可渗透壁自适应高度补偿喷管工作机理数值研究

Numerical study on operational mechanism of a permeable wall adaptive altitude-compensating nozzle

提出了一种带有可渗透壁面的自适应高度补偿概念喷管(可渗透喷管),对该喷管的典型工作状态进行了数值模拟并对其高度补偿机理进行了解释。数值模拟结果显示,在低落压比条件下,外界大气透过喷管可渗透段进入喷管内部,抑制了喷管壁面处的回流产生,削弱了壁面处分离斜激波的强度,从而提高了喷管的低空推力性能。而在高落压比条件下,喷管内部燃气透过可渗透段壁面泄出,削弱了燃气的膨胀能力,使得喷管的高空推力性能有所损失。当可渗透喷管的低空推力性能提升幅度大于其高空推力性能损失时,喷管即具备了高度补偿能力。对喷管的推力构成分析表明,低落压比时,喷管可渗透段处外界大气流入所导致的喷管内压升高是其具有高度补偿能力的主要原因。基础扩张比的大小对可渗透喷管高度补偿性能影响显著,可渗透喷管比传统喷管的推力提升幅度最高可达34%,不同基础扩张比的可渗透喷管低空推力补偿能力相差最大25%。将不同基础扩张比喷管的高度平均比冲进行对比可发现,存在最优的喷管基础扩张比,该可渗透喷管高度平均比冲比传统喷管高度平均比冲高3%。

A conceptual adaptive altitude compensation nozzle with a permeable wall(permeable nozzle for short)is proposed in the present study.The typical operating states of the nozzle are demonstrated using numeri-cal methods and the underlying mechanism of its altitude compensation is interpreted.The numerical results show that,at low nozzle pressure ratios,the external atmosphere enters the nozzle through its permeable wall section,which inhibits the backflow at the nozzle wall,weakens the strength of the separated oblique shock,thus im-proves the low-altitude thrust performance of the nozzle.However,at high nozzle pressure ratios,the exhaust gas leaves the nozzle through its permeable wall,which weakens the expansion of the exhaust gas and reduces the thrust performanceat high altitude.The permeable nozzle is considered to possess altitude compensation ability when the enhancement in its low-altitude thrust performance surpasses the deterioration in high-altitude thrust performance.The thrust composition analysis of the permeable nozzle reveals that its altitude compensation ability derives from the internal pressure rise due to the atmospheric air penetration into the nozzle at low nozzle pressure ratios.The basic expansion ratio substantially impacts the altitude compensation characteristics of the permeable nozzle.Compared to conventional nozzles,the thrust improvement of permeable nozzles can be up to 34%at maxi-mum.The low-altitude thrust compensation capabilities differ by up to 25%between permeable nozzles with dif-ferent basic expansion ratio.Comparing the average height-specific impulse of permeable nozzles with different base section expansion ratios,it is evident that there should be an optimal base section expansion ratio.The aver-age specific impulse of the permeable nozzle is 3%higher than of the conventional nozzle.