Study On The Mechanism And Effect Of Shallow Cavity Noise And Resonance Caused By Wake

Aerodynamic noise is one of the main noises caused by the running of the transport like automobile and locomotive. As the main forms of the aerodynamic, The mechanism research of the cavity noise and wake noise has been paid more and more attention. The high speed air flow through the shallow chamber will produce a strong aerodynamic noise around the shallow cavity when it meets a certain aerodynamic acoustic condition. Periodic vortex shedding is generated behind the barrier while the high speed air flow passing through it, which leads to the generation of the aerodynamic noise. Some mechanical structure would possibly failure when the SPL of aerodynamic noise is high. In this paper, the mechanism and characteristics of shallow cavity noise and flow noise are studied based on computational fluid dynamics and acoustic analogy method, and seek ways to reduce the response of mechanical structure under noise load. The research contents and conclusions are as follows:(1) The process of air’s self-oscillation while the air flow over the shallow cavity was simulated using large eddy simulation. Based on this result, the spectrum characteristic and the distribution of the noise caused by air flow was analyzed by acoustic analogy method. The self-oscillation of the cavity is formed due to the periodic generate, growth and disappearance of the vertex. The frequency of vertex, equals to the frequency of self-oscillation in the flow field, is the fundamental frequency of the noise around the cavity. Based on this, Effect of air velocity and dimension of cavity on flow and noise field were studied. The frequency and SPL of the noise would increase with the increase of the inlet velocity. And it can also increase the main frequency of the noise. The noise and the flow were chaos while the length of the cavity are too long or the depth of the cavity are too shallow.(2) Acoustic finite element and numerical simulation method are used to analyze the acoustic mode of the cavity including plate, flow field distribution and the noise characteristics when air flow over the plate. The distribution of the flow field behind the wake is caused by periodically vortex shedding on the tail of plate. The noise caused by wake contains the frequency of wake flow field and the 5th acoustic mode frequency. in the frequency domain(3) Based on the study of two typical aerodynamic noise mechanisms, the time-domain signal of noise excitation was simulated by Monte-Carlo method aim at the characteristic of white noise signal source. The finite element model of the titanium alloy plate and the viscoelastic constrained titanium alloy plate were built. The vibration response of the plates under heavy noise excitation was analyzed by FEM method combined with its finite element model. The dynamic response of two plates were contracted. Furthermore, the damping performance of the viscoelastic constrained treatment was estimated. The results showed that the viscoelastic constrained treatment could change the frequency of titanium alloy plate and reduce the displacement and stress caused by noise excitation.