Thermal plasma sheaths in hypersonic boundary layers: A preliminary numerical study

At the high temperatures typical for hypersonic shock and boundary layers, thermal plasma sheaths form naturally near the surfaces. Thermal plasma sheath effects on hypersonic boundary layers have not yet been studied either experimentally or numerically. We here perform the first detailed study of the plasma sheaths taking place within hypersonic boundary layers throughout the flight Mach number range 10-24. The study is performed using a in-house-developed code based on a novel method recently developed which reduces the computational effort needed to solve fully coupled plasma/fluid flows by a factor of 1000. Preliminary results indicate that the thermal plasma sheaths coexist with hypersonic boundary layers for a Mach number higher than 12, have a height commensurate with the boundary layer thickness, and reduce the temperature to the surface by as much as 1000 K. Further, the ratio between the body force exerted by the sheath and the boundary layer momentum is similar to the one observed previously in low-temperature DBD plasma actuator flow control. Such preliminary results indicate that the plasma sheath that forms naturally in hypersonic flows has the potential to affect significantly boundary layer transition as well as heat flux to the surfaces.