Transition-zone models for 2-dimensional boundary layers: a review

Abstract

Models for the laminar-turbulent transition zone have in recent years become increasingly important, especially in technological applications where the design is driven by peak heat-transfer rates or extensive regimes of laminar or transitional flow. Models in current use can be classified into three types, namely linear-combination, algebraic and differential. The first type based on the principle of combining mean laminar and turbulent velocities, in proportions determined by the intermittency, is shown to be both successful and relatively easy to implement, especially if recent improvements in estimating turbulent spot formation rates and ideas concerning the possibility of sub-transitions within the transition zone are incorporated. Algebraic models, where the eddy viscosity is released by the intermittency, and differential models involving fairly elaborate schemes for determining the kinetic energy of turbulent fluctuations and their length scale, are found to require further development for handling flows with large pressure gradients.