Student engineers use subsonic wind tunnels for class experiments

By Damon Lowney
Daily Titan Asst. News Editor

A jet traveling at the speed of sound covers about 1,100 feet every second, slicing through the air like a butcher knife cleaves through meat. When the speed of sound is surpassed, Mother Nature protests the gross exploitation of metal and jet fuel in the form of an earsplitting sonic boom.

Unfortunately for her, the jet’s pilot won’t hear it.

The sound barrier isn’t an easy one to break through.

Like a butcher sharpening his knife to cut through meat, engineers spend considerable amounts of time in wind tunnels studying airflow with the goal of streamlining aircraft.

At Cal State Fullerton’s College of Engineering and Computer Science, engineering students have access to four wind tunnels on campus – three subsonic and one supersonic – to study the flow of air over different objects.

Students use the wind tunnels in Mechanical Engineering 306B.

“We have six or seven experiments through the class. The wind tunnel is one,” said Peter Othmer, chair of mechanical engineering.

Two wind tunnels no longer than large dinner tables and about chest high are powered by an electric motor plugged into the wall.

Here students learn about lift and drag, two forces that affect every aircraft and automobile.

A small airfoil (wing) is attached to a scale in the test section of the wind tunnel.

“You can adjust the flap, the slat and the angle of attack (on the airfoil) so you simulate take off and landing,” said Othmer.

When the wind tunnel is running, students can see how lift and drag is affected by different airfoil configurations and airspeeds.

Wedges, cones and spheres are tested as well, Othmer said.

“Lift and drag go up together,” said Fred Hogarth, senior mechanical engineering major.

“You want to make as much lift as the plane weighs,” for cruising to keep the drag to a minimum, he said.

“There are some instances when you want a lot of lift and a lot of drag,” such as when landing a plane, Hogarth said.

In another room reside the much larger and much louder subsonic wind tunnel and supersonic wind tunnel.

The subsonic tunnel runs the length of the room and it “Sounds like you have a jet engine inside the building,” said Paul Rahmanian, a graduate of CSUF’s engineering program.

He said the wind tunnel is a valuable tool for students to learn about fluid dynamics, a topic covered only in books until they take EGME 306B.

This wind tunnel is mainly used for a different experiment, however. A “whistling tube,” as Othmer calls it, is placed in the test section and air is blown through it at different speeds.

Two rings placed inside the tube disturb the airflow and produce whistling sounds, which are recorded and sent to a computer.

“You got about a foot worth of screens that you can put in (the intake side of the wind tunnel),” Othmer said. “The more screens we put in the nicer the flow is on the test section,” because the flow is more uniform, he said.

A 75 horsepower motor powers this wind tunnel’s fan, which pulls air through the tunnel, just like the two smaller ones. The biggest difference is size. To run this wind tunnel, a garage door needs to be opened to let air rush out the exhaust side.

Other objects can be put into it as well, such as larger versions of the cylinders and airfoils used in the two smaller wind tunnels.

The supersonic wind tunnel is out of commission, however, due to a leak discovered in an inspection, Othmer said.

The school will only allow use of the tunnel if it can pass the inspection.

Daily Titan Staff Writer Greg Lehman contributed to this story.

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