Cfd introduction

INTRODUCTION
Computational
Fluid
Dynamics

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CFD is the process of solving the fluid flow equation of
mass, moment and energy on a computer as applied to a
particular geometry and flow conditions.
The basic flow variables such as velocity, pressure and
temperature are computed at thousands of location.
The CFD solution is based on the first-principle of
conservation of mass, moment and energy
A tool for solving PDE’s

3 fundamental principles:

Mass is conserved (Continuity equation);

Newton’s second law (Navier-Stokes Eqn);

Energy is conserved (Bernoulli’s Equation)

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The Approach of Fluid Dynamics

Pure Pure Theory
Experimental

Computational Fluid
Dynamics

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“A theory is something nobody believes except the person proposing the
theory and an experiment is something everybody believes except the
person doing the experiment”
--Albert Einstein
Experimental Investigation
• Involve full-scale equipment
•Full scale test are, in most cases, prohibitively expensive and often
impossible.
•Perform experiment on small-scale models. Information must be
extrapolated to full scale, and general rules for doing this are often
unavailable.
• Small scale models do not always simulate all the features of the full-
scale equipment.
• There are serious difficulties of measurement in many situations.
Theoretical Calculation
• Consequences of a mathematical model, rather than those of an actual
physical model.
• Consists of set of differential equations.
• A tiny fraction of the range of practical problems can be solved.

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Advantage of Theoretical Calculations

Low cost Speed

Complete
information
Ability to
Ability to
simulate
simulate ideal
realistic
conditions
conditions

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Why CFD?
Growth in complexity of unsolved engineering
problems
Need for quick solutions of moderate accuracy
Absence of analytical solutions
The prohibitive costs involved in performing even
scaled laboratory experiments
Efficient solution algorithms
Developments in computers in terms of speed and
storage
Sophisticated pre and post processing facilities

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Complements actual engineering
testing
Reduces engineering testing costs
Provides comprehensive data not
easily obtainable from experimental
tests.
Reduces the product-to-market
time and costs
Helps understand defects,
problems and issues in
product/process

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Advantages of CFD
It complements experimental and theoretical fluid
dynamics by providing an alternative cost effective
means of simulating real flows.
Insight
Better visualization and enhanced understanding of
designs.
Foresight
Testing many variations until you arrive at an optimal
result before physical prototyping and testing.
Practically unlimited level of detail of results at virtually
no added expense.
Efficiency
Compression of design and development cycle.
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The simulation results in prediction of the flow fields
and engineering parameters, which are very useful in the
Design and Optimization of processes and equipments.
Substantial reduction of lead times and costs of new
designs
Ability to study systems where controlled experiments
are difficult or impossible to perform (e.g. very large
systems)
Ability to study systems under hazardous conditions at
and beyond their normal performance limits (e.g. safety
studies and accident scenarios)
CFD is slowly becoming part and parcel of Computer
Aided Engineering(CAE)

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Applications of CFD
Aerodynamics of aircraft : lift and drag
Automotive : External flow over the body of a vehicle
or internal flow through the engine, combustion,
Engine cooling
Turbo machinery: Turbines, pumps , compressors
etc.
Flow and heat transfer in thermal power plants and
nuclear power reactors
HVAC
Manufacturing–Casting simulation, injection
moulding of plastics
Marine engineering: loads on off-shore structures
Hydrodynamics of ships, submarines, torpedo etc.
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Applications of CFD
Electrical and electronic engineering: cooling of equipment like
transformers, Computers, microcircuits, Semiconductor processing,
Optical fibre manufacturing
Chemical process engineering: mixing and separation, chemical
reactors, polymer molding
Transport of slurries in process industries
Environmental engineering: External and internal environment of
buildings, wind loading, Investigating the effects of fire and smoke,
distribution of pollutants and effluents in air or water,
Hydrology and oceanography: flows in rivers, oceans
Meteorology: weather prediction
Enhanced oil recovery from rock formations
Geophysical flows: atmospheric convection and ground water
movement
Biomedical engineering: Flow in arteries, blood vessels, heart,
nasal cavity, Inhalers
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Pressure distribution on a pickup van with
path lines

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Streamlines on a Submarine with the surface
colored with Pressure

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Aerospace Applications

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Automotive Applications

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Methodology in CFD

Pre processor

Solver

Post Processor
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Pre processor
Geometry generation
Geometry cleanup
Meshing

Solver
Problem specification
Additional models
Numerical computation

Post Processor
Line and Contour data
Average Values
Report Generation
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Pre processor
Definition of the geometry of the region of interest: the
computational domain

Creating regions of fluid flow, solid regions and surface
boundary names

Grid generation–the sub-division of the domain in to a
number of smaller, non-overlapping sub-domains: a
grid(or mesh) of cells(or control volumes or elements)

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Accuracy of a solution, calculation time and cost in
terms of necessary computer hardware are dependent
on the fineness of the grid.

Over 50% of time spent in industry on a CFD project is
devoted to the definition of domain geometry and grid
generation.

Selection of the physical and chemical phenomena
that need to be modeled.

Definition of fluid properties.

Specification of appropriate boundary conditions at
cells which coincide with or touch the domain boundary
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Solver
CFD is the art of replacing the differential equation
governing the Fluid Flow, with a set of algebraic
equations (the process is called discretization), which
in turn can be solved with the aid of a digital computer
to get an approximate solution

Finite difference method
Finite Element Method
Finite volume method

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Post-processor
Versatile data visualization tools.
Domain geometry and grid display
Vector plots showing the direction and magnitude of the flow.
Line and shaded contour plots
2D and 3D surface plots
Particle tracking
View manipulation(translation, rotation, scalingetc.)
Visualization of the variation of scalar variables(variables which
have only magnitude, not direction, such as temperature, pressure
and speed) through the domain.
Quantitative numerical calculations.
Charts showing graphical plots of variables
Hard copy out put
Animation for dynamic result display
Data export facilities for further manipulation external to the
code
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Cfd introduction

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