Applied Computational Aerodynamics

Applied Computational
Aerodynamics
Review and Reinforcement
Applied Computational Aerodynamic
Governing Solution Drag Applications

Codes
equations methods Comput.
Laplace Singularity
Singularity Concepts Singularity
Singularity Airfoil
Airfoil
Laplace Concepts
Panel
Panel Method
Method Panel
Panel design
P-G
P-G design
VLM
VLM Airfoil
Airfoil
TSDE
TSDE Near
Near field
field
Field
Field Pablo
Pablo
Potential
Potential Wing
Wing
finite
finite diff.
diff. VLM
VLM
Euler
Euler Far
Far field
field design
design
finite
finite vol.
vol. Tornado
Tornado
N-S
N-S CMARC
CMARC
Pan
Pan Air
Air Configuration
Configuration
Field
Field design
design
Thinfoil
Thinfoil
Viscous flows Grid generations TSfoil
TSfoil 22
MGAERO
MGAERO
•• Boundary •• Structured
Structured FASTRAN
FASTRAN
Boundary layer
layer
•• Viscous-inviscid
Viscous-inviscid Algebraic
Algebraic Drag
Drag
Coupling
Coupling Partial
Partial diff.
diff. Eq.
Eq. friction
friction
•• Reynolds
Reynolds averaged
averaged Multi-Block,
Multi-Block, Harris’
Harris’
N-S
N-S eqs.
eqs. Adaptive
Adaptive ….….
•• turbulence
turbulence models
models •• Unstructured
Unstructured
Using Computational
Aerodynamics
• Code Development
• Code Validation
• Code Selection
• Problem Solving with Computational
Aerodynamics
Code development
• Start Simple
• Debug and test on a coarse mesh first (reduces cycle time)
• Print out “enough” information:
– some at each step
– lots sometimes
– print good diagnostic function
• Use graphics to look at the whole field
• Always check on the finest mesh possible before releasing code
• Test convergence to machine accuracy
• Try to check all option combinations in a production program
• Check convergence/stability over the widest possible range of
parameters
• Test accuracy against:
– approximate solutions
– experimental data
– exact solutions
• Avoid unnecessary hardware dependence
Issues for CFD codes
• Are incremental effects better predicted than absolute

values ?
• Is the math model adequate?
• Can the solution technique be improved ?
• Has the grid been refined sufficiently where large
changes occur ?
Issues for Experiment
• Is the instrumentation adequate/accurate ?

• Can another tunnel/model support be used ?
• Is flow quality/uniformity or transition a factor ?
• Has the wall-interference been evaluated ?
Error sources in CFD codes
• math model/equation set
• Artificial Viscosity/dissipation
• geometry representations
• solution not converged
• round off error/truncation error
• bugs
• solution algorithm
• boundary conditions
• grid resolution
• turbulence model
• Reynolds number
Error Sources in Wind Tunnel Data
• sting effects (model mounting)
• Reynolds number
• transition
• geometry definition and accuracy
• flow uniformity
• wall effects
• flow quality/noise
• instrumentation
• aeroelasticity
• surface finish
Code Selection Considerations
• capability
• problem setup time/grid generation
• turnaround time
• availability
• cost
• confidence
What is required to use a code ?
• CFD code validation
– CFD validation experiments may be required
• Validated CFD Code

– CFD code “calibration”
Problem solving using CA
• What do you want from the computation
– The decision here is the key: should you or shouldn’t you ?
• Model the physics as a properly posed problem (BC’s)

• Select the appropriate code (previously validated)
• Define the geometry, the mesh and the input
• Check the input (visual displays are essential)
• Run the program
• Display and interpret the results !
Which governing equation should be used ?
• For high Reynolds number attached flow, the pressure

can be obtained very accurately without considering
viscosity.
– VLM or Panel Methods work well for subsonic flows
– If the onset flow is uniform, and any shocks are weak, Mn < 1.25
or 1.3, then the Full Potential Flow Approximation or Transonic
Small disturbance Equation is valid.
– When shocks begin to get strong and are curved, the solution of
the complete Euler equations is required.
Which governing equation should be used ?
• When the flow remains attached

– Inviscid calculations with boundary layer corrections can provide
quite accurate predictions of lift and drag
– But iteration between the inviscid outer solution and the
boundary layer solution becomes increasingly difficult with the
onset of separation.
• Procedures for solving the full viscous equations are

likely to be needed for the simulation of arbitrary
complex separated flows, which may occur at high
angles of attack or with bluff bodies.
That is it
• You now have tools for aerodynamic
design using computational methods
• Goals for the course
– Knowledge
– Perspective
– Skill
Grade Basis
• Your course grade will be determined by
examination and assigned homework.
• The weighting of each of these components
is as follows:
– Exam : 30%
– Project : 30%
– Homework : 30%
– Attendance: 10%
– Total : 100%
• Exam date: June 22 , 2005

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Applied Computational

Governing Solution Drag Applications

• Are incremental effects better predicted than absolute

• Is the instrumentation adequate/accurate ?

• Validated CFD Code

• Model the physics as a properly posed problem (BC’s)

• For high Reynolds number attached flow, the pressure

• When the flow remains attached

• Procedures for solving the full viscous equations are

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