Indian Journal of Science and Technology

Abstract

Objective: To find the best mesh based on wall y+ approach and to model turbulence flow numerically over a surface mounted cube so that appropriate mesh can be selected and thereby the best grid configuration can be found. Methods: The study uses three mesh configuration based on wall y plus to capture the turbulence and its complex characteristic for moderate high Reynolds number. The study depends on Reynolds number 40,000 which is based on height of the cube and bulk velocity and the numerical and analysis results are compared with the recognised published work on the flow past ground mounted prismatic body placed in a fully developed turbulent channel flow. The turbulence model used in this work is large eddy simulation incorporating Smagorinsky scheme. The investigation of near wall treatments is done for maximum wall y+≈5 covering the viscous sub layer, maximum y+≈23 the buffer region and maximum y+≈40 resolving the log-law region.OpenFoam platform under Linux OS is used for the study. Findings: After completion of three numerical simulations based on three grids various results in terms of fluid parameters are discussed such as drag and lift, velocity profile, pressure profile, Q criteria etc. It has been found that the drag force varies from 1.13 to 1.38 and lift coefficients varies from 0.8 to 1.0. Strouhal number varies from 0.45 to 2.17. Maximum and minimum pressure values are also been found and is discussed in the result & discussion section of this paper. Application: The method described in the present study is very helpful in finding the best suitable grid for CFD analysis. As it is very well known fact that, if the grid is not good enough for any CFD study, the result of the simulation will be wayward. Finding the best grid or mesh is a time consuming process and also involves high cost. This method can minimize the cost and also saves lots of computational time.

Keywords: Buffer, Drag Coefficient, External Flow, LES, Lift Coefficient, Pressure Coefficient, Reynolds Number, Smagirinsky, Turbulence, Viscous, Yplus