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Research Papers: Flows in Complex Systems

Strategies for Simulating Flow Through Low-Pressure Turbine Cascade

[+] Author and Article Information
Andreas Gross

Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721agross@email.arizona.edu

Hermann F. Fasel

Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721

J. Fluids Eng 130(11), 111105 (Sep 23, 2008) (13 pages) doi:10.1115/1.2969463 History: Received November 05, 2007; Revised July 02, 2008; Published September 23, 2008

Laminar separation on the suction side of low-pressure turbine blades at low Reynolds number operating conditions deteriorates overall engine performance and has to be avoided. This requirement affects the blade design and poses a limitation on the maximum permissible blade spacing. Better understanding of the flow physics associated with laminar separation will aid in the development of flow control techniques for delaying or preventing flow separation. Simulations of low-pressure turbine flows are challenging as both unsteady separation and transition are present and interacting. Available simulation strategies have to be evaluated before a well-founded decision for the choice of a particular simulation strategy can be made. With this in mind, this paper provides a comparison of different flow simulation strategies: In particular, “coarse grid” direct numerical simulations, implicit large-eddy simulations, and simulations based on a hybrid turbulence modeling approach are evaluated with particular emphasis on investigating the dynamics of the coherent structures that are generated in the separated flow region and that appear to dominate the entire flow. It is shown that in some instances, the effect of the dominant coherent structures can also be predicted by unsteady Reynolds-averaged Navier–Stokes calculations.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Coarse grid. (a) Block structure (blocks 1–5 from left to right) and (b) entire grid. The lines indicate where profiles in Figs.  910111617 were taken.

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Figure 2

Isosurfaces of Q-criterion, Q=1. Results for (a) DNS, (b) ILES, and (c) FSM. (Left) coarse grid and (right) fine grid.

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Figure 3

Isocontours of (a) eddy viscosity, μT∕μ, (b) contribution function, f, and (c) effective eddy viscosity, fμT∕μ, for (left) coarse grid and (right) fine grid FSM

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Figure 4

Isocontours of grid resolution, Δ∕Lk, for (a) coarse grid and (b) fine grid FSM

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Figure 8

Skin friction coefficient, cF

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Figure 9

Wall-normal profiles of the total velocity. Comparison with experimental data (2,4).

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Figure 10

Wall-normal profiles of model contribution obtained from the FSM simulation

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Figure 11

Wake profiles of the total velocity

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Figure 12

Isocontours of spanwise vorticity, ωz. The results were obtained with (a) LB, (b) k-ε EASM, (c) k-ω, and (d) k-ω EASM model.

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Figure 13

Isocontours of eddy viscosity μT∕μ. The results were obtained with (a) LB, (b) k-ε EASM, (c) k-ω, and (d) k-ω EASM model.

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Figure 14

Wall pressure coefficient, cp

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Figure 15

Skin friction coefficient, cF

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Figure 16

Wall-normal profiles of the total velocity. Comparison with experimental data (2,4).

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Figure 17

Wall-normal profiles of turbulence intensity, Tu

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Figure 18

Fourier mode amplitude, A(k)(s,t), of (a) skin friction coefficient, cF, and (b) wall pressure coefficient, cp, for modes k=0 (left) and k=1 (right) obtained from fine grid DNS data

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Figure 19

Flow visualization near the trailing edge (fine grid DNS). Isocontours of the total velocity of time-averaged data (vtot=0,…,2, Δvtot=0.2) superimposed with isocontours of spanwise vorticity of instantaneous data (gray lines, ωz=−100,…,100, Δωz=40). Indicated in white are lines along which velocity profiles were obtained.

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Figure 20

Separation and reattachment locations obtained from the fine grid FSM in (a) time and (b) frequency domains

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Figure 21

Fourier mode amplitude, A(k)(s,f(n)), of wall pressure coefficient, cp, for modes k=0 (left) and k=1 (right) obtained from fine grid DNS data

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Figure 22

Fourier mode amplitudes, A(s,z=0,f(n)), of wall pressure coefficient, cp, for coarse grid (left) and fine grid (right). Results for (a) DNS, (b) ILES, and (c) FSM.

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Figure 5

Wall pressure coefficient, cp

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Figure 23

Fourier mode amplitudes, A(s,z=0,f(n)), of wall pressure coefficient, cp. URANS results obtained with (a) LB and (b) k-ε EASM model.

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Figure 24

Frequency spectra, A(s,z=0,f(n)), of wall pressure coefficient, cp, at (a) s∕Cx=1(x∕Cx=0.80), (b) s∕Cx=1.2(x∕Cx=0.89), and (c) s∕Cx=1.4(x∕Cx=0.98)

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Figure 6

Isocontours of streamfunction. Results for (a) coarse grid and (b) fine grid FSM

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Figure 7

Instantaneous flow visualizations near the trailing edge. Isocontours of velocity in the cascade exit flow direction superimposed with isocontours of spanwise vorticity (gray lines, ωz=−100,…,100, Δωz=40).

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