Wall y + Strategy for Dealing with Wall-bounded Turbulent Flows

 Abstract— A strategy for dealing with turbulent flows over a two dimensional surface mounted obstacle using the wall y + as guidance in selecting the appropriate grid configuration and corresponding turbulence models are investigated using Fluent. The CFD results were compared with experimental data from Zeidan's Turbulent Shear Recovery behind Obstacles on Smooth and Rough Surfaces. Both undisturbed and disturbed (over ridge) flows are studied. For both cases, a wall y + in the range of 30 to 60 is determined to be sufficiently accurate, where the log-law region is resolved. It is also advisable to avoid having the wall-adjacent mesh in the buffer region since neither wall functions nor near-wall modeling approach accounts for it accurately. RSM predicts the flow properties more consistently because it accounts for all the Reynolds Stress components. Undisturbed and disturbed turbulent flows over a flat plate, with and without a 2-D solid ridge, respectively, are simulated using Fluent 6.2 and the wall skin friction coefficient, Cf , and mean velocity profiles are validated against reliable experimental data obtained by Zeidan (3). The present study aims at drawing up recommendations for cases where experimental data might not be available for validation, including the behavior and suggested usage of the available models and near wall functions using Fluent. This serves to increase confidence of using commercial CFD package for industrial simulation instead of solely relying on experimentation, when dealing with wall-bounded complex turbulent flows.