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Wind Tunnel Ex

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Wind Tunnel Ex

1. 1. Wind Tunnel Experiments for Grades 8 - 12 Dr. Judy Foss Van Zante Dynacs Engineering Co., Inc. Cleveland, OH 6/15/99
2. 2. Contents Sample Experiments 3 Governing Equations 15 Flow Visualization Techniques 19 How to Make the Measurements 24 Background - Why Test in Wind Tunnels 27 Selected References 31
3. 3. Sample Experiments
4. 4. Ideas for Wind Tunnel Experiments Model: Airfoil or Flat Plate <ul><li>L vs.  Lift vs. Angle of Attack </li></ul><ul><li>L vs. V Lift vs. Velocity </li></ul><ul><li>C D vs. Re Drag vs. Reynolds Number i.e. , vary Speed and/or Size </li></ul><ul><li>Investigate the effects of contamination on the leading edge (sand paper, paper mache) to mimic ice accretion, bug splat, etc... This should reduce max lift & increase drag. </li></ul>
5. 5. Wind Tunnel Test Section with Airfoil Mounting Options Airfoil on Sting Wall-Mounted Flow
6. 6. Lift vs. Angle of Attack As the angle of attack increases, so should the lift - until a certain point (the stall angle of attack). Angle of attack (  ): angle between flow and chord line. Chord line: straight line between most forward and most aft points Lift Flow  
7. 7. Lift vs. Angle (cont.) Angle Lift Visual: See airfoil lift as angle increases Measure: airfoil lift as a function of angle scale
8. 8. Wind Tunnel Experiment Lift vs. Angle Worksheet
9. 9. Lift vs. Velocity As the velocity (speed) increases, so should the lift. Note: Keep the angle of attack constant. The greater the angle (prior to stall) the greater the change in lift. Lift Velocity (Speed)
10. 10. Lift vs. (Velocity) 2 Visual: See airfoil lift as speed increases Measure: airfoil lift as a function of speed Velocity Lift scale V 2 L
11. 11. Wind Tunnel Experiment Lift vs. Velocity Worksheet
12. 12. Ideas for Wind Tunnel Experiments Model: Drag Body <ul><li>Double Elimination Competitions </li></ul><ul><li>Build two objects. In a head-to-head comparison, see which one has the least drag. </li></ul><ul><li>Which way will the object with the most drag move? </li></ul><ul><ul><li>Race Cars </li></ul></ul><ul><ul><li>Geometric shapes </li></ul></ul>
13. 13. Wind Tunnel with Drag Objects Mounting Options Bluff Bodies Race Cars Rotating Sting Pulley
14. 14. Ideas for Wind Tunnel Experiment Model - Drag Body <ul><li>Notes: </li></ul><ul><ul><li>The frontal area (the side facing the flow) must be the same. Drag is directly related to the surface area. </li></ul></ul><ul><ul><li>If using the pivot & sting, objects must be mounted equally far apart from the pivot point. It is important that each object has the same moment arm. </li></ul></ul><ul><ul><li>If using the pulley system, it might be better to have two pulleys. </li></ul></ul>
15. 15. Governing Equations
16. 16. Governing Equations <ul><li>Lift & Drag are equal to the </li></ul><ul><li>Dynamic Pressure * Surface Area * Coefficient </li></ul><ul><li>These Coefficients are a function of </li></ul><ul><li>Angle of Attack, Model Geometry & Mach number </li></ul>
17. 17. Nomenclature <ul><li>Dynamic Pressure, ½  V 2 </li></ul><ul><li> = density (of air); “rho” </li></ul><ul><li>V = velocity (speed) </li></ul><ul><li>Surface Area, S </li></ul><ul><li>S = chord * span </li></ul><ul><li>chord is wing length, span is wing width </li></ul><ul><li>Coefficient of Lift C L = function (  , model, Ma) </li></ul><ul><li>Coefficient of Drag C D = function (  , model, Ma) </li></ul>
18. 18. <ul><li>The Lift and Drag can be changed most easily by changing the angle of attack (  ) or speed ( V ). Of course, the surface area ( S ) can also be adjusted. If a water tunnel is also available, the working fluid (  ), e.g . air to water, can also be a variable. </li></ul><ul><li>During the course of one experiment, it is important to only change one variable at a time. </li></ul>Governing Equation Notes
19. 19. Flow Visualization Techniques
20. 20. Flow Visualization Techniques <ul><li>Flow Visualization illustrates the flow on or near the object. On the surface, regions of reverse flow become visible. </li></ul><ul><li>Yarn Tufts, Tuft Probe, Tuft Grid </li></ul><ul><li>Smoke Wand, Smoke Wire </li></ul><ul><li>Trailing Edge Cone (String & paper cone) </li></ul>
21. 21. Flow Visualization Techniques Yarn <ul><li>Yarn Tufts - tape ~1” segments of yarn directly to the surface. </li></ul><ul><li>Tuft Probe - tape ~3” light-weight (and visible) string to end of rod. Probe the flow. </li></ul><ul><li>Tuft Grid - attach ~1” segments of yarn to a wire mesh (screen) and place behind object (perpendicular orientation to the flow) </li></ul><ul><li>Trailing Edge Cone - tape one end of string to paper cone, and the other end to (spanwise) edge of model. This illustrates streamwise vorticity, if present. It’s great for delta wings. </li></ul>
