超声速来流条件下等离子体合成射流的激波衍射机理与调控方法

Plasma synthetic jet is a pulsed active flow control method, which injects enormous momentum instantaneously and has attractive potential in supersonic/hypersonic external/internal flow control. A shock diffraction phenomenon arises during the releasing process of the plasma synthetic jet. However, due to the interference of supersonic incoming flow, it behaves quite different to that in a shock tube, and the generated perturbations travel upstream, forming a large scale separation region ahead of the jet, which has detrimental even counteractive effects on the control capability of the plasma synthetic jet. Therefore, in this project, the flow mechanisms of the shock diffraction within plasma synthetic jet under supersonic flow condition are the key issues. The effects of momentum ratio, the geometrical parameters of the actuator and the electrical parameters on the shock diffraction features will be studied, then the flow evolution mechanism of the diffracted shock and the propagation of perturbations will be uncovered. To suppress the forward motion of perturbations, the control method is studied and a new actuator will be introduced. Wind tunnel experiments will be carried out to validate such control method, and the design method of such actuator will be achieved. The achievements of the project lay theoretical foundations and offer necessary technical supports for practical plasma synthetic jet.

等离子体合成射流是一种脉冲式的主动流动控制方法，具有瞬间注入动量高的特性，在超/高超声速内外流控制中具有诱人的应用潜力。一般，等离子体合成射流在压力释放过程中会出现明显的激波衍射现象。然而，受超声速外流干扰，这一现象和激波管中的激波衍射有显著的不同，并且会伴随出现明显的扰动前传现象，在射流上游形成大尺度的分离，严重削弱激励器的流动控制效果，甚至起到反作用。为此，本项目围绕超声速来流条件下等离子体合成射流中的激波衍射现象开展研究，揭示衍射激波的演化机理和扰动传播特性，掌握动量比、激励器几何设计参数、电参数对激波衍射特性的影响规律，探索激波衍射特性的调控原理，提出一种可削弱扰动前传的新型激励器构型，并开展风洞吹风实验验证，掌握其设计方法，为实现等离子体合成射流在超声速流场的有效控制提供理论基础和必要的技术支撑。

结合仿真、理论与试验，揭示了等离子体合成射流激励器在静止和超声速来流状态下的激波衍射机理与一般性的流场演化规律，发现射流主要包含初始激波衍射过程和浮力主导的分层流动阶段，且Richardson数在分层流动阶段保持在1的量级。获得了衍射过程中的激波形态、旋涡和射流的演化特性，掌握了衍射激波强度、射流倾角、出口倒圆半径、保护电阻、工作频率等参数对激波衍射特性的影响规律，阐释了超声速外流与衍射激波的相互作用机理，结果表明占空比是决定干扰强度的关键，占空比越大，射流与主流的动量比越大，干扰越强。基于自由干扰理论，提出了前驱衍射分离激波角预测模型，预测误差在5%以内。进一步，提出了可削弱扰动前传的新型等离子体激励器构型，获得了该类激励器的激波衍射特性，发现前传的衍射激波呈现出高度三维形态，激波前传速度中间最高，且衰减很快，两侧接近声速，验证了该新型激励器的有效性。最后，开展了基于该新型激励器的压缩拐角激波/边界层干扰流动控制，获得了其在典型状态下的控制效果。