Effects of high-speed tunnel noise on laminar-turbulent transition

It is well known that the high levels of noise present in conventional hype rsonic ground-test facilities cause transition to occur earlier than in Eig ht. Flight measurements of incoming noise are reviewed and compared with me asurements in ground-test facilities, of both conventional and quiet design , at hypersonic and high supersonic speeds. The low noise present in flight is apparently the reason for the very large transition Reynolds numbers so metimes measured in Eight, when roughness, crossflow, and other factors are controlled. Design mill usually involve consideration of the trend in tran sition when a parameter is varied. The effect of facility noise on these tr ends is reviewed. In some cases, the trend of conventional-tunnel data is o pposite to the trend in quiet-tunnel data. Thus, transition measurements in conventional ground-test facilities are not reliable predictors of flight performance, except perhaps in special cases.