细长圆柱构件表面扰流降噪机理的研究

Noise reduction mechanism of the surface vortex generator set on a slender cylinder

通过大涡模拟结合声比拟的方法,研究长方形截面扰流条对光滑圆柱气动噪声的影响。研究中光滑圆柱直径D=0.016 m,设置了四种扰流条圆柱工况,即扰流条高度直径比H/D分别为1/8,1/4,3/8和1/2。无扰流措施时,圆柱噪声源位于边界层分离点附近。在圆柱两侧设置扰流措施后,圆柱附近流域具有低湍流特性,大尺度涡结构的展向相关性被破坏,使圆柱表面压力脉动存在较大相位差;扰流条上游出现滞留涡结构,抑制了上游分离剪切层增长,降低了圆柱上下表面压力脉动。两机制共同作用抑制了圆柱绕流噪声。当扰流条高度直径比H/D=3/8时,降噪效果最好,在主要辐射方向上,音调噪声下降了18.17 dB。

Usinglarge eddy simulation and acoustic analogy,the influence of the rectangular strip used as a vortex generator on the aerodynamic noise of a circular cylinder was studied.The diameter of the cylinder was 0.016 m in the research.Four kinds of cylinders with strips were analysed,of which the ratios of the strip height to the cylinder diameter were respectively 1/8,1/4,3/8 and 1/2.Without strips,the noise source of the cylinder was in the vicinity of its boundary layer separation point.After setting strips,it is found that the flow field around the cylinder is of low-turbulent characteristics,and the transverse correlation of the large scale vortex structure is destroyed,resulting in the large phase difference of pressure fluctuation on the surface of the cylinder.The trapped vortex structure appears in the upstream of strip,which inhibits the growth of separated shear layer and reduces pressure fluctuation on the upper and lower surfaces of the cylinder.The couple action of the two mechanisms suppresses aerodynamic noise around the cylinder.When the height diameter ratio of strip is 3/8,the noise reduction measure performs best and in the main radiation direction,the tonal noise is reduced by 18.17 dB.