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Research Papers: Flows in Complex Systems

Reliable and Accurate Prediction of Three-Dimensional Separation in Asymmetric Diffusers Using Large-Eddy Simulation

[+] Author and Article Information
Hayder Schneider1

Institut für Thermische Strömungsmaschinen, Karlsruher Institut für Technologie (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germanyhayder.schneider@kit.edu

Dominic von Terzi, Hans-Jörg Bauer

Institut für Thermische Strömungsmaschinen, Karlsruher Institut für Technologie (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany

Wolfgang Rodi

Institut für Hydromechanik, Karlsruher Institut für Technologie (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany

1

Corresponding author.

J. Fluids Eng 132(3), 031101 (Mar 04, 2010) (7 pages) doi:10.1115/1.4001009 History: Received August 20, 2009; Revised December 23, 2009; Published March 04, 2010; Online March 04, 2010

Large-eddy simulations (LES) and Reynolds-averaged Navier–Stokes (RANS) calculations of the flow in two asymmetric three-dimensional diffusers were performed. The setup was chosen to match an existing experiment with separation. Both diffusers possess the same expansion ratio but differ in performance. The aim of the present study is to find the least expensive method to reliably and with reasonable accuracy account for the impact of the change in geometry. RANS calculations failed to predict both the extent and location of the separation. In contrast, LES with wall-functions delivered results within the accuracy of the experimental data.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Diffuser design; flow in positive x-direction (from left to right)

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Figure 2

Mean wall-pressure coefficient Cp at z/B=0.5 along the lower wall of diffuser D1: x is normalized with the diffuser length L, pref is taken at x=y=0, and the experimental data are shifted accordingly

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Figure 3

Mean streamwise velocity U/Ub profiles at z/B=0.5 for diffuser D1; from left to right: x/H=0, 5, 12, and 16

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Figure 4

Mean streamwise velocity U/Ub contours of experiments and simulations Ia, Ib, and IIa (left to right) in a cross section at x/H=12 for diffuser D1; same velocity contours with interval 0.1 shown for all plots: thicker line indicates zero-velocity contour

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Figure 5

Mean streamwise velocity U/Ub (top row) and mean vertical velocity V/Ub (bottom row) profiles at z/B=0.5 for diffuser D1; from left to right: x/H=0, 5, 12, and 16

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Figure 6

Mean streamwise velocity U/Ub (top row) and urms/Ub (bottom row) profiles in diffuser D1 at x/H=12; from left to right: z/B=0.25, 0.75, 0.875, and 1

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Figure 7

Mean streamwise velocity U/Ub (top row) and mean vertical velocity V/Ub (bottom row) profiles at z/B=0.5 for diffuser D2; from left to right: x/H=0, 5, 12, and 16

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Figure 8

Mean streamwise velocity U/Ub contours of experiments (left) and simulation IIIa (right) in a cross section at x/H=12 for diffuser D2; same velocity contours with interval 0.1 shown for all plots; thicker line indicates zero-velocity contour

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Figure 9

Mean streamwise velocity U/Ub profiles in diffuser D2 at x/H=12; from left to right: z/B=0.25, 0.75, 0.875, and 1

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Figure 10

Mean fraction of cross-sectional area separated in experiments and simulations IIb and IId for diffuser D1 (left) and simulations IIIa and IIIb for diffuser D2 (right); RANS data of diffuser D1 deviate substantially (not shown)

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Figure 11

Mean streamwise velocity iso-contour U/Ub=0 for diffuser D1 (simulation IIb, left) and D2 (simulation IIIb, right) until x/L=1.67; white dashed lines indicate separation bubbles; no presence of separation in the regions not shown

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