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High Bandwidth Actuator Non-linear Acoustic Waves in Resonators
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High Bandwidth Actuator
Computer controlled high bandwidth Powered Resonance Tube actuator (PRT) system used in the present study.
Time-averaged near field sound pressure levels at actuation frequency in the YZ plane. A high bandwidth powered resonance tube actuator that is potentially useful in noise and flow control applications was developed and characterized. Such high bandwidth actuators are required if Active Flow Control (AFC) is to be used at various locations on aircraft over a range of flight speeds. The first part of our study consisted of selecting a candidate actuator and then devising a method to extend its bandwidth. The actuator selected for bandwidth enhancement was the Powered Resonance Tube (PRT) actuator. This actuator consists of a high speed jet aimed at the open end of a cylindrical tube which is closed at the other end by an air-tight piston. The device is capable of producing high frequency and high amplitude oscillations. Our approach was to vary the depth of the resonance tube that determines the frequency produced by the device. A look-up table approach that relied on an extensive experimental data base was used in conjunction with a computer controlled piston to obtain the desired results based on user prescribed frequencies. Then, a closed loop feedback controller was implemented to enhance the actuator and reduce the error. Our actuator could produce frequencies ranging from 1600 to 15,000 Hz at amplitudes as high as 160 dB. In the second part of our study we provided a detailed characterization of the unsteady pressures in the nearfield of the actuator. Detailed measurements revealed that the device produced propagating fluctuations that were biased towards the upstream direction (relative to the supply jet). Despite the symmetry of the relative phase in axial plane the pressure fluctuations exhibited strong anisotropy. No such bias was observed in the transverse plane.
Effectiveness of various control strategies in obtaining a prescribed frequency. The comparison includes the input frequency, Quarter Wave Length estimation (QWL), Look Up Table method (LUT) and Single Input Single Output (SISO) (stage 1) Feed Back controller (FB) (using QWL as initial estimator)
Picture of the device in the anechoic chamber |
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