SOME ASPECTS IN NUMERICAL SIMULATION OF WIND FLOW AROUND BLUFF BODIES

Abstract

Numerical simulation of wind flow around bluff bodies has been a widely studied subject in the literature. There are various issues involved in the numerical simulation. Some of these may include the development of an efficient numerical algorithm, improvements in turbulence closure model, selection of appropriate boundary conditions, etc. For the past few decades, efforts have been devoted towards the development of robust numerical codes and several modifications to the turbulence closure models. Despite these, there are certain issues which need more attention. In the present study, these issues have been identified and used to frame a set of objectives, i.e. (i) to study the significance of inlet boundary prescription from the analysis of reported simulation results; (ii) to study certain velocity fields to monitor the variation of flux at different sections of the flow domain with a view to assist the prescription of often missed or approximate velocity measurements in the vicinity of boundary as well as to ascertain the appropriate location of the outlet boundary; (iii) to study stress-strain characteristics of linear as well as non-linear turbulence models as well as variations of certain model constants; (iv) to develop a simplified approach for the estimation of eddy viscosity through analysis of reported flow field data and to ascertain its relative magnitudes in different zones of flow field; and (v) to develop a numerical code for studying certain aspects of numerical simulations. Based on the present study, the following facts have been observed: (i) Based on the analysis of available simulation results, the hypothesis that inlet boundary condition is a part of flow field is validated; (ii) an approach for prescription of s profile at the inlet is proposed and the utility of this approach is demonstrated through comparisons with the profiles proposed in the literature; (iii) mass flux is computed for several experiments as well as simulation data revealing the fact that in many of these, the influx mass is found to differ from the outgoing mass from the outlet boundary; (iv) the notion ofusing the term linear model is not observed from the stress-strain spectra studied in the work; (v) based on the control volume formulations and the flow field data available, an approach is outlined for the evaluation of eddy viscosity; (vi) uniqueness of correlation coefficients proposed for obtaining missing velocity components are found of limited use; and (vii) sensitivity studies indicate that the variation of certain variables close to the boundary may significantly influence the results. The study is expected to provide an impetus to the subject ofnumerical simulation ofwind flow around bluff bodies. 111