CIVL 321 LABORATORY Spring 2023 Objective: Fluid Mechanics Lab #11 Aerodynamic Drag and Lift To determine the drag and lift coefficients of a model using the closed-loop wind tunnel with 28"x20" test section in LANG 122. Specifically, determine the drag and lift coefficients of a NACA 4412 airfoil- shaped wing model at relatively high Reynolds number(s) as a function of the angle of attack (a) and compare with published data. Theory: The total drag force of an immersed body consists of viscous drag (skin friction) and pressure (form) drag. Lift is solely due to pressure effects. The drag and lift coefficients and Reynolds number for airfoil- shaped wings are normally defined as: CD = 2FD PAU² CL = 2F PAU² Uc Re= V where FD is the measured drag force, FL the measured lift force, p is the fluid density, U the upstream fluid velocity (relative to a stationary body), A, is the planform area of the body (i.e., the area seen from above at zero angle-of-attack), c is the chord length of the airfoil-shaped wing, and v is the fluid kinematic viscosity. Refer to Sections 9.3 and 9.4 of your textbook for more information. Procedure: 1. If necessary, install airfoil mount and secure airfoil-shaped wing with screws with the help of the instructor. 2. Turn power to Force Balance Pitch/Yaw Control system ON. Release locking bolts on the wind tunnel force balance (do NOT lean on the frame) and then tare lift and drag displays. 3. The RP240 PITCH and YAW control panel should now be displaying a short prompting message. Re- tare the lift and drag displays if necessary. 4. Start the wind tunnel by performing steps 1 through 8 of the closed loop wind tunnel start-up procedure shown below. 5. Set the speed control to a value indicated by the instructor and record 1) the pitot-static tube deflection in inches of H2O; 2) the local static pressure in inches of H₂O; 3) the barometric pressure in kPa, and 4) the temperature in °C. The difference between the local static pressure and barometric pressure is a measure of how much the static pressure in the wind tunnel is below atmospheric pressure. This will allow you to calculate the air density in the wind tunnel using the Ideal Gas Law. Watch your units!!! 6. Select the PITCH axis (Press F1 on the RP240) and enter -12° (angle of attack). Record the drag and lift forces (lbs) indicated on the meters. 7. Increase the airfoil/wing angle of attack in increments of 2° up to +20°, recording lift and drag values for each angle. Return the airfoil to 0° angle of attack when finished. 8. To obtain lift and drag for other velocities, repeat steps 5 through 7 and record the necessary data. 9. Return airfoil to 0° angle of attack and follow the shutdown procedure for the wind tunnel below. 10. Press EXIT (F6) on the RP240 PITCH and YAW control panel. 11. Carefully secure all four locking bolts. Pay close attention to the load cell displays - try to keep displayed loads <2 lbs. as the bolts are being tightened. 12. Turn power to force balance control system OFF. Operating Procedure for Closed-Loop Wind Tunnel: Start-up: 1. Make a visual inspection to ensure no loose objects were inadvertently left in the wind tunnel and latch the door(s) shut. Scanned with CamScanner 2. Turn on the Test Section Lights. 3. Turn on the wind tunnel Master Power switch. The Wind Tunnel Speed Control should illuminate and control should initialize to the stopped condition. 4. Open (if not already) the Magnetic Clutch Water Valve (ball valve on left) and press the Clutch Cooling On button. Make sure water is circulating by checking the drain valve in the Southeast corner of the lab. 5. SLOWLY open the heat exchanger water inlet valve (it is the ball valve on the right) 6. Press the Motor Start button. The clutch output will slowly reach an idle speed of 250-300 RPM 7. Press P1 on the Wind Tunnel Speed Control to access manual control on the Run potentiometer. 