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TECHNICAL PAPERS

# Assessment of Predictive Capabilities of Detached Eddy Simulation to Simulate Flow and Mass Transport Past Open Cavities

[+] Author and Article Information
Kyoungsik Chang

KAIST, Daejeon 305-701, South Koreakschang76@kaist.ac.kr

George Constantinescu1

Civil and Environmental Engineering Department and IIHR Hydroscience and Engineering, The University of Iowa, Iowa City, IA 52242sconstan@engineering.uiowa.edu

Seung-O Park

KAIST, Daejeon 305-701, South Koreasopark@kaist.ac.kr

1

Corresponding author.

J. Fluids Eng 129(11), 1372-1383 (Jun 05, 2007) (12 pages) doi:10.1115/1.2786529 History: Received August 01, 2006; Revised June 05, 2007

## Abstract

The three-dimensional (3D) incompressible flow past an open cavity in a channel is predicted using the Spalart–Almaras (SA) and the shear-stress-transport model (SST) based versions of detached eddy simulation (DES). The flow upstream of the cavity is fully turbulent. In the baseline case the length to depth $(L∕D)$ ratio of the cavity is 2 and the Reynolds number $ReD=3360$. Unsteady RANS (URANS ) is performed to better estimate the performance of DES using the same code and meshes employed in DES. The capabilities of DES and URANS to predict the mean flow, velocity spectra, Reynolds stresses, and the temporal decay of the mass of a passive contaminant introduced instantaneously inside the cavity are assessed based on comparisons with results from a well resolved large eddy simulation (LES) simulation of the same flow conducted on a very fine mesh and with experimental data. It is found that the SA-DES simulation with turbulent fluctuations at the inlet gives the best overall predictions for the flow statistics and mass exchange coefficient characterizing the decay of scalar mass inside the cavity. The presence of inflow fluctuations in DES is found to break the large coherence of the vortices shed in the separated shear layer that are present in the simulations with steady inflow conditions and to generate a wider range of 3D eddies inside the cavity, similar to LES. The predictions of the mean velocity field from URANS and DES are similar. However, URANS predictions show poorer agreement with LES and experiment compared to DES for the turbulence quantities. Additionally, simulations with a higher Reynolds number $(ReD=33,600)$ and with a larger length to depth ratio $(L∕D=4)$ are conducted to study the changes in the flow and shear-layer characteristics, and their influence on the ejection of the passive contaminant from the cavity.

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## Figures

Figure 1

Computational domain

Figure 2

Mean streamwise velocity profiles for SA DES with different mesh sizes. (a) x∕D=−0.1, (b) x∕D=1.0, and (c) x∕D=1.7.

Figure 3

Power spectra of vertical velocity at a point situated close to the trailing edge corner for SA DES with different mesh sizes

Figure 4

Decay of scalar mass inside the cavity shown in log-linear scale for SA DES with different mesh sizes

Figure 5

Mean velocity streamlines. Experimental data are from Pereira and Sousa (4-5).

Figure 6

Mean streamwise velocity profiles at several streamwise stations. Symbols correspond to the experiment of Pereira and Sousa (4-5).

Figure 7

Variation of shear-layer vorticity thickness (δ) with distance from the leading edge

Figure 8

Distribution of turbulent kinetic energy and turbulence production

Figure 9

Resolved Reynolds stresses at different streamwise stations. Symbols correspond to the experiment of Pereira and Sousa (4-5). (a) Normal streamwise stress and (b) primary shear stress.

Figure 10

Vertical velocity time history at point 1 (frames (a) and (b)) situated close to the leading edge corner and at point 2 (frames (c) and (d)) situated close to the trailing edge corner

Figure 11

Power spectra of vertical velocity at a point situated close to the trailing edge corner inside the separated shear layer for simulations with L∕D=2

Figure 12

Instantaneous vorticity magnitude contours in an x-y plane (left) and in a spanwise y-z plane (right) cutting through the middle of the cavity (x∕D=1.0) for simulations with L∕D=2. (a) SST-URANS-R, (b) SST-URANS-L, (c) SA-DES-R, (d) SA-DES-L, and (e) SA-DES-L-HRE.

Figure 13

Decay of scalar mass inside the cavity shown in log-linear scale for simulations with L∕D=2

Figure 14

Statistics for cavity with L∕D=4 (SA-DES-L). (a) 2D streamlines, (b) 2D streamlines from Shieh and Morris (13), (c) turbulent kinetic energy, and (d) turbulence production.

Figure 15

Power spectra of vertical velocity at a point situated close to the trailing edge corner inside the separated shear layer for simulations with L∕D=4

Figure 16

Instantaneous vorticity magnitude contours in an x-y plane (left) and in a spanwise y-z plane (right) cutting through the middle of the cavity (x∕D=1.0) for simulations with L∕D=4. (a) SST-URANS-L and (b) SA-DES-L.

Figure 17

Decay of scalar mass inside the cavity shown in log-linear scale for simulations with L∕D=4

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