fluent噪声培训资料(中)

Tutorial:Broadband Noise Modeling

Purpose

The purpose of this tutorial is to provide guidelines and recommendations for the basic setup and solution procedure for solving an acoustics?eld generated from a sedan car using the broadband noise model.The problem is initially solved for steady state,and then the broadband 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 solution procedures in FLUENT.This tutorial does not cover mechanics of using the broadband noise model,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?rst review FLUENT6.2User’s Guide and FLUENT6.2Tutorial Guide.

Problem Description

The problem involves a sedan car model as shown in Figure1.The car is traveling at70 miles per hour.You will study only the acoustics?eld generated by the motion of the car to highlight the noise source on the sedan body,therefore the mirrors and the wheels of the car are ignored.

Figure1:The Sedan Car

Broadband Noise Modeling

Preparation

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

rectory.

2.Start the3D version of FLUENT.

Setup and Solution

Step1:Grid

1.Read the mesh?le,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...

Figure2:Grid Display

Broadband Noise Modeling Step2:Models

1.Keep the default solver settings.

De?ne?→Models?→Solver...

2.Enable the standard k-epsilon turbulence model.

De?ne?→Models?→Viscous...

Step3:Materials

De?ne?→Materials...

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

Step4:Operating Conditions

De?ne?→Operating Conditions...

1.Keep the default operating conditions.

Step5:Boundary Conditions

De?ne?→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.

Broadband Noise Modeling

i.Specify a value of31for Velocity Magnitude.

ii.Select Intensity and Length Scale in the Turbulence Speci?cation Method drop-down list.

iii.Specify a value of2and0.35for Turbulence Intensity and Turbulence Length Scale respectively.

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

3.Keep the default boundary conditions for other walls.

Broadband Noise Modeling Step6:Solution

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

Solve?→Controls?→Solution...

2.Enable the plotting of residuals during the calculation(Figure3).

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?le(sedan.cas.gz).

5.Start the calculation by requesting70iterations.

Solve?→Iterate...

6.Write the data?le(sedan.dat.gz).

Broadband Noise Modeling

Figure3:Scaled Residuals

Step7:Enable the Broadband Acoustic Model

De?ne?→Models?→Acoustics...

1.Under Model,select Broadband Noise Sources.

(a)Specify a value4e-10for Reference Acoustic Power(w).

(b)Set the Number of Realizations to50.

Broadband Noise Modeling

(c)Retain the default values for the rest of the model constants and click OK to

close the panel.

Step8:Postprocessing

1.Display the?lled contours of Acoustics Power Level(dB)on the surfaces of the sedan

car,i.e.,front,rear,and cabinet(Figure4).

Display?→Contours...

(a)Under Options,select Filled.

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

lists.

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

(d)Click Display.

2.Similarly,display the?lled contours of Surface Acoustics Power Level(dB)(Figure5),

and Lilley’s Total Noise Source(Figure6)on the surfaces of the sedan car.

Broadband Noise Modeling

Figure4:Contours of Acoustic Power Level

Figure5:Contours of Surface Acoustics Power Level

Broadband Noise Modeling

Figure6:Contours of Lilley’s Total Noise Source

Summary

This tutorial demonstrated the use of FLUENT’s broadband noise acoustic model to solve an acoustics?eld generated from a sedan car.You have learned how to set up the relevant parameters and postprocess the noise signals to highlight the source of noise on the sedan car body.