1. CFD basics & Use of ANSY FLUENT in
Engineering Application: A Brief
Introduction
Prepared by:
MD SHUJAN ALI
GTA for Aero-3
Graduate Student
Aerospace Engineering
Auburn University
Auburn, Alabama, USA

2. Fluid Dynamics
• Fluid Dynamics is both interesting & challenging
field for study and research. In real world almost
everywhere fluid is present. So, we need fluid
dynamics to describe or model these fluid flows.
• In brief any fluid flow can be solved/Described by
three basic physical law, or by three equations.
(1)Continuity equation- Mass is conserved.
(2)Momentum equation (Widely knows as
Navier-Stokes equation)- Newton’s Second Law.
(3)Energy equation- Energy is conserved.

3. Three ways of solving problems
Any problem/phenomena can be analyzed by three ways
•Analytical/Theoretical approach- using laws/theories and associated
equations, such as using Newton’s law of viscosity to solve a fluid flow
problem, these solutions are exact.
•Experimental approach- do experiments and try to understand the
phenomena and relation between various variables, such as wind
tunnel experiments which helps to design and optimize external shape
of airplanes, ships, automobiles etc.
•Numerical approach-Solve a fluid flow problem using numerical
techniques. These solutions are approximate, not exact.

4. What is CFD
• Computational Fluid Dynamics (CFD) is a set of
numerical methods applied to obtain
approximate solutions of problems of fluid
dynamics and heat transfer.
• So, CFD is not a science by itself, it is a way to
apply the methods of one discipline
(numerical analysis) to another (fluid
flow/mass transfer and heat transfer).

5. Why CFD
• CFD solutions are not exact, then why not use
Analytical approach???
• Experimental approach is more reliable, such as
wind tunnel experiments, why not use
experimental approach instead of CFD???
CFD is used because there are many engineering
problems that can’t be solved by analytical or
Experimental approach, or it is difficult to use
analytical or experimental approach.

6. Difficulties in other approaches
• Theoretical approach: This approach gives exact
solution which is a great advantage. But analytical
solutions are only possible for a limited number of
problems, usually formulated in an artificial, idealized
way.
• Experimental approach: These approaches are reliable,
and depict real world situations. For example, in
aerospace industries Wind Tunnel experiments are
very reliable. But some times these are very expensive,
and some times these also have some technical
difficulties (Sometimes it takes several years before an
experiment is set up and all technical problems are
resolved).

7. Application of CFD
CFD is a very powerful technique and spans a wide a wide range of
industrial and non-industrial applications. Some examples are –
•Aerodynamics of aircrafts and vehicles: Drag & Lift
•Power plant: Combustion in internal combustion engines & Gas
turbines.
•Hydrodynamics of ships
•Biomedical engineering: Blood flow through arteries and veins
•Environmental engineering: distribution of pollutants
In a nutshell, CFD is applied in almost every disciplines of
Engineering. From the 1960s onwards Aerospace industries has
integrated CFD techniques in the design, R&D, and manufacturing of
Aircrafts and Jet engines.

8. Own Coding vs Commercial CFD codes
CFD is solving basic equations of fluid flow and heat
transfer by applying Numerical techniques. There
are two different approach-
(1)Write your own CFD code to solve a specific
problem, or a type of problem. For example, you
can write your own MATLAB program to solve a
incompressible pipe flow.
(2)There are some commercial CFD software
package. Some of them are very puseful & popular.
Example: ANSYS FLUENT, STAR-CD, CFX,
OpenFOAM, and COMSOL.

9. Problem solving using commercial
CFD packages
CFD codes are structured around the numerical algorithms that can
tackle fluid flow problems. In order to provide easy access to their
solving power all commercial CFD packages include sophisticated user
interfaces to input problem parameters and to examine the results.
Hence all codes contain three main elements: (i) a pre-processor, (ii) a
solver and (iii) a post processor.
Pre-processor: This step includes creating Geometry and Mesh.
Solver: This part is to numerically solve the fluid flow equations in the
computational domain.
Post-Processor: In this steps, result of simulation is analyzed, or
represented in useful form.
In ANSYS WORKBENCH, Design Modeler & Meshing works as
pre-processor, FLUENT is the Solver, and CFD-post is the post-
processor.

