Numerical prediction of turbulent boundary layer in transition from smooth to rough surface

Abstract

The thesis describes a computational investigation of turbulent boundary layer in transition from smooth to rough surface. The scope of the present computational study is limited to numerical prediction of the flow parameters of steady two dimensional turbulent flow over smooth to rough surface at different Reynolds numbers. "TEACH-T", a general computer programme has been used for this purpose. The governing partial differential equations expressed in cartesian co-ordinate system are discretised in a finite difference technique. A staggered arrangement of variables has been used in conjunction with the SIMPLE algorithm. The upwind differencing scheme is employed to evaluate the convective terms. The time averaged governing equations of mean flow is closed using the standard k-e turbulence model. The surface texture of the rough portion used in experiment is simulated in the present computation in two different ways (i) Mean height type: computational cells of total height equal to the height of the average stone chips used in the experiment are continuously blocked off to incorporate the rough surface into t.he flow domain. (ii) Saw tooth type: computational cells are blocked off in such a way that the blocked cells give the bottom surface a saw tooth type configurat.ion with the saw tooth height equal to the average stone chips height. The prediction is in good agreement with the experimental data in the smooth surface. Whereas, in the rough surface: for mean height type; the velocity profiles conform with the experimental data but pressure gradient is under predicted, for saw tooth type; pressure gradient conform with the experimental data but velocity profile is under predicted .