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