Structure Design And Performance Analysis Of Silencing Device For Water Piping System

Installation of silencing device is an effective way to control hydrodynamic noise in water piping system. Nowadays, the finite element method (FEM) is the most commonly used method to predict the acoustic performance of silencing devices. FEM is a frequency-domain method and its advantages are the fast computation and convenient employment. However,FEM cannot include the effects of water viscosity and complex internal flow on the sound propagation and attenuation in the silencing devices. The time-domain method, solving the propagation process of sound wave in time-domain, may overcome these shortages of FEM.This paper is mainly about applying the time-domain impulse method to compute and analyze the acoustic performance of water silencing devices.Based on the straight duct model, the selecting criterion of mesh size and time step is explored when using the time-domain impulse method to analyze the cases with water flow,and reasonable mesh size and time step is provided. Taking the case of straight-through perforated pipe silencer without flow as an example, the predicted result of time-domain impulse method is verified by FEM for acoustic attenuation performance predicting of water-filled silencing devices. Considering the advantages of time-domain method in coupling the effects of water viscosity and complex flow in acoustic performance predicting of silencing devices, the time-domain impulse method is applied to investigate the effects of flow velocity, diameter and porosity of orifices on the sound attenuation behaviors of the straight-through perforated pipe silencer, cross-flow perforated pipe silencer and partially plugged straight-through perforated pipe silencer respectively. The results show that sound attenuation behavior of perforated silencers is improved when the flow velocity rises,especially in mid to high frequency range. When the porosity remains the same, the orifice diameter has little effect on acoustic performance of perforated pipe silencers. And the acoustic performance of perforated pipe silencers is tightly related to the porosity of perforated pipe, especially for the cross-flow and partially plugged straight-through perforated pipe silencers. Later, a folded straight-through perforated pipe silencer is designed based on the above analysis, and the pass-through frequency is eliminated by directing the layout of orifices in the fold reasonably. Also the flow effect is utilized to improve the sound attenuation performance in mid to high frequency range. By comparing the pressure loss results of inlet and outlet faces of perforated pipe silencers with different flow conditions,straight-through perforated pipe structures rather than cross-flow perforated components are suggested to be used when designing water silencing device to ensure the silencing devices have good fluid dynamic performance.Then, the time-domain impulse method is used to examine the flow effect on acoustic performance of resonators and the predicted results show that the transmission loss of resonant frequency decreases due to the water flow, while the resonant frequency is not affected. Two types of tunable resonators are designed,and the FEM is used to investigate the frequency adjustment characteristic. The predicted results show that the resonant frequencies are in cubic curve relationship with displacements of adjustment cylinder.At last,the acoustic performance of water silencing devices in high sound pressure level and high background pressure is investigated separately based on the time-domain impulse method. The predicted results show that the high sound pressure level has little effect on the acoustic performance of both straight-through perforated pipe silencer and resonator. The high background pressure level shifts the transmission loss curve slightly to higher frequencies,which has little effect on the acoustic performance of straight-through perforated pipe silencer.However, for the resonant silencer, this effect should be considered.