Purpose Prerequisites

Tutorial: Broadband Noise Modeling

Purpose

The purpose of this tutorial is to provide guidelines and recommendations for the basicsetup and solution procedure for solving an acoustics field generated from a sedan car usingthe broadband noise model. The problem is initially solved for steady state, and then thebroadband acoustic model is included in the calculation to perform postprocessing.

Prerequisites

This tutorial assumes that you are familiar with the user interface, basic setup and solutionprocedures in FLUENT. This tutorial does not cover mechanics of using the broadband noisemodel, but focuses on setting up the problem for a sedan car and performing postprocessing.It also assumes that you have a basic understanding of aeroacoustic physics.

If you have not used FLUENT before, it would be helpful to first review FLUENT 6.2 User’sGuide and FLUENT 6.2 Tutorial Guide.

Problem Description

The problem involves a sedan car model as shown in Figure 1. The car is traveling at 70miles per hour. You will study only the acoustics field generated by the motion of the carto highlight the noise source on the sedan body, therefore the mirrors and the wheels of thecar are ignored.

Figure 1: The Sedan Car

c© Fluent Inc. March 18, 2005 1

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Broadband Noise Modeling

Preparation

1. Copy the mesh file, sedan-acoustics.msh from the input file into your working di-rectory.

2. Start the 3D version of FLUENT.

Setup and Solution

Step 1: Grid

1. Read the mesh file, sedan-acoustics.msh.

File −→ Read −→Case...

2. Check the grid.

Grid −→Check...

3. Keep default scale for the grid.

Grid −→Scale...

4. Display the grid.

Display −→Grid...

GridFLUENT 6.2 (3d, segregated, lam)

Z

Y

X

Figure 2: Grid Display

2 c© Fluent Inc. March 18, 2005


Step 2: Models

1. Keep the default solver settings.

Define −→ Models −→Solver...

2. Enable the standard k-epsilon turbulence model.

Define −→ Models −→Viscous...

Step 3: Materials

Define −→Materials...

1. Keep the default selection of air in the Materials panel.

Step 4: Operating Conditions

Define −→Operating Conditions...

1. Keep the default operating conditions.

Step 5: Boundary Conditions

Define −→Boundary Conditions...

1. Set the boundary conditions for velocity inlet (inlet).

(a) Under Zone, select inlet.

The Type will be reported as velocity-inlet.

(b) Click Set... to open the Velocity Inlet panel.



i. Specify a value of 31 for Velocity Magnitude.

ii. Select Intensity and Length Scale in the Turbulence Specification Method drop-down list.

iii. Specify a value of 2 and 0.35 for Turbulence Intensity and Turbulence LengthScale respectively.

2. Set the boundary conditions for pressure outlet (outlet) as shown in the panel.

3. Keep the default boundary conditions for other walls.



Step 6: Solution

1. Retain the default under-relaxation factors and discretization schemes.

Solve −→ Controls −→Solution...

2. Enable the plotting of residuals during the calculation (Figure 3).

Solve −→ Monitors −→Residual...

3. Initialize the solution.

Solve −→ Initialize −→Initialize...

(a) Select inlet in the Compute From drop-down list and click Init.

4. Write the case file (sedan.cas.gz).

5. Start the calculation by requesting 70 iterations.

Solve −→Iterate...

6. Write the data file (sedan.dat.gz).



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Scaled ResidualsFLUENT 6.2 (3d, segregated, ske)

Iterations706050403020100

1e+03

1e+02

1e+01

1e+00

1e-01

1e-02

1e-03

1e-04

1e-05

1e-06

epsilonkz-velocityy-velocityx-velocitycontinuityResiduals

Figure 3: Scaled Residuals

Step 7: Enable the Broadband Acoustic Model

Define −→ Models −→Acoustics...

1. Under Model, select Broadband Noise Sources.

(a) Specify a value 4e-10 for Reference Acoustic Power (w).

(b) Set the Number of Realizations to 50.



(c) Retain the default values for the rest of the model constants and click OK toclose the panel.

Step 8: Postprocessing

1. Display the filled contours of Acoustics Power Level (dB) on the surfaces of the sedancar, i.e., front, rear, and cabinet (Figure 4).

Display −→Contours...

(a) Under Options, select Filled.

(b) Select Acoustics... and Acoustic Power Level (dB) from the Contours of drop-downlists.

(c) Under Surfaces, select front, rear, and cabinet.

(d) Click Display.

2. Similarly, display the filled contours of Surface Acoustics Power Level (dB) (Figure 5),and Lilley’s Total Noise Source (Figure 6) on the surfaces of the sedan car.



Contours of Acoustic Power Level (dB)FLUENT 6.2 (3d, segregated, ske)

5.06e+014.80e+014.55e+014.30e+014.05e+013.79e+013.54e+013.29e+013.03e+012.78e+012.53e+012.28e+012.02e+011.77e+011.52e+011.26e+011.01e+017.58e+005.06e+002.53e+000.00e+00 Z

YX

Figure 4: Contours of Acoustic Power Level

Contours of Surface Acoustic Power Level (dB)FLUENT 6.2 (3d, segregated, ske)

5.30e+015.04e+014.77e+014.51e+014.24e+013.98e+013.71e+013.45e+013.18e+012.92e+012.65e+012.39e+012.12e+011.86e+011.59e+011.33e+011.06e+017.95e+005.30e+002.65e+000.00e+00 Z

YX

Figure 5: Contours of Surface Acoustics Power Level



Contours of Lilley’s Total Noise Source (1/s3)FLUENT 6.2 (3d, segregated, ske)

6.21e+135.90e+135.59e+135.28e+134.97e+134.66e+134.35e+134.04e+133.73e+133.42e+133.11e+132.80e+132.48e+132.17e+131.86e+131.55e+131.24e+139.32e+126.21e+123.11e+121.03e+06

Z

YX

Figure 6: Contours of Lilley’s Total Noise Source

Summary

This tutorial demonstrated the use of FLUENT’s broadband noise acoustic model to solvean acoustics field generated from a sedan car. You have learned how to set up the relevantparameters and postprocess the noise signals to highlight the source of noise on the sedancar body.


Purpose Prerequisites

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