MAE 171A/175A/126 Wind Tunnel Experiment 1/9/2008 1 1 WIND TUNNEL EXPERIMENT MAE 171A/175A/126 PART I Pressure Distribution over an airfoil and Drag by the wake survey method OBJECTIVE : To … … measure the pressure distribution over a Clark Y-14 Airfoil at various angles of attack and determine the drag coefficient of the wing by the wake survey method. Data are obtained up to and beyond the stall angle, where the flow separates from the upper surface of the airfoil. INTRODUCTION: An airfoil develops Lift through generally lower …

MAE 171A/175A/126 Wind Tunnel Experiment 1/9/2008 2 2 examine the assumptions made in the momentum balance analysis in order to identify which of these assumptions are violated by the flow over a stalled airfoil. This method of drag measurement is often used on portions of airplane wings in flight to test special drag profiles or surface treatments. The pitching moment can also be obtained from the chordwise pressures by use of (Ref. 1) where: = distance from leading edge (or other selected reference point). PROCEDURE : 1. Using the barometer and thermometer in the laboratory determine the density of the air flowing in the wind tunnel. 2. Using the Wing Tunnel Calibration VI calibrate the wind tunnel test section by generating a plot of velocity (m/sec) versus motor frequency (0- 60 Hz) using the upstream pitot-static tube and Bernoulli’s equation. U   Static pressure Freestream Pressure ­ 1 ²h b a Pitot Probe: Measurement of Airspeed P a 1 2a U a 2 P b 1 2b U b 2 where: and P a P b 1 2 U2 q or P a P b 1 hg e and:
MAE 171A/175A/126 Wind Tunnel Experiment 1/9/2008 3 3 or 3. Use standard propagation of error analysis to estimate the error in . Yf (x i ) Y f x i 2 x i 2 1 i 1 2 4. A pressure wing is mounted vertically in the wind tunnel. The pressure tubes (18 with locations indicated above) from wing are connected to the inlet nipples of the multiplexed tunnel pressure sampling system. The static pressure of the test section is connected to the reference connection of the pressure transducer. The dynamic pressure of the air stream is measured with the Pitot probe. Dividing the pressure measured with the sampling system by gives the pressure coefficient at the point of the measurement: 5. Operate the tunnel at airspeeds of 20, 35 and 50 m/sec and make pressure measurements on the wing at angles of attack of 0°, 4°, 8° , 12°, and 16°. Always check the zero velocity pressure measurements from the wing and pitot probe before each data set. You will need to measure and correct for any offsets in the pressure transducer at zero velocity. Results: 1.Plot the pressure coefficient data points (upper and lower surface) as a function of distance along the chord line of the wing and integrate to find the Normal Force coefficient C n which is given as C n 1 c (C p L C p U ) dx 0 c . Find this normal force coefficient for all angles of attack and flow speeds. 2. Determine the Lift coefficients C L from C N and Plot C L vs. for each airspeed.. Show the results on one graph for comparison purposes. 3. On a separate graph plot C d vs. for each airspeed. Note that this method does not measure drag viscous forces due to shear stresses and thus may underrepresent the total drag force on the wing. The drag force and drag coefficient measured in this experiment is the component of the

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