Publications

Toward transition statistics measured on a 7-degree hypersonic cone for turbulent spot modeling

Casper, Katya M.; Beresh, Steven J.; Henfling, John F.; Spillers, Russell W.; Pruett, Brian O.M.

High-frequency pressure sensors were used in conjunction with a high-speed schlieren system to study the growth and breakdown of boundary-layer disturbances into turbulent spots on a 7° cone in the Sandia Hypersonic Wind Tunnel at Mach 5 and 8. To relate the intermittent disturbances to the average characteristics of transition on the cone, the statistical distribution of these disturbances must be known. These include the boundarylayer intermittency, burst rate, and average disturbance length. Traditional low-speed methods to characterize intermittency identify only turbulent/nonturbulent regions. However at high M, instability waves become an important part of the transitional region. Algorithms to distinguish instability waves from turbulence in both the pressure and schlieren measurements are being developed and the corresponding intermittency, burst rate, and average burst length of both regions have been provisionally computed for several cases at Mach 5 and 8. Distinguishing instability waves from turbulence gives a better description of the intermittent boundary layer at high M and will allow the fluctuations associated with boundary-layer instabilities to be incorporated into transitional models.