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