Numerical Investigation On Scale Effects Of Flow Field At Bottom Of Large Rocket

With large dimensions,heavy-lift carrier rocket require multiple rockets to provide launching power.Due to high temperature of the rocket motor plume,there exists intense radiation heat flux to the carrier bottom and its heat environment will be deteriorated with the backflow of the motor plume at high altitudes.The related technical problems are of great significance to rocket engineering.In particular,heavy-lift carrier rocket has large dimensions and rocket motors of high pressure and high total temperature,Therefore,wind tunnel experiments with scaled model on various conditions are needed to provide basic data for thermal protection design.However,the influence of scale on the rocket bottom heat environment is still rarely studied.Meanwhile,experiment with rated total pressure of the rocket motor plume needs expensive cost and serious safety assurance,possibility of experiment with reduced total pressure needs to be evaluated.In this paper,with CFD method coupled with radiation model,a large multi-nozzle carrier rocket model was established to conduct simulations of the plume flow structure at different flight altitudes for different scales and total pressure reduction.The heat flux changing laws to the bottom of the rocket were examined carefully.The main works and conclusions of the study is as follows:(1)The viscous model,radiation model and the radiation parameters were verified to ensure the reliability of the methods and models adopted.(2)The scale effects at high altitude for simplified 2D rocket model were simulated:.The results showed that:the flow field ensure a good similarity for different scales,and the maximum heat flux at the bottom of the rocket presented a nonlinear increase trend with the decrease of the model scale.(3)The altitude effect with a full-size 3D rocket model were conducted.The results showed that:with the increase of altitude,the rocket motor plume expands rapidly,and the backflow phenomenon begins to occur after about 20 km.At this time,the radiation intensity of the plume near the nozzle is high and quickly decreased at the downstream.When the flight altitude grows within a certain range,the maximum heat flux at the bottom of the rocket presents a nonlinear increasing trend.(4)The scale effects at different altitudes with 3D rocket model were simulated.The results showed that:the flow field maintained good similarity with various scaled models at different conditions.With the decrease of size scale,the convective heat transfer is increase while the radiative heat transfer increase at low altitude but decrease at high altitude.In summary,the maximum heat flux at the bottom of the rocket presents a nonlinear increasing trend.(5)The effect of reducing rocket motor total pressure at higher altitudes with 3D rocket model were also conducted.The results showed that:with the decrease of engine total pressure,the radiation intensity of rocket plume is reduced,both the convection and radiation heat transfer also decreased correspondingly,the maximum heat flux at the bottom of rocket presents a roughly linear downward trend.