NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 1 Wind Tunnel Experiments for Grades Dr. Judy Foss Van Zante Dynacs Engineering Co., Inc. Cleveland, OH 6/15/99

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 2 Wind Tunnel Experiments for Grades Contents Sample Experiments 3 Governing Equations15 Flow Visualization Techniques19 How to Make the Measurements24 Background - Why Test in Wind Tunnels 27 Selected References 31

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 3 Wind Tunnel Experiments for Grades Sample Experiments

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 4 Wind Tunnel Experiments for Grades Ideas for Wind Tunnel Experiments Model: Airfoil or Flat Plate L vs.  Lift vs. Angle of Attack L vs. VLift vs. Velocity C D vs. ReDrag vs. Reynolds Number i.e., vary Speed and/or Size 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.

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 5 Wind Tunnel Experiments for Grades Wind Tunnel Test Section with Airfoil Mounting Options Airfoil on StingWall-Mounted Flow

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 6 Wind Tunnel Experiments for Grades 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

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 7 Wind Tunnel Experiments for Grades scale Lift vs. Angle (cont.) Angle Lift Visual: See airfoil lift as angle increases Measure: airfoil lift as a function of angle

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 8 Wind Tunnel Experiments for Grades Wind Tunnel Experiment Lift vs. Angle Worksheet

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 9 Wind Tunnel Experiments for Grades 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)

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 10 Wind Tunnel Experiments for Grades Lift vs. (Velocity) 2 Velocity Lift Visual: See airfoil lift as speed increases scale Measure: airfoil lift as a function of speed V2V2 L

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 11 Wind Tunnel Experiments for Grades Wind Tunnel Experiment Lift vs. Velocity Worksheet

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 12 Wind Tunnel Experiments for Grades Ideas for Wind Tunnel Experiments Model: Drag Body Double Elimination Competitions Build two objects. In a head-to-head comparison, see which one has the least drag. Which way will the object with the most drag move? – Race Cars – Geometric shapes

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 13 Wind Tunnel Experiments for Grades Wind Tunnel with Drag Objects Mounting Options Bluff Bodies Race Cars Rotating StingPulley

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 14 Wind Tunnel Experiments for Grades Ideas for Wind Tunnel Experiment Model - Drag Body Notes: –The frontal area (the side facing the flow) must be the same. Drag is directly related to the surface area. –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. –If using the pulley system, it might be better to have two pulleys.

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 15 Wind Tunnel Experiments for Grades Governing Equations

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 16 Wind Tunnel Experiments for Grades Governing Equations Lift & Drag are equal to the Dynamic Pressure * Surface Area * Coefficient These Coefficients are a function of Angle of Attack, Model Geometry & Mach number

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 17 Wind Tunnel Experiments for Grades Nomenclature Dynamic Pressure, ½  V 2  = density (of air); “rho” V = velocity (speed) Surface Area, S S = chord * span chord is wing length, span is wing width Coefficient of Lift C L = function ( , model, Ma) Coefficient of Drag C D = function ( , model, Ma)

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 18 Wind Tunnel Experiments for Grades 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. During the course of one experiment, it is important to only change one variable at a time. Governing Equation Notes

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 19 Wind Tunnel Experiments for Grades Flow Visualization Techniques

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 20 Wind Tunnel Experiments for Grades Flow Visualization Techniques Flow Visualization illustrates the flow on or near the object. On the surface, regions of reverse flow become visible. Yarn Tufts, Tuft Probe, Tuft Grid Smoke Wand, Smoke Wire Trailing Edge Cone (String & paper cone)

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 21 Wind Tunnel Experiments for Grades Flow Visualization Techniques Yarn Yarn Tufts - tape ~1” segments of yarn directly to the surface. Tuft Probe - tape ~3” light-weight (and visible) string to end of rod. Probe the flow. Tuft Grid - attach ~1” segments of yarn to a wire mesh (screen) and place behind object (perpendicular orientation to the flow) 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.

