Abstract: A three-dimensional model was presented to study the occurrence of rotating waves in vaneless diffusers of centrifugal compressors. By solving 3D incompressible linearized Euler equations via finite difference method and the singular value decomposition (SVD) technique, the critical inlet flow angle and propagation speed of rotating stall in vaneless diffusers were predicted. The results show that both the critical inlet flow angle and the propagation speed are affected not only by the diffuser geometry, but also by the departure from axial uniform distribution of the undisturbed radial velocity at the diffuser inlet. The predictions of 3D model show a better agreement with experimental results than those of 2D model.

Key words: centrifugal compression system, vaneless diffuser, stall, 3D modeling