Investigation On Control Mechanism Of Flow Past A Bluff Body

As a classical phenomenon in fluid dynamics,the basic principles of flow around a bluff body have been widely used in aerospace,energy,water conservancy and other fields,and also have been studied by many researchers.Based on the passive control principles,the flow around a bluff body has been numerically analyzed in present work.The mechanism and control method for fluid instability have been studied.To achieve the purpose of controlling the wake with minimum energy consumption,the flow field characteristics and the heat transfer mechanism also have been analyzed.Based on the investigations on the flow field control and heat transfer enhancement,the control positions with optimal characteristics are obtained through the comprehensive search in the whole flow field,which has important theoretical guiding significance for flow stability analysis and engineering application.In present work,the flow and heat transfer features of flow past a circular cylinder with an additional cylinder at low Reynolds numbers varying from 50 to 150 is numerically studied.The movement of the additional small cylinder is realized by Dynamic Mesh Method,which greatly improves the efficiency of numerical calculation.When Re=80 and 120,the unsteady region where vortex shedding derived from the main cylinder are found.The single objective function based on the drag coefficient and the Nusselt number of the main cylinder is constructed,and the multi-objective optimization model based on two single objective functions is used.Meanwhile,the drag coefficients,the Nusselt numbers and the flow features are investigated.It’s found that the position of the additional small cylinder has obvious influence on the drag reduction and heat transfer performance of main cylinder.Based on three different objective functions and different influences,three kinds of regions are determined.When the additional cylinder is located within the three kinds of regions,the maximum drag reduction,the optimum heat transfer performance,and the superior comprehensive characteristics can be obtained respectively.Based on the results obtained by two-dimensional numerical simulations,in order to improve the calculation efficiency,the three-dimensional simulations are carried out for h/D varying from 0.5625 to 1.625.When Re=100,it’s found that the position of the additional small cylinder has obvious influence on the vortex shedding frequency,drag reduction and heat transfer performance of main cylinder.Furthermore,the region with maximum vortex shedding frequency is determined.To summarize,it’s found that the position of the additional small cylinder has obvious influences on the flow characteristics and heat transfer performance of main cylinder.The results have broad applicability and practical significance.