Discrete frequency sound generation in axial flow turbomachines

Abstract

A calculation method is described for unsteady, subsonic flow through an infinite, two-dimensional cascade of flat plate blades at zero mean incidence. The unsteady blade lift and moment, generated acoustic waves and shed vortex wakes can be calculated when the blades are subjected to bending or torsional vibration, incoming acoustic waves, or convected wake velocity perturbations. The results are in good agreement with those obtained by existing methods, and demands upon computer time and storage are slight. Measurements have been made of the acoustic waves generated by a single compressor rotor excited by a convected wake velocity perturbation, with the blades in both an unloaded and a loaded condition. Agreement between theory and experiment is good in the unloaded blade case, but the present theory is inadequate to deal with the extra sound sources introduced by blade steady loading, and underestimates the generated wave amplitude in this case.