Air Force Office of Scientific Research
2/28/2008 – 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
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.