SwirlProp: A tool for sound propagation and attenuation in swirling flows

Abstract

The current trends for next generation turbofan engines are towards shorter nacelles and increased distances between the fan and the outlet guide vanes. This leads to an overall reduction in lined surface areas as well as an increase in the relative importance of the interstage liner, which is the liner placed between the rotor blades and the stator vanes. So far most of the efforts have been on liners for intakes and bypass ducts. The interstage is different in that the liner is subject to a mean flow with a strong swirl component and shear. The SwirlProp code was developed to contribute to understanding and predicting the effect of the swirl on liner attenuation. The code is based on the linearized Euler equations together with the Ingard–Myers boundary condition. An eigenvalue problem is formulated and discretized using a finite difference method. The code is exhaustively compared against predicted values obtained by other methods for uniform, sheared and swirling mean flows and hard-walled and lined ducts. A cross-validation between SwirlProp and an in-house code from Rolls-Royce was carried out for a more realistic case. Also, details on the implementation of the boundary condition are proposed and details are presented.