| Vortex generators are widely used in heat exchangers to improve energy transfer efficiency because of their low cost and high efficiency.In this paper,a new type of bending vortex generator is proposed,and its thermal hydraulic performance characteristics are studied by numerical simulation to obtain the variation law of output performance with structural parameters,and the optimization of vortex generator structure is carried out for the comprehensive performance.Subsequently,in order to further reveal its enhanced performance,the flow field and thermal field distribution characteristics of the vortex generator are explored and analyzed in detail.During the study,a new vortex generator model in the flow channel is firstly given and a suitable grid division of the computational domain is constructed.Subsequently,the k-kl-ω turbulence model is selected for the flow field calculation,and the grid-independence verification and theoretical validation are performed to ensure that the simulation data have sufficient reliability.The final results compared with the known data show that the calculated deviations of Nusser number Nu and f factor are 3.8% and 11.96%,respectively,which prove that the computational model has credible solution accuracy.Next,the vortex generator structural morphology is determined,and three structural parameters of curl(α),angle of attack(β)and pitch(Pt)are extracted from it.A series of case configurations based on the central composite design method is used to efficiently extract the data characteristics of the vortex generator output performance.Next,in order to investigate the variation of the vortex generator thermal hydraulic performance with the structural parameters,the regression equation of the calculated data was obtained and used to perform a response surface analysis process with Nu and f factors as performance indicators.The results of the response surface analysis show that smaller angle of attack,appropriately sized curvature and pitch help to enhance the heat transfer performance of the vortex generator,and the larger the values of these structural parameters are,the smaller the corresponding flow losses will be.A statistical model of the data is used to complete the structural optimization of the vortex generator,and the integrated thermal performance factor η is used as the optimization target to measure the overall output performance.Both the response surface model and the radial-based neural network model were used to fit the distribution characteristics of the computational data and achieved significant prediction accuracy.As a result,each of the two models found the best combination of structural parameters to optimize the overall performance within the study.To verify the accuracy of the results,simulations were performed for the different optimized structures and the predicted and calculated results were compared.The obtained data show that the integrated thermal performance factor of the optimized structure obtained from the radial-based neural network model is increased to1.092,which is a 3.06% improvement in the integrated performance,while the prediction error rate of the model is 0.22%.Therefore,it can be concluded that the optimized structure achieves the best performance output.Finally,in order to investigate the mechanism of the action of the vortex generator to enhance the flow heat transfer performance,the flow and thermal fields of the new vortex generator with different structures were analyzed.The analysis results show that the new vortex generator enhances the heat transfer capability mainly through the paired vortices generated at the rear,and the formation of this core vortex region also significantly increases the flow friction losses.In addition,backflow and flow impact near the vortex generator are also important sources of energy loss.The analysis on the structural parameters shows that the curvature and angle of attack can significantly adjust the morphology and intensity of the main vortex to achieve the effect of promoting the heat exchange between hot and cold fluids and improving the heat transfer performance;the pitch can change the distribution area of the core vortex zone,and the heat transfer performance decreases when the distribution interval is too large or too small. |
