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Combined free-stream disturbance measurements and receptivity studies inhypersonic wind tunnels were conducted by means of a slender wedge probe anddirect numerical simulation. The study comprises comparative tunnel noisemeasurements at Mach 3, 6 and 7.4 in two Ludwieg tube facilities and a shocktunnel. Surface pressure fluctuations were measured over a wide range offrequencies and test conditions including harsh test environments notaccessible to measurement techniques such as pitot probes and hot-wireanemometry. Quantitative results of the tunnel noise are provided in frequencyranges relevant for hypersonic boundary layer transition. In combination withthe experimental studies, direct numerical simulations of the leading-edgereceptivity to fast and slow acoustic waves were performed for the slenderwedge probe at conditions corresponding to the experimental free-streamconditions. The receptivity to fast acoustic waves was found to becharacterized by an early amplification of the induced fast mode. For slowacoustic waves an initial decay was found close to the leading edge. At allMach numbers, and for all considered frequencies, the leading-edge receptivityto fast acoustic waves was found to be higher than the receptivity to slowacoustic waves. Further, the effect of inclination angles of the acoustic wavewith respect to the flow direction was investigated. The combined numerical andexperimental approach in the present study confirmed the previous suggestionthat the slow acoustic wave is the dominant acoustic mode in noisy hypersonicwind tunnels.

Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels by means of a slender wedge probe and DNS