Computational Fluid Dynamics (CFD) is a computational method for predicting fluid flow phenomena using numerical analysis and high speed digital computers. It is widely used across various industries including aerospace, automotive, biomedical, oil & gas, and power generation for simulation-based design and analysis. The CFD process involves geometry description, flow condition specification, model selection, and numerical solution while addressing challenges such as physical models and numerical errors.

1. Computational Fluid Dynamics
(CFD)
Hashim Hasnain Hadi(13ME36)
M. Hanzla Tahir(13ME37)
Sardar Gulshan Lal(13ME39)
AND ALL CLASMATES
Batch 2013-14
Dept. of Mechanical Engineering
Balochistan University of Engineering &
Technology,
Khuzdar.
.

2. 2
Outline
 What is CFD?
 Why use CFD?
 Where is CFD used?
 Physics
 Modeling
 Numerics
 CFD process
 Resources

3. 3
What is CFD?
 What is CFD and its objective?
– Computational Fluid Dynamics
– Historically Analytical Fluid Dynamics (AFD) and EFD
(Experimental Fluid Dynamics) was used. CFD has become
feasible due to the advent of high speed digital computers.
– Computer simulation for prediction of fluid-flow phenomena.
– The objective of CFD is to model the continuous fluids with
Partial Differential Equations (PDEs) and discretize PDEs into an
algebra problem , solve it, validate it and achieve simulation
based design.

4. What is CFD?
 The field in which computers and numerical
analysis are combined to solve fluid
problems/Energy prblems is termed as
Computational fluid dynamics
4

5. 5
Why use CFD?
 Why use CFD?
– Analysis and Design
 Simulation-based design instead of “build & test”
– More cost effectively and more rapidly than with experiments
– CFD solution provides high-fidelity database for interrogation of
flow field
 Simulation of physical fluid phenomena that are difficult to be
measured by experiments
– Scale simulations (e.g., full-scale ships, airplanes)
– Hazards (e.g., explosions, radiation, pollution)
– Physics (e.g., weather prediction, planetary boundary layer,
stellar evolution)
– Knowledge and exploration of flow physics

6. 6
Where is CFD used? (Aerospace)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports
F18 Store Separation
Wing-Body Interaction Hypersonic Launch
Vehicle

7. 7

8. 8
Where is CFD used? (Appliances)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports
Surface-heat-flux plots of the No-Frost
refrigerator and freezer compartments helped
BOSCH-SIEMENS engineers to optimize the
location of air inlets.

9. 9
Where is CFD used? (Automotive)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports
External Aerodynamics Undercarriage
Aerodynamics
Interior Ventilation
Engine Cooling

10. 10
Where is CFD used? (Biomedical)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports Temperature and natural
convection currents in the eye
following laser heating.
Medtronic Blood Pump

11. 11
Where is CFD used? (Chemical Processing)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports
Polymerization reactor vessel - prediction
of flow separation and residence time
effects.
Shear rate distribution in twin-
screw extruder simulation
Twin-screw extruder
modeling

12. 12
Where is CFD used? (HVAC&R)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports
Particle traces of copier VOC emissions
colored by concentration level fall
behind the copier and then circulate
through the room before exiting the
exhaust.
Mean age of air contours indicate
location of fresh supply air
Streamlines for workstation
ventilation
Flow pathlines colored by
pressure quantify head loss
in ductwork

13. 13
Where is CFD used? (Hydraulics)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports

14. 14
Where is CFD used? (Marine)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports

15. 15
Where is CFD used? (Oil & Gas)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports
Flow vectors and pressure
distribution on an offshore oil rig
Flow of lubricating
mud over drill bit
Volume fraction of water
Volume fraction of oil
Volume fraction of gas
Analysis of multiphase
separator

16. 16
Where is CFD used? (Power Generation)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports
Flow pattern through a water
turbine.
Flow in a
burner
Flow around cooling
towers
Pathlines from the inlet
colored by temperature
during standard
operating conditions

