Reliability of time-linearized flutter predictions near the surge line

Abstract

In the context of the flutter analysis of a modern transonic axial compressor two different CFD codes have been compared: based on the same three-dimensional steady solution, the timelinearized Navier-Stokes flow solver TRACE of the German Aerospace Center DLR as well as the industrial time-linearized Euler code Lin3D (developed at MTU Aero Engines) were used to assess the global aerodynamic damping of the rotor. No major differences could be observed for operating points on the working line. However, several operating points (at different shaft speeds) near the surge line were susceptible to flutter according to TRACE whereas Lin3D predicted aeroelastic stability. The capturing of shock movements as well as the modeling of the tip gap is identified to be responsible for these discrepancies. In this paper the sources of the different local excitation and damping mechanisms are highlighted. Moreover influence coefficient representations for the different approaches are compared in the complex plane.