# Presentation: 376959

## Wind Tunnel ExperimentsforGrades 8 - 12

**Dr. Judy Foss Van Zante**
**Dynacs Engineering Co., Inc.**
**Cleveland, OH**

***6/15/99***

## 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**

## Sample Experiments

## Ideas for Wind Tunnel ExperimentsModel: Airfoil or Flat Plate

** ****L vs. ******** ****	****Lift vs. Angle of Attack**
** ****L vs. V****	****Lift vs. Velocity**
** ****C****D**** vs. Re****	****Drag 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.**

## Wind Tunnel Test Section with AirfoilMounting Options

**Airfoil on Sting****	****	****Wall-Mounted**

## Lift vs. Angle of Attack

***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**

**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 

## Lift vs. Angle (cont.)

***Lift vs. Angle (cont.)***

**Angle**

**Lift**

**Visual: See airfoil lift**
**as angle increases**

**Measure: airfoil lift as**
**a function of angle**

## Wind Tunnel Experiment Lift vs. Angle Worksheet

## Lift vs. Velocity

***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)**

## Lift vs. (Velocity)2

**Visual: See airfoil lift**
**as speed increases**

**Measure: airfoil lift as**
**a function of speed**

## Wind Tunnel Experiment Lift vs. Velocity Worksheet

## 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

## Wind Tunnel with Drag ObjectsMounting Options

**Bluff Bodies****	****	****	****    Race Cars**
**Rotating Sting****	****	****	****Pulley**

## 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.

## Governing Equations

## 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**

## Nomenclature

**Dynamic Pressure,  1⁄2 ******** 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)**

## 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.

***During the course of one experiment, it is important to only change one variable at a time.***

***Governing Equation******Notes***

## Flow VisualizationTechniques

## 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)**

## 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.

## Flow Visualization TechniquesIllustrated

- Tuft Probe

**Delta**
** ****Wing**

- Trailing Edge Cone

***Flow Visualization Techniques******Illustrated***

## 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”. **

## How to Make the Measurements

## Measuring Lift 
For airfoil and sting: measured from the scale (ounces). Wt0 = weight at zero velocity. 
L = Wt0 – Wt
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. 

**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***

## 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**

## BackgroundWhy Test in Wind Tunnels?

## 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

## Two of NASA’s Wind Tunnels

**Ames 80’ x 120’**

**Langley**

**Notes:**
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)

## 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/******

**Notes:**
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)

**	**

***Selected References***

_**Aerodynamics**_
- Abbott, Ira A. & von Doenhoff, Albert E., “Theory of Wing Sections,” Dover Publications, 1959.
- Anderson, John D., “Fundamentals of Aerodynamics,” McGraw-Hill, Inc., 2nd Ed., 1991.
- Anderson, John D., “Introduction to Flight,” McGraw-Hill, Inc., 3rd Ed., 1989.
- Shevell, Richard S., “Fundamentals of Flight,” Prentice-Hall, Inc., Englewood Cliffs, NJ, 1983.
_**Fluid Mechanics**_
- 5.	Potter, Merle C. & Foss, John F., “Fluid Mechanics,” The Ronald Press Co., NY, 1975 	         (now published by Great Lakes Press).
- White, Frank M., “Fluid Mechanics,” McGraw-Hill Inc., 2nd Ed., 1986.
- Shapiro, Ascher H., “Shape and Flow: The Fluid Dynamics of Drag,” Science Study Series, Anchor Books, Doubleday & Co., Inc.,Garden City, NY, 1961.
_**Flow Visualization**_
- 8.	Van Dyke, Milton, “An Album of Fluid Motion,” Parabolic Press, P.O. Box 3032, Stanford, CA 94305-0030, 1982.
- 9.	Japan Society of Mechanical Engineers, “Visualized Flow,” Pergamon Press, 1988.
- 10.	National Committee for Fluid Mechanics Films, “Illustrated Experiments in Fluid Mechanics,” The MIT Press, Cambridge, MA and London, England, 1972.