Influence of acoustic reflections on flutter stability of an embedded blade row

The use of blisks is becoming more common in modern aero-engine designs. Such structures have very low mechanical damping and hence are more susceptible to flutter instability. Therefore, accurate prediction of blade aerodynamic damping in a multi-row environment becomes vital. The aim of this work is to understand the effects of acoustic reflections on flutter stability of an embedded rotor in a multi-stage compressor. To achieve this goal, flutter analysis of an embedded rotor blade in a high pressure compressor is undertaken using a validated 3D unsteady RANS solver with mesh movement. In the first part of this work, flutter computations are performed on the rotor with and without the presence of its adjacent blade rows and the influence of reflections on aerodynamic damping of the embedded row is studied. In the second part of this work, reflective boundary conditions are used to reflect pressure waves from known locations. A wave-splitting procedure is performed to split the unsteady pressure into an outgoing wave and a reflected wave. Using this technique a relationship between the phase of the reflected wave and the susceptibility to flutter is established.