Investigation On Tracking Response Characteristics And Turbulence Modyfication Of PIV Tracer Particles In High Speed Flows

The aero-optical effect of the aircraft optical window is obvious in the process of high speed flight.In depth study of the tracking and response characteristics and the turbulence modification of the PIV tracer particles in the high speed flow,which is of great significance for the accurate measurement of the complex flow field around the aircraft optical window.The good tracking and response characteristics of the tracer particles are the premise of the PIV measurement in high speed flow,and the weaken turbulence modification by the tracer particles on the flow field is the key to ensure the real result of the PIV experiment.Gas phase coupled with discrete phase are simulated by large eddy simulation and Lagrangian particle trajectory model.Oblique wedge model,supersonic mixing layer and backward step flow are numerical simulated,respectively.The particle diameters and mass loadings by numerical simulation is the experimental reference of oblique wedge model,both results are consistent with each other.Particle tracking characteristics negatively related with diameter,the larger particle diameter with worse tracking characteristics;turbulence modification caused by particle mass loading,the larger particle mass loadings has the more obvious turbulence modification of original flow field.The PIV measurement results can be obtained clear shock wave boundary when the particle mass loading is about 0.1092.The investigation on the 2D spatial development supersonic gas-solid two-phase mixing layer shows that,the smaller particle size,than the sooner the particles response will be;the stronger particle mixing ability,the better the PIV tracking characteristics will be.The maximum dispersion distance increases with the particle diameter increasing at first,and the particles Stokes number between 1 and 10 has the maximum dispersion distance.The preferential dispersion is more serious and the particle tracking characteristics is worse as the particle diameter is larger.The larger particle diameter,the longer the heat transfer time between the two phases will be.Particle diameter(about 50 nm in this particle)and mass loading(about 0.1)have the minimal turbulence modification impact by analyzing the normalized root mean square stream-wise velocity,normalized root mean square transverse velocity and normalized Reynolds stress.The local particle mass loadings increasing with the larger convective Mach number,and which leads to the turbulence modification effect is obvious.The motion response of PIV tracer particles in the backward step flow means that large particles pass the expansion shock and oblique shock produce large distance and time slip.Only the Nanoparticles can reach the recirculation zone of the backward step flow.The velocity and temperature change between gas and discrete phase is severe as particles are in the mixing layer,expansion shock,recirculation and oblique shock zone.In those zones,momentum and thermal response time for Nanoparticles is shorter than medium and large particle size,the response capacity of small size particles is more powerful than large size particles.The influence of shock wave on the gas-solid two-phase is more significant than expansion shock on the time-average flow section.Only the Nanoparticles can quickly response the velocity change of gas phase,and the velocity slip is very small.The small particles(525nm)have good response characteristics than the other two particle sizes around the mixing layer center,the interface between the mixing layer and the expansion wave,and the interface between the expansion wave and the recirculation region.And the momentum response of the tracer particles to gas phase is faster than that of the temperature response.