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 22 Wind Tunnel Experiments for Grades Yarn Tufts on surface x xx x x xx x x xxxx x x xx x x xxx x x x xx x x xx x x xx xx x x xx x x xx x x x x xx x x xx x x xx xx x x xx x x xx x x x x xx x x xx x x xx xx x x xx x x xx x x x Tuft Probe Delta Wing Trailing Edge Cone Flow Visualization Techniques Illustrated Tuft Grid

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 23 Wind Tunnel Experiments for Grades Flow Visualization Techniques Cautions For yarn & string: If the inertia (mass) of the yarn/string is too large, it won’t “follow” the flow. For smoke: If the airspeed is too high, the smoke and air will mix and “blur”.

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 24 Wind Tunnel Experiments for Grades How to Make the Measurements

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 25 Wind Tunnel Experiments for Grades Measuring Lift For airfoil and sting: measured from the scale (ounces). W t0 = weight at zero velocity. L = W t0 – W t Caution: try to minimize the friction (binding) at the tunnel/sting interface, e.g., with a brass bearing. For wall mounted: measured from a load cell. Caution: this is a non-trivial pursuit. Wind Tunnel Experiment Details

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 26 Wind Tunnel Experiments for Grades Wind Tunnel Experiment Details Measuring Velocity Pitot-static tube  P = P total - P static Bernoulli’s Equation:  P = (1/2)  V 2,  1 kg/m 3 (units!) V =  2*  P/   Three-cup anemometer

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 27 Wind Tunnel Experiments for Grades Background Why Test in Wind Tunnels?

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 28 Wind Tunnel Experiments for Grades Why Test in Wind Tunnels? The Ultimate Goal: to Understand the Fluid Mechanics or Aerodynamics of an Aircraft in Flight Submarine in Water Automobile on Road New Structure (Building, Bridge) in City How do you get There from Here? Build a model and test it –In a Wind Tunnel –On a Computer

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 29 Wind Tunnel Experiments for Grades Two of NASA’s Wind Tunnels Ames 80’ x 120’ Langley

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 30 Wind Tunnel Experiments for Grades Types of Wind Tunnels Full Scale / Full Geometry( 1999 price estimates) NASA Glenn 10’ x 10’ Supersonic$2000/hr NASA Ames 80’ x 120’ $1000/hr Sub-Scale / Single Component NASA Glenn 20” x 30” Low Speed $2/hr How does one scale a model? Geometric Dynamic(e.g. Reynolds Number, Re =  UL/ 

NASA Glenn Research Center Icing Branch - Van Zante / Dynacs Page 31 Wind Tunnel Experiments for Grades Selected References Aerodynamics 1.Abbott, Ira A. & von Doenhoff, Albert E., “Theory of Wing Sections,” Dover Publications, Anderson, John D., “Fundamentals of Aerodynamics,” McGraw-Hill, Inc., 2nd Ed., Anderson, John D., “Introduction to Flight,” McGraw-Hill, Inc., 3rd Ed., Shevell, Richard S., “Fundamentals of Flight,” Prentice-Hall, Inc., Englewood Cliffs, NJ, Fluid Mechanics 5.Potter, Merle C. & Foss, John F., “Fluid Mechanics,” The Ronald Press Co., NY, 1975 (now published by Great Lakes Press). 6.White, Frank M., “Fluid Mechanics,” McGraw-Hill Inc., 2nd Ed., Shapiro, Ascher H., “Shape and Flow: The Fluid Dynamics of Drag,” Science Study Series, Anchor Books, Doubleday & Co., Inc.,Garden City, NY, Flow Visualization 8.Van Dyke, Milton, “An Album of Fluid Motion,” Parabolic Press, P.O. Box 3032, Stanford, CA , Japan Society of Mechanical Engineers, “Visualized Flow,” Pergamon Press, National Committee for Fluid Mechanics Films, “Illustrated Experiments in Fluid Mechanics,” The MIT Press, Cambridge, MA and London, England, 1972.