17. 17
Where is CFD used? (Sports)
• Where is CFD used?
– Aerospace
– Appliances
– Automotive
– Biomedical
– Chemical Processing
– HVAC&R
– Hydraulics
– Marine
– Oil & Gas
– Power Generation
– Sports

18. 18
Physics
 CFD codes typically designed for representation
of specific flow phenomenon
– Viscous vs. inviscid (no viscous forces) (Re)
– Turbulent vs. laminar (Re)
– Incompressible vs. compressible (Ma)
– Single- vs. multi-phase (Ca)
– Thermal/density effects and energy equation (Pr, g, Gr,
Ec)
– Free-surface flow and surface tension (Fr, We)
– Chemical reactions, mass transfer
– etc…

19. 19
Physics
Fluid Mechanics
Inviscid Viscous
Laminar Turbulence
Internal
(pipe,valve)
External
(airfoil, ship)
Compressible
(air, acoustic)
Incompressible
(water)
Components of Fluid Mechanics

20. 20
Claude-Louis Navier George Gabriel Stokes
g
v
p
v
Dt
D


 



 2
Navier-Stokes Equation

21. 21
Modeling
 Mathematical representation of the physical problem
– Some problems are exact (e.g., laminar pipe flow)
– Exact solutions only exist for some simple cases. In
these cases nonlinear terms can be dropped from the N-
S equations which allow analytical solution.
– Most cases require models for flow behavior [e.g.,
Reynolds Averaged Navier Stokes equations (RANS)
or Large Eddy Simulation (LES) for turbulent flow]
 Initial —Boundary Value Problem (IBVP), include:
governing Partial Differential Equations (PDEs), Initial
Conditions (ICs) and Boundary Conditions (BCs)

22. 22
Governing Equations
x
zx
yx
xx
x
z
x
y
x
x
x
g
z
y
x
x
p
z
u
u
y
u
u
x
u
u
t
u




 






































Continuity
x - Equation of motion
0












z
y
x u
z
u
y
u
x
t
v



(Equations based on “average” velocity)

23. 23
Numerics / Discretization
 Computational solution of the IBVP
 Method dependent upon the model equations and
physics
 Several components to formulation
– Discretization and linearization
– Assembly of system of algebraic equations
– Solve the system and get approximate solutions

24. 24
Finite Differences
Methods of Solution
Direct methods Iterative methods
Cramer’s Rule, Gauss elimination
LU decomposition
Jacobi method, Gauss-Seidel
Method, SOR method
    



































 
6
2
2
,
3
3
,
2
2
,
,
1
,
x
x
u
x
x
u
x
u
u
x
u
j
i
j
i
j
i
j
i
j
i
Finite difference
representation
Truncation error

25. 25
Numeric Solution
(Finite Differences)
o x
i i+1
i-1
j+1
j
j-1
imax
jmax
x

y

    





































6
2
3
,
3
3
2
,
2
2
,
,
,
1
x
x
u
x
x
u
x
x
u
u
u
j
i
j
i
j
i
j
i
j
i
Taylor’s Series Expansion
u i,j = velocity of fluid
Discrete Grid Points

26. 26
CFD process
 Geometry description
 Specification of flow conditions and properties
 Selection of models
 Specification of initial and boundary conditions
 Grid generation and transformation
 Specification of numerical parameters
 Flow solution
 Post processing: Analysis, and visualization

27. 27
Domain for bottle filling
problem.
Filling
Nozzle
Bottle
CFD - how it works
 Analysis begins with a mathematical
model of a physical problem.
 Conservation of matter, momentum,
and energy must be satisfied
throughout the region of interest.
 Fluid properties are modeled
empirically.
 Simplifying assumptions are made in
order to make the problem tractable
(e.g., steady-state, incompressible,
inviscid, two-dimensional).
 Provide appropriate initial and
boundary conditions for the problem.

