The Research Of Jet Mixing Based On Two Pulsed Mini-jets

With the development of industry and the deep research of jet technology,fluidics is in an increasingly wide use in various industrial fields,such as the improvement of combustion efficiency of internal combustion engine,the control of the chemical reaction rate,automobile drag reduction,noise reduction and the increase of thrust for aircraft and rockets,among all of which it has important research significance.A large number of experiments and simulations have been done on the jet,and the mixing process of the controlled jet has been analyzed in depth.Based on the previous studies,this project will mainly investigate in the effect of mini-jet on mixing characteristics under the circumstance when there is phase difference between two branches of micro jet.This dissertation mainly adopts two pulsed mini-jets which are arranged in three relative positions respectively: 60 degrees,120 degreesand 180 degrees to control jet.Under these circumstances,it will separately probe into the effects on jet mixing characteristics of mass flow ratio,the excitation frequency of the mini-jet actuator as well as the duty ratio and phase difference of mini-jet actuator.And in addition,the value of mass flow ratio is 0~7%,the excitation frequency is from 0 to250 Hz,duty cycle is from 3 to 80% and the value of phase difference is from 0 to180°.Research shows that the mixing of mini-jets is affected by those important factors including the mass flow ratio of mini-jet,the excitation frequency of mini-jet controller,duty cycle and the incident angle and phase difference of two mini-jets.Additionally,there are optimal excitation frequency,optimal duty cycle and optimal phase difference.The optimal control parameters are found by the control variable method,and the optimal control parameters are used one by one to find the maximum velocity attenuation rate.At this time,the control effect is the best.For example,when the Reynolds number is 6667,the two pulsed mini-jets turn on at 120 degrees.At 100 mm downstream of the jet,the attenuation rate of velocity under optimal control increases from 0.07 to 0.62,which is close to 9 times that under uncontrolled condition.The effect of velocity attenuation rate on the reaction jet control,and the larger the velocity attenuation rate is,the better the control effect is.When the two mini-jets are arranged at 60 degrees,in-phase opening can enhance the mixing effect and make the mixing effect better;when 120 is arranged,two mini-jets opened in reverse phase deflect the main jet and enhance the mixing effect;when the two mini-jets are arranged at 180 degrees,in-phase opening can achieve better control effect.The attenuation velocity of the main jet under the interferenceof the pulsed mini-jet is much faster than that without control.The phenomenon of entrainment and entrainment is obviously intensified under the control of mini-jet.Changing the parameters will lead to the change of vortex structure and turbulence state,which will lead to the change of control effect.