A nonlinear receptivity process generating Tollmien-Schlichting waves

Abstract

Our ability to predict the boundary layer transition relies heavily on our understanding of receptivity, the process through which external disturbances excite Tollmien–Schlichting (T–S) waves. In this paper, a nonlinear process generating T–S waves, found in our experiment on the ribbon-induced transition in plane Poiseuille flow, is reported and examined through a direct numerical simulation. The results show that external forcing of frequency f can generate a T–S wave of frequency 2f (as well as a T–S wave of f) through the receptivity process if frequency f is much below the lower branch of the neutral stability curve.