28. 28
Geometry description
 Typical approaches

– Make assumptions and
simplifications
– CAD/CAE integration
– Engineering drawings
– Coordinates include Cartesian
system (x,y,z), cylindrical system (r,
θ, z), and spherical system(r, θ, Φ)

29. 29
Selection of models for flow field
 Direct Numerical Simulations (DNS) is to solve the N-S
equations directly without any modeling. Grid must be fine
enough to resolve all flow scales. Applied for laminar flow
and rare be used in turbulent flow.
 Reynolds Averaged Navier-Stokes (NS) equations (RANS)
is to perform averaging of NS equations and establishing
turbulent models for the eddy viscosity. Too many
averaging might damping vortical structures in turbulent
flows
 Large Eddy Simulation (LES), Smagorinsky’ constant
model and dynamic model. Provide more instantaneous
information than RANS did. Instability in complex
geometries
 Detached Eddy Simulation (DES) is to use one single
formulation to combine the advantages of RANS and LES.

30. 30
Mesh for bottle filling
problem.
CFD - how it works (2)
 CFD applies numerical methods (called
discretization) to develop approximations of the
governing equations of fluid mechanics in the
fluid region of interest.
– Governing differential equations: algebraic.
– The collection of cells is called the grid.
– The set of algebraic equations are solved
numerically (on a computer) for the flow field
variables at each node or cell.
– System of equations are solved simultaneously
to provide solution.
 The solution is post-processed to extract
quantities of interest (e.g. lift, drag, torque, heat
transfer, separation, pressure loss, etc.).

31. 31
Discretization
 Domain is discretized into a finite set of control volumes
or cells. The discretized domain is called the “grid” or the “mesh.”
 General conservation (transport) equations for mass, momentum,
energy, etc., are discretized into algebraic equations.
 All equations are solved to render flow field.
Fluid region of pipe flow
discretized into finite set of control
volumes (mesh).
control
volume

32. 32
Design and create the grid
 Should you use a quad/hex grid, a tri/tet grid, a hybrid grid, or a
non-conformal grid?
 What degree of grid resolution is required in each region of the
domain?
 How many cells are required for the problem?
 Will you use adaption to add resolution?
 Do you have sufficient computer memory?
triangle
quadrilateral
tetrahedron pyramid
prism or wedge
hexahedron
arbitrary polyhedron

33. 33
Tri/tet vs. quad/hex meshes
 For simple geometries, quad/hex
meshes can provide high-quality
solutions with fewer cells than a
comparable tri/tet mesh.
 For complex geometries, quad/hex
meshes show no numerical
advantage, and you can save
meshing effort by using a tri/tet
mesh.

34. 34
Set up the numerical model
 For a given problem, you will need to:
– Select appropriate physical models.
– Turbulence, combustion, multiphase, etc.
– Define material properties.
 Fluid.
 Solid.
 Mixture.
– Prescribe operating conditions.
– Prescribe boundary conditions at all boundary zones.
– Provide an initial solution.
– Set up solver controls.
– Set up convergence monitors.

35. 35
Initial and boundary conditions
 For steady/unsteady flow
 IC should not affect final solution, only convergence path, i.e.
iteration numbers needed to get the converged solution.
 Robust codes should start most problems from very crude IC, .
But more reasonable guess can speed up the convergence.
 Boundary conditions
– No-slip or slip-free on the wall, periodic, inlet (velocity
inlet, mass flow rate, constant pressure, etc.), outlet
(constant pressure, velocity convective, buffer zone,
zero-gradient), and non-reflecting (compressible flows,
such as acoustics), etc.

36. 36
Compute the solution
 The discretized conservation equations are solved iteratively. A
number of iterations are usually required to reach a converged
solution.
 Convergence is reached when:
– Changes in solution variables from one iteration to the next
are negligible.
– Residuals provide a mechanism to help monitor this trend.
– Overall property conservation is achieved.
 The accuracy of a converged solution is dependent upon:
– Appropriateness and accuracy of the physical models.
– Grid resolution and independence.
– Problem setup.

