Variable N-factor method for transition prediction in three-dimensional boundary layers

Linear amplitude methods are presented for estimating the location of transition caused by crossflow instabilities, intended for moderate- to low-turbulence environments. A linear amplitude-based method combines receptivity, linear growth, and an amplitude correlation for predicting transition. Information about the model surface finish (and/or suction distribution) and the freestream disturbance environment is accounted for through the receptivity process. The variable N-factor method is presented as a limiting case, following simplifying assumptions about the receptivity. Transition N factors are presented as a function of the surface roughness. Results show a very good correlation between the variable N-factor method and experimental data.