Investigation of Transitional SBLIs using Plasma Based Disturbances*

Plasma-based disturbances are used to generate second-mode instability wave

packets in a Mach 5 laminar boundary layer (BL) and in the presence of a

cylinder induced shock boundary layer interaction (SBLI). The experiments

are performed in an indraft wind tunnel at fixed Re_u = 2.7 x 10⁶ m^-1. Local-

ized Arc Filament Plasma Actuators (LAFPAs) are first characterized in a

vacuum chamber to determine the effect of ambient pressure on the plasma

regime and the electrical energy deposition. Linear Stability Theory (LST)

predicts that second-mode frequency content varies between 20 kHz to 30 kHz

over the length of the wind tunnel test section. Synchronized wall pressure

(PCB) measurements and phase-locked Z-type schlieren imaging are used to

characterize the instability waves created by actuation. Frequency and wave-

length of the observed second mode wave packets match well with estimates

from LST. In the presence of an SBLI, a decrease in the frequency and an

increase in the associated wavelength is observed. Future work will address

the introduction of stronger forcing to study non-linear wave packets as well

as extend the scope of measurements and data analysis techniques relevant

to transitional SBLIs.