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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 “non-dimensionalize” these parameters
Wind Tunnel and Instrumentation
chord
Pitot tube
Lift/Drag
DynamometerVelocity meter
BlowerAirfoil
And D/P cell
Uschord
Pitot tube
Lift/Drag
DynamometerVelocity meter
BlowerBlowerAirfoil
And D/P cell
UsUs
NACA 0012 Air Foil
width
chord
Lift
Drag
is the angle of attack
Scaled-down Physical Modeling
• Consider size for a given shape
AreaPressure Dynamic
Force DragCdrag
AreaPressure Dynamic
Force LiftClift
Width FoilLength ChordArea
2
2uPressure Dynamic air
318.1
m
kgair
Au
FC
air
dragdrag 2
2
Au
FC
air
liftlift 2
2
Lift and Drag Plots
LiftDrag
Fo
rce
(N
)
Attack angle (degrees)
Co
effi
cie
nt
Attack Angle
LiftDrag
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
uc
R aire
251081.1
m
sN
Pitot Tube and Bernoulli Eqn.• Frictionless flow with only mechanical
energy– No heat transfer– No change in internal energy
22
22
11
21
22gz
Pugz
Pu
2112 2
1uPP
Calibrate Dynamometer
Lift
Drag
Post
Dynamometer
meter
weight
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
Dynamometer Calibration Curves
1.10 1.15 1.20 1.25 1.30 1.35 1.40 1.45 1.50 1.55
Lift
Fo
rce
(N
)
volts0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Dra
g F
orc
e (
N)
volts
Experimental Procedure1. 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 cross-sectional 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
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