Wind tunnel helps determine impact of hypersonic speeds

ARLINGTON, Va: Funding provided by the Air Force Office of Scientific Research has resulted in the world's only quiet hypersonic wind tunnel, which researchers are now using to test the performance of vehicles traveling at hypersonic speeds, or approximately 4,000 mph.

A team of researchers at Purdue University, led by Dr. Steven Schneider, is using the Boeing/AFOSR Mach 6 Quiet Wind Tunnel to study airflow over the nose of a new hypersonic vehicle prototype, called the X-51A.

The team has been perfecting the wind tunnel for over a decade. NASA pioneered quiet facilities many years ago, but Purdue maintains the only such facility in the world capable of operating at hypersonic speeds.

"Engineers are compiling detailed information about when and how airflow changes from laminar (or smooth) to turbulent as it speeds over the X-51A's surfaces," Dr. Schneider said in an article published by the Purdue News Service.

In the same article, Dr. Schneider noted that increasing smooth airflow over the X-51A's upper surface is important because it reduces friction and heat that could destroy the vehicle. The transition from laminar to turbulent flow can increase surface heat by almost 10 times.

To achieve the quiet test environment, researchers modify the curves of a tunnel segment called the nozzle and polish its surface to a mirror-like finish. These conditions delay the onset of turbulent flow in the nozzle, so airflow that enters the test section is as quiet and smooth as possible. In a conventional tunnel, turbulent flow in the nozzle would radiate noise into the test section that could interfere with or mask critical findings.

"Using the unique research capability made possible by the Mach 6 tunnel, Dr. Schneider and a team of researchers are now able to characterize, or describe, the onset of the laminar to turbulent transition on hypersonic aircrafts such as the X-51A with clarity that would be impossible using a conventional wind tunnel," said Dr. John Schmisseur, the AFOSR program manager.

By funding research programs like this, AFOSR continues to expand the horizon of scientific knowledge through its leadership and management of the Air Force's basic research program. As a vital component of the Air Force Research Laboratory, AFOSR supports the Air Force mission of control and maximum utilization of air and space.