When the spacecraft flies much faster than the sound speed (~1200 km/h), the airflow disturbances deflected forward from the spacecraft cannot get away from the spacecraft and form a shock wave in front of it. Shock waves have been a detriment for the development of supersonic aircrafts, which have to overcome high wave drag and surface heating from additional friction. Shock wave also produces sonic booms. The noise issue raises environmental concerns, which have precluded routine supersonic flight over land. Therefore, mitigation of shock wave is essential to advance the development of supersonic aircrafts. A plasma mitigation technique is studied. A theory is presented to show that shock wave structure can be modified via flow deflection. Symmetrical deflection evades the need of exchanging the transverse momentum between the flow and the deflector. The analysis shows that the plasma generated in front of the model can effectively deflect the incoming flow. A non-thermal air plasma, generated by on-board 60 Hz periodic electric arc discharge in front of a wind tunnel model, was applied as a plasma deflector for shock wave mitigation technique. The experiment was conducted in a Mach 2.5 wind tunnel. The results show that the air plasma was generated symmetrically in front of the wind tunnel model. With increasing discharge intensity, the plasma deflector transforms the shock from a welldefined attached shock into a highly curved shock structure with increasing standoff distance from the model; this curved shock has increased shock angle and also appears in increasingly diffused form. In the decay of the discharge intensity, the shock front is first transformed back to a well-defined curve shock, which moves downstream to become a perturbed oblique shock; the baseline shock front then reappears as the discharge is reduced to low level again. The experimental observations confirm the theory. The steady of the incoming flow during the discharge cycle is manifested by the repeat of the baseline shock front.
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机译：当航天器飞行的速度快于声速（〜1200 km / h）时，从航天器向前偏转的气流扰动无法脱离航天器并在其前方形成冲击波。冲击波一直对超音速飞机的发展有害，超音速飞机必须克服由于附加摩擦而产生的高风阻和表面发热。冲击波还会产生音爆。噪音问题引起了对环境的关注，这已使常规超音速飞行无法在陆地上进行。因此，减轻冲击波对于推进超音速飞机的发展至关重要。研究了等离子体缓解技术。提出了一种理论，表明可以通过流动偏转来修改冲击波的结构。对称的偏转避免了在流动和偏转器之间交换横向动量的需要。分析表明，在模型前面生成的等离子体可以有效地偏转进入的流。在风洞模型前面通过板载60 Hz周期性电弧放电产生的非热空气等离子体被用作减轻冲击波技术的等离子体偏转器。实验在2.5马赫风洞中进行。结果表明，空气等离子体在风洞模型的前面对称地产生。随着放电强度的增加，等离子偏转器将电击从明确定义的电击转变为高度弯曲的电击结构，并且与模型之间的距离增加了。这种弯曲的冲击增加了冲击角，并且也以越来越分散的形式出现。随着放电强度的衰减，激波前部首先转变为轮廓分明的曲线激波，然后向下游移动，成为扰动的斜激波。然后，当放电再次降低到较低水平时，基线冲击前沿将再次出现。实验观察证实了这一理论。排放循环期间流入流量的稳定程度通过基线激波前沿的重复来体现。
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