ME 388 – Applied
Instrumentation Laboratory
Wind Tunnel Lab
References
• Munson, Young and Okiishi,
Fundamentals of Fluid Mechanics
• Zucker, Fundamentals of Gas Dynamics
• Zucrow and Hoffman, Gas Dynamics
• Any fluids text
Experimental Objectives
• Measure lift and drag forces
– NACA 0012 airfoil (National Advisory Committee on Aeronautics)
– At various angles to air stream
• Determine coefficients of lift and drag and
compare to published values
• Determine coefficients of lift and drag at the
stall angle
Wind Tunnel Testing
• Allows engineers to predict the amount of
lift and drag that airfoils can develop in
various flight conditions.
• A 747 aircraft can weigh over 200,000 lbs.
2D Components of Lift and Drag
• Resultant force due to airflow across an
asymmetric body is not in the direction of
the airflow
Lift
• Generated by pressure difference over the
airfoil when the air moving over the body
takes a different path to reach the same
point
Drag
• Result of fluid friction
• Opposes body motion
Lift and Drag Dependence
• Size
• Shape
• Fluid flow
• Principle of Similitude allows us to “nondimensionalize” these parameters
Wind Tunnel and Instrumentation
Pitot tube
Airfoil
Us
Velocity meter
And D/P cell

chord
Lift/Drag
Dynamometer
Blower
NACA 0012 Air Foil
width
chord
Lift

Drag
 is the angle of attack
Scaled-down Physical Modeling
• Consider size for a given shape
Drag Force
C drag 
Dynamic Pressure  Area 
Lift Force
Clift 
Dynamic Pressure  Area 
Area  Chord LengthFoil Width
Dynamic Pressure 
 air  1.18
kg
m
3
 air u
2
2
C drag 
Clift 
2 Fdrag
 air u A
2
2 Flift
 air u A
2
Lift and Drag Plots
Lift
Drag
Attack angle (degrees)
Coefficient
Force (N)
Lift
Drag
Attack Angle
Lab Measurements
• Drag and Lift forces are measured with a
dynamometer
• Chord and width are measured with a ruler
• Air velocity is measured with a Pitot tube
• Angle of attack is measured with a
protractor
Fluid Conditions
• For similitude, fluid conditions must also
be similar
• Fluid flow is non-dimensionalized via the
Reynolds number
 air uc
Re 


5 N  s
 1.81  10
2
m
Pitot Tube and Bernoulli Eqn.
• Frictionless flow with only mechanical
energy
– No heat transfer
– No change in internal energy
2
2
u1 P1
u2 P2
  gz1 

 gz2
2

2
1 2
P2  P1  u1
2

Calibrate Dynamometer

Lift
Drag
weight
Post
Dynamometer
meter
Calibration Procedure
• Remove air foil from dynamometer post
• Attach string and weights from
dynamometer post and calibrate (use
weights to at least 1000 g)
• Remove weights and turn-on wind tunnel
and adjust for air velocity for Re = 160,000
• Record voltages from dynamometer
• Turn-off air and re-install air foil
• Record voltage (weight) of airfoil
• Run experiment
Drag Force (N)
Lift Force (N)
Dynamometer Calibration Curves
1.10
1.15
1.20
1.25
1.30
1.35
volts
1.40
1.45
1.50
1.55
0.0
0.1
0.2
0.3
volts
0.4
0.5
0.6
0.7
Experimental Procedure
1. Let dynamometer heat-up 15 minutes
before taking data
2. Adjust airfoil to 0° attack angle and take
dynamometer reading
3. Take readings every 3°
4. When lift force decreases (voltage drops),
decrease attack angle in 1° increments to
determine stall angle
Lab Requirements Summary
• Develop dynamometer calibration curves
• Plot lift and drag coefficients as a function
of attack angle
• Compare data to published NACA 0012
data at Re = 160,000, and for a flat plate
• Determine angle of maximum lift, a.k.a.
the stall angle
• Calculate uncertainty of the lift coefficient
at the stall angle
• In 1915, the U.S. Congress created the National
Advisory Committee on Aeronautics (NACA -- a
precursor of NASA). During the 1920s and
1930s, NACA conducted extensive wind tunnel
tests on hundreds of airfoil shapes (wing crosssectional shapes). The data collected allows
engineers to predictably calculate the amount of
lift and drag that airfoils can develop in various
flight conditions. Reference?
NASA Photo