windtunnelex-091119025051-phpapp01
Transcript of windtunnelex-091119025051-phpapp01
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NASA Glenn Research Center
Icing Branch - Van Zante / Dynacs Page 1
Wind Tunnel Exper iments for Grades 8 - 12
Wind Tunnel Exper iments
for
Grades 8 - 12
Dr. Judy Foss Van ZanteDynacs Engineering Co., Inc.
Cleveland, OH
6/15/99
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NASA Glenn Research Center
Icing Branch - Van Zante / Dynacs Page 2
Wind Tunnel Exper iments for Grades 8 - 12
Contents
Sample Experiments 3
Governing Equations 15
Flow Visualization Techniques 19
How to Make the Measurements 24
Background - Why Test in Wind Tunnels 27
Selected References 31
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Wind Tunnel Exper iments for Grades 8 - 12
Sample Experimen ts
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Wind Tunnel Exper iments for Grades 8 - 12
Ideas fo r Wind Tunnel Exper iments
Model: A irfoi l o r Flat Plate
• L vs. a Lift vs. Angle of Attack
• L vs. V Lift vs. Velocity
• CD vs. Re Drag vs. Reynolds Number
i.e., vary Speed and/or Size
• Investigate the effects of contamination onthe leading edge (sand paper, paper mache) tomimic ice accretion, bug splat, etc... This shouldreduce max lift & increase drag.
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Wind Tunnel Exper iments for Grades 8 - 12
Wind Tunnel Test Sect ion w ith A ir fo i lMount ing Opt ions
Airfoil on Sting Wall-Mounted
Flow
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Wind Tunnel Exper iments for Grades 8 - 12
Li f t vs. Ang le of A t tack
As the angle of attackincreases, so should the lift- until a certain point (the
stall angle of attack).
Angle of attack (a):
angle between flow andchord line.
Chord line:
straight line between mostforward and most aft points
a
a
Lift
Flow
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Wind Tunnel Exper iments for Grades 8 - 12
scale
L if t vs . Ang le (con t.)
Angle
L i f t
Visual: See airfoil lift
as angle increases
Measure: airfoil lift as
a function of angle
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Wind Tunnel Exper iments for Grades 8 - 12
Wind Tunnel Exper imentLi f t vs. Ang le Worksheet
angle Lift(deg) (oz)
0 0
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Wind Tunnel Exper iments for Grades 8 - 12
L if t vs. Veloc i ty
As the velocity (speed)increases, so should the lift.
Note: Keep the angle ofattack constant.
The greater the angle (priorto stall) the greater thechange in lift.
Lift
Velocity
(Speed)
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Wind Tunnel Exper iments for Grades 8 - 12
L if t vs . (Veloc i ty) 2
Velocity
L i f t
Visual: See airfoil lift
as speed increases
scale
Measure: airfoil lift as
a function of speed
V2
L
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Wind Tunnel Exper iments for Grades 8 - 12
Wind Tunnel Exper imentLi f t vs. Veloc i ty Wo rksheet
DP Wt Vel V^2 Lift
(oz) (m/s) (m/s)^2 (oz)
0 0 0 0
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Wind Tunnel Exper iments for Grades 8 - 12
Ideas fo r Wind Tunnel Exper iments
Model : Drag Body
Double Elimination Competitions
Build two objects. In a head-to-head comparison,see which one has the least drag.
Which w ay w i l l the object w i th the most d rag
move?
– Race Cars
– Geometric shapes
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Wind Tunnel Exper iments for Grades 8 - 12
Wind Tunnel w ith Drag ObjectsMount ing Opt ions
Bluff Bodies Race Cars
Rotating Sting Pulley
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Wind Tunnel Exper iments for Grades 8 - 12
Ideas fo r Wind Tunnel Exper iment
Model - Drag Body
Notes:
– The frontal area (the side facing the flow) must be thesame. Drag is directly related to the surface area.
– If using the pivot & sting, objects must be mounted equally
far apart from the pivot point. It is important that each
object has the same moment arm.
– If using the pulley system, it might be better to have twopulleys.
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Wind Tunnel Exper iments for Grades 8 - 12
Governing Equat ions
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Wind Tunnel Exper iments for Grades 8 - 12
Governing Equat ion s
Lift & Drag are equal to the
Dynamic Pressure * Surface Area * Coefficient
These Coefficients are a function ofAngle of Attack, Model Geometry & Mach number
D
2
L
2
C *S *V 2
1 D
C *S *V
2
1 L
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Wind Tunnel Exper iments for Grades 8 - 12
Nomenclature
Dynamic Pressure, ½ V2
= density (of air); “rho”
V = velocity (speed)
Surface Area, S
S = chord * spanchord is wing length, span is wing width
Coefficient of Lift CL = function (a, model, Ma)
Coefficient of Drag CD = function (a, model, Ma)
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Wind Tunnel Exper iments for Grades 8 - 12
The Lift and Drag can be changed most easily by
changing the angle of attack (a) or speed (V). Of
course, the surface area (S) can also be
adjusted. If a water tunnel is also available, the
working fluid (), e.g . air to water, can also be a
variable.During the course of one exper iment, i t is
important to only change one var iable at a t ime.
