Research On Control Of Aerodynamic Noise Of Circular Cylinder Using Bio-inspired Method

The aerodynamic noise of equipments which composed of circular cylinder isextremely outstanding in high speed, different methods and approaches for circular cylinderself noise control have been used and constantly improved in the field of aeroacoustics inrecent years. This article is mainly to explore the noise reduction performance of sawtoothstructures of owl wing’s leading edge. Combining with the previous research results of ourresearch group, through the combined method of wind tunnel tests and numerical simulation,we studied the aerodynamic noise reduction performance of bio-inspired structures on thesurface of circular cylinder, revealed the mechanisms of the noise reduction, and asloexplored the noise reduction performance of bio-inspired structures on the high-speedpantograph model.We choosed the long-eared owl, that can soundless flight, as the research object. We firsttested the effects of the sawtooth structures of owl wing’s leading edge on its flapping flightnoise. After removing the sawtooth structures, the long-eared owl’s flapping flight noise inthe low frequency band below200Hz had significantly increased, at frequencies above200Hz had no obvious change. The results showed that the sawtooth structures have someinfluence on the long-eared owl’s flapping flight noise, which can effectively reduce the lowfrequency noise of long-eared owl’s flapping flight noise. Based on the leading edgesawtooth structures of owl wing’s leading edge and previous research results in our researchgroup, three kinds of shapes that serrated structures, V-ring surface and wavy surface weredesigned on the surface of circular cylinder.The aerodynamic noise characteristics of the circular cylinder with bio-inspiredstructures were studied by the Large Eddy Simulation（LES）and the Ffowcs Williams andHawkings （FW-H） equation. At free stream speed of14m/s. The Reynolds number is5.6×10~4based on the cylinder diameter D of60mm. The aerodynamic noise of the cylinderwith serrated structures was reduced by8.2dB compared to the smooth cylinder. The vortexmotions in the wake of the cylinder with serrated structures are alleviated and thefluctuations of the wake flow are also reduced. Serrated structures are capable of reducing the frequency of the vortex shedding and controlling the fluctuating lift force induced byunstable vortices acting on the cylinder surface. At free stream speed of42m/s. TheReynolds number is1.62×10~5based on the cylinder diameter D of58mm. The aerodynamicnoise of the V-ring surface cylinder and the wavy surface cylinder were reduced by4.1dBand6.7dB, respectively, compared to the smooth cylinder. The sound pressure of V-ringsurface cylinder model and the wavy surface cylinder model were reduced when the liftfluctuation becomes lower. The V-ring surface and the wavy surface are capable of reducingthe frequency of the vortex shedding and controlling the fluctuating lift force induced byunstable vortices acting on the cylinder surface.We processed out smooth cylinder model、cylinder with bionic serrated structures、V-ring surface cylinder model and wavy surface cylinder model. We tested the fluctuatingpressure of the surface of these models by pulsating pressure sensors in FD-09wind tunnelof China Academy of Aerospace Aerodynamics（CAAA）at wind speed of14、28、42and56m/s. At wind speed of14m/s, the fluctuating pressure on the test points of the cylinderwith serrated structures was significant decreased compare with the smooth cylinder model,the overall fluctuating pressure on the No.7test point of the cylinder with serrated structureswas decreased by9.4dB compare with the smooth cylinder model. At wind speed of42m/s,the overall fluctuating pressure on the test points of the V-ring surface cylinder and wavysurface cylinder were significant decreased compare with the smooth cylinder model.We processed out a single arm high-speed pantograph model and explored theapplication of these bionic flow control methods on the noise reduction of high-speedpantograph. Using microphone arrays and beamforming method, we tested the aerodynamicnoise of this pantograph model in FD-09wind tunnel of China Academy of AerospaceAerodynamics（CAAA） at wind speed of56m/s（200km/h）. The test results showed thatin the1/3octave center frequency800Hz, the head of the pantograph model is the majoraerodynamic noise source. According to the test results, we designed periodic holes andserrated structures on the head of the pantograph model. The flow field, the distribution ofdipole noise source at the surface of pantograph model, the sound pressure of the sound fieldand the sound pressure level at the noise receivers were numerically predicted by thecombination of incompressible fluid flow analysis using the finite element method （FEM）and acoustic analysis using the boundary element method （BEM） at free stream speed of83.3m/s（300km/h）. The analysis results indicated that the main aerodynamic noise sourcesof this pantograph model are the head, knee, arms around knee and foot region; theaerodynamic noise of this type of pantograph model was mainly the low-frequency andmid-frequency noises below1000Hz. The sound pressure levels of the modified pantograph model were respectively reduced by0.1、3.0、3.3、3.8and1.9dB, compared to the originalpantograph model.