NASA LANGLEY MACH-6 QUIET WIND-TUNNEL PERFORMANCE

The Bow in the NASA Langley Mach 6 quiet wind tunnel has been investig ated to quantify the effectiveness of laminar-flow control techniques used to delay transition of the nozzle-wall boundary layer, The result s of this investigation include an assessment of the mean and unsteady nozzle flow to define the quiet core length, and hence performance, o ver the operating range of the facility, A large, uniform region of Ma ch 5.91 flow was documented for a variety of unit Reynolds numbers. By using a prototype constant-voltage anemometer to measure the unsteady flowfield, acoustic radiation patterns from the transitional nozzle w all boundary layers were mapped, These disturbances originating at the irregular edge of the transitional nozzle-wall boundary layer were sh own to follow Mach lines into the test section of the nozzle, thereby limiting the length of the quiet core, With a virtual origin downstrea m of the nozzle throat, a Reynolds number dependency was found for the amplitudes of the acoustic radiation, The spectral evolution of noisy Bow in the quiet tunnel was shown, and measurable freestream disturba nces, outside the region of quiet flow, were found to be qualitatively similar to those documented for conventional high-speed tunnels. In s um, the laminar-flow control techniques used to delay nozzle-wall boun dary layer transition in the Mach 6 nozzle test chamber facility have succeeded in producing a substantial region of quiet flow suitable for high-speed boundary layer stability research.