Numeriacal Study Of Circular Turbulent Jet With Unsteady Microjets Control

Turbulent round jet is widely used in environment and industry, and receives a lot of attention in the last decade. To get a better combustion mixing ratio of fossil fuels, decreasing carbon dioxide, toxic gases and PM2.5 emissions, rapid diffusion for cooling, and denoising, etc, mixing enhancement of turbulent jet is popular in those research, and fluidic injection is an effective choice among the means to get this.This paper built a simulation platform of turbulent round jet with unsteady micro-jet control based on the open source C++ library which is Open FOAM, and compared with CFD commercial software Ansys Fluent. We numerically simulated the mixing characteristics of the turbulent round jet( =8000eR) under unsteady micro-jet control based on and Open FOAM. Firstly, different geometries(with nozzle and without nozzle), four mesh generation solutions and LES turbulent models were discussed without micro-jet control. Then we compared the numerical results with the experimental results in order to validate the mathematical model. To further analyzing the mechanism of mixing enhancement, the effect of actuation frequency and mass flow ratio of the micro-jet on the mixing characteristics were investigated.It has been numerically found out that: the decay rate of the mean velocity first increase then decreases as the actuation frequency increasing when two microjet control was used. When the actuation frequency equals to the vortex shedding frequency of the turbulent jet, the decay rate reaches the maximum, which indicates the mixing is greatly enhanced. Also we found that when the mass flow ratio is0.66%, the decay rate has maximum value.By analyzing the vortical structure recognized based on Q riterion, it has been found that whenmC <0.25% the micro-jets were assimilated into the shear layer of the main jet; AsmC increases to 0.33%, the shear layer was penetrated by the micro-jets, and the micro-jets interact with the ring vortices at the outlet of main jet, resulting in enhanced mixing; WhenmC increases to 4.1%, two micro-jets collide and evolve into oppositely structures, which interact with ring vortices at the downstream. This work gained an improved understanding of the enhanced mixing mechanism with unsteady micro-jet control, which provides a basis for promoting the application and development of the micro-jet control technique.