NUMERICAL INVESTIGATION OF LAMINAR-TURBULENT TRANSITION ON REENTRY CAPSULES

Transition from laminar to turbulent flow in the boundary layer of blu nt cones under re-entry conditions from space is investigated using th e tool of numerical simulation, Two- and three-dimensional disturbance s appear to be linearly stable (using classical linear stability theor y) in a wide range of wave numbers under conditions for which wind-tun nel experiments exhibit turbulence. Therefore, linear mechanisms canno t describe transition, and the e(N) method cannot be used for transiti on prediction, It is shown that a nonlinear instability with respect t o finite amplitude local disturbances exists, This instability leads t o 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 la minar, our investigation does not exhibit any instability as expected, At 20 km, where the boundary layer is turbulent, nonlinear instabilit y is found. Therefore, our theory provides suitable ground for the dev elopment of new nonlinear transition criteria.