Control of flow-induced noise by structural compliance

Flow-induced noise generation by external flow devices operating at low to intermediate Reynolds number is an overriding concern associated with their design and operations. Over the years, a number of passive noise control methods have been proposed and developed, however, their implementation is limited by the associated aerodynamic performance degradation. In this regard, we propose a novel method of utilizing the structural compliance for noise reduction of external flow devices with minimum or no sacrifice in the overall aerodynamic characteristics. The key idea is to design a structurally compliant elastic surface that vibrates in structural resonance fluid loading for absorbing the energy from the flow to sustain its vibration. We have implemented the method for the two unique noise generation problems: a deep cavity flow driven by flow acoustic resonance and a symmetric airfoil exhibiting feedback phenomenon. The effectiveness of the compliant surface in tonal noise reduction for both test cases is analyzed numerically using high-fidelity direct aeroacoustic simulations. Despite the prevalence of different flow regimes, the application of compliant surface provides a significant overall noise reduction for each case up to different extents. Design strategy of the compliant surface along with its limitations are also discussed.