Low Dimensional Modeling of Zero-Net Mass-Flux Actuators

The flow field generated by a zero-net mass-flux (ZNMF) actuator is investigated via both numerical simulations and experiments to augment the current understanding of the flow physics of the orifice. The results aid in improving the accuracy of low dimensional lumped element ZNMF models suitable for design. Dimensional analysis yields a number of key parameters that govern the characteristics of this flow. Among them for a sharp rectangular slot or circular orifice are the Reynolds number, the dimensionless stroke length, and the orifice height-to-diameter ratio. Variation of these parameters shows that the flow field differs appreciably from the exact linear solution of pipe flow driven by an oscillatory pressure gradient. In particular, depending on the stroke length and the orifice geometry, the pressure drop in the orifice may be dominated by nonlinear “minor” losses due to entrance/exit effects, or linear “major” losses associated with the presence of a nominally fully-developed region in the central region of the orifice/slot.