A Two-dimensional Compressible Navier-Stokes Simulation of Transient Flows in Compressor Rotor/Stator Cascades. 3rd Report. Flow Structure of a Deep Rotating Stall Cell.

Abstract

Detailed flow structure of a deep rotating stall cell in a single-stage axial compressor is studied based on a numerical simulation of simplified quasi-three-dimensional compressible Navier-Stokes equations a linear cascades system and unsteady flow measurements in a test compressor. The computational system is expanded to a maximum combination of 15 rotor blades/25 stator vanes, so that cell growth is not hampered by spatial constraint of the field. The simulation is performed at a blade Mach number of 0.3 to meet the rig test condition. It is found that the stall cell is composed of sub-cell vortices, each extending over 3-5 rotor pitches, which align circumferentially ahead of the rotor, and counter-rotating vortices occupying the stator passages. The computed cell speed agrees well with the measured speed. In the computed time trace of flow velocity at the rotor inlet, multiple peaks, corresponding to the sub-cell vortices, appear during a cell passage. These are also seen in the measured traces taken by split-film probes. The agreement indicates that multiple sub-cell vortices may constitute a deep stall cell in the real situation.