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Supersonic Inlet Tests Show Promise
Glenn recently completed testing on an advanced high-speed inlet for propulsion systems to power air transport vehicles at supersonic speeds.

"Compared to typical inlets in this operating range, tests showed high pressure recovery, low cowl drag, reduced complexity, increased safety, significant manufacturing cost reduction and weight, as well as increased efficiency," said David Lam, Aeropropulsion Projects Office.

Parametric Inlet testing in Supersonic Wind Tunnel. Image on left is a Parametric Inlet ready for testing in Glenn's 10-by-10-Foot Supersonic Wind Tunnel.

Seeking potential applications to supersonic cruise vehicles, NASA has vigorously pursued an alternative to previously used inlet designs.

Prior to this latest testing, nearly 75 hours of testing the inlet late last year confirmed the advantages of the Parametric Inlet. Unlike typical inlets for supersonic cruise that rely on a mix of external and internal compression, this inlet accomplishes all of the supersonic compression externally. Comparable performance to typical inlets was shown to be possible, with the added benefits of relatively low weight and the elimination of unstart, which is a recurring problem in propulsion systems with mixed compression inlets.

Unstart occurs in mixed compression supersonic inlets due to the mismatch between the inlet air supply flow and the engine required flow, resulting in shock waves that are violently expelled from the engine. This often results in compressor stall combustor blowout and large increases in drag, which in turn decreases efficiency. Additional aircraft structure and larger control surfaces are necessary to compensate for the possibility of inlet unstart.

"NASA's tests of its Parametric Inlet have proven that this type of inlet can operate safely in the flow regime normally reserved for mixed compression inlets," said Dave Davis, Inlet Branch.

Four years ago, Boeing Aircraft, Seattle, WA, and TechLand Research, Inc., North Olmsted, OH, which received NASA funding through NASA's Small Business Innovation Research (SBIR) program, jointly conceived conceptual design of the Parametric Inlet. The inlet came to be known as the Parametric Inlet due to the wide range of geometric variables designed into it. After competing the three phases of the SBIR process in designing the inlet, Glenn took the lead in refining the aerodynamic lines and mechanical design, with help from TechLand. NASA's Vehicle Systems Program funded testing of the Parametric Inlet. Additional funding for testing was provided by the U.S. Air Force.

NASA's Glenn Research Center