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Research Papers: Flows in Complex Systems

Flow and Dipole Source Evaluation of a Generic SUV

[+] Author and Article Information
Jonas Ask

Department of 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 132(5), 051111 (May 14, 2010) (12 pages) doi:10.1115/1.4001340 History: Received November 14, 2007; Revised January 18, 2010; Published May 14, 2010; Online May 14, 2010

Accurately predicting both average flow quantities and acoustic sources at the front window of today’s ground vehicles are still a considerable challenge to automotive companies worldwide. One of the most important aspects in terms of obtaining not only trustworthy results but also the most tedious one and therefore perhaps overlooked, is the control and outcome of the mesh generation process. Generating unstructured volume meshes suitable for large eddy simulations with high level representation of geometrical details is both a time consuming and an extremely computer demanding activity. This work investigates two different mesh generation processes with its main aim to evaluate their outcome with respect to the prediction of the two dominating dipole sources in a temporal form of the Curle’s equation. Only a handful of papers exists that report a high level representation of the vehicle geometry and the aim of predicting the fluctuating exterior noise sources. To the author’s knowledge no studies have been conducted in which both these source terms are evaluated quantitatively against measurements. The current paper investigates the degree to which the amplitude of these two source terms can be predicted by using the traditional law-of-the-wall and hex-dominant meshes with isotropic resolution boxes for a detailed ground vehicle geometry. For this purpose, the unstructured segregated commercial FLUENT finite volume method code is used. The flow field is treated as incompressible and the Smagorinsky–Lilly model is used to compute the subgrid stresses. Mean flow quantities are measured with a 14 hole probe for 14 rakes downstream of the side mirror. The dynamic pressure sensors are distributed at 16 different positions over the side window to capture the fluctuating pressure signals. All measurements in this work were conducted at Ford’s acoustic wind tunnel in Cologne. All three simulations accurately predict the velocity magnitude closest to the window and downstream of the mirror head recirculation zone. Some variations in the size and shape of this recirculation zone are found between the different meshes, most probably caused by differences in the detachment of the mirror head boundary layer. The Strouhal number of the shortest simulation was computed from the fundamental frequency of the drag force coefficient. The computed Strouhal number agrees well with the corresponding results from similar objects and gives an indication of an acceptable simulation time. The dynamic pressure sensors at 16 different locations at the vehicle side window were also used to capture the levels of the two dipole source terms. These results are compared with the three simulations. With the exception of three positions, at least one of the three simulations accurately captures the levels of both source terms up to about 1000 Hz. The three positions with less agreement as compared with measurements were found to be in regions sensitive to small changes in the local flow direction.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Vehicle geometry

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Figure 2

Mirror geometry, front view

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Figure 3

Mesh cut planes for GSM2I and GSM3H: (a) cut through the mesh of case GSM2I and (b) cut through the mesh of case GSM3H

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Figure 4

Positions of the 14 hole probe: (a) probe location, top view and (b) probe location, side view

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Figure 5

Positions of the dynamic pressure sensors

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Figure 6

Flow field for case GSM2I. Contours denote prms. Black corresponds to high values (150 Pa) and white is prms=0.

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Figure 7

Velocity magnitude for cases GSM3H and GSM2I: (a) velocity magnitude for case GSM3H and (b) velocity magnitude for case GSM2I

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Figure 8

|U| along rakes 1–6, GSM1I (△), GSM2I (○), and, GSM3H (+) measured (−): (a) |U| along rake 1, (b) |U| along rake 2, (c) |U| along rake 3, (d) |U| along rake 4, (e) |U| along rake 5, and, (f) |U| along rake 6

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Figure 9

|U| along raked 7–12, GSM1I (△), GSM2I (○), and, GSM3H (+) measured (−): (a) |U| along rake 7, (b) |U| along rake 8, (c) |U| along rake 9, (d) |U| along rake 10, (e) |U| along rake 11, and, (f) |U| along rake 12

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Figure 10

Cd and Cℓ for GSM3H: (a) mirror streamwise and floor normal force coefficient and (b) PSD of the force coefficients

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Figure 11

Contours of the two dipole source terms: (a) contours of source term 1 and (b) contours of source term 2

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Figure 12

Power spectral density of source term 1 for cases GSM1I (△), GSM2I (○), and, GSM3H (+) measured (−), where pref=2e−5 Pa: (a) PSD of source term 1 at position 1, (b) PSD of source term 1 at position 2, (c) PSD of source term 1 at position 3, (d) PSD of source term 1 at position 4, (e) PSD of source term 1 at position 5, and, (f) PSD of source term 1 at position 6

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Figure 13

Power spectral density of source term 1 for cases GSM1I (△), GSM2I (○), and, GSM3H (+) measured (−), where pref=2e−5 Pa: (a) PSD of source term 1 at position 7, (b) PSD of source term 1 at position 8, (c) PSD of source term 1 at position 9, (d) PSD of source term 1 at position 10, (e) PSD of source term 1 at position 11, and (f) PSD of source term 1 at position 12

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Figure 14

Power spectral density of source term 1 for cases GSM1I (△), GSM2I (○), and GSM3H (+) measured (−), where pref=2e−5 Pa: (a) PSD of source term 1 at position 13, (b) PSD of source term 1 at position 14, (c) PSD of source term 1 at position 15, and (d) PSD of source term 1 at position 16

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Figure 15

Power spectral density of source term 2 for cases GSM1I (△), GSM2I (○), and GSM3H (+) measured (−), where pref=2e−5 Pa: (a) PSD of source term 2 at position 1, (b) PSD of source term 2 at position 2, (c) PSD of source term 2 at position 3, (d) PSD of source term 2 at position 4, (e) PSD of source term 2 at position 5, and (f) PSD of source term 2 at position 6

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Figure 16

Power spectral density of source term 2 for cases GSM1I (△), GSM2I (○), and GSM3H (+) measured (−), where pref=2e−5 Pa: (a) PSD of source term 2 at position 7, (b) PSD of source term 2 at position 8, (c) PSD of source term 2 at position 9, (d) PSD of source term 2 at position 10, (e) PSD of source term 2 at position 11, and (f) PSD of source term 2 at position 12

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Figure 17

Power spectral density of source term 2 for cases GSM1I (△), GSM2I (○), and GSM3H (+) measured (−), where pref=2e−5 Pa: (a) PSD of source term 2 at position 13, (b) PSD of source term 2 at position 14, (c) PSD of source term 2 at position 15, and (d) PSD of source term 2 at position 16

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