Direct Numerical Simulations of Boundary-Layer Transition for a slender cone at Mach 6 initiated with Random Disturbances

Direct Numerical Simulations (DNS) were carried out to investigate the laminar-turbulent transition process for a slender (2.5^◦ half-angle) straight (right) cone at Mach 6 and zero angle of attack. The slender cone geometry of the experiments in the Boeing/AFOSR Mach 6 Quiet Tunnel (BAM6QT) at Purdue University was the basis for the numerical investigations. Transition was initiated by random disturbances introduced at the inflow boundary. A formation of “hot” streaks on the surface of the cone have been observed in the experiments at the BAM6QT and also in our previous “controlled” breakdown simulations. These numerical investigations indicated that the fundamental breakdown is likely the dominant mechanism relevant for the streak development for the slender cone. In the present paper, random disturbances were introduced at the inflow of the computational domain in an attempt to model “natural” transition as observed in experiments. Preliminary, axisymmetric calculations provided guidance regarding the required amplitude of the random disturbances so that laminar-turbulent transition could be observed within the computational domain. In this paper DNS results are presented and discussed for which the laminar-turbulent transition process was initiated using random disturbances at the inflow of the computational domain (“natural” transition).