Numerical Study On The Morphology Evolution Of Rocket Exhaust Plume During Lunar Landing

During the landing process of a lunar probe,the rocket exhaust plume constantly erodes the lunar regolith,causing a large amount of lunar dust particles to spread out,which has a certain impact on the surrounding environment.In addition,when the probe descends to a lower altitude,the deflected plume will strike some components of the probe,which may be adversely affected by the torque and heat flux exerted by the plume.The study on the morphology evolution of rocket exhaust plume during landing can give a more intuitive understanding of the impact of plume.Because the background atmosphere on the moon is negligibly thin,the lunar environment can be regarded as a vacuum.The high vacuum and low gravity environment makes it very difficult to investigate the influence of plume morphology evolution by experiments on the ground.Therefore,numerical simulation method is indispensable in this study.In this paper,the evolution of the rocket exhaust plume during the lunar landing is studied numerically by combining the finite volume method to solve the Navier-Stokes(N-S)equation and the direct simulation Monte Carlo(DSMC)method through a regional decoupling approach.The main research contents are as follows:(1)In the study of plume morphology under different engine hovering altitude,the characteristics of plume morphology corresponding to different engine hovering altitude were summarized,and the changes of force and heat on the lunar surface were analyzed.It is found that the oblique shock waves generated from the throat of the nozzle will have an important effect on the plume morphology,the oblique shock waves regularly intersect to produce transmitted shock waves,and the interaction between transmitted shock waves and surface shock waves will have less effect on the plume morphology,but will have some effect on the lunar surface pressure,shear stress,and heat flux density distribution.When the oblique shock wave changes from the regular intersection to Mach intersection,the plume morphology changes obviously,the surface shock wave shape is no longer "bow",the plume field appears stagnant bubbles,the lunar surface pressure,shear stress,heat flux density distribution changes significantly.(2)In the study of the effect of lunar surface temperature and tilt angle on plume morphology,the plume morphology and the corresponding force and heat on the lunar surface were compared for different lunar surface temperatures and tilt angles,and it was found that the change in lunar surface temperature has almost no effect on the plume morphology and only changes the peak value of the lunar surface heat flux density.And the change of the lunar surface tilt angle will have some effect on the plume morphology,and the surface shock tilt angle is larger and the shock intensity is stronger on the side of the lunar surface closer to the engine.And for different engine altitudes,the effect of the change of the lunar surface tilt angle on the force and heat on the lunar surface is not consistent due to the difference of the plume morphology.(3)In the study of the effect of plume morphology evolution on the distribution of lunar surface erosion rate,the law of lunar surface erosion rate change during the engine altitude decrease is summarized,and the effect of lunar surface tilt angle change on the lunar surface erosion rate is analyzed.It is found that the lunar surface erosion rate increases with decreasing engine altitude,and the change in lunar surface tilt angle changes the value and location of the peak erosion rate.And when stagnant bubbles appear in the plume field,the lunar surface erosion rate appears to increase steeply,and the lunar surface erosion rate distribution changes from a single-peaked distribution to a double-peaked distribution.