| With the development of hypersonic aircraft technology,it is of great significance to study the problem of light transmission in the shock layer around the hypersonic vehicle.The complex turbulent structure in the shock layer will cause the aero-optical effects such as attenuation,jitter and blur of the optical signal.The turbulence distribution in the flow field needs to be first understood,and the influence of turbulence on the light transmission is studied.ICEM software is used to establish different half-cone angle blunt cone models.Combining research issues,the entire computational domain is divided into modules,and local encryption processing is performed on the study area grid to improve the computational efficiency on the basis of ensuring the calculation accuracy.The settings and values of important parameters in the simulation of hypersonic flow fields were analyzed,such as the turbulence model selection,flow conditions,and wall conditions.In the condition of residual oscillation converging,observe the flow flow field of the Mass flow rate to prove the reliability of the flow field.Comparing with the simulation results of the density model of the ballistic model in the literature,the results are in good agreement.Based on Fluent software,the flow field around 5-8Ma at 20-50 km height was simulated.The distribution of temperature,pressure and density in the flow field was analyzed and the reasons for the differences in distribution were given.Based on the simulation results,the variation of density and refractive index was analyzed.The change of the position of the maximum density along the direction perpendicular to the wall surface under different conditions is compared.The results show that the semi-cone angle of the model has the greatest influence on this position,followed by the flight speed and flight altitude.The influences of wavelength,different positions,different flight conditions,and model half cone angle on the refractive index distribution were analyzed.The results showed that the flying height was the main factor affecting the refractive index magnitude,and the wavelength had little effect on the refractive index magnitude,while the remaining factors mainly affected the refractive index distribution.Affects the rate of change of refractive index along the direction perpendicular to the wall.The “2/3 law” and the formula of the structural function are used to obtain a densitybased refractive index structure constant model,and the refractive index structure constant at each position in the two-dimensional flow field is calculated.The effects of model parameters,such as wavelength of light and step length,on the calculation results were analyzed.The variation regularity of refractive index structure constants in the shock layer,shear layer,and turbulent boundary layer were compared.And the regularity as flight state and model half cone angle changed.The results show that the distribution is similar to that of the refractive index.The difference is that the layered structure of the shock layer will cause the refractive index structure constant to change by orders of magnitude.The step-by-step Fourier method was used to solve the wave equation and the spectrum inversion was used to construct the phase screen.The Von Karmann spectrum was applied to calculate the refractive index structure constant with the position of the flow field,the flight state and the model half cone angle.The inner and outer scales of turbulence have been revised.The simulation of the light intensity distribution after passing through a fixed flow field was performed for 1000 times.The statistical characteristics of the intensity fluctuation of the emitted light were obtained by numerical methods.The variation of light intensity fluctuation with flight state and model half cone angle was analyzed.The results show that the flight height is the main factor affecting the variance of light intensity fluctuations.The position of the flow field,the flight speed and the model half-cone angle are secondary factors. |
