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Dielectric barrier discharge (DBD) plasma actuators can generate a wall jetwithout moving parts by interacting with ionized and neutral molecules in anelectric field. The coupling between electrohydrodynamic (EHD), turbulence,inertial and viscous effects in the flow boundary layer remains poorlyunderstood and requires investigation. We present an experimental investigationof momentum injection by DBD actuators into the free stream flow with Re =35,000 and 75,000 in co-flow and counter-flow scenarios over a range of VAC =12 kV - 19.5 kV peak-to-peak at a frequency of 2 kHz. In the co-flowconfiguration, the DBD actuator injects momentum into the boundary layer. Inco-flow, the momentum injection results in the thinning boundary layer, whilein the counter-flow configuration, flow separation can occur. For the testedcondition, a separation bubble is observed at Re = 35,000. The momentumdisplacement in the counter-flow configuration is six times greater than theEHD jet momentum in a quiescent environment. Both co-flow and counter-flowmomentum injections show diminishing effects with increasing externalvelocities. This work highlights that the resulting flow pattern is not asimple superposition of the EHD jet and the free stream but is determined bythe coupling of inertial, viscous, and Coulombic effects in the EHD-driven walljet and the external flow. The velocity profiles and momentum measurementspresented here can be used to validate numerical models and inform the designof DBD actuators for active flow control.

Dielectric Barrier Discharge Actuators: Experimental and Numerical Study of Momentum Injection into Co-flow and Counter-flow Freestream