Aerodynamic Force
Measurement
Wednesday 13 February 2013
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Objective
Wind tunnels and experimental equipment
Experimental setup, procedure and measurements
Momentum equation and drag
Wake
Expected Results
Examples
Reference
• Gain experience with setting up and
performing aerodynamic experiment
• Learn some basic concepts in aerodynamic
force measurement
• Gain experience with flow visualization
• Gain hands-on experience with common
instrumentation used in the aerodynamic
experiments
• Test Section
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Closed loop
Open loop
• Speed
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Low speed wind tunnel (0.3 > M)
High Speed wind tunnels (0.4 < M < 0.75)
Transonic wind tunnel (0.75 < M < 1.2)
Super sonic wind tunnels (1.2 < M < 5)
Hypersonic wind tunnels Mach (5 < M < 15)
• Principle of Operation Bernoulli’s Equation
• Stagnation pressure = static pressure + dynamic pressure
1
1
2
p1  V1  p0  V02
2
2
1
p1  V12  p0
2
2 p0  p1 
V1 
P1= Static Pressure
V1= Velocity of Flow
P0= Total pressure
  Density

Total Pressure
Velocity
Static Pressure
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NACA 0015 Airfoil
Max. thickness =2.24
Chord: c = 16 inch
Span : b = 16 inch
• Atmospheric data (Temperature and Pressure)
• Airfoil at 0o and 2o
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Drag
Lift
Velocity at various height
• Airfoil at 2o and 20o flap deflection
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Drag
Lift
• Flow Visualization
General Form Of Momentum equation
 u 
p
 .uV     f x  ( Fx )Viscous
t
x
Integral form of momentum equation for steady inviscid flow with no
body forces

DE
E
dv   E (v.nˆ )ds   F

Dt v t
b
2  u 
u 
Cd    1  dy
c h  u  u 
U = Velocity of flow at a given location
U = Free Stream velocity
1 2
D  v SC d
2
 = Density Of fluid
v = Velocity of fluid
S = Area of the wing
Cd = Coefficient of Drag
•A wake is the region of recirculating flow immediately behind a moving
solid body, caused by the flow of surrounding fluid around the body.
•Wake flow is generally turbulent
•As with all wave forms, it spreads outward from the source until
its energy is overcome or lost, usually by friction or dispersion.
5o Angle of Attack
10o Angle of Attack
15o Angle of Attack
• Drag
• Calculation using momentum theory
• Graphical representation of drag
b
2  u 
u 
Cd    1  dy
c h  u  u 
U 
U 
y
 versus
* 1 
U  U 
dc
• Velocity deficit
• Plot Velocity deficit to show wake in flow field
U
y
versus
U
dc
• Flow visualization
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Describe flow at various setups of airfoil
• Fundamentals Of Aerodynamics
• J. D. Anderson
+ Similarity Of flows, Pages (40-50) Chapter 1, section 1.8
+ Equation of Drag, Pages (127-133) Chapter 2, section 2.6
+ Pages (197-210) Chapter 3, section 3.3
+ Wind tunnels Pages (197-210) Chapter 3, section 3.3
+ Pitot Tube Pages (210-219) Chapter 3, section 3.4
• History Of Wind Tunnels
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http://www.grc.nasa.gov/WWW/k-12/WindTunnel/history.html
• Mercedes-Benz SLS AMG Development and Testing Wind
tunnel
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http://www.youtube.com/watch?v=sV_6E1Lh7yo
• BMW Aerodynamic Testing
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http://www.youtube.com/watch?v=eszhVxE_9-8