8. Set the Run to desired RPM by adjusting the potentiometer and press Run. This initiates live control of the fan motor. For the first test use 800 RPM. When ready for the second test, SLOWLY adjust the potentiometer to 1100 RPM. Shut-down: 1. Press the Stop button on the Wind Tunnel Speed Control. 2. Allow the motor to coast to idle speed of 250-300 RPM. 3. Press the Motor Stop button. 4. SLOWLY close the heat exchanger water inlet valve (located on right) 5. When motor has coasted to a stop, push the Clutch Cooling Off button to stop the motor/clutch cooling water. 6. If the Magnetic Clutch Cooling Valve (ball valve on the left) was open when you started, then leave it open. Otherwise close it. 7. Turn off Master Power switch. 8. Turn off the Test Section Lights. 9. Turn off Main Electrical Cutoff Box. Velocity Measurement with the Pitot Tube: The Pitot tube, when properly connected to a manometer or pressure transducer, measures the difference between the stagnation pressure and static pressure of a fluid flow (AP). The velocity of the fluid at the static pressure tap, which is essentially the freestream velocity (U); can be determined from the Bernoulli equation: U = 2AP P = 2pmgh P where p is the density of the flowing fluid, pm is the density of the manometer liquid at standard conditions, and h is the deflection of the manometer liquid level read from the inclined scale. This scale is calibrated to read inches of H2O, so pm is the density of water at room temperature. The measured drag force includes both the drag on the wing and the vertical mounting strut. The drag on the mount was determined independently as: Fam = 1.4604×10-5V2.281, where V is measured in ft/s. Subtracting Fam from the measured drag force will correct for the additional drag on the strut so you obtain just the drag force on the wing. Material to be Included in Report in Addition to Normal Requirements: 1. Prepare an Excel graph of the lift coefficient (CL) versus angle of attack (a). Indicate the angle of attack at the point of stall (acmax) and the zero-lift angle of attack (ac=0). Compare with published results and discuss any differences. Compare the plots for the data collected at 70 mph versus 100 mph (you can plot both data on the same graph). Why does this result occur even though they are collected at different speeds? 2. Prepare an Excel graph of the drag coefficient (CD) versus lift coefficient (CL) and label each data point with the corresponding angle of attack. This is called a drag polar diagram (Figure 9.35b). Find the angle of attack where lift- to-drag ratio is maximum. Compare with published results given in your lab manual and discuss any differences. Note: Drag polar plots in many aerodynamics books are plotted with the drag coefficient on the y-axis and the lift coefficient on the x-axis. 2 Scanned with CamScanner Airfoil Designation: NACA 4412 chord: 5 in. span: 16 in. 800RPM 1100RPM Settings Test 1 Test 2 Yaw: 0 0 degrees Initial Pitch: 0 0 degrees Pitch increment: 2 2 degrees Pitot-static Pressure: 2,67 4.61 in. H₂O Local Static Pressure: 387 .710 in. H₂O Barometric Pressure: 10016 100.6 kPa Air Temperature:| 22.2 22.9 °C Tunnel Static Pressure: units Air Density units Air Speed units units Kinematic viscosity (air)| Reynolds No. (chord length): Test 1 Test 2 Angle of Attack, a Drag Force (degrees) (lbs) Lift Force (lbs) Drag Force Lift Force (lbs) (lbs) -12 1.212 2. h 2.242 4.47 -10 1.033 -1.33 1.874 -3.19 -8 0.831 1.20 1.438 -1.79 -6 2.723 10.48 1.298 -0.19 -4 0.677 0.32 1.262 1.50 -2 0.665 1.17 1.277 3.88 0 9.653 1.97 1. 330 5.68 2 0.708 3.10 1.447 7.45 4 0.776 4.01 1.597 9.13 6 0.854 4,84 1.776 10.58 8 0.972 5.61 1.998 11.97 10 1.101 6.26 2.235 13.12 12 1.224 6.79 2.532 14.99 14 1.350 7.10 2.353 14.73 16 1.541 7.39 4.210 11.09 18 1.729 7.43 4.592 11.10 20 2.338 5.37 4.803 11.17 Scanned with CamScanner