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.