Heat Transfer Enhancement By Vortex-induced Vibration Of Flexible Plate Induced By Cylinder

It has been recognized that vibration can enhance heat transfer long ago,and the introduction of vibration into fluid can destroy the boundary layer and enhance heat transfer consequently.In recent years,the enhanced heat transfer technology using fluid-induced vibration to thin the boundary layer has been developed.This technology combines the advantages of both active and passive heat transfer enhancement.In this paper,the flow and heat transfer of the channel which has both flexible plate and cylinder are studied.When the fluid flows around the cylinder,vortices will be generated.Under the influence of vortices,the flexible plate will vibrate steadily in a constant amplitude and sweep the vortices to the channel wall,thus promoting the mixing of fluids near the wall,reducing the thickness of the thermal boundary layer and improving the heat transfer on the channel wall.The technology of heat transfer enhancement by vortex-induced vibration has the characteristics such as simple structure and strong heat transfer ability,so it has wide application prospect.In this paper,the theory of vortex-induced vibration is introduced,and the research on the enhancement of heat transfer by vortex-induced vibration is summarized.Vortex-induced vibration problem is a typical fluid-structure interaction problem,which depends on dynamic grid and grid deformation of fluid-solid interface between solid and fluid exchange of data.In this paper,the dynamic meshing theory and fluid-structure interaction problem are summarized.The influence of length-diameter ratio and channel blockage ratio on heat transfer enhancement by vibration of cylindrical flexible plates under different Re conditions was investigated.To better study the heat transfer problems by vortex induced vibration,this article first studied the flow and heat transfer in the channel with built-in fixed cylinder and plate,the vortex shedding frequency under the different speed and length-diameter ratio was obtained.The frequencies are converted to St,and the young’s modulus under different length-diameter ratio is calculated.Then modal analysis is carried out with the calculated young’s modulus of the flexible plate.The vibration frequency of the flexible plate with different order is obtained and the natural frequency of the flexible plate is determined.When the length-diameter ratio is 1.5,the first-order mode is selected for vibration.At different times,the displacement at the same point changes periodically like a sine function,and the vibration period at different positions on the flexible plate is the same.Compared with the case which the flexible plate is fixed,the dissipation of the vortex at the end of the channel is smaller,but there is still a more obvious temperature boundary layer at the end of the channel and the weakening effect of the boundary layer is relatively limited.When the length-diameter ratio is 2 to 3.5,the high-order vibration mode of the flexible plate is selected.At this time,the amplitude of the end of the flexible plate is close to a sinusoidal curve.With the increase of the length-diameter ratio of the flexible plate,the separation point of the vortex moves forward from the end of the flexible plate gradually.the vortex range increases,and the mixing effect of the high-temperature fluid near the wall and the low-temperature fluid inside the channel is enhanced.When the length-diameter ratio is 3,the area of the low-temperature area at the rear of the channel is smaller,the temperature gradient near the wall is larger,and the average temperature of the fluid is also higher.When the aspect ratio is 3,the Nu number is the largest,and increased by 96.7% compared with the length-diameter ratio is 1.5;Compared with the channel built-in fixed cylinder,the Nu can be increased by 30%.With the increase of the length-diameter ratio of the flexible plate,f first increases and then decreases,and when the length-diameter ratio is 2.5,f reaches the maximum.Under different Re,the differences in JFc2 is small when the length-diameter ratio is between 1.5 and 2,and also small when the length-diameter ratio is between 2.5～3.5.With the increase of the length-diameter ratio of the flexible plate,JFc2 first increases and then decreases.When the length-diameter ratio is 3,the JFc2 is the largest,and can reach 1.2.The heat transfer difference in channels with different widths is large.As the blockage ratio decreases,the wall is less affected by the sweep of the flexible plate.So the vortex intensity decreases and the area of the low temperature area increases in the back section of the channel,and the temperature gradient near the wall decreases.At the same time,the maximum value of Nulocal gradually move towards the end of the channel.Under different Re,Nu is the largest when the blockage ratio is 0.333.As the blockage ratio decreases,Nu gradually decreases;Under different blockage ratio,Nu increases with the increase of Re.Nu is close and can reach 3 times of smooth channel when the blockage ratio are 0.333 and 0.286.Under different Re,when the blockage ratio is 0.333,the pressure difference and JFc1 are both large,and JFc1 can reach 1.5...