FUNDAMENTAL STUDY AND DEVELOPMENT OF TUNED ACTIVE FLOW CONTROL ACTUATORS

A novel, multi-level, flow-control actuator was developed using piezoceramic materials. Several actuators were fabricated in various shapes and sizes to produce a variety of effects for flow control applications. The actuators were studied in a quiescent-air bench test to understand the vibrations produced by various actuator shapes. The actuator flow-control effect was studied experimentally with flat-plate and cavity configurations, and was studied numerically using moving boundary conditions and dynamic meshing. The disturbances produced by the actuator couple with the cavity flow field producing increased cavity tones, increased vorticity, and sustainment of large-scale vorticity downstream of the cavity. The combined actuation result, from perturbations upstream of the cavity to increased vorticity downstream of the cavity, is the novel multi-level actuator developed and studied in this research.

The largest actuator was experimentally tested in boundary layers with free-stream Mach numbers from 0.1 to 0.5 and Reynolds numbers, based on momentum thickness, from approximately 800 to 3600. Actuator effects were measured using high-frequency-response pressure instrumentation in the floor downstream of the actuator. The actuator produced disturbances with amplitudes at least 30 dB above the noise floor and frequencies nine-times the actuator driving frequency. The disturbances created by the actuator coupled with the boundary layer flow and were observable up to 62 kHz. A time-dependent effect from changing actuation frequency was observed on the stability of the flow.

A compact, multi-actuator pack was designed to study multi-level flow control using experimental tests of a two-dimensional cavity flow at Mach numbers of 0.1, 0.2, and 0.3. Actuator operation did not produce amplified cavity oscillations at all Rossiter tones in the experiments. However, significant flow coupling occurred when the actuator driving frequency matched a Rossiter tone and a fundamental cavity acoustic tone. The cavity amplifications were stronger when the distance between the actuator and the cavity leading edge was increased. The numerical simulations showed that the actuator produced cavity flow amplifications at the first Rossiter tone about 8 dB higher amplitude than without actuation.