Active flow control (AFC) has the potential to improve the efficiency of systems that involve both internal and external fluid flow. The primary driver in AFC is the expectation that the control will result in significant performance benefits at the system level with all trade-offs factored in. Successful application to aircraft systems can produce lighter, stealthier, agile aircraft with increased range, payload and a muffled acoustic signature. The design of an AFC system requires knowledge of flow phenomena and the selection of appropriate actuators, sensors and a control algorithm. The present overview focuses on actuators. Examples of flow and noise control presented here are restricted to open-loop systems. Various aspects of actuator utilization include actuator output characterization, exploiting resonances (plenum, structural or aeroacoustic) to enhance actuator amplitude and the different modes of actuation. A brief description of a high-bandwidth actuator is also provided, followed by a variety of application examples including edgetone suppression, cavity noise suppression, impingement noise suppression and jet mixing enhancement. The review concludes with a description of the successful application of AFC to the exhaust plume from an aircraft engine (JT8D).
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