固体微推力器点火过程数值研究

Numerical Study on Ignition Process of a Solid Propellant Microthruster

关键词:  固体微推力器  局部点火模型  逆压梯度  回流  热反馈

Key words:  Solid propellant microthruster  Local ignition model  Adverse pressure gradient  Backflow  Heat feedback

摘要:

为研究点火元器件加热区域受限下固体微推力器的局部点火过程，通过数值模拟手段，基于流固耦合传热模型和局部网格重构技术建立了推力器局部点火模型，研究了常压环境下的固体微推力器点火过程，分析了点火过程中推力器内燃气的流动和传热特性，并结合仿真所得推力-时间曲线与全表面点火模型和Jongkwang Lee提出的局部点火模型进行了对比。仿真结果表明，随着推进剂产生燃气往未燃推进剂表面的热反馈，推进剂燃面逐渐扩大。点火过程中喷喉燃气流速未达到声速，外界反压使微喷管内产生逆压梯度，导致喷管扩张段内出现边界层分离。由于喷管扩张段后部逆压梯度随时间增大，喷管扩张段后部回流相应加剧，从而增强了壁面表面的对流换热和燃气主流的动能耗散。模型的推力上升趋势与实际情况更加吻合。

Abstract:

In order to investigate the local ignition process of a solid propellant microthruster with restricted ignition device heating surface，by numerical simulation，a local ignition model based on solid-fluid coupled heat transfer model and local remeshing technique was proposed，and the solid propellant microthruster ignition process under normal pressure was studied. The flow and heat transfer property of gas inside the microthruster was analyzed. Based on the thrust-time curve，the proposed model was compared with the whole surface ignition model，as well as the local ignition model proposed by Jongkwang Lee. Simulation results clearly show that the burning surface expands due to the heat feedback of the gas to unburned propellant surface.The gas velocity is under local sound speed at the nozzle throat，which generates adverse pressure gradient in the divergent nozzle，hence causes boundary layer split. As the adverse pressure gradient at the backward of the divergent nozzle increases，the backflow becomes more significant，and enhances heat transfer and kinetic energy dissipation of the gas. The thrust increasing tendency agrees better with experimental results.