An Indian Civilizational Perspective

'Quiet' Mach 6 wind tunnel helps shape future aircraft

Is this the future of air travel? If the noise, heat and friction could be reduced at high speeds – then it could mean more efficient aircrafts!

Purdue University engineers have developed a wind tunnel that is the only one of its kind in the world capable of running quietly at “hypersonic” speeds, helping researchers to design advanced aircraft and missiles.

No other wind tunnel runs quietly while conducting experiments in airstreams traveling at Mach 6 – six times the speed of sound, said Steven Schneider, an aerospace engineer and professor in Purdue’s School of Aeronautics and Astronautics.

Researchers will use the $1 million wind tunnel to help design advanced aircraft that travel at hypersonic speeds, or faster than Mach 5, which is about 4,000 miles per hour at sea level.

Purdue engineers will present a paper about the wind tunnel on Thursday (Jan. 12) during the American Institute of Aeronautics and Astronautics’ Aerospace Sciences Meeting and Exhibit in Reno, Nev. The paper was written by Schneider and graduate research assistants Matthew P. Borg and Thomas J. Juliano.

A team of Purdue engineers led by Schneider finished assembling the wind tunnel in 2001.

“After four years of debugging, recent tests have shown that it does, indeed, run quietly at Mach 6,” Schneider said. “The wind tunnel airflow has about one-tenth to one-thirtieth of the noise in other high-speed wind tunnels.”

The quiet operation is critical for recreating the smooth, or laminar, flow of air over the surfaces of aircraft, spacecraft or missiles re-entering the Earth’s atmosphere. Data from tests with models studied in the wind tunnel will lead to a better understanding of when and how the air flowing over a surface changes from smooth to turbulent. Engineers must better understand this transition from smooth to turbulent flow if they are to design improved aircraft and missiles. One aim is to design aircraft that heat up less from atmospheric friction as they re-enter the atmosphere.

“Laminar airflows can have eight times less heating than turbulent ones,” Schneider said.

Designs that heat up less would require less shielding, enabling engineers to build lighter-weight, lower-cost vehicles.

“Designers are considering a new re-entry vehicle with a metal skin,” Schneider said. “This would eliminate the tile system used on the space shuttle, which is expensive to maintain.”

Another major application will be to design a generation of aircraft that will use “scramjets” to travel more than 7,000 mph, allowing them to leave the atmosphere and fly halfway around the world in a few hours.

A future fleet of space planes using scramjets might be far less expensive to operate than the current space shuttles, making it more affordable to haul payloads into orbit. Unlike rockets, which must carry their own supply of liquid oxygen to combust fuel, scramjets would scoop oxygen out of the atmosphere.

For scramjets to work properly, however, a steady, smooth flowing supply of air must be moving continuously at hypersonic speeds into the engine’s combustion chamber. Poor control of turbulence near the aircraft’s surface might disrupt this crucial air supply, and turbulent flow over the front of the vehicle would cause excessive heating.

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