| As an important part of fluid pipeline,variable cross-section pipeline is widely used in daily life,construction engineering and military equipment.However,due to the different inlet and outlet area of the variable cross-section pipeline,this brings serious noise problems.It will not only cause harm to health,but also have a negative impact on industrial production,civilian life and military security.Therefore,it is necessary to study the noise generation mechanism and the law of noise variation.Firstly,in this paper,3-D numerical models are established for three kinds of variable-section pipelines with different diametral ratios under national standard size,and its geometric model is meshed.Based on Fluent software,the flow field and sound field in variable section pipeline is researched by LES method and FW-H equation.The accuracy of the numerical simulation method is verified by comparing the numerical results with the experimental results.Secondly,the distributions of the pressure field and velocity field in the variable section pipeline under different working conditions are studied.The results of average cross section pressure and average cross section velocity are obtained under the different conditions such as variable diameter angle(?)inlet velocity(?)and pipe-diameter ratio(?)change.In addition,the evolution law of sound source characteristics in a variable section pipeline is investigated.It can be seen from the results that the flow noise is mainly concentrated at the variable diameter angle.In addition,based on the simulation results of flow field,the acoustic field of a variable section pipeline is studied.The results show that the flow noise is mainly low frequency noise that below 200Hz.At rated flow velocity(v=3m/s),the Sound pressure level(SPL)decreases with the pipe-diameter ratio(?)increases.Under the different variable diameter angle conditions,the change rule of SPL values at ?=0.5,?=0.6 and ?=0.8 cases are basically the same.The SPL value of flow noise increases with the increase of the variable diameter angle.In addition,a criterion relation to predict the flow noise of variable section pipeline is presented.The accuracy was checked and the variance was 0.99.The results show the accuracy of the prediction model.Finally,the fluid-solid coupling characteristics of the variable section pipeline under different working conditions are studied.The first order modal vibration frequency,second order modal vibration frequency and the average exciting force in the time-frequency domain are obtained.Besides,the distribution law of sound pressure of the vibration noise and the SPL of fluid-solid coupling case are obtained.Based on the simulation results of flow and vibration noise,the results of fluid-solid coupled noise and non-fluid-solid coupled noise are compared.The results show that the SPL values of the fluid-solid coupling case are greater than the SPL values of the non-fluid-solid coupling case,and the difference value between them increases with the increase of the flow velocity.When v is 1m/s,2m/s,and 3m/s,in the ?=0.5 case,the difference value is 0.50dB,2.12dB,and 6.99dB,respectively.However,in ?=0.6 and ?=0.8 cases,the SPL difference values between fluid-solid coupled case and non-fluid-solid case under the same velocity conditions are 0.28db,0.82db,2.42db and 0.20db,0.42db and 0.88db,respectively.In this paper,the flow noise and fluid-solid coupling characteristics of variable-section pipeline under different pipe-diameter ratio,inlet velocity and variable diameter angle are studied.The distribution characteristics of the flow field in the variable section pipeline are analyzed,and the mechanism and evolution of flow noise are revealed.Futhermore,the effects of vibration characteristics on fluid-solid coupled noise are described.The results of this paper lay a theoretical foundation for the structural optimization and noise control of variable section fluid pipeline. |
PDF Full Text Request