introduction to cfd.pdf

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INTRODUCTION TO CFD ANASISLY

FLUID AERODYNAMICS LABORATORY

Advisor ~ Prof . F. B. Hsiao

Advisee ~ C. J. Bai

Date ~ 2007/12/11

(FLUENT & GAMBIT)

INTRODUCTION TO CFD ANALYSIS

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PARTⅠ

Introduction to CFD analysis

PARTⅡ

Mesh Generator

PARTⅢ

FLUENT Setup and Solution

FALab


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How Does CFD Work ?

Fluid region of pipe flow is

discretized into a finite set

of control volume (mesh).

Fluent solves are based on finite

volume method.

- Domain is discretized onto a finite set of

control vol ume (or cells).

- General conservation (transport) equations for

mass, momentum , energy, species, etc. are

solved on this set of control volumes.

- Partial differential equations are discretized into a

system of algebraic equations.

- Al l algebr aic equat ions are then s olved

numerically to render the solution field.


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CFD Modeling Overview

SolidModeler

MeshGenerator

Pre-Processing Transport Equation

-Mass

-Momentum-Energy

Equations of state

Supporting physical models

Physical Models

-Turbulence

-Combustion-Radiation

-Multiphase

-Phase Change

-Moving Zones

-Moving Mesh

Material Properties

Boundary Conditions

Initial Conditions

Solver setting

Postprocessing

Solver


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CFD Analysis - The Basic Step

Problem Identification and Preprocessing

-Define your modeling goals.

-Identify the domain you w ill model.

-Design and create the grid.

Solver Execution

-Set up the numerical.

-Compute and monitor the s olution.

Post-Processing

-Examine the results.

-Consider revisions to the model.

Catia AutoCADGambitIcem-CFD

.

.

CFXCFDRCCOSMOSFluent

.

.


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Design and Create the Grid

Hybrid mesh for an IC

engine value port


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Turbulence Models Available in FLUENT

Reynolds-Averaged Navier-Stokes (RANS) models

One-order Equation Models

-Spalart-Allmaras

Two-order Equation Models

-Standard k-ε

-RNG k-ε

-Realizable k-ε

-Standardω-ε

-SST k-ω

Reynolds Stress Model

RANS based

models

Increase in

computational

cost per

iteration


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TheThe viscosityviscosity--affected region is notaffected region is not

resolved, instead is bridged by theresolved, instead is bridged by the

wall function.wall function.

HighHigh--Re turbulence models can beRe turbulence models can be

used.used.

The near The near --wall region is resolved all thewall region is resolved all the

way down to the wall.way down to the wall.

The turbulence models ought to be validThe turbulence models ought to be valid

throughout the near throughout the near --wall region.wall region.

-Standard k-ε

-RNG k-ε

-Realizable k -ε

-RSM

-Spalart-Allmaras

-Standardω

-ε

-SST k-ω

Wall Boundary Conditions


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Placement of The First Grid PointWall functi on ~ y+≒ 30-300

Near-wall function ~ y+≒

1

Non-dimensional distance from a wall in a

turbulent boundary layer is given by y+

μ

ρ yu y t =

+

where ut is the friction velocity, define as

(τw/ρ)0.5.

The shear stress on the surface:

N

w

RU

73.0

2

1 2=

ρ

τ


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PARTⅠ


PART

Ⅱ

Mesh Generator

PARTⅢ



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Case1 2-D Airfoil

Problem Description

RE=1x106

Angle of attack=4

Naca4412

Chord length = 1c


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Mesh command button → Mesh → Mesh edgesMesh command button → Mesh → Mesh edges


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Mesh command button→

Mesh→

Mesh edges


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Boundary-layer → Create boundary l ayer


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Mesh→

Mesh edges


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Mesh command button → Mesh → Mesh edges


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Mesh→

Mesh edges


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Mesh command button → Mesh → Mesh faces


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Zones co mmand button→

Specify boundary types


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Zones co mmand button → Specify boundary types


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Zones co mmand button→

Specify boundary types


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Zones co mmand button → Specify c ontinuum t ypes


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File→ Export→ Mesh…


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PARTⅠ


PART

Ⅱ

Mesh Generator

PARTⅢ



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Step 1 Grid

Read the grid file airfoil-2D.mesh

File → Read → Case….

Check t he grid.

Grid → Check

Display the grid

Display→

Grid….

The Entire Grid


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Step 2 Models

Specify the solver settings.

Define→ Models → Solver….

Note

Seclect Green-Gauss Node Based

This option uses better numerics, in

particular in unstr uctured meshs. It also

tends to predict drag more accurately.


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Enable the k- epsilon turbulence model.

Define→ Models → Viscous….


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Set the properties for air, the default fluid materials.

Define→ Materials….

Step 3 Materials


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Step 4 Boundary Conditions

Define→ Boundary Conditions….


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1.Set the boundary conditions for velocity-inlet

Note

Enter 0.997564 and 0.069756

for the X-Y components of

flow direction.

Note The viscosity ratio should

be between 1 and 10 for

external flows .


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2.Set the boundary conditions for pressure-outlet


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Step 5 Solution

Define a force monitor to print, write, and drag coefficient for the walls of the airfoil.

Note

Enter 7.28588 for X and

0.50948 for Y in the Force

Vector B ox.


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Define a force monitor to print, write, and lift coefficient for the walls of the airfoil.

Note Enter -0.50948 for X and

7.28588 for Y in the Force

Vector B ox.


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Define the residual monitor to print and plot.


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Initialize the solution.

Solver→ Initialize → Initialize….


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Set the reference value that are used to compute the lift and drag coeff icients .

Report → Reference values….


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Save the case and data files(airfoil -2D.cas and airfoi l-2D.dat)

Start the calculation by requesting 100 iterations.

Step 6 Postprocessing


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Thanks!!

FALab

introduction to cfd.pdf

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