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8/17/2019 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
FLUENT & GAMBIT
1/392007/12/11
PARTⅠ
Introduction to CFD analysis
PARTⅡ
Mesh Generator
PARTⅢ
FLUENT Setup and Solution
FALab
8/17/2019 introduction to CFD.pdf
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2
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.
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
2/392007/12/11 FALab
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
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
3/392007/12/11 FALab
8/17/2019 introduction to CFD.pdf
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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
.
.
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
4/392007/12/11 FALab
Design and Create the Grid
Hybrid mesh for an IC
engine value port
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
5/392007/12/11 FALab
8/17/2019 introduction to CFD.pdf
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8/17/2019 introduction to CFD.pdf
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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
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
8/392007/12/11 FALab
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
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
9/392007/12/11 FALab
8/17/2019 introduction to CFD.pdf
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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
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
10/392007/12/11 FALab
PARTⅠ
Introduction to CFD analysis
PART
Ⅱ
Mesh Generator
PARTⅢ
FLUENT Setup and Solution
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
11/392007/12/11 FALab
8/17/2019 introduction to CFD.pdf
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Case1 2-D Airfoil
Problem Description
RE=1x106
Angle of attack=4
Naca4412
Chord length = 1c
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
12/392007/12/11 FALab
Mesh command button → Mesh → Mesh edgesMesh command button → Mesh → Mesh edges
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
13/392007/12/11 FALab
8/17/2019 introduction to CFD.pdf
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Mesh command button→
Mesh→
Mesh edges
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
14/392007/12/11 FALab
Mesh command button→
Boundary-layer → Create boundary l ayer
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
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Mesh command button→
Mesh→
Mesh edges
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
16/392007/12/11 FALab
Mesh command button → Mesh → Mesh edges
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
17/392007/12/11 FALab
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Mesh command button→
Mesh→
Mesh edges
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
18/392007/12/11 FALab
Mesh command button → Mesh → Mesh faces
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
19/392007/12/11 FALab
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Zones co mmand button→
Specify boundary types
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
20/392007/12/11 FALab
Zones co mmand button → Specify boundary types
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
21/392007/12/11 FALab
8/17/2019 introduction to CFD.pdf
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Zones co mmand button→
Specify boundary types
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
22/392007/12/11 FALab
Zones co mmand button → Specify c ontinuum t ypes
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
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File→ Export→ Mesh…
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
24/392007/12/11 FALab
PARTⅠ
Introduction to CFD analysis
PART
Ⅱ
Mesh Generator
PARTⅢ
FLUENT Setup and Solution
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
25/392007/12/11 FALab
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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
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
26/392007/12/11 FALab
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.
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
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Enable the k- epsilon turbulence model.
Define→ Models → Viscous….
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
28/392007/12/11 FALab
Set the properties for air, the default fluid materials.
Define→ Materials….
Step 3 Materials
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
29/392007/12/11 FALab
8/17/2019 introduction to CFD.pdf
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Step 4 Boundary Conditions
Define→ Boundary Conditions….
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
30/392007/12/11 FALab
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 .
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
31/392007/12/11 FALab
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2.Set the boundary conditions for pressure-outlet
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
32/392007/12/11 FALab
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.
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
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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.
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
34/392007/12/11 FALab
Define the residual monitor to print and plot.
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
35/392007/12/11 FALab
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Initialize the solution.
Solver→ Initialize → Initialize….
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
36/392007/12/11 FALab
Set the reference value that are used to compute the lift and drag coeff icients .
Report → Reference values….
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
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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
INTRODUCTION TO CFD ANALYSIS
FLUENT & GAMBIT
38/392007/12/11 FALab
Thanks!!
FALab