices at different stages make the turboexpander flow unsteady. Computational Fluid Dynamics (CFD) analysis of this flow is essential to identify the scope for improvement in efficiency. The trailing edge vortex formed due to the mixing of the pressure and suction side streams is an important phenomenon to analyse, as this leads to efficiency degradation of the machine. Additionally, there are mechanical vibrations and dynamic loading associated with. This flow non-uniformity at the exit should be suppressed as this may affect the pressure recovery process in the diffuser and thereby the turboexpander's performance. The strength of this vortex depends upon the geometrical parameters like trailing edge shape, thickness etc. In this paper, transient CFD analyses of a cryogenic turboexpander designed for helium refrigeration and liquefaction cycles using Ansys CFX ® were performed to investigate the effect of trailing edge thickness on the turboexpander performance and the performance characteristics and the flow patterns were compared to understand the flow characteristics in each case.

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“…Predicting the absolute values of the base pressure correctly can be very difficult due to the highly complex nature of the flow in the trailing edge. Vagnoli et al [29] showed that steady state simulations usually predict the wrong shape or distribution of pressure around the trailing edge, whereas large eddy simulation (LES) or Unsteady Reynolds-Averaged Navier-Stokes (URANS) capture much better the shape and the pressure values when compared to experimental data. The pressure distribution shown in Figure 7a is a nearly-uniform pressure around the trailing edge, which is suspected to be different to the real pressure distribution profile.…”

Section: Base Pressurementioning

confidence: 99%

Optimization of the LS89 Axial Turbine Profile Using a CAD and Adjoint Based Approach †

Torreguitart

Verstraete

Mueller

2018

IJTPP

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The LS89 high pressure axial turbine vane was originally designed and optimized for a downstream isentropic Mach number of 0.9. This profile has been widely used for computational fluid dynamics (CFD) validation in the open literature but very few attempts have been made to improve the already optimized design. This paper presents a sound methodology to design and optimize the LS89 using computer-aided design (CAD) at design conditions. The novelty of the study resides in the parametrization of design space, which is done at the CAD level, and the detailed analysis of the aerodynamic performance of the optimized design. Higher level constraints are imposed on the shape, such as the trailing edge thickness, the axial chord length, and G2 geometric continuity between the suction side and pressure side at the leading edge. The gradients used for the optimization are obtained by applying algorithmic differentiation to the CAD kernel and grid generator and the discrete adjoint method to the CFD solver. A reduction of almost 12% entropy generation is achieved, which is equivalent to a 16% total pressure loss reduction. The entropy generation is reduced while keeping the exit flow angle as a flow constraint, which is enforced via the penalty formulation. The resulting unconstrained optimization problem is solved by the L-BFGS-B algorithm. The flow is governed by the Reynolds-averaged Navier-Stokes equations and the one-equation transport Spalart-Allmaras turbulence model. The optimal profile is compared and benchmarked against the baseline case.

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Prediction of the unsteady turbine trailing edge wake flow characteristics and comparison with experimental data

Cited by 14 publications

References 18 publications

LES of the LS89 cascade: influence of inflow turbulence on the flow predictions

LES of the LS89 cascade: influence of inflow turbulence on the flow predictions

Effect of trailing edge thickness on the performance of a helium turboexpander used in cryogenic refrigeration and liquefaction cycles

Optimization of the LS89 Axial Turbine Profile Using a CAD and Adjoint Based Approach †

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