Wind Tunnel Aerodynamics

By

Dr. Charles Trefny

20 Sept 2002

Aerodynamics

The field of science and engineering dealing with the effects of air moving around solid objects.

Aerodynamicists

Predict what will happen in a given situation using physical laws, math, wind-tunnels and computers

Air has mass and obeys Newton’s laws.

100 gallons of air has a mass of about 1 pound.

We must speed-up, slow-down, or change the direction of the air to generate a force.

Look for this in the following examples of aerodynamics…

Wind tunnels are used to predict the amount of force generated by solid objects.

This helps aerodynamicists choose the proper size for things such as wings, spoilers, and parachutes.

Information obtained in wind tunnels is used to improve the design of anything affected by wind.

Wind-Tunnels come in all shapes and sizes…

Open-Return Type Wind-Tunnel

Closed-Return Type Wind-Tunnel

Blow-Down Type Tunnel

Wind Tunnel Test Examples

Similarity Principle

Allows us to test a small model and get information about the full-size object

We’ll use a parachute for example…

Will the egg break?…

Similarity Principle:

For similar shapes, this ratio always comes out to the same number.

Weight

Density x Speed x Speed x Diameter x Diameter

Don’t worry, it’s just a FRACTION!!!

Density x Speed2 x Diameter2= CWeight

Density x Speed2 x Diameter2C =

Do a wind tunnel test to find out what “C” is for the parachute

Weight

All “known” in the wind tunnel!

Computers can also be used to solve problems in aerodynamics.

The computer solves complex mathematical equations that are based on Newton’s laws of motion

The wing or “airfoil” is a classic problem…