Numerical investigation of laminar-turbulent transition on re-entry capsules

Abstract

Transition from laminar to turbulent flow in the boundary layer of blunt cones under re-entry conditions from space is investigated using the tool of numerical simulation. Two- and three-dimensional disturbances appear to be linearly stable (using classical linear stability theory) in a wide range of wave numbers under conditions for which wind-tunnel experunents exhibit turbulence. Therefore, linear mechanisms cannot describe transition, and the eN method cannot be used for transition prediction. It is shown that a nonlinear instability with respect to finite amplitude local disturbances exists. This instability leads to the formation of turbulent spots. Using a generic trajectory of a re-entry capsule at an altitude of 75 km, where the boundary layer is laminar, our investigation does not exhibit any instability as expected. At 20 km, where the boundary layer is turbulent, nonlinear instability is found. Therefore, our theory provides suitable ground for the development of new nonlinear transition criteria.