Effect of Bleed Flows on Flutter and Forced Response of Core Compressors

This paper presents a methodology for the modeling of flutter and forced response in axial compressors while taking into account the effect of bleed off-takes. Usually, aeroelasticity analyses are performed assuming smooth solid end walls. This type of analysis has two main shortcomings. Firstly, it does not account for the change in the aerodynamic speed of the stages downstream of the bleed off-take, so that aeroelasticity analyses are not performed at the correct aerodynamic conditions. Secondly, bleed off-takes influence the flow pattern particularly in the stages around or close to the bleed off-take, thus leading to possibility of obtaining the wrong aeroelastic response. Another objective of this paper is to present a methodology for the accurate prediction of the flow in a compressor with bleed off-take, by both including the geometry of the bleed off-take and performing the calculations on the entire compressor, thus eliminating errors resulting from prescribing boundary conditions at inter-blade row boundaries. It is concluded that bleed off-takes could influence significantly the aeroelastic response of the blades.