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Research Papers: Flows in Complex Systems

A Numerical Investigation of the Flow Past a Generic Side Mirror and its Impact on Sound Generation

[+] Author and Article Information
Jonas Ask

Environment and Fluid Dynamics Centre, Volvo Car Corporation, SE-405 31 Göteborg, Sweden

Lars Davidson

Department of Applied Mechanics, Division of Fluid Dynamics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden

J. Fluids Eng 131(6), 061102 (May 14, 2009) (12 pages) doi:10.1115/1.3129122 History: Received October 19, 2007; Revised March 19, 2009; Published May 14, 2009

The case investigated is the flow past a generic side mirror mounted on a flat plate at the Reynolds number of ReD=5.2×105 based on the mirror diameter. The present work studies both flow and acoustic sources by evaluating two second-order advection schemes, different levels of turbulence modeling, and three different grids. The advection schemes discussed in the present study are a second-order upwind scheme and a monotonic central scheme. The turbulence models investigated cover three levels of modeling. These are the original formulation of the detached eddy simulation (DES) model, the Smagorinsky–Lilly sub-grid scale (SGS) model with near-wall damping, and a dynamic Smagorinsky model. The different grids are as follows: a primary grid where all parameter studies are conducted and a second grid with significantly higher wake resolution and to some extent also increased plate resolution, while maintaining the resolution at the front side of the mirror. The final grid uses a significantly higher plate resolution and a wake resolution similar to that of grid two, but a comparably lower mirror front side resolution as compared with the two other grids. The general outcome of this work is that the estimation of the grid cutoff frequency through a relation of the velocity fluctuation and the grid size matches both the experimental results and trend lines perfectly. Findings from the flow field show that the horseshoe vortex in front of the mirror causes pressure fluctuations with a magnitude exceeding the maximum levels at the rear side of the mirror. Its location and unsteady properties are perfectly captured in the final simulation as compared with the experiments conducted by Daimler–Chrysler. A laminar separation at the front side of the mirror is more or less found for all wall resolved cases except the DES simulation. The third grid fails to predict this flow feature, but it is shown that this effect has no significant effect on either the static pressure sensors at the mirror surface or at the dynamic sensors located downstream of the mirror. The simulation also supports the fundamental frequency based on the eddy convection in the mirror shear layer, which is shown to be twice as high as the frequency peak found in the lateral force spectra.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Mirror geometry: side view and front view, respectively

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Figure 2

Mirror and plate: x−z plane

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Figure 3

Location of static pressure sensors over the front and rear side of the mirror: (a) Static sensor distribution over the front side and (b) static senor distribution over the rear side

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Figure 4

Location of dynamic pressure sensors over the rear side of the mirror and the plate: (a) Dynamic sensor distribution over the rear side and (b) dynamic senor distribution over the plate

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Figure 5

Effect of advection scheme at sensor S119, DES and Dynamic Smagorinsky models

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Figure 6

Effect of advection scheme at sensor S123, DES and Dynamic Smagorinsky model, respectively

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Figure 7

Oil film visualization and snapshot of wall shear stresses for the M1SLBCD case: (a) Oil film visualization (courtesy of Daimler Chrysler Research and Technology), and (b) wall shear stress, M1SLBCD, 0<τwall<2.0

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Figure 8

Snapshot of wall shear stresses for the M1DSBCD and M1SABCD casese: (a) Wall shear stress, M1DSBCD, 0<τwall<2.0 and (b) wall shear stress, M1SABCD, 0<τwall<2.0

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Figure 9

Effect of different turbulence models

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Figure 10

Effect of resolution at four different positions in the mirror wake

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Figure 11

Characterization of dominating flow structures

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Figure 12

Mean pressure over mirror: (-) measured, (△) M2SLBCD, and (○) M3SLBCD

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Figure 13

Force coefficient results for the M3SLBCD case

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Figure 14

RMS of wall pressure (Pa) and sensor positions for the M3SLBCD case: (a) RMS of pressure on the rear side of the mirror and (b) RMS of pressure fluctuations over the plate

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Figure 15

SPL at sensors S111 and S114

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Figure 16

SPL at sensors S112 and S113

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Figure 17

SPL at sensors S116 and S117

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Figure 18

SPL at sensors S118 and S119

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Figure 19

SPL at sensors S120 and S121

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Figure 20

SPL at sensors S122 and S123

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