Further development of an algebraic intermittency model for separation-induced transition under elevated free-stream turbulence

A constitutive law for the Reynolds stresses during boundary layer laminar-to-turbulent transition, constructed in previous work by elastic-net regression on an experimental data base, has been incorporated in an algebraic intermittency model. The objective is prediction improvement of transition in a separated layer under an elevated free-stream turbulence level. The modelling for such cases functions through additional production terms in the transport equations of turbulent kinetic energy and specific dissipation rate of a k-ω turbulence model. A sensor detects the front part of a separated layer and activates the production terms. These express the effect of Klebanoff streaks generated upstream of separation on the Kelvin-Helmholtz instability rolls in the separated part of the layer. By the Klebanoff streaks, the breakdown is faster and the speed of breakdown increases by the combined effects of a large adverse pressure gradient and an elevated free-stream turbulence level.