me 388 – applied instrumentation laboratory wind tunnel lab
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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/DragDynamometerVelocity meter
BlowerAirfoil
And D/P cell
Us chord
Pitot tube
Lift/DragDynamometerVelocity 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 DynamicForce DragCdrag
AreaPressure DynamicForce 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
Forc
e (N
)
Attack angle (degrees)
Coe
ffici
ent
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
22gzPugzPu
2112 2
1 uPP
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
Forc
e (N
)
volts0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Dra
g Fo
rce
(N)
volts
Experimental Procedure1. Let dynamometer heat-up 15 minutes
before taking data2. Adjust airfoil to 0° attack angle and take
dynamometer reading3. 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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