MER331 Lab 5

1
MER331 Lab 5

• An Introduction to Computational Fluids Dynamics
• Professor Anderson

2
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

3
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

4
Applications

• Aerospace
• Automobile and Engine Applications
• Appliances
• Boats
• Computers

5
How Does a CFD Code Work?

• CFD codes are structured around the numerical
  algorithms that can tackle fluid flow problems
• Three main elements
• Pre Processor
• Solver
• Post Processor

6
1) Pre-Processor

• Consists of the input of a flow problem to CFD by
  means of a user friendly interface and
  transformation of this input to a form usable by
  the solver
• User Activities
• define geometry generate grid (50 time)
• selection of phenomena to be modeled
• definition of fluid properties
• Specification of boundary conditions

7
2) Solver

• Three primary numerical solution techniques
• finite difference, finite element, finite control
  volume
• The numerical method performs the following
• Approximation of 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

8
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 often 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

9
Solver - Finite Volume Method

• Special formulation of the finite difference
  method
• Central to 4 of 5 main commercially available CFD
  codes PHOENICS, FLUENT, FLOW3D, STARCD

10
Solver - Finite Volume Method

• Numerical Algorithm
• Formal integration of the governing equations of
  fluid flow over all the (finite) control volumes
  of the solution domain
• Discretization involves the substitution of a
  variety of finite difference type approximations
  for the terms in the integrated equation
  representing flow processes such as convection,
  diffusion and sources. This converts the integral
  equations into a system of algebraic equations.
• Solution of the algebraic equations by an
  iterative method.

11
Solver - Finite Volume Method

• The control volume integration distinguishes the
  finite volume method from other CFD techniques
• Expresses the exact conservation of relevant
  properties for each finite size cell.
• Clear relationship between the numerical
  algorithm and the underlying physical
  conservation principles
• Conservation of a flow variable, f, can be
  expressed as a production equation
• rate of change of f
• net flux of f due to convection
• net flux of f due to diffusion
• net rate of creation of f

12
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
• Details about

13
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.

14
Performing a Simulation

• Specification of the domain geometry and grid
  design
• A successful simulation has
• converged solution
• grid independence

15
In Lab Today

• We will use StarWorks (part of StarCD) which is a
  CFD Add-On to Solidworks.
• Complete the on line Tutorial
• Build your own CFD model of something!
• To Pass In (at end of lab)
• A picture of your model that shows the boundary
  conditions.
• Flow results for your model (a vector plot and a
  pressure contour).
• A brief description of what you modeled and what
  the results mean.