QUIET-FLOW LUDWIEG TUBE FOR HIGH-SPEED TRANSITION RESEARCH

Low-noise supersonic wind tunnels are required for unambiguous experim ental research into high-speed laminar-now instability and transition. The experience of the successful NASA Langley quiet-tunnel developmen t program has been used to design and construct a new kind of low-cost , short-duration, quiet-how tunnel. Measurements of the how quality in , the 9.7 x 10.9 cm Mach 4 test section were obtained using fast respo nse pressure transducers mounted in the tip of a pitot tube. When the rms pitot pressure is approximately 0.05-0.10% of the mean pitot press ure, bursts of noise appear in the pitot-pressure signals. These burst s appear to be the radiated signature of turbulent spots in the bounda ry layers on the nozzle walls. Their appearance confirms the presence of laminar nozzle-wall boundary layers and quiet how when the rms pito t pressure is about 0.06% or less. Based on this criterion, quiet flow is achieved to Reynolds numbers based on the axial length of the quie t-flow test region of more than 400,000 at unit Reynolds numbers of ap proximately 40,000 per cm. This performance is sufficient for research into receptivity, roughness, and instability effects at high speeds.