An improved method for modelling fully rough turbulent boundary layer flows

A discrete element model has been implemented into an existing two-dimensional parabolic Navier-Stokes code for thin shear layers in order to model the effects of surface roughness on flow behaviour in boundary layers. The model modifies the equations of motion by including a form drag term in the momentum equation and accounting for the blockage effects of the roughness elements on the flow. Three turbulence models and a roughness element drag coefficient correlation were used for closure. The modified equations were derived in surface normal curvilinear co-ordinates and the effect of the roughness element blockage on the definition of flow parameters was assessed. It was found that the definitions of displacement and momentum thickness should be redefined to include blockage effects although this redefinition will not alter their values in a significant way. It was also shown that previous discrete element models use modified equations which are not consistent with the roughness blockage definitions. Validation of the implemented model was done using experiments involving roughness elements of two dimensional and three dimensional shape and agreement was found to be within acceptable error margins.; Original contributions in this thesis include: (1) Derivation of the governing equations with improved definition of blockage factors in surface normal curvilinear co-ordinates; (2) Assessment of the effect of roughness blockage on flow parameters; (3) Implementation of the discrete element method in the thin shear layer computer code TSL; (4) Assessment of the performance of the discrete element method for roughness elements of two dimensional and three dimensional shape; (5) Assessment of the compatibility of the discrete element method in conjunction with the Baldwin-Lomax and k-{dollar}omega{dollar} turbulence models.