Optimal interstage liner design: A parametric study

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 focus of this paper is on the effect of swirling flow on optimal liner attenuation in the interstage region. A broadband source downstream at the Outlet Guide Vanes (OGV) consisting of all propagating modes with equal power in each mode is used. Optimum impedance plots are generated for approach and take-off mean flow conditions. The effect of swirl on liner optimum resistance and reactance and optimum insertion loss is observed for a frequency range characteristic of real turbofan engines.