Study On Reynolds Number Effect Of Flow Field Around Cylinder With Different Roughness

Flow around a cylinder has always been an important direction for fluid research.The stay cable of a bridge structure is a typical cylinder.Wind-induced vibration of a stay cable will affect the durability of the bridge structure.Therefore,the study of the flow around a cylinder has important engineering significance and research value.As the Reynolds number increases,the flow around a cylinder can be divided into subcritical regions,critical regions,and supercritical regions.This article mainly studies the Reynolds number effect of the flow field around a cylinder with different roughness,reveals the law of the aerodynamic coefficient changing with the Reynolds number,and changes from three aspects: the pressure distribution of the cylinder with different roughness,the correlation of the span direction,and the characteristics of the flow field.This article analyzes the reasons for these laws.The following research work was mainly carried out:Firstly,the aerodynamic characteristics of different rough cylinde rs are studied,and the aerodynamic coefficient changes with Reynolds number are summarized.A rough cylinder can advance the flow transition.The rougher the cylinder is,the earlier the flow transition occurs,the smaller the critical Reynolds number is,and the larger the critical region advances.The changes of aerodynamic coefficient with Reynolds number are as follows: First,the lift coefficient and drag coefficient remain unchanged at the beginning,and the phenomenon of rapid decline occurs at the critical area.After reaching the lowest point,it starts to enter the supercritical area,and the root mean square value of the lift coefficient is fast.After increasing,it keeps stable,and the average value of the drag coefficient rises slowly.This phenomenon of rapid decline in resistance is called a drag crisis.Second,in the process of the drag crisis,the vortex frequency increases rapidly,which leads to the Strouha number rapidly increases;third,the opposite number of the back stagnation point pressure coefficient,that is,the base coefficient,the changing pattern of the base coefficient is similar to the drag coefficient.The larger the roughness is,the earlier the base coefficient drops.Then,the effect of Reynolds number on the spanwise correlation coefficient and the surface pressure distribution of cylinders with different roughness is studied.The reasons for the change of the aerodynamic coefficient with the Reynolds number are analyzed.First,the correlation between the spanwise direction of the critical area of the rough cylinder decreases rapidly.This shows that the spanwise correlation damage affects the stability of the flow field and changes the aerodynamic coefficient.Second,the coarse cylinder has a backward sh ift of the position of the flow separation point during the increase of the Reynolds number,and the width of the negative pressure zone of the average pressure coefficient becomes narrowing.Increasing the pressure coefficient in the negative pressure zone and the minimum value of the pressure coefficient become smaller,which makes the drag smaller,and the decrease of the pressure pulsation value is beneficial to the reduction of the root mean square value of the lift coefficient.Finally,the particle image velocimetry(PIV)technology was used to study the characteristics of the flow field,and the cause of the aerodynamic coefficient change was further analyzed.It was found that the vortex formation length increased first and then suddenly decreased in the critical region.Change in the flow width and the position of the vortex core cause a reduction in the turbulent kinetic energy and a decrease in the pressure coefficient pulsation.Comparing under similar flow conditions,it was found that changes in vorticity and vortex position changed the pressure distribution on the surface of the cylinder,which eventually led to a decrease in the drag coefficient.