The results of a computer study of a new analytical model of transition from laminar to turbulent flow are presented. The model is two-dimensional in the mean flow but threedimensional in the disturbance flow. In particular, an onset of transition boundary is derived for the case of fairly large disturbances introduced into a laminar flat-opiate boundary layer at approximately the critical layer. The nature of the upper and lower branches of this onset of transition map is related to the physical processes going on in the modeled boundary layer. It is found that the upper branch of this curve is defined by a balance of dissipative effects and tendency-towards-isotropy effects as they affect the normal component of turbulent kinetic energy in the boundary layer. The lower branch is denned by a balance of diffusive effects and tendency-towards-isotropy effects on the same normal velocity correlation. Within the framework of these observations, the effect of a “favorable” pressure gradient on transition is discussed. It is suggested that the conventional approach to computing the stability boundaries of laminar flows in the presence of pressure gradient is incorrect in that it does not account for stream tube stretching effects that are shown to be important in a region near the stagnation point of blunt bodies. Finally the nature of a complete transition, as defined by the model, is discussed, and several suggestions for future research are put forth. © 1969 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.
