Some Observations on the Structure and Modeling of 3-d Turbulent Boundary Layers and Separated Flow

This paper presents some key features of the behavior and structure of three-dimensional turbulent boundary layers and separated flows that have been observed through experiments. These include the anisotropic nature of the eddy viscosity and the lags between the mean flow gradients and the turbulent stresses. These cases are rarely in equilibrium so lags between the production, diffusion, redistribution, and dissipation mechanisms become important. The skewing of the mean flow leads to decorrelation of the turbulent structure. Large-scale meandering vortical motions are often present in separated flows. Some computations of these types of flow are also examined. Better modeling of pressure and turbulence diffusion and pressure/rateof-strain terms to account for lags within the flow is needed, especially near the wall. Some advances in experimental techniques that promise to provide more insights to such flows are mentioned.