Transcript AE 3903 Airfoil Design Lecture 1

AE 3903/4903
Airfoil Design
Lecture 1
OVERVIEW
• Introductory Remarks
• Your first analysis tool – Panel Method
Introductory Remarks
• Airfoil Design is an “open-ended” process.
– There may not be a unique shape meeting the design
specs.
– Each one of you may come up with different shapes
for the same design specifications.
– In some cases, no airfoil shape may exist that will
meet the design specifications. You may need to
settle for the closest or “optimum” answer, rather than
the “exact” answer.
– Airfoil design is often an iterative process, where
small but steady improvements are made to the airfoil
shape until the design specifications are closely met.
Example:
Design an airfoil that has the best L/D ratio
at a specified lift coefficient.
Airfoil 2
Cl
Airfoil 1
Airfoil 2
Cd
Target lift
Airfoil 1
Target lift
a
Cl
Two airfoils may have the same minimum “Lift to Drag ratio” at the
Same target lift coefficient.
In the above example, both airfoils meet the design specifications
(example lowest L/D at a specified Lift)
Their off-design performance may differ significantly, however.
Example 2
Sometimes there may be no airfoil shape
that will meet the design specifications
Cp
Designer specifies a desired
Pressure distribution
x/c
A fish tail shape may occur
An open-ended trailing edge
May occur.
If this occurs, the design specifications may need to be modified.
For example, the designer may need to change the target pressure
Distribution.
Design Specifications
• Design specifications (or design criteria) that the
airfoil should meet may vary from one
application to another. Here are some examples.
– Target Cl given, lowest L/D is required.
– Target pressure distribution, known to have good
boundary layer characteristics, is given. This requires
expertise on the part of the designer.
– Higher lift stall angle is required or specified.
– Higher moment stall angle is required or specified.
– Trailing edge (or leading edge) separation is to be
eliminated.
– Laminar flow is required.
Single Point vs. Multi-Point Design
• In some design problems, it is enough to meet a
single operation point. This is called a single
point design.
– For example, design an airfoil that has the lowest L/D
at Cl=0.5, at a cruise Mach number of 0.75.
• In other cases, the design must meet
satisfactory performance at two or more
conditions. This is called a multi-point design.
– Example, satisfactory subsonic cruise performance
(lowest L/D at M=0.78 at Cl=0.5), and acceptable
supersonic dash performance ( L/D ~ 4 at M=2.0)
Steps to a Successful Design
• Acquire analysis tools – potential flow analysis of
flow over an airfoil, boundary layer analysis
• Validate the tools before you use them.
• Specify design criteria.
• Start with a known airfoil shape, as close to the
target as you can.
• Use an iterative process to gradually improve
the starting geometry/shape.
• Use the new design in a 3-D analysis (or tunnel
test) to make sure that the new airfoil does
indeed perform better.
For this course, choose from one of
the following
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Laminar airfoil design
General aviation airfoil Design
Supercritical airfoil Design
Wind Turbine Airfoil Design
Tools needed: panel method or CFD method
(supplied), laminar and turbulent boundary layer
analyses (supplied), transition prediction method
(supplied), design method (needed)
• Verify your design in a 3-D lifting line or CFD
method (supplied)
Assignment I
Due on September 10, 2002
• Write a 5 page report summarizing
– Design problem you have decided to study (one of the four
choices)
– Why did you choose this problem
– Literature survey of previous work related to your specific design
– What are some of the design criteria that have been used in past
– The specific design point you would like to work on
• You may change your mind later. If you decide to work
on a different problem, just let me know. However, the
sooner you settle on the design problem, the sooner you
will get it done.
• All work must be done independently. It is Ok to
exchange your sources of information.
Some Sources
• NASA Technical Report Server
http://techreports.larc.nasa.gov/cgi-bin/NTRS/
• Papers by Eppler (laminar airfoil, general
aviation airfoil)
• Papers, books by: (a) Tranen, (b) BauerGarabedian-Korn on supercritical airfoil
• Papers and website by Prof. Selig at U. Illinois
• National Renewable Energy labs web site:
http://www.nrel.gov/wind
• I will complement this with papers by my
students, colleagues, and me.
First Set of Tools
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Panel method
Laminar Boundary layer Analysis
Turbulent Boundary layer Analysis
Transition prediction methods
We will start on panel method today. The
source code and sample input are available
at our AE 2020 web site:
http://www.ae.gatech.edu/~lsankar/AE2020