| Due to the limited space available in the cooling system of internal combustion locomotives,it is necessary to upgrade the heat exchanger of internal combustion locomotives by combining various enhanced heat transfer technologies in order to achieve the optimal design and meet its compact structure and high efficiency of heat dissipation.In recent years,the vortex generator enhanced heat transfer technology has developed rapidly due to the advantages of convenient processing,high feasibility and wide range of application.The main mechanism of enhanced heat transfer is to enhance fluid disturbance as well as destroying and thinning the development of thermal boundary layer without causing significant pressure loss,thereby achieving the purpose of improving heat transfer performance.By combining the advantages of delta winglet vortex generator and wavy winglet vortex generator,a novel wavy delta winglet vortex generator is proposed in this paper.In the range of laminar and turbulent flows,numerical simulations were used to study the effects of changes in the attack angle,location central angle,location circumferential radius and chord length of the vortex generator on the fluid flow and heat transfer characteristics in the heat transfer channel.The optimal values and combination arrangement of various parameters of the vortex generator were obtained.The main research conclusions are as follows:When the wavy delta winglet vortex generator is arranged in the upstream region of the circular tube,it can induce the formation of longitudinal vortex with greater intensity.When the tail end of the right angle edge of the vortex generator is closer to the wall surface of the circle tube,the formed nozzle-like structure of the narrow channel can greatly divert the fluid to the back side of the circle tube,promote the fluid disturbance in this region,reduce the area of the heat transfer dead zone,and thus achieve improvement in the overall heat transfer performance of the heat exchanger.Compared with the counterclockwise arrangement of the wavy delta winglet vortex generator,the strength of the longitudinal vortex formed when the vortex generator is arranged in the clockwise direction is significantly greater,and the improvement of the heat transfer performance of the fins is also more obvious.For different attack angles and central angles of wavy delta winglet vortex generator,the comprehensive heat transfer performance evaluation factor JF reaches the maximum when the attack angle is-30° and the central angle is 60°.Compared with the plain fin without vortex generator,the average Nu increases by 44.87%,the friction factor f increases by 47.31%,while the final JF reaches a maximum value of 1.29 at Re=1000.Under the same attack angle and central angle conditions,the JF of the wavy delta winglet vortex generator is improved by a maximum of 4.3% over the flat delta winglet vortex generator.The correlations of attack angle,central angle and operating parameters Re with respect to the average Nu,f and JF were derived for the laminar and turbulent flow states,respectively,and the maximum differences between the results of the correlations and the numerical calculations fell within ±7%,±15% and ±4% for laminar flow and ±7%,±13% and ±3% for turbulent flow,respectively.For different location circumferential radius and basic chord length of wavy delta winglet vortex generator,the comprehensive heat transfer performance evaluation factor JF reaches the maximum when the chord length is 6.65 mm and the location circumferential radius is 9mm.Compared with the case where the basic chord length is 3.45 mm and the location circumferential radius of the vortex generator remains unchanged,the average Nu increases by 14.45%,accompanied by a significant increase in the friction factor f by 41.35%,while the final JF reaches a maximum value of 1.34 at Re=1000. |
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