10. Three methods of CFD
There are three basic methods to solve problem
in CFD.
(1)Finite difference method
(2)Finite element method
(3) Spectral methods
Finite Volume Method is a special case
of Finite difference method. It is a very popular
method.

11. ANSY FLUENT
ANSYS, Inc. is an engineering simulation software
(computer-aided engineering, or CAE) developer
headquartered south of Pittsburgh in the
Southpointe business park in Cecil Township,
Pennsylvania, United States. One of its most
significant products is Ansys CFD, a proprietary
computational fluid dynamics (CFD) program
(Source-Wikipedia).
ANSYS FLUENT is one of the most popular
commercial CFD software packages. We will use
ANSYS FLUENT in this course to solve Engineering
problems.

12. ANSYS FLUENT CFD Solver is based on
the Finite Volume method
***Domain is discretized into
a finite number of control
volumes.
***General conservation (transport)
equations for mass, momentum,
energy, species, etc. are solved on this set of control
volumes

13. Steps solving problem by ANSYS
FLUENT
To solve Engineering problems using ANSYS
FLUENT the necessary steps are-
(1)Pre-analysis
(2)Geometry
(3)Mesh
(4)Physical Setup
(5)Numerical Solution
(6)Verification & Validation

14. ANSYS WORKBENCH
ANSYS WORKBENCH is a Graphical User
Interface(GUI) that allows the user to use all the
required tools/software from a single place. You
can access pre-processor, solver and post-
processor tools from ANSYS WORKBENCH. You
will control your workflow between various
tools through Workbench.

16. Steps for your Simulation
• Pre-Analysis: You want to solve a real world
Engineering problem numerically using ANSYS FLUENT.
Then you will need boundary condition. You will
observe the real physical situation, or you will obtain
data so that you Can represent the actual case. You
will also obtain corresponding theoretical or
experimental results to compare it will your
simulation. These steps are important, especially to
obtain the correct boundary condition. For example, if
you want to simulate airflow over the wing of a
commercial airplane you have to know the range of
speed for that wing, you will also look for previous
experimental or numerical results, and the relavent
theories.

17. Steps for your Simulation
• Geometry: You have to make the geometry. You can
use ANSYS design modeler software, which you can
use from ANSYS WORKBENCH. You can also use any
other CAD Software you like, such as AutoCAD,
Solidworks, CATIA, Autocad Inventor etc.
• Meshing: Meshing is one of the most important step
for your simulation. Simulation results depend on
Mesh quality. Low quality Mesh can produce poor
simulation result, even divergence.
These steps are pre-possessing. In this
course, you don’t have to deal with Geometry & Mesh
now. These will be provided, so that you can start from
the next steps.

18. Steps for your Simulation
• Physical Setup: It is done in the solver ANSYS.
Your concentration will be to understand and
perform physical setup, numerical result, and
Verification & Validation.
In physical setup step, you give inputs
for solution accuracy, boundary condition,
physics involved, material involved, properties
of involved etc. In a nutshell, here you
numerically depict the real situation you want
to simulate.

19. Starting ANSYS
• ANSYS WORKBENCH >>> Analysis systems >>> Fluid
Flow(FLUENT)
you will state FLUENT solver using this path. FLUENT
tree will appear which looks like
This tree showing the all the steps you
have to complete for a successful
simulation. Now you can skip
Geometry & Meshing. You will start
from Setup tab which is physical setup.

20. Starting ANSYS
• Now if you click the setup icon, FLUENT
starting options will appear like

21. Starting FLUENT
• Here you have to specify you solver about your
geometry(2D/3D), and accuracy you want(click double precision
if you want better accuracy)
• Unmarking double precision makes the solver single precision, it
means FLUENT will use 16-bit floating points for its calculation.
Double precision solver uses 32-bit floating points.
• Processing Options are to speed up your simulation, and using
full power of your cluster computer or your fancy desktop which
is a fun. If you select only 1 core of your computer’s processor
will be used, although your desktop(i7 4790k) may has 8
cores/threads. By selecting parallel you can select how many
cores/threads you want to use. However, to use more than one
core you need additional license from ANSYS.

