| To extend fluid-based flow control techniques that have been demonstrated at low subsonic speeds, it is necessary to develop actuators having sufficient momentum to manipulate high speed flows. Two fluidic actuation approaches are developed where the control jet may reach supersonic velocities. The first actuator is a compressible synthetic (zero net mass flux) jet. This is an extension of previous work on synthetic jets with an increase in driver power yielding substantial pressurization of the cavity such that the flow is compressible. The effects of variation of the orifice diameter, actuation frequency, and compression ratio are investigated, and the unique effects of operation in the compressible regime on the cavity pressure are documented. The structure of the jet is analyzed using particle image velocimetry and Schlieren flow visualization, indicating that the jet flow is dominated by a starting jet rather than the starting vortex typical of low-speed synthetic jets. A simple, quasi-static numerical model of the cylinder pressure is developed with generally good agreement with the experimental results. Finally, an experiment is described with self-actuated valves mounted into the cylinder head which effectively overcome some of the limitations inherent to compressible operation.;The second actuation concept is the combustion-driven jet actuator, which consists of a small-scale (nominally 1 cc) combustion chamber which is filled with premixed fuel and oxidizer. The mixture is ignited using an integrated spark gap, creating a momentary high pressure burst within the combustor that drives a high-speed jet from an exhaust orifice. The combustion process is complete within several milliseconds and the cycle resumes when fresh reactants are fed into the chamber and displaces the remaining combustion products. The actuator performance is characterized using dynamic measurements of the combustor pressure along with flow visualization, thrust measurements, and flame photography. The effects of variation in fuel type and mixture ratio, exhaust orifice diameter, chamber aspect ratio, chamber volume, fuel/air flow rate, ignition frequency, and ignition energy are documented. Finally, a proof-of-concept experiment demonstrates the utility of the combustion-driven jet actuators at low-speed for reattachment of a separated flow over an airfoil at high angles of attack. |
