Research On Structural Characteristics And Heat Transfer Performance Of Self-excited Oscillating Vortex

Currently one of research hotspots in the field of heat transfer is how to use vortex for efficient heat transfer.With the special structure of self-excited oscillation,the initial jet can generate periodic and efficient pulsating flow inside the hot runner without unnecessary external excitation,thus promoting the generation of eddy current conducive to heat transfer in the runner,so it has high research value.At present,the influence process of vortex structure behavior on self-excited oscillation pulsation effect is not clear and the mechanism of vortex influence on heat transfer is not clear.In this paper,vortex structure recognition technology and heat transfer enhancement means are combined,self-excited oscillation heat runner is taken as the research object,and the formation mechanism of self-excited oscillation pulsation effect is explained by numerical simulation and theoretical analysis.The behavior and characteristics of vortex affecting heat transfer are explained.The main work and conclusions of this paper are as follows:(1)The physical model and geometric model of the self-excited oscillation hot runner were constructed,and the numerical simulation of the internal flow field characteristics of the self-excited oscillation runner was carried out by using large eddy simulation method.Based on the pulsation effect of the self-excited oscillation,a numerical model was established to study the enhanced heat transfer characteristics,and the grid-independent test and turbulence model verification were carried out.(2)The influence of certain pulsating pressure on the evolution process of vortex ring structure in a self-excited oscillation chamber was analyzed.Liutex-Omega vortex recognition method was used to analyze the motion behavior of vortex ring structure.The related factors affecting the pulsation effect of vortex structure were obtained.Liutex components with normal and spanwise characteristics dominate the motion of vortex structures.(3)The flow state of different velocity components in the chamber is studied.The fluid motion shows strong three-dimensional flow characteristics in the chamber.The statistical characteristics of velocity flow are analyzed.The turbulent kinetic energy and turbulent viscosity formed in the process of fluid flow will also affect the characteristics of self-excited oscillating flow field.(4)The influence of pulsating flow on heat transfer enhancement is analyzed.Heat transfer in self-oscillating heat runner mainly depends on longitudinal eddy current to accelerate the exchange of hot and cold fluid.Pulsating jet can accelerate the mixing of fluids,destroy the boundary layer and improve the heat transfer efficiency.When the inlet pressure is 25000 Pa,the maximum value of comprehensive heat transfer factor PEC within a single pulsation period is 1.636.