Structure and modeling of the three dimensional boundary layer on a rotating disk. Final report

Almost all practical turbulent flows include three dimensional boundary layers (3DTBL`s), and in many cases, the 3DTBL is the dominant feature of the flow. A boundary layer is defined as a thin layer adjacent to the surface in which the velocity drops rapidly from the freestream value to zero at the wall. A 3D boundary layer is one in which the flow direction also changes rapidly approaching the wall. This change in the flow direction called skewing is caused by transverse pressure gradients, centrifugal forces, or motion of the surface. Most research on turbulent boundary layers has been done in simple two dimensional flows in carefully controlled wind tunnels. Such boundary layers are now well understood, and excellent models are available describing both the fluid mechanics and heat transfer behavior. Recent fluid mechanics studies have shown that skewing can have a pronounced effect on the boundary layer turbulence. Models based on eddy-viscosity concepts fail, and more complex stress transport models cannot capture the reduction of turbulent mixing that usually accompanies skewing. It was unknown prior to the present study what effect the skewing might have on turbulent heat transfer. It was suspected that turbulent heat transport would be reduced in analogy to the reductions of turbulent shear stress. It was also unknown how the skewing would effect the turbulent Prandtl number, a quantity which is embedded in most turbulent heat transfer prediction schemes. The objectives of the present study were then to study the surface heat transfer rate and the turbulent heat flux in a simple three dimensional boundary layer. In particular, the research addressed the heat transfer from a heated disk rotating in an otherwise quiescent environment