Development of a Disturbance from a Local Discharge in a Laminar Boundary Layer at M = 1.43

Abstract

Disturbances generated by a short-period spark discharge in a laminar boundary layer on a plate at a free-stream Mach number of M = 1.43 have been examined. The study consists of experimental and numerical components. In the experiment, a spark discharge has been initiated in the boundary layer lasting less than a microsecond, which is an order of magnitude shorter than the characteristic times of boundary layer disturbances. The numerical simulation has been used to study in more detail the process of receptivity and disturbance development in the boundary layer as a function of the energy input. The numerical simulation showed that the Tollmien–Schlichting wave is unambiguously detected starting at a distance of approximately 50δ from the discharge. It is found numerically that, for a small energy input, the most rapidly growing oblique waves are those of the first mode, which agrees with the estimate according to the linear stability theory. As the energy input increases, a second type of disturbance, reminiscent of a longitudinal structure, starts to be manifested in the mass flow pulsations. In the experiment, with a higher energy supply value than in the calculation, it was possible to record only the second type of disturbances, while the maximum amplitude of mass flow pulsations reaches 30%.