Active Control Of Flow-Induced Cavity Oscillations With Piezoelectric Bimorphs

Flow-induced cavity oscillations are common in the aviation field. They can generate huge noises, increase the drag force, damage the structure of aircrafts, and influence the characteristics of store separation. Until now, there have been many methods to suppress the oscillations, among which the active control method based on piezoelectric actuators is one of the promising methods due to the characteristics of the actuators. They are compact, easy to manufacture, consume little amounts of energy and have good control performance to the flows. In this paper, an active control method with piezoelectric bimorphs is presented for open cavity flows.(1) The main formulas and common models describing flow dynamics are presented first. Flow fields are different in cavities with different L/D ratios. The classification and specific characteristics of open cavity flow, closed cavity flow and transitional cavity flow are introduced. The first three Rossiter frequencies of the studied cavity are calculated with the modified Rossiter equation. The flow field and pressure distribution of the flows within and around open cavities, closed cavities and transitional cavities are studied with FEM software. Fluid-structure interaction model is setup to analyze the suppression of flow-induced cavity oscillations with an active structure. The results show that with certain disturbances in the leading edge of the cavity, the oscillations within the cavity are suppressed.(2) The characteristics of piezoelectric ceramics are introduced and the coefficient matrixes of PZT-5H are listed. By analyzing the piezoelectric actuators, the structure of piezoelectric bimorph and the loading method are determined. By modeling the piezoelectric bimorph, its DC response and natural frequency are derived. The relationship of its performance with its dimensions is analyzed. Based on its natural frequency and DC response, the structure of the piezoelectric bimorph is optimized. The quasi-static response and natural frequency of the piezoelectric bimorph are analyzed with FEM software, which validates the theoretical models. Finally, the piezoelectric bimorphs are designed and fabricated.(3) Finally, experiments are conducted to test the characteristics of the piezoelectric bimorphs. The displacement responses of the piezoelectric bimorphs to step signals are measured. To get a better understanding of the quasi-static response, hysteresis loop of quasi-static displacement to voltage is obtained. The characteristics of the hysteresis loop with different voltage ranges are analyzed, as well as its repeatability. The frequency spectrums of the piezoelectric bimorphs under the excitation of sinusoidal signals with amplitude of200V are obtained. From the spectrums, natural frequencies and harmonic responses in resonance frequencies are gained. Experimental results have a discrepancy with the theoretical models, which is analyzed in this paper. Active vibration damping experiments with piezoelectric bimorphs based on PID controller and fuzzy PD controller are conducted respectively. Results show that vibration is damped effectively.