Numerical Studies on Flowfield Characteristics of Four-Engine Rockets Impinging Jet with Different Flame Deflectors

Abstract

[Objective] To explore the further deep space, many countries are developing the new generation launch vehicle which has higher effective loads [1, 2]. To upgrade capacity, a scheme with multiple engines working simultaneously has often been adopted in the propulsion system of heavy launch vehicles [3, 4]. Therefore, the rocket jet impact problem has been the vital factor which seriously affected the launch safety. Due to the rocket engines are close to the launch platform during launching phase, the exhaust jets of rocket engine not only disturb the attitude of rocket in the take-off, but also have a thermal impact on the rocket base and ground control system [5]. Potential dangers would threaten secure and stable of launch missions if these problems could not be solved properly. Therefore, carrying out research on the flow field characteristics of multi-engine rockets exhaust plume has a great significance for the risk aversion and improvement of achievement ratio in launching [6-9]. This paper researches the four-engine rockets flow field during launching phase, compares and analyzes the plume impact characteristics with two shapes of flame deflector by numerical simulation methods. [Methods] The study object of this paper is a three-stage liquid rocket which utilizes kerosene/liquid oxygen (LOX) propellant as propulsion system for the first stage. Structured meshes with tensor product structure have better numerical ability than unstructured grids that using a multi-block, structured mesh to improve the fidelity of the flow solutions and assure a good resolution of shock waves in the flow field. The liquid rocket exhaust is considered as an ideal gas with the continuum assumption. The numerical solution of the compressible, multi-species, Reynolds-Averaged Navier-Stokes equations for multi-component flow has been obtained with finite volume spatial discretization on a structured three-dimensional grid implemented. The supersonic jet impingement on deflector was computed the realizable k-ε turbulence model. The model has shown superior improvements over the standard-model where the flow features include strong streamline curvature and vortices. The accuracy and effectiveness of the impact model was verified by comparison between the calculated results and the measured date. [Results] The temperature, pressure, and contours on the symmetry plane with wedge-shaped and cone-shaped deflectors are obtained, three shock cells are established before the plume impacts the deflector surface. A high temperature region occurs immediately through excessive high temperature gas accumulation on the deflector surface. The core and developed region and boundary of plume are clearly visible downstream of flow field. The supersonic exhaust plume was diverted into outlet with two directions and circumferential direction in the wedge-shaped and cone-shaped flame deflector, respectively. It can be shown from the temperature and pressure contours in the deflector surface that the region of peak temperature and pressure occur directly under the rocket nozzle, and the temperature drops gradually from the center to the outlet of the flame deflector. The simulation results show the planar static temperature contours for the rocket motor gas impingement on wedge-shaped and cone-shaped deflectors at Z/D = 3, 4.5, and 6 in axial plume direction, where Z/D = 0 corresponds to the nozzle exit. The exhaust gas inlet of the wedge-shaped deflector has the same temperature as atmosphere except for jet flow region, and not affected by the reverse flow. The temperature edge region of planar in the cone-shaped deflector, as well as the central region, is much higher than ambient temperature. The temperature in the edge at Z/D =3 where is closest to the exhaust gas inlet may reach up to 800 K. [Conclusions] By comparative analysis between the four-engine rockets impinging jet on different deflector, the main conclusions are as follow. The region of peak temperature and pressure occurs directly under the rocket nozzle. The wedge-shaped and cone-shaped deflectors have different diversion directions. The maximum pressure and temperature in the wedge-shaped deflector are, respectively, 62% and 18% higher than those in the cone-shaped flame deflector. Compared with the wedge-shaped deflector, the cone-shaped deflector has better performance for deflecting, and increased the distance and optimized the structure of the sidewalls can further improve the exhaust gas flow conductivity. The results provide engineering guidance and theoretical significance for design of the flame deflector of the launch platform.The full version of this extended abstract will appear in Defence Technology in 2020.