Low-Speed Control Mechanism of High-Frequency Tone Generator for Nose Bay Cavity Flow

Abstract

In this paper, the low-speed control mechanism of a high-frequency tone generator (HFTG) on the nose bay cavity flow is investigated through wind tunnel experiments and numerical simulations jointly. A novel cavity model considering the geometry of the nose bay is proposed, whose prominent features are the arc-shaped leading edge and unequal height between the fore/aft wall, influencing the evolution of the shear layer over the cavity mouth. Only broadband noise is observed in the power spectral of fluctuating wall pressure, indicating that the weak feedback mode dominates the cavity oscillation. Based on the overall sound pressure level, the desirable suppression effect of HFTG is apparent on the low-speed cavity flow. The high-frequency excitement through shedding vortex is observed in the spectrum. The high-fidelity numerical simulations through improved delayed detached eddy simulation, which correspond reasonably well with the experimental results, help to reveal the underlying control mechanism. The introduction of HFTG elevates the shear layer, promoting the fluid mass downstream rather than into the cavity, which thus weakens the impact of the shear layer on the aft cavity wall. The interaction between the shedding vortex induced by the HFTG and the shear layer plays a crucial role in the control mechanism. Overall, the HFTG provides an ideal passive control strategy for the nose bay cavity in the low-speed flow. Cavity resonance is extensively utilized in aerospace engineering. During takeoff and landing, when the aircraft doors open, cavity resonance occurs. The noise generated from this phenomenon constitutes a significant portion of the overall noise produced by aircraft landing gear and can lead to fatigue or even structural damage within the landing gear bay. Consequently, numerous researchers have implemented various techniques to suppress cavity resonance. Given that flow velocities are relatively low during these phases of flight, and most control strategies are predicated on high-speed airflow over rectangular cavities, existing approaches may not adequately represent practical flow conditions within the landing gear bay. This study focuses on a cavity model that reflects the real geometry of a landing gear bay while employing a high-frequency tone generator to suppress cavity resonance at low speed. This investigation not only elucidates the control mechanisms of the high-frequency tone generator under low-speed conditions but also establishes a foundation for further research into noise suppression strategies for landing gear bay.