This document discusses computational fluid dynamics (CFD) and its application in Ansys. CFD uses physics equations and computer simulations to predict fluid flow, heat transfer, chemical reactions, etc. It helps reduce testing costs and study systems too large for experiments. The CFD process in Ansys involves pre-processing (CAD, meshing), solving the governing equations, and post-processing the results (graphs, contours). Examples demonstrate setting up and solving a CFD problem of air mixing in a tee pipe.

1. Introduction
What is CFD?
- Stands for Computational Fluid Dynamics
- Science of predicting fluid flow, heat and mass
transfer, chemical reactions , etc
Why CFD?
- Helps in design and optimization
- Reduces testing costs
- Helps to understand defects and problems in design
- Very large systems where practical experiments are
impossible can be easily studied

2. Applications of CFD
External aerodynamic
simulations Turbomachinery
applications
IC engine
simulations
HVAC applications Biomedical
applications

3. Physics of CFD
• CFD calculations are governed by 3 fundamental equations
Mass conservation or continuity
equation
Momentum conservation equation
Energy equation
These 2 equations
are collectively
known as “Navier
Stokes” Equation

4. Basic steps in CFD
Pre-processing
Solver
Post Processing
Meshing
CAD clean-up
Tools available in
ANSYS
SpaceClaim
Designmodeler
Ansys Meshing
Setting up of
boundary
conditions
Fluent, CFX,
Forte ,etc
Representation of
output values in
graphs, contours, etc
CFD post

5. Ansys Interface
Pre Processor
Solver
Post Processor

6. Pre- Processing
• Pre-Processing in CFD mainly deals with 2 aspects:
1. CAD generation- This involves creation of a new computational geometry or
modifying any existing geometry, on which analysis needs to be done. For this, there are 2
tools available in Ansys- SpaceClaim and Designmodeler, both of which can be used for
CAD purposes. Both of these tools have similar features like any popular CAD tools like
Creo, Solidworks, etc.
2. Mesh generation- Meshing is the process of dividing a larger geometry into finite
number of discrete elements. Each such discrete element is called a cell, and each cell is
composed of nodes. All equations are solved on these nodes throughout the entire domain.
A typical meshed surface in 3D and its cross section are shown below:

7. Classification of
Mesh
2D 3D
Triangle
Tetrahedron
Triangular prism
Pyramid
Hexahedron
Quadrilateral
Pre- Processing

8. SpaceClaim interface in Ansys

9. Meshing interface in Ansys

10. Solver
• This is the part where we give all required input parameters are fed into the
system so that the calculation can start. Some of the major parameters which
needs to be decided over here are:
1. Boundary conditions
2. Type of solver i.e Pressure based or Density based ( Density based solvers are mainly
used for higher Mach numbers)
3. Steady state or unsteady state
4. Materials to be used
5. Turbulence models ( K-epsilon, K-omega, etc)
6. Specific case models like combustion models, multiphase models, discrete phase
models can be selected from here

11. Solver
• Major types of boundary conditions available in Ansys:
1. Pressure inlet/ Pressure outlet- Here pressure values are given as an input conditions
at corresponding inlet and outlet areas
2. Velocity inlet- Velocity values can be given as input
3. Mass flow inlet/outlet- Value of mass flow rate can be given as input
4. Wall- This condition is used to bind the fluid and and solid regions.
5. Symmetry- This is given to those planes which have zero normal velocity and zero
normal gradients of all variables.
6. Fan- This is used for modelling exhaust or intake fans

12. Solver interface in Ansys

13. Post Processor
• Post processing in Ansys is done with the help of a tool called “CFD-Post”. Post processing
is used to analyse the results which we get after the simulation is over in a well defined
format. Some of the features of CFD post are:
1. Creation of 2D and 3D plots
2. Vector plots showing direction and magnitude of flow
3. Contour plots
4. Animation making
5. Quantitative numerical calculations
6. Visualizing of properties like temperature, pressure throughout the entire domain
7. Charts for various properties

14. CFD post interface in Ansys

15. Analysis of hot and cold air mixing in a tee pipe
• Objective- In this case, we are studying the effectiveness of mixing of hot
and cold air in a tee pipe
Cold air inlet
Hot air inlet Outlet

16. Input parameters
Conditions/Parameters Values
Hot air inlet velocity 8 m/s
Cold air inlet velocity 6 m/s
Hot air inlet temperature 353 K
Cold air inlet temperature 293 K
Outlet pressure Atmospheric condition

17. Meshing details
• Average mesh size- 10 mm
• Mesh type- Tetrahedron

18. Solver settings
Conditions/Parameters Values/Types
Solver Type Pressure based
Solver Time Steady state
Number of iterations 350
Fluid used Air
Turbulence Model Laminar

19. Post processing
Final temperature
profile
Temperature animation-
click on image to play

20. Results obtained
Final velocity
profile
Velocity animation-
click on image to play