22. Playing with FLUENT Solver

23. FLUENT tabs
These tabs allow you to describe your
problem’s physics and control your
simulation. For this course, our
current objective is to be familiar with
these tabs, know some details about
them and use them for a successful
simulation. These will be discussed
briefly.

24. FLUENT tabs: General
First you have to deal with this
tab. Here you will define general
type of your case, for example
time is steady/transient.

25. FLUENT tabs: General
• Two types of solvers are available-Pressure based &
Density based. Details about these tabs are beyond the
scope of this course.
• You can remember a rule of thumb, if density is not
changing then you will use Pressure based solver.
• Pressure based solver is the default, and should used
for most cases, handles the Mach number in the range
0~2-3.
• For solving higher Mach number problems, Density
based solver are used. Or they are used for special
cases, for example, to capture interacting shock waves.

26. FLUENT tabs: Models
***Here you actually define
the governing equation
(or Model) you want
to use to solve your problem.
***If you select
viscous-Laminar, continuity &
N-S equations suitable for
Laminar flows are on. If you
on Energy, Energy equation
will on in your solver. For
Viscous- Turbulent models
equations would be solved
for turbulent flow, and solver
will include relevant turbulent
models to solve your problem.

27. FLUENT tabs: Models
• Currently we will use viscous-laminar & viscous-
turbulence models.
• Viscous-laminar model is straight forward, it is very
simple to use.
• Viscous-turbulent models have different varieties.
There are 1, 2, 3 equations turbulent models. 2
equations models, especially k-epsilon & k-omega
models are very popular. We will use k-epsilon
standard model immediately. After selecting K-epsilon
Standard model you have to choose wall functions- we
will use enhanced wall function in our immediate
analysis.

28. FLUENT tabs: Materials
This tab is like a inventory. You can use the
edit/create button to copy any material
from ANSYS database, or edit properties of
the selected material. Here you will keep all
the material you are working with, or you
want to work in future.

29. FLUENT tabs: Cell Zone condition
Here you will select material form the material zone,
to your cell zone. First, you have to select the zone for
modification, then select the material type from the
option tab called type , then press edit to select the
material.

30. FLUENT tabs: Boundary condition
You have to use the
type, edit options to
assign the boundary
conditions.

31. FLUENT tabs: Boundary condition
• Here you have to select boundary type for each
boundary(surface/edge/point) of your case geometry.
• Available Boundary conditions type: Here various
boundary types are given for your reference. Later
description of the important boundary types will be given.
• External Boundaries:
General:
-Pressure Inlet
-Pressure outlet
Incompressible:
-Velocity inlet
-Outflow

32. FLUENT tabs: Boundary condition
Compressible
-Mass flow inlet
-Pressure far field
Other
-Wall
-Symmetry
-Axis
-Periodic
Special
-Inlet/Outlet vent
-Intake/Exhaust Fan
Internal Boundaries
-Fan
-Interior
-Porous Jump
-Radiator
-Wall

33. FLUENT tabs: Boundary condition
• Above mentions boundary types is only for reference. You will
encounter will all of them in Future if you work in CFD. Presently
you can concentrate to understand only the most commonly used
boundary types. These will be discussed now in brief.
• Velocity Inlet:
-These are suitable for incompressible flow, and not recommended for
compressible flow.
-It applies a uniform velocity profile at the boundary unless UDF (user
defined function) is used.
-Velocity specification method s:
(1)Magnitude normal to boundary
(2)Components
(3)Magnitude and direction
(4)Turbulent quantities (if you are using turbulent models)
(5)Thermal conditions(if Energy equation is on)

34. FLUENT tabs: Boundary condition
• Pressure Outlet: It is suitable for both
incompressible and compressible flow. Here the
input is the static gauge pressure of the
environment into which the flow exists.
• Wall Boundaries: It works like physical wall. In
viscous flow, no slip conditions are applied at
walls. For Turbulent flows, wall roughness can be
defined.
• Axis boundaries: These are only used for 2D
axisymmetric flows. Here no user inputs are
required. It defines the axis of symmetry.

