大涡模拟的FLUENT算例2D

Tutorial:Modeling Aeroacoustics for a Helmholtz Resonator Using the Direct Method(CAA)

Introduction

The purpose of this tutorial is to provide guidelines and recommendations for the basic setup and solution procedure for a typical aeroacoustic application using computational aeroacoustic(CAA)method.

In this tutorial you will learn how to:

•Model a Helmholtz resonator.

•Use the transient k-epsilon model and the large eddy simulation(LES)model for

aeroacoustic application.

•Set up,run,and perform postprocessing in FLUENT.

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 acoustics model,but focuses on setting up the problem for Helmholtz-Resonator and solving it.It also assumes that you have basic understanding of aeroacoustic physics.

If you have not used FLUENT before,it would be helpful tofirst review FLUENT6.3User’s Guide and FLUENT6.3Tutorial Guide.

Problem Description

A Helmholtz resonator consists of a cavity in a rigid structure that communicates through a

narrow neck or slit to the outside air.The frequency of resonance is determined by the mass of air in the neck resonating in conjunction with the compliance of the air in the cavity.

The physics behind the Helmholtz resonator is similar to wind noise applications like sun roof buffeting.

We assume that out of the two cavities that are present,smaller one is the resonator.The motion of thefluid takes place because of the inlet velocity of27.78m/s(100km/h).The flow separates into a highly unsteady motion from the opening to the small cavity.This unsteady motion leads to a pressurefluctuations.Two monitor points(Point-1and Point-2) act as microphone points to record the generated sound.The acoustic signal is calculated within FLUENT.Theflow exits the domain through the pressure outlet.

Modeling Aeroacoustics for a Helmholtz Resonator Using the Direct Method(CAA) Preparation

1.Copy thefiles steady.cas.gz,steady.dat.gz,execute-by-name.scm,stptmstp4.scm,

ti-to-scm-jos.scm and stptmstp.txt into your working directory.

2.Start the2D double precision(2ddp)version of FLUENT.

Setup and Solution

Step1:Grid

1.Read the initial case and datafiles for steady-state(steady.cas.gz and steady.dat.gz).

File−→Read−→Case&Data...

Ignore the warning that is displayed in the FLUENT console while reading thesefiles.

2.Keep default scale for the grid.

Grid−→Scale...

3.Display the grid and observe the locations of the two monitor points,Point-1and

Point-2(Figure1).

Figure1:Graphics Display of the Grid

4.Display and observe the contours of static pressure(Figure2)and velocity magnitude

(Figure3)for the initial steady-state solution.

Display−→Contours..