Investigation On Thermo-Fluid-Solid Coupling Characteristics And The Influencing Factors Of Constant Temperature Cylinder In Flow Induced Vibration

As the simplest and most important unit equipment,heat exchanger plays an important role in energy and power,petroleum,chemical,food,pharmaceutical and other industrial production,and is widely used.With the development of economy and the increase of human energy consumption,the heat transfer performance of heat exchanger has become a hot issue in all walks of life.In order to improve the heat transfer performance,the structure design of heat exchanger gradually adopts high-strength materials,and the thickness of the heat exchanger tube wall is becoming thinner and thinner,which makes the flow-induced vibration(FIV)become a problem that must be considered in the structure design.In order to study the thermo-fluid-solid coupling characteristics of FIV heat exchange tube bundle,and understand the influence of FIV on heat exchange characteristics.In this paper,the influence of FIV on the convective heat transfer characteristics of single cylinder and two cylinders are simulated by using the commercial software Fluent and user defined function.The effects of reduced velocity,degree of freedom,spacing ratio and staggered angle on vortex formation,vibration response and heat transfer characteristics are discussed.Firstly,the FIV and heat transfer characteristics of a circular cylinder are studied,and the effects of FIV on the heat transfer characteristics are discussed.The results show that the dimensionless amplitude of the two-degree-of-freedom(2DOF)FIV increases first and then decreases with the increase of the reduced velocity in the x and y directions.The motion trajectories are "figure-eight" shape,and the vortex shedding mode is 2S.When U*=5,the maximum amplitude response is 0.63 D.The dimensionless displacement and the surface-averaged Nusselt number change periodically with time.A transverse vibration period includes two periods of the surface-averaged Nusselt number.The maximum averaged Nusselt number is obtained at U*=6,compared with the stationary cylinder and the 1DOF FIV cylinder,the heat transfer of the 2DOF FIV cylinder is increased by 5.73% and 2.46% respectively.Secondly,the FIV response and heat transfer characteristics of the upstream stationary cylinder and the downstream FIV cylinder in tandem are studied,and the influence of the distance between the upstream and downstream cylinder centers on the FIV and heat transfer characteristics is discussed.The results show that when the spacing ratio and the reduced velocity are small,the wake of upstream cylinder wraps downstream cylinder,which restrains the vibration of downstream cylinder,and the vortex falls off in2 S mode at a distance.The local Nusselt number at the rear stagnation point of upstream cylinder is small,and there is almost no heat exchange at the front stagnation point of downstream cylinder.When the spacing ratio or the reduced velocity is large,the vortices of upstream cylinder merge with the vortices of downstream cylinder to form larger size vortices and fall off together,which promotes the FIV of downstream cylinder.The vibration amplitude of downstream cylinder is large,the local heat transfer at the front stagnation point increases,the maximum local Nusselt number of downstream cylinder is obtained at the front stagnation point.The local Nusselt number at the rear stagnation point of upstream cylinder increases,the second peak appears.When S/D=3.0 and U*=13,the vortex mode changes 2S→2P,the maximum amplitude is obtained 1.44 D,and the averaged Nusselt numbers of upstream cylinder and downstream cylinder are the maximum.Compared with the flow around two statitionary cylinders in tandem,the maximum averaged Nusselt numbers of upstream cylinder and downstream cylinder can be increased by 19.51% and 150.42% respectively.When the spacing ratio S/D=4.0 and5.0,the interaction between the two cylinders decreases.With the change of the reduced velocity,the average Nusselt number of the upstream cylinder is basically stable,and the variation of the average Nusselt number of the downstream cylinder is similar to that of the single cylinder.Finally,in order to deeply analyze the influence of FIV of heat exchange tube bundle on the heat transfer characteristics,the FIV response characteristics and heat transfer characteristics of stationary cylinder and oscillating cylinder with staggered arrangement are studied,and the influence of the staggered angle of the two cylinders on the FIV and heat exchange is discussed.The results show that with the increase of staggered angle and spacing ratio,the vortex shedding mode changes,including two rows vortex streets,2S→S+P→three rows vortex streets,2S.The amplitude of oscillating cylinder decreases first,then increases,and finally decreases with the increase of staggered angle.The angles of obtaining the maximum amplitudes are different under different spacing ratios.When the spacing ratio is small(S/D=1.5 and 2.0),the maximum amplitude is obtained at φ=45°,and when the spacing ratio is large(S/D=3.0-5.0),the maximum amplitude is obtained atφ=30°.The maximum amplitude of oscillating cylinder is about 0.79 D,which is obtained when φ=45° and S/D=1.5.The averaged Nusselt number of stationary cylinder is complex with the staggered angle when the spacing is smaller(S/D=1.5),and the maximum value is obtained at φ=45°.When the spacing ratio is large,the averaged Nusselt number of stationary cylinder and oscillating cylinder increase with the increase of staggered angle.When the staggered angle is large,the averaged Nusselt value of oscillating cylinder is approximately equal under different spacing ratios.