The Effects Of Miniature Vortex Generator(s) On Flow And Heat Transfer Characteristics In Turbulence Boundary Layer

Decreasing energy consumption and improving energy efficiency in industrial production can be realized by enhancing heat transfer performance and reducing flow resistance of industrial equipment.It has become a research hotspot to enhance heat transfer under the condition of adding less flow resistance.Therefore,there are more and more studies on flow control and heat transfer enhancement.However,these relevant researches need to be based on the understanding of the complex flow structures in the turbulent flow field.And turbulent coherent structures play an important role in flow and heat transfer near the wall.By large eddy simulation method,it is studied the effects of a range of miniature cuboid vortex generators and a single miniature cuboid vortex generator on flow and heat transfer characteristics of channel.Every type of vortex generator is respectively put on the viscous layer,the transition region and the logarithmic law region.Results have important guidance value to the practice.The top height of the miniature cuboid vortex generators and the gap between the channel bottom and the single cuboid vortex generator are the main factors that affect the original flow field structures.The study reached the following conclusions:(1)“Wake blocking wall” induced by a range of miniature cuboid vortex generators includes the wake(recirculation zone)and newly induced vortexs(especially the streamwise vortexs),which is ribbon-like.It can restrict the motion of speed streaks and streamwise vortexs in the spanwise direction and make channel turbulence more steady.(2)When the gap between the single cuboid vortex generator and channel bottom is smaller,the cuboid can block the flow from upstream,but the impact distance is very short due to the size of cuboid.And with the increase of the gap,the influence of the single cuboid on near-wall flow structures become smaller.(3)The wake(recirculation zone)and the newly induced vortexs in the two types can regulate the velocity distribution in the viscous sublayer,making near-wall turbulence more steady and reducing the bottom shear stress.However,the flow mixing in the region above the viscous sublayer is enhanced by miniature cuboid vortex generator,and most of the lines of the velocity gradient and temperature gradient are increased and the corresponding fluid mixing and heat transfer are enhanced.The miniature cuboid vortex generator can be used to flow drag reduction and synthesis performance enhancement.(4)In all conditions under the two types,the bottom shear stress and corresponding bottom friction coefficient are reduced compared with the empty channel,and the minimum bottom friction coefficient of these conditions was 8.67%lower than that of the empty channel.When the miniature cuboid vortex generator(s)is put in the transition region and the logarithmic law region of the channel,these corresponding synthesis performance coefficients of the channel are greater than 1.By contrast,when the miniature cuboid vortex generator(s)is put in the viscous layer,the synthesis performance coefficients of the channel are less than 1.Setting miniature cuboid vortex generator(s)in transition region can lead to a big difference to the flow and heat transfer characteristics.The maximum synthesis performance coefficient can be achieved by placing the miniature cuboid vortex generator(s)in the transition region.