In supersonic wind tunnels, the humidity content of the working fluid is known to have a significant effect on flow conditions in the test section. The intent of this paper is to evaluate the influence of moisture on the test section flow quality for the indraft supersonic wind tunnel located at the Muroran Institute of Technology. The static-pressure fluctuation is measured by means of an unsteady pressure sensor buried in a 10-degree-aperture cone model installed in the test section. The results show that supersonic flow at Mach 2 is contaminated by the self-sustained oscillation of a condensation shock wave for ambient relative humidity greater than approximately 50%. It is also found that for the Mach 2 flow, that the ratio of the static-pressure fluctuation to the dynamic pressure is less than 0.1%, if the absolute humidity is kept below a critical value of 2[g/m3]. Experimental observations also reveal that the three-dimensional boundary-layer transition process is hypersensitive to the influence of free-stream humidity.
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