快速声散射方法在变截面管道中的应用

Numerical Simulation of Sound Propagation from Varying Cross-section Ducts by Fast Scattering Method

快速声散射方法(FSM)是一种基于无流动Helmholtz方程边值问题的声散射预测工具,具有快速、灵活的特点。以航空发动机消声短舱的声学设计为背景,用该方法对变截面管道声传播特性进行数值模拟研究,用直接边界元方法(DBEM)进行数值求解,避免了求解管口反射系数,有效地提高了计算速度。数值研究了刚性壁面和不同位置壁面声衬组合对变截面圆环管道形状声传播的影响,并分析了管道厚度对散射声场的影响,数值结果与声类比方法结果进行了相互验证。最后,还对一种真实转子声源进行了管道声散射的数值研究,结果表明本方法在航空发动机声学设计中具有工程应用价值。

The fast scattering method（FSM） is a fast and flexible way to predict the sound propagation and radiation from a ducted-fan by solving the Helmholtz equation with specific boundary conditions and no flow.For the design of the ducted-fan acoustic liner,the method is applied to the simulation of sound propagation in a varying cross-section duct.The time harmonic and linearized acoustic equation is employed in the present study,and the flow field is assumed to be a uniform flow from the far field.By introducing a 3D Lorentz transformation,the acoustic scattering problem with flow is transformed to a problem of no flow described by the exterior Helmholtz equation with specific boundary conditions.The direct boundary element method（DBEM） is used for solving the homogeneous linear Helmholtz equation,which can avoid solving the reflection coefficients at the inlet and outlet duct surfaces and thus save much computational time.In addition,the effects of different impedances of the liner in a varying cross-section ducted-fan on sound propagation are also investigated.A comparison of numerical results by using the fast scattering method and by using the acoustic analogy method is also performed.Finally,the method is applied to an examination of the noise reduction by the duct liner in a real high-speed rotor.The results demonstrate that the fast scattering method is suitable for application to the design of a duct liner in aero engines.