The Infrared Radiation And Mixing Enhancement Characteristics Of Nozzle Plumes Influenced By Cross-flow

The research of this thesis is specific to the enhanced mixing and infrared suppression technology of the high temperature plume of aero-engine by cross-flow.The cross-flow is added downstream of the nozzle.By using the large eddy simulation method,the numerical simulation of the cross-flow incidence,frequency characteristics and the matching relationship with the main frequency is carried out.The infrared radiation intensity distribution of the tail jet under different conditions is analyzed by ray tracing method further.First the macroscopic effects of the potential core-length,the area of high temperature and the intensity of infrared radiation in 3~5?m band are compared and analyzed.Further,the large eddy simulation algorithm is used to analyze the cross-flow penetration depth,and Rayleigh shear stress characteristics of transient changes after the injection of cross-flow.The influence mechanism of cross-flow on the flow and heat transfer characteristics of jet under different injection forms is revealed.Finally,the results of this paper are verified by experiments on the velocity field distribution of the tail jet and the change of Reynolds shear stress after the cross flow incidence under different conditions.Research indicates:(1)The results show circle-rectangular transition model potential core-length reduction,the area of high temperature shrinks,and the intensity of the infrared radiation at different detection planes decrease,compared with the axial symmetric nozzle.In the jet flow field,the rapider development of vortex,the increase of vortex dissipation rate and the increase of velocity boundary layer fluctuation are the essential factors leading to mix enhancement and potential core-length reduction.(2)After the cross-flow injection,the length of the core area and the area of the high temperature area of the tail jet flow are obviously reduced,the infrared suppression effect is also further improved.The influence mechanism of cross-flow is induced counter-rotating vortex pairs(CVP),which dissipates velocity vortex faster and the peak shear stress and bandwidth increase,it also effectively enhance the energy dissipation efficiency of the flow field and jet shear.The effect of CVP is related to the penetration depth,while the vortex strength and penetration depth of CVP increase with the increase of cross-flow incident momentum ratio.The greater the penetration depth of entrapment,the more severe the shear layer pulsation and the better the mixing effect.(3)Steady cross-flow injection model results show that,the shape change of cross-flow has a great effect on enhancing mixing and infrared suppression.The rectangular hole has the strongest reinforcement effect,followed by the square hole and the circular hole is weaker.This is due to the change of the geometry of the hole,which strengthens the expansion range and dissipation speed of the vortex.In terms of the influence of the arrangement of the crossflow holes,on the axisymmetric nozzle model,the mixing effect of the symmetric two injecting,which the length and area of the core in the high temperature and the intensity of the infrared radiation in the 3~5?m band are the smallest.Single injecting followed,while the worst four injecting.Study on circle-rectangular transition model results also showed that cross-flow injecting on broad side is stronger than injecting on narrow side with enhanced mixing and infrared suppression,and is also a symmetric two injecting is stronger than that of single hole incident incident,and peripheral four holes less effective.(4)In the simulation of St?0.25,the turbulent mixing characteristics of pulsed cross-flow is better than that of steady cross-flow.And with the increase of the pulsed cross-flow frequency,the mixing characteristic is further enhanced.The coherent structure shows that the pulsed cross-flow will intensify the unstable oscillation mode of the jet column,and there will be a region where the velocity shear layer fluctuates strongly near the outlet of the jet column,which results in the deeper and deeper penetration of the CVP structure generated by cross-flow.The optimal matching of the phase difference during the pulsating incidence of multi-injecting cross-flow is beneficial to strengthening the blending.(5)Compared with the steady cross-flow and single-pulsed cross-flow model,the mixing characteristics and infrared suppression effects of cross-flow and tail-jet flow at coupled pulsed incidence are further enhanced.This is due to coupled pulsed models of vortex in the core region is more abundant,the structure is more irregular,vortex wound more overlap,higher dissipation caused.(6)Using hot-wire anemometers to perform experiments under similar geometry and flow conditions.The jet velocity field and shear stress distribution of axial symmetric nozzle,circle-rectangular transition model,and steady cross-flow single-injection model nozzles were obtained.The reliability of the above numerical simulation results was verified,and the mechanism of the mixing revealed by the shear stress distribution in the simulation was verified.