35. FLUENT tabs: Dynamic Mesh
• You can ship this step now. It is used only for
simulating moving objects, such as for
simulation a moving turbine blade.

36. FLUENT tabs: Reference Values
***In the compute from option, you will choose from
where computation will start, in most cases it is the inlet.
***In the reference zone, you will select the zone that
represent your whole computational domain.
***You have to select other reference values for your
problem. These values are uses only for calculation some
additional quantity, such as to calculate Drag coefficient,
or skin friction coefficient. General solution of the
simulation is not affected by the reference values.
For example, the solution of continuity & N-S equations
are not affected by the reference values.

37. FLUENT tabs: Solution Methods
***Here you will select the
solution method you want to use.
Each method has it’s own benefit &
weaknesses. You can also choose
the discretization method for
pressure & momentum.
***Try to use Second order upwind
for discretization. Second order
schemes give more accurate result,
and first order scheme helps in
convergence.

38. FLUENT tabs: Solution Methods
• SIMPLE method is very popular & widely used.
We will use SIMPLE method in our first
examples in classes.
• Coupled method is also popular, and helps in
convergence. If you get divergence in SIMPLE
method for any simulation, you can try to use
Coupled method, sometimes this technique
solves the problem of divergence.

39. FLUENT tabs: Solution Control
***We will use default values in this
tab. But if you get divergence under
SIMPLE method, you can lower the
under-factor for the variable that
causing the error.

40. FLUENT tabs: Solution Monitors

41. FLUENT tabs: Solution Control
• Here you can monitor your simulation. In the
residual monitor you can select the level of
floating point accuracy you want. You can add
additional monitors for additional properties.
For example, you can add additional monitors
to plot drag coefficient, lift coefficient,
momentum coefficient. We will demonstrate
these in classes.

42. FLUENT tabs: Solution Initialization
***Before run your simulation, you have
to initialize the simulation. You can
both standard & Hybrid initialization.
***In Standard initialization, all cells
have the same value at initial.
***Hybrid initialization makes
non-uniform initial guess, which is
sometimes helpful, specially for
complex geometry hybrid initialization
sometimes results convergence in less
iteration.

43. FLUENT tabs: Calculation activity
***You can Autosave your
simulation result
(case & data files) after a fixed
iteration.

44. FLUENT tabs: Run Calculation
***Here you simply command that
how many iterations you want to
perform.
***Here Solver setting ends.

45. Next Steps
• The steps are post processing, i.e., analyzing your
simulation results and data, and verification.
• We will use CFD-post for post processing. We can
also use FLUENT solver for post-processing, but
CFD-post is easier & convenient.
• We want to verify whether or not our simulation
is correct? For verification, we can check whether
basic physical laws are maintained or not, using
FLUENT. For example, we can check that, does
our solution satisfy continuity equation? We will
see details about it in class.

46. Opening CFD Post
***If you open Solution tab from
FLUENT tree in WORKBENCH, CFD
post will open.
***We will work in CFD-post in
classes.

47. Notes
• I try to make this slide as a quick & easy tutorial. You
will be familiar with CFD & ANSYS FLUENT by using this
slide. If you try to run ANSYS FLUENT by yourself, you
will be able to understand most of the things.
• We will do complete simulation step by step in class,
then you will get the full picture.
• Next you can contact me if you have confusion, or
want to know more. You can contact me in my office
at Room-323 in my office time :
Tuesday & Thursday- 11:30am-1:30pm
Wednesday-10:30pm-1:30pm

48. References
• FLUENT Help, User’s guide, Theory Guide.
• http://www.ansys.com/Products/Simulation+Tec
hnology/Fluid+Dynamics/Fluid+Dynamics+Produc
ts/ANSYS+Fluent
• https://www.youtube.com/channel/UCdymxOTZ
SP8RzRgFT8kpYpA
• http://www.ansys.com/Industries/Academic/Stu
dent+Product/Product+Information
• An Introduction to Computational Fluid
Dynamics-THE FINITE VOLUME METHOD, Second
Edition, H K Versteeg and W Malalasekera

49. References
• ESSENTIAL COMPUTATIONAL FLUID
DYNAMICS, OLEZ ZIKANOV