Improved Finite Element Modeling of the Turbofan Engine Inlet Radiation Problem

The finite element model of the acoustic radiated field from a turbofan engine inlet in the presence of a mean flow was improved. The finite element mesh was altered in search of an improved solution. The mean flow problem was reformulated with new boundary conditions to make it theoretically rigorous. A finite element duct eigenvalue problem was solved on the fan face modeled as a combination of positive and negative propagating duct eigenfunctions. The resulting modal matrix was used to implement a source boundary condition on the fan face. Acoustic pressure was evaluated in the post processing of the solution. A study of the effect of the geometric position of the transition circle between conventional finite elements and wave enveloped showed that the transition can be made nearer to the inlet than previously assumed.