Transcript MER034 - The Homepage for antipasto.union.edu

MER331 – Week 6
An Introduction to Computational
Fluids Dynamics
Professor Anderson
What is CFD?






the analysis of systems involving fluid flow, heat
transfer, chemical reactions, by means of
computer based simulation
17th century the “hydraulicists”
18th and 19th - the “mathematicians”
1960 - two fold approach – theory and experiments
Now we have CFD as a tool that complements
theory and experiments (it will never replace
these!)
CFD is both a research tool and design tool
What is CFD?



CFD has lagged behind developments in stress
analysis codes
Powerful computers now make CFD more
accessible
Advantages of CFD over experiments
 reduction
in lead time and costs of new designs
 ability to study systems where controlled
experiments are difficult to perform (large systems)
 ability to study systems under hazardous conditions
at and beyond normal performance limits
 detail of results
Applications





Aerospace
Automobile and Engine Applications
Appliances
Boats
Computers
How Does a CFD Code Work?


CFD codes are structured around the numerical
algorithms that can tackle fluid flow problems
Three main elements:
1.Pre Processor
2.Solver
3.Post Processor
1) Pre-Processor
Consists of the input of
a flow problem to CFD
 User Activities:

 define
geometry &
generate grid (50% time)
 selection of phenomena
to be modeled
 definition of fluid
properties
 specification of
boundary and initial
conditions
2) Solver
Three primary numerical solution techniques

finite difference, finite element, finite control volume
The numerical method performs the following:



Approximates the unknown variables by simple functions
Discretization by substitution of the approx-imations into
the governing flow equations and subsequent
mathematical manipulations
Solution of the algebraic equations
Solver - Finite Difference Method


Finite difference methods describe the unknowns f of the
flow problems by means of point samples at the node
points of a grid co-ordinate lines
Truncated Taylor series expansions are used to generate finite
difference approximations of the
derivatives of f in terms of point
samples of f at each grid point
and its immediate neighbors
Solver - Finite Volume Method
 Based
on control volume formulation of analytical fluids
 The domain is divided into a number of control volumes
(aka cells, elements) - the variable of interest is located at
the centroid of the control volume.
 The differential form of the governing equations are
integrated over each control volume.
 Finite difference approximations are substituted for the terms
in the integrated equations (discretization) converts the
integral equations into a system of algebraic equations.
 Set of algebraic equations are solved by an iterative
method.
3) Post Processor

Provides a “user friendly” (??) way to look at the
results of a simulation
 Domain
geometry and grid display
 Vector Plots
 Contour Plots
 Particle Tracking
Problem Solving With CFD




Results of CFD are at best as good as the physics
embedded in it as at worst as good a its operator
THESE PROBLEMS ARE COMPLEX
Prior to running a simulation there is a stage of
identification and formulation of the flow problem in
terms of the physical and chemical phenomena
that need to be considered.
A successful simulation has
 converged solution
 grid independence
In Lab Today




We will use StarCCM which is a one of the
major commercial CFD codes.
Complete the tutorial on Introduction to
STARCCM (handout of online)
Geometry File is in: C:\Program Files\CD-adapco\STARCCM+7.06.012\DOC\startutorialsdata\introductions\data
To Pass In: Nothing!