级间分离是大型火箭和导弹发射过程中必不可少的步骤，其过程短暂、流动复杂、变化剧烈，对火箭发射的成败有至关重要的影响。因此，必须加强对火箭级间分离特性的认识，以便为级间段的设计和改进提供参考。本文在分区重叠网格上利用Chimera/Overset方法，对两类串联多级火箭的级间分离过程（即，一二级热分离和二三级冷分离）进行了流体力学和刚体动力学耦合数值模拟。本文对实际飞行和地面实验条件下的二三级冷分离进行了数值模拟研究，证实了遥测数据合理，并得到了其成因：80 km高空的飞行环境接近于真空，因此二级前封头空腔内的高压燃气能够前传并冲击三级后封头；地面实验的外场压力较高，燃气受三级后封头内压力较高空气的阻隔不能直接冲击三级后封头，即环境压力的差异造成了飞行遥测存在50 kW/m2的热流密度峰值而地面实验未能测量到热流。本文对级间流动机理的数值模拟研究表明：下面级前封头空腔内燃气向外场泄露与上面级喷管燃气来流之间针锋相对的竞争引起级间流场的剧烈振荡，火箭级间分离流场出现气动谐振现象，这是上、下级轴对称分离情况下的主要特征。该气动谐振的强度随分离距离变化，谐振现象在某些分离位置消失，然后在下游又重新出现，即谐振具有间歇现象。喷口下游的流场结构、两级之间的相对位置和下面级前封头的径向尺寸是级间流场谐振存在间歇现象的主要影响因素。然而，当上面级喷管偏转时，轴对称消失，燃气来流与泄露流之间的竞争失衡，级间流场比轴对称工况平稳。级间无谐振现象时，CFD计算可以考虑采用定常的近似假设来预测级间流场。本文对热分离过程安全性的研究表明：一级前封头和级间壳体的压力分布决定了一二级之间能够安全完成热分离，两级之间不易发生碰撞。火箭在100 km高空飞行时，外场接近于真空，燃气能够膨胀、回卷并冲击到箭体上。本文采用定常流场计算的方式研究了三喷管喷流干涉对火箭推力特性和热环境的影响，结果表明：喷流干涉对前场有效载荷基本没有影响，该结果为火箭的头罩分离提供了依据；主、侧喷管之间的喷流干涉使高温燃气受到压缩，然后向前方膨胀并冲击到仪器舱尾端面上，因此对其产生较强的、持续作用的对流传热，因此需要对其加强热防护；喷流干涉产生的附加推力对火箭推力特性影响非常小。关键词：级间分离；流场；气动谐振；间歇现象；喷流干涉

Stage separation plays a critical role in the flight course of multi-stage rockets and missiles for the reason of its behavior of complicated flow field and fierce change. Therefore, it is necessary to investigate the behavior and characteristics of the multi-stage rocket stage separation for the sake of providing reference for the design of interstage. In this dissertation, coupled CFD and rigid body dynamics simulation by means of Chimera/Overset method is performed to study the dynamic and aerodynamic characteristics of the tandem stage separation of a multi-stage rocket.Numerical simulations are performed for the processes of flight test at an altitude of 80 km and ground test under standard atmosphere which confirm the remarkable difference between telemetry data of flight and ground test result. Simulation results show that the tremendous distinction of the ambient pressure is the reason for this remarkable difference. The compressed gas of the second stage cavity is able to expand upstream and impinge against the aft dome of the third stage at an altitude of 80km where ambient pressure is vey low, while the gas is unable to impinge directly against the aft dome in ground test under standard atmosphere, therefore telemetry data of flight shows that there was a heat flux peak value of 50 kW/m2 on the midpoint of aft dome of the third stage and there is almost no heat flux in ground test.The interstage flow mechanism is investigated numerically which shows that flow field of the axisymmetric case features significant unsteady oscillation. The periodically violent oscillation of the interstage flow is excited by the competition between the jet of upper stage nozzle and discharging flow of the lower stage cavity. Therefore gas resonance phenomenon also occurs in the course of the tandem stage separation which behaves in an intermittent manner with increasing distance of separation, i.e. the gas resonance disappears at some position of separation and appears again downstream. The analysis shows that shock wave structures of interstage, relative distance between the two stages and the diameter of the lower stage cavity are the main conditions and factors which lead to this interesting phenomenon. However，when there is an angular deflection of the upper stage nozzle, the competition is out of balance between the jet of upper stage nozzle and the discharging flow of the lower stage cavity, therefore the interstage flow field is relatively smooth. The present study also shows that when there is no gas resonance phenomenon, the steady assumption can be used for CFD simulation to predict the interstage flow field. The study on the hot stage separation shows that the first stage and the second stage of the rocket are able to separate safely which profits from the pressure distribution on forward dome and interstage shell of the first stage.While the rocket is flying at high altitude of 100km where ambient atmosphere is almost in a vacuum state, jets of the rocket’s three nozzles interact, expand and impinge on the body of the rocket. Steady CFD simulation is carried out to study the impact of interacting jets on the thrust performance and thermal environment of the rocket. The results show that interacting jets hardly have an impact on the payload which warrants the separation of head shield; the flow is compressed in jets interaction zone, therefore it expands upstream, impinges against the instrument cabinets and transmits heat to them upon which thermal protection should be taken; the interacting jets exert very little influence on the thrust performance of the rocket.Key words: stage separation; flow field; gas resonance; intermittent phenomenon; jets interaction