37. 37
Numerical parameters & flow
solution
 Typical time
history of
residuals
 The closer the
flow field to the
converged
solution, the
smaller the speed
of the residuals
decreasing.
Solution converged, residuals do
not change after more iterations

38. 38
Post-processing
 Analysis, and visualization
– Calculation of derived variables
 Vorticity
 Wall shear stress
– Calculation of integral parameters: forces,
moments
– Visualization (usually with commercial software)
 Simple X-Y plots
 Simple 2D contours
 3D contour carpet plots
 Vector plots and streamlines (streamlines are
the lines whose tangent direction is the same
as the velocity vectors)
 Animations (dozens of sample pictures in a
series of time were shown continuously)

39. 39
Examine the results
 Visualization can be used to answer such questions as:
– What is the overall flow pattern?
– Is there separation?
– Where do shocks, shear layers, etc. form?
– Are key flow features being resolved?
– Are physical models and boundary conditions appropriate?
– Numerical reporting tools can be used to calculate
quantitative results, e.g:
 Lift, drag, and torque.
 Average heat transfer coefficients.
 Surface-averaged quantities.

40. 40
Velocity vectors around a
dinosaur

41. 41
Velocity magnitude (0-6 m/s)
on a dinosaur

42. 42
Pressure field on a dinosaur

43. 43
Advantages of CFD
 Relatively low cost.
– Using physical experiments and tests to get essential
engineering data for design can be expensive.
– CFD simulations are relatively inexpensive, and costs are
likely to decrease as computers become more powerful.
 Speed.
– CFD simulations can be executed in a short period of time.
– Quick turnaround means engineering data can be introduced
early in the design process.
 Ability to simulate real conditions.
– Many flow and heat transfer processes can not be (easily)
tested, e.g. hypersonic flow.
– CFD provides the ability to theoretically simulate any
physical condition.

44. 44
Limitations of CFD
 Physical models.
– CFD solutions rely upon physical models of real world
processes (e.g. turbulence, compressibility, chemistry,
multiphase flow, etc.).
– The CFD solutions can only be as accurate as the physical
models on which they are based.
 Numerical errors.
– Solving equations on a computer invariably introduces
numerical errors.
– Round-off error: due to finite word size available on the
computer. Round-off errors will always exist (though they
can be small in most cases).
– Truncation error: due to approximations in the numerical
models. Truncation errors will go to zero as the grid is
refined. Mesh refinement is one way to deal with truncation
error.

45. 45
poor better
Fully Developed Inlet
Profile
Computational
Domain
Computational
Domain
Uniform Inlet
Profile
Limitations of CFD (2)
 Boundary conditions.
– As with physical models, the accuracy of the CFD solution
is only as good as the initial/boundary conditions provided to
the numerical model.
– Example: flow in a duct with sudden expansion. If flow is
supplied to domain by a pipe, you should use a fully-
developed profile for velocity rather than assume uniform
conditions.

46. 46
Software and resources
 CFD software was built upon physics, modeling, numerics.
 Two types of available software
– Commercial (e.g., FLUENT, CFX, Star-CD)
– Research (e.g., CFDSHIP-IOWA, U2RANS)
 More information on CFD can be got on the following website:
– CFD Online: http://www.cfd-online.com/
– CFD software
 FLUENT: http://www.fluent.com/
 CFDRC: http://www.cfdrc.com/
 Computational Dynamics: http://www.cd.co.uk/
 CFX/AEA: http://www.software.aeat.com/cfx/
– Grid generation software
 Gridgen: http://www.pointwise.com
 GridPro: http://www.gridpro.com/
 Hypermesh
– Visualization software
 Tecplot: http://www.amtec.com/

47. Software Used
 1. Matlab
 2. Ansys
 3. Pro-Engineer
 4. Autodesk Inventor professional
 . CATIA
 6. Fluent
 7. Maple
47

48. Sofware Used
 Tecplot
 IcemCFD
 Femlab
48

49. THANK YOU
49