22. 22. Yarn Tufts on surface Tuft Probe Delta Wing Trailing Edge Cone Flow Visualization Techniques Illustrated x x x x x x x x x x x x x x x x x x x x Tuft Grid
23. 23. Flow Visualization Techniques Cautions <ul><li>For yarn & string: If the inertia (mass) of the yarn/string is too large, it won’t “follow” the flow. </li></ul><ul><li>For smoke: If the airspeed is too high, the smoke and air will mix and “blur”. </li></ul>
24. 24. How to Make the Measurements
25. 25. <ul><li>Measuring Lift </li></ul><ul><li>For airfoil and sting: measured from the scale (ounces). W t0 = weight at zero velocity. </li></ul><ul><li>L = W t0 – W t </li></ul><ul><ul><li>Caution: try to minimize the friction (binding) at the tunnel/sting interface, e.g., with a brass bearing. </li></ul></ul><ul><li>For wall mounted: measured from a load cell. </li></ul><ul><ul><li>Caution: this is a non-trivial pursuit. </li></ul></ul>Wind Tunnel Experiment Details
26. 26. Wind Tunnel Experiment Details <ul><li>Measuring Velocity </li></ul><ul><li>Pitot-static tube </li></ul><ul><li> P = P total - P static </li></ul><ul><li>Bernoulli’s Equation:  P = (1/2)  V 2 ,  1 kg/m 3 (units!) </li></ul><ul><li>V =  2*  P/  </li></ul><ul><li> </li></ul><ul><li>Three-cup anemometer </li></ul>
27. 27. Background Why Test in Wind Tunnels?
28. 28. Why Test in Wind Tunnels? <ul><li>The Ultimate Goal : to Understand the Fluid Mechanics or Aerodynamics of an </li></ul><ul><li>Aircraft in Flight </li></ul><ul><li>Submarine in Water </li></ul><ul><li>Automobile on Road </li></ul><ul><li>New Structure (Building, Bridge) in City </li></ul><ul><li>How do you get There from Here? </li></ul><ul><li>Build a model and test it </li></ul><ul><ul><li>In a Wind Tunnel </li></ul></ul><ul><ul><li>On a Computer </li></ul></ul>
29. 29. Two of NASA’s Wind Tunnels Ames 80’ x 120’ Langley
30. 30. Types of Wind Tunnels <ul><li>Full Scale / Full Geometry ( 1999 price estimates ) </li></ul><ul><li>NASA Glenn 10’ x 10’ Supersonic \$2000/hr </li></ul><ul><li>NASA Ames 80’ x 120’ \$1000/hr </li></ul><ul><li>Sub-Scale / Single Component </li></ul><ul><li>NASA Glenn 20” x 30” Low Speed \$2/hr </li></ul><ul><li>How does one scale a model? </li></ul><ul><li>Geometric </li></ul><ul><li>Dynamic ( e.g. Reynolds Number, Re =  UL/  </li></ul>
31. 31. Selected References <ul><li>Aerodynamics </li></ul><ul><li>Abbott, Ira A. & von Doenhoff, Albert E., “Theory of Wing Sections,” Dover Publications, 1959. </li></ul><ul><li>Anderson, John D., “Fundamentals of Aerodynamics,” McGraw-Hill, Inc., 2nd Ed., 1991. </li></ul><ul><li>Anderson, John D., “Introduction to Flight,” McGraw-Hill, Inc., 3rd Ed., 1989. </li></ul><ul><li>Shevell, Richard S., “Fundamentals of Flight,” Prentice-Hall, Inc., Englewood Cliffs, NJ, 1983. </li></ul><ul><li>Fluid Mechanics </li></ul><ul><li>5. Potter, Merle C. & Foss, John F., “Fluid Mechanics,” The Ronald Press Co., NY, 1975 (now published by Great Lakes Press). </li></ul><ul><li>White, Frank M., “Fluid Mechanics,” McGraw-Hill Inc., 2nd Ed., 1986. </li></ul><ul><li>Shapiro, Ascher H., “Shape and Flow: The Fluid Dynamics of Drag,” Science Study Series, Anchor Books, Doubleday & Co., Inc.,Garden City, NY, 1961. </li></ul><ul><li>Flow Visualization </li></ul><ul><li>8. Van Dyke, Milton, “An Album of Fluid Motion,” Parabolic Press, P.O. Box 3032, Stanford, CA 94305-0030, 1982. </li></ul><ul><li>9. Japan Society of Mechanical Engineers, “Visualized Flow,” Pergamon Press, 1988. </li></ul><ul><li>10. National Committee for Fluid Mechanics Films, “Illustrated Experiments in Fluid Mechanics,” The MIT Press, Cambridge, MA and London, England, 1972. </li></ul>

Editor's Notes

• Need: Airfoil Sting (rod) (Tygon) tube partially filled w/ water Pitot-Static Tube Scale (measure in ounces) Attach the sting to the airfoil and rest the assembly on the scale. (Tygon) tube partially filled w/ water attached to the Pitot-Static Tube Rest the
• Dollar estimates are guesses. Ma : Mach number = U/a ; compressible flow St : Strouhal number = fd/U ; oscillating flow Fr : Froude number = U^2/gL ; free-surface flow We : Weber number = rU^2L/G ; surface tension Pr : Prandtl number = mcp/k ; heat convection (r = density, m = viscosity)
• Dollar estimates are guesses. Ma : Mach number = U/a ; compressible flow St : Strouhal number = fd/U ; oscillating flow Fr : Froude number = U^2/gL ; free-surface flow We : Weber number = rU^2L/G ; surface tension Pr : Prandtl number = mcp/k ; heat convection (r = density, m = viscosity)