来流情况下入口状态对吸气式激光推力器冲量耦合系数的影响

Effects of Inlet States on Impulse Coupling Coefficient for Air-breathing Laser Propulsion

激光推力器在高空环境下飞行不可避免地会受到来流的影响,而其入口状态直接影响激光聚焦点火之前的定常流场状态,从而影响推力器的推进性能。在来流马赫数为5的条件下,对某种吸气式推力器模型的入口在打开、关闭以及半开3种状态下的内外流场演化过程进行了数值模拟。结果表明:入口打开时,轴向阻力低于同工况下入口关闭和半开的情况;入口关闭时,聚焦区的激波传播速度明显增加,正推力峰值明显增大,抵消了入口关闭带来的额外负推力;入口半开时,正推力较入口关闭没有得到有效提高,轴向阻力较入口打开却大幅增加,导致其冲量耦合系数最低,推进性能最差。通过计算和分析预测,入口构形的改进设计可大幅度提高来流情况下推力器的推进性能,对入口构形优化还需进行大量工作。

Laser thruster will inevitably expose itself to inflow when flying in the atmosphere at a high altitude,and the inlet states will exert a direct influence on its propulsion performance because of their effects upon the steady flow field before laser ignition.A second order method is used to simulate the detailed evolving process of the inner and outer flow fields of an air-breathing laser thruster model with a circular focusing for a free-stream at Mach number 5 under three conditions：when the inlet was open,closed and ajar respectively.The results indicate that the wave drag is lowest when the inlet is open.When the inlet is closed for a long enough time,there is an obvious increase in the propagation velocity of the shock wave,which induces the maximal peak value of the rising positive thrust and counteracts the additional negative thrust brought about by inlet closing.Impulse coupling coefficient is lowest and propulsion poorest when the inlet is ajar.Since propulsion performance may be improved greatly by improving the design of inlet configuration according to numerical calculation and analysis,much further work is required for its optimization in future.