Governing Equat ion
Notes
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Wind Tunnel Exper iments for Grades 8 - 12
Flow Visualizat ion
Techniques
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Wind Tunnel Exper iments for Grades 8 - 12
Flow Visual izat ion Techniques
Flow Visualization illustrates the flow on
or near the object. On the surface, regionsof reverse flow become visible.
• Yarn Tufts, Tuft Probe, Tuft Grid
• Smoke Wand, Smoke Wire• Trailing Edge Cone (String & paper cone)
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Wind Tunnel Exper iments for Grades 8 - 12
Flow Visual izat ion Techniques
Yarn
• Yarn Tufts - tape ~1” segments of yarn directly to the
surface.
• Tuft Probe - tape ~3” light-weight (and visible) string to endof rod. Probe the flow.
• Tuft Grid - attach ~1” segments of yarn to a wire mesh
(screen) and place behind object (perpendicular orientation to
the flow)
• Trailing Edge Cone - tape one end of string to paper cone,
and the other end to (spanwise) edge of model. This illustrates
streamwise vorticity, if present. It’s great for delta wings.
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Wind Tunnel Exper iments for Grades 8 - 12
Yarn Tufts on surface
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Tuft Probe
Trailing Edge Cone
Flow Visual izat ion Techn iques
Il lustrated
Tuft Grid
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Wind Tunnel Exper iments for Grades 8 - 12
Flow Visual izat ion Techniques
Caut ions
• For yarn & string: If the inertia (mass) of
the yarn/string is too large, it won’t“follow” the flow.
• For smoke: If the airspeed is too high,
the smoke and air will mix and “blur”.
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Wind Tunnel Exper iments for Grades 8 - 12
How to Make the
Measurements
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Wind Tunnel Exper iments for Grades 8 - 12
Measuring Lift
• For airfoil and sting: measured from the scale
(ounces). Wt0 = weight at zero velocity.
L = Wt0 – Wt
Caution: try to minimize the friction (binding) at the
tunnel/sting interface, e.g., with a brass bearing.
• For wall mounted: measured from a load cell.Caution: this is a non-trivial pursuit.
Wind Tunnel Exper iment Detai ls
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Wind Tunnel Exper iments for Grades 8 - 12
Wind Tunnel Exper iment Detai ls
Measuring Velocity
• Pitot-static tube
DP = Ptotal - Pstatic
Bernoulli’s Equation: DP = (1/2) V2, 1 kg/m3 (units!)
V = 2* DP/
• Three-cup anemometer
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Wind Tunnel Exper iments for Grades 8 - 12
Background
Why Test in Wind Tunnels?
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Wind Tunnel Exper iments for Grades 8 - 12
Why Test in Wind Tunnels?
The Ultimate Goal : to Understand the FluidMechanics or Aerodynamics of an
• Aircraft in Flight
• Submarine in Water• Automobile on Road
• New Structure (Building, Bridge) in City
How do you get There from Here?
• Build a model and test it
– In a Wind Tunnel
– On a Computer
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Wind Tunnel Exper iments for Grades 8 - 12
Two of NASA’s Wind Tunnels
Ames 80’ x 120’
Langley
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Wind Tunnel Exper iments for Grades 8 - 12
Types of Wind Tunnels
Full Scale / Full Geometry (1999 price est imates )
• NASA Glenn 10’ x 10’ Supersonic $2000/hr
• NASA Ames 80’ x 120’ $1000/hr
Sub-Scale / Single Component
• NASA Glenn 20” x 30” Low Speed $2/hr
How does one scale a model?• Geometric
• Dynamic (e.g. Reynolds Number, Re = UL/m
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Wind Tunnel Exper iments for Grades 8 - 12
Selected References Aerodynamics
1. Abbott, Ira A. & von Doenhoff, Albert E., “Theory of Wing Sections,” Dover Publications, 1959.
2. Anderson, John D., “Fundamentals of Aerodynamics,” McGraw-Hill, Inc., 2nd Ed., 1991.
3. Anderson, John D., “Introduction to Flight,” McGraw-Hill, Inc., 3rd Ed., 1989.
4. Shevell, Richard S., “Fundamentals of Flight,” Prentice-Hall, Inc., Englewood Cliffs, NJ, 1983.
Fluid Mechanics
5. Potter, Merle C. & Foss, John F., “Fluid Mechanics,” The Ronald Press Co., NY, 1975(now published by Great Lakes Press).
6. White, Frank M., “Fluid Mechanics,” McGraw-Hill Inc., 2nd Ed., 1986.
7. Shapiro, Ascher H., “Shape and Flow: The Fluid Dynamics of Drag,” Science Study Series, Anchor
Books, Doubleday & Co., Inc.,Garden City, NY, 1961.
Flow Visualization
8. Van Dyke, Milton, “An Album of Fluid Motion,” Parabolic Press, P.O. Box 3032, Stanford, CA 94305 -
0030, 1982.
9. Japan Society of Mechanical Engineers, “Visualized Flow,” Pergamon Press, 1988.
10. National Committee for Fluid Mechanics Films, “Illustrated Experiments in Fluid Mechanics,” The
MIT Press, Cambridge, MA and London, England, 1972.