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

NACA 0012 Air Foil

Scaled-down Physical Modeling Consider size for a given shape

Lift and Drag Plots

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

Pitot Tube and Bernoulli Eqn. Frictionless flow with only mechanical energy No heat transfer No change in internal energy

Calibrate Dynamometer

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

Experimental Procedure Let dynamometer heat-up 15 minutes before taking data Adjust airfoil to 0° attack angle and take dynamometer reading Take readings every 3° 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