The characteristics of a typical flow control actuator design are discussed. The device is based on a resonating structure that interacts with a closed volume of fluid to create a concentrated jet through an exit orifice. The resulting unsteady flow through the orifice introduces viscous effects that are characterized by the Stokes parameter based on the orifice diameter. An optimum operating Stokes parameter is then computed by matching this viscous dominated solution to an ideal, inviscid result. The actuator is modeled with a system of coupled equations that describe its fluid-structural behavior.