variavel0=<b>Marcelo J.S. De Lemos</b> - delemos@mec.ita.br ITA
<b>Mila R. Avelino</b> - milara@uol.com.br UERJ
<b>Atila P. Silva Freire</b> - atila@serv.com.ufrj.br COPPE/UFRJ
<b>Abstract.</b> The effects of sudden changes are predicted in the cases of turbulent flow around surface-mounted two-dimensional ribs when subjected to a sudden change in surface roughness. A particular interest of this study is to investigate the sudden changes in the surface roughness for developing boundary layer flow. A two -equation k-e turbulence model is employed to simulate the turbulent transport. Equations of boundary-layer type were used and a forward marching method was employed for sweeping the computational domain. Wall functions that take into account surface roughness are used to specify the boundary conditions at the surface. The effects of the sudden changes of roughness accounted for the wall functions in the k-e turbulence model are compared with available experimental data. Four configurations are simulated here, namely one extensive uniformly smooth surface, and three cases where the surface roughness varies suddenly from a smooth to rough, each one being with a different roughness geometry. For the vicinities of the surface change algebraic expressions are empirically obtained to predict the growth of the displacement in origin. Those heuristic expressions are incorporated into the numerical code to predict the velocity profiles more accurately. Results are presented for velocity and skin friction coefficient, in addition to comparisons with experimental data. The use of the algebraic expressions in a parabolic solver showed good agreement with experimental values for the mean and local quantities.
<b>Keywords.</b> Turbulent Flow, Numerical Study, Surface Roughness.