Crossflow instabilities under plasma actuation: Design, commissioning and preliminary results of a new experimental facility

Plasma-based flow control poses a simple and robust technique for transition delay on swept wings. However, a clear understanding of how plasma actuators affect crossflow instabilities is necessary to develop and mature crossflow control based on plasma actuators. In this paper, the design of a new swept wing model optimised for the study of crossflow receptivity and stability under plasma actuator is described in detail. First, a 2D wing shape is designed, to match the nearing leading edge pressure distribution of a reference high-Reynolds number swept wing model (M3J) which has been used extensively in past investigations. The aerodynamic performance of this new shape is investigated using CFD simulations and the results show a good agreement for the pressure coefficient. In manufacturing design, the wing model features provisions to accept plasma actuators, such as non-conductive material as well as an appropriately designed recess for the actuator assembly. The new model in conjunction with a recently refurbished low turbulence windtunnel facility are characterized in a preliminary experiment. The uniformity and quality of the flow is identified using pressure measurements and the results confirm the new model achieved near-invariant spanwise conditions until 40% of the chord. Infrared thermography is used to capture the surface footprint of stationary primary crossflow vortices. Clear formations of stationary vortices created by discrete roughness are captured and no visible transition is observed. Finally, the effects of plasma actuation on crossflow instabilities are inspected by Infrared Thermography and PIV scanning. The results validate the prediction of Linear Stability Theory with respect to the most unstable stationary mode and traveling mode. The appearance of secondary crossflow instabilities is observed at relatively upstream chord locations even without transition detected. The outcome positively confirms the ability of this new model to reproduce receptivity and initial growth of crossflow instabilities of the reference model (M3J) under plasma actuation.