Observations On The Influence Of Ambient Pressure On Boundary Layer Transition

NASA Technical Note

Observations on the Influence of Ambient Pressure on Boundary-layer Transition

For at least 15 yrs it has been known that the Reynolds number characterizing transition form laminar to turbulent boundary-layer flow (based on local properties and wetted length to transition) may be influenced by the local unit Reynolds number or some still unidentified, related quantity under both subsonic and supersonic conditions. Because examples of this were available almost exclusively from wind tunnel work, and because of the possibility that free-stream disturbances were responsible, there has been uncertainty as to whether the so-called unit Reynolds number effect exists in atmospheric free flight. The study described in the report was conducted in a free-flight range, thereby circumventing 'wind tunnel effects, ' and it has resulted in a demonstration of the variation of transition Reynolds number with range pressure (or unit Reynolds number) under conditions of fixed Mach number and average wall temperature ratio. Some preliminary measurements of sound pressures in the range air are reported for comparison with published results for wind tunnels. (Author).

An Empirical Equation for Prediction of Transition Location on Cones in Super-or Hypersonic Flight

An empirical equation has been developed for the prediction of transition location on blunt and sharp cones. The equation predicts the transition location fairly well for 48 ballistics range tests for cones without ablation and for 40 flight tests for cones with ablation ranging from zero to large. The equation is applicable for cones in supersonic or hypersonic flight. The experimental data cover a range of local Mach numbers at transition from 2.8 to 14.7 and a range of the ratio of local wall to local stream temperature at transition from .074 to 1.43.