An Approach to Predict Ducted Fan Noise by Boundary Integral Equation Method

Abstract

In this paper a new approach to predict ducted fan noise by boundary integral equation method (BIEM) is presented. The fundamentals of boundary value problem (BVP) for ducted fan noise is referred to TBIEM3D which is an efficient program developed by NASA Langley Center to predict ducted fan noise and has been used as powerful tool in liner optimization study [1] . At present a direct boundary element method is used to solve the same boundary value problem, herewith the acoustic pressure and normal particle velocity distributed on the duct surface are directly used as unknown variables which is different from the unknown layer densities in TBIEM3D [2] of indirect boundary element that are related to the jumps of acoustic pressure and its radial derivative across the duct wall. In this paper the boundary value problems are composed of two parts, one is for duct interior, another one is for duct outer area. The two boundary value problems are related by the continuing condition on the duct inlet and outlet surfaces. The scattering of sound by a finite length cylindrical duct with locally reacting liner on its interior and with inflow is considered. The thickness of duct wall is considered to avoid the singularity at the duct leading edge in infinitesimally thin duct model. The numerical results agree well with the results of TBIEM3D [2] and other boundary integral method [3] .