University Researchers Use Lab-Developed Wind Tunnel for Hypersonic Testing

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ARLINGTON, Va. --  AFRL funded the research that ultimately produced the world's only quiet hypersonic wind tunnel. Purdue University researchers are now using this unique resource to test the performance of vehicles traveling at hypersonic speeds (i.e., approximately
4,000 mph). The research team, led by Purdue's Dr. Steven Schneider, is using the AFRL/Boeing Mach 6 Quiet Wind Tunnel to study the flow of air over the nose of the X-51A, a new hypersonic vehicle prototype.

Specifically, the team is compiling information detailing when and how airflow changes from laminar (i.e., smooth) to turbulent as it speeds over X-51A surfaces. Dr. Schneider notes that smoothing the flow of air over the aircraft's upper surface is important because doing so reduces friction and heat that could potentially destroy the vehicle. The transition from laminar to turbulent airflow can precipitate a tenfold increase in surface heat.

Achieving the quiet test environment requires that the curves of a tunnel segment called the nozzle be modified, and its surfaces subsequently polished, to a mirrorlike finish. These conditions delay the onset of turbulent flow in the nozzle, so that airflow entering the test section is as quiet and smooth as possible. In a conventional wind tunnel, turbulent flow in the nozzle radiates noise into the test section, potentially interfering with--or masking--critical findings. 

By leveraging the novel research capability made possible by the Mach 6 tunnel, Dr. Schneider's team is able to investigate the impact of airflow on vehicles such as the X-51A, characterizing the onset of the transition from laminar to turbulent airflow with a clarity that would be impossible using a conventional wind tunnel. 

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