A Periodically Perturbed Backward-Facing Step Flow by Means of LES, DES and T-RANS: An Example of Flow Separation Control

[+] Author and Article Information
S. Šarić, S. Jakirlić, C. Tropea

Chair of Fluid Mechanics and Aerodynamics,  Darmstadt University of Technology, Petersenstrasse 30, D-64287 Darmstadt, Germany

J. Fluids Eng 127(5), 879-887 (Jul 07, 2005) (9 pages) doi:10.1115/1.2012502 History: Received July 23, 2004; Revised July 07, 2005

Turbulent flow over a backward-facing step, perturbed periodically by alternative blowing∕suction through a thin slit (0.05H width) situated at the step edge, was studied computationally using (LES) large eddy simulation, (DES) detached eddy simulation, and (T-RANS) transient Reynolds-averaged Navier–Stokes techniques. The flow configuration considered (ReH=UcHν=3700) has been investigated experimentally by Yoshioka (1-2). The periodic blowing∕suction with zero net mass flux is governed by a sinusoidal law: ve=0.3Ucsin(2πfet), Uc being the centerline velocity in the inlet channel. Perturbation frequencies fe corresponding to the Strouhal numbers St=0.08, 0.19, and 0.30 were investigated (St=feHUc). The experimental observation that the perturbation frequency St=0.19 represents the most effective case, that is the case with the minimum reattachment length, was confirmed by all computational methods. However, the closest agreement with experiment (the reattachment length reduction of 28.3% compared to the unperturbed case) was obtained with LES (24.5%) and DES (35%), whereas the T-RANS computations showed a weaker sensitivity to the perturbation: 5.9% when using the Spalart–Allmaras model and 12.9% using the kω SST model.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 2

Grid detail in the region around step

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Figure 1

Schematic of the flow configuration considered

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Figure 10

Resolved vs modelled: streamwise turbulence intensities, St=0.0

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Figure 11

Mean streamwise velocity profiles for the unperturbed case (St=0.0) at selected streamwise locations normalized by H (upper) and corresponding reattachment length XR (lower)

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Figure 20

Instantaneous velocity contours and vectors, St=0.19

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Figure 3

Semilog profiles of the mean velocity

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Figure 4

Streamwise and normal-to-wall stresses

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Figure 5

Reynolds shear stress profiles

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Figure 6

Computed and modelled SGS kinetic energy

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Figure 7

Frequency-spectra of the streamwise velocity fluctuations at the symmetry plane −y+=188

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Figure 8

LES vs DES: streamwise turbulence intensities, St=0.0

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Figure 9

Streamwise turbulence intensities, St=0.0

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Figure 12

Profiles of streamwise, normal-to-wall and shear stress components, St=0.0

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Figure 13

Time-averaged streamlines and kinetic energy contours for unperturbed (upper) and perturbed (St=0.19; lower) cases

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Figure 14

Evolution of the relative reattachment lengths in terms of St. Exp.: Obi (2002)

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Figure 15

Mean streamwise velocity profiles, St=0.19

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Figure 16

Profiles of streamwise, normal-to-wall and shear stress components, St=0.19

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Figure 17

Mean velocity profiles in terms of St

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Figure 18

Streamwise stress profiles in terms of St

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Figure 19

Shear stress profiles: comparison of LES, DES, and T-RANS results with experiments




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