Effects of Compressibility and Turbulence Level on Bypass Transition

The influences of compressibility and turbulence level on boundary layer transition are studied using a Ludwieg tube set-up. Heat transfer measurements are performed on the flow over a flat plate. The Mach number is varied between 0.16 and 0.56 while the unit-Reynolds number is kept constant. Several turbulence generating grids are used giving turbulence levels between 1.2% and 4.4%. Increasing the Mach number results in a decreasing turbulence level. Besides, the transition start Reynolds number increases.The results indicate that besides the turbulence level another parameter is desired for the existing transition models. The dimensionless spot parameter is influenced by both the turbulence level and the Mach number. A tentative conclusion is that the start of transition depends on the inertial range minimum frequency in the energy spectrum while the shape of the transition curve, i.e. the intermittency, depends on the corresponding length scale.Copyright © 1998 by ASME