Lab 10: Wind Tunnel

1. Lab 10: Wind Tunnel

2. Presentations Next Week!! • Last week you learned how to predict the path of a hurricane. • Each Member predicts its path. • Making Cone of Uncertainty • Presentation • 15-20 minutes, each member presents

3. Keep in Mind • Three Letters • All Forecast using given initial conditions! • Brian Trust = Too All Members and contains questions for all to keep in mind. • Forecasters = Take each members forecast and put on another map to make your cone. YOU will issue a forecast and summarize lifetime of storm. Turn in 1 page (typed, 12pt font) summary and forecast tracks. NOTE back page of letter for new forecast info! • Head Honchos = You are in charge of towns and cities. Address issues in letter in write-up, subset in presentation. Turn in 1 page (typed, 12pt font) summary explaining why you will or will not evacuate your towns. Keep in mind cost of evacuation and lost of trust from public in unnecessary evacuations.

4. AnyQuestions Office Hours E-mail Ask After Class

5. Back to Lab: Wind Tunnel • Before • Gas Pressure = randomly moving air molecules • Now • Dynamic Pressure = bulk motion of air molecules

6. Gas Pressure from Lab #5 • Randomly moving molecules • Equation explains the force that results from randomly moving molecules hitting the walls of a container.

7. Dynamic Pressure • BULK motion of air molecules (i.e. wind) hitting a surface. • Equation pdynamic = ρ(v²/2) p = pressure, ρ = density, v=speed • Using this law today! What would happen if the wind speed, v, double? pnew = 4 x pold

8. Hurricane Example • Plug v = 50m/s and ρ = 1.225kg/m³ into • pdynamic = ρ(v²/2) … • pdynamic = 1531 N/m2 = 1531 Pa = 32 lb/ft² • Force on a person! • Force=pdynamic*Area • For a 6ft tall person … • Area = 6 ft x 1.5 ft • Force = 32 lb/ ft2 x 9 ft2 • So Force = 288 lbs!!!! • If v ↑ the force … ? • Increases also • Questions???

9. Relation to Outside World?

10. Models vs. “True” Scale • We are using MODELS in this Lab. • Engineers use models to experiment with wind, pressure, and temperature changes on smaller versions of larger items to test their durability. • Saves money and time, perfecting product. • Questions in Part II: Scaling your Data. • Real Force = 40,000 x Model Force • Real Area = 2,500 x Model Area • Real Pressure = (40,000/2,500) x Model Pressure = 16 x Model Pressure. • Real Wind = (16)1/2 x Model Wind = 4 x Model Wind

11. Part I • Verify that pressure ↑ as velocity/wind ↑ • Equipment • pitot tube, turbometer, and manometer. • You MUST level your manometers BEFORE you begin this experiment, and DON’T MOVE IT, once you’ve leveled it. • Adjust the wind speed with the Veriac. • Note: The manometer’s readings will be in Pascals, and the Turbometer’s readings will be in m/s. • Record the pressure and wind (from 20-50) using the dial in the spreadsheet.

12. Part II • Choose ONE vehicle from the box and place it in broadside to the wind. • SLOWLY crank up the speed of the wind by using the dial. • One group member should stand at the end of the wind tunnel to catch the vehicle as it is blown out, but DO NOT turn off the wind machine yet. • RECORD the wind with your Turbometer. This measures the wind speed that was required to blow your vehicle out of the tube. • Record wind speed and car type in spreadsheet.

13. Part III Pitot Tube ~1mm away from hut • Position and Secure Quanset Hut in tunnel. • What sort of pressure readings will we expect on the “front” side of the mini-hut? (Pos? Neg?) • What sort of pressure readings will we expect on the “back” side of the mini-hut? (Pos? Neg?)

14. IMPORTANT: Negative Pressure Values and Manometers • The MOMENT you start getting values that decrease to 0 and become negative, you MUST, MUST, MUST switch the rubber tube to the opposite gauge side of the manometer. • Consequence! = oil in the Manometer will come shooting out of the little spout in response to the negative pressure, and get all over the place. • Remember to show units and calculations in lab write-up.

15. Questions