A Two-Dimensional Compressible Navier-Stokes Simulation of Transient Flows in Compressor Rotor/Stator Cascades. 2nd Report. Unsteady Flow and Stall Process in Multi-Bladed Rotor and Stator.

Abstract

Various aspects of unsteady stall flows arising in linear rotor-stator cascades of a single-stage axial compressor are studied numerically by a TVD finite-difference analysis of two-dimensional compressible Navier-Stokes equations. The computational system consists of a rotor and a stator, where the flow is assumed to be periodic over either three blades and five vanes, or six blades and ten vanes, respectively, depending on the scale of vortical structure induced by the rotor motion. Relative motion of the cascades is simulated by sliding the grid fixed to the rotor past the stationary grid fixed to the stator. Although the flow is constrained in a two-dimensional plane, and the analysis is conducted without a turbulence model, computed stage characteristic from high-flow to deep stall is found to be similar with the rig test data. Features of unsteady flowfield under normal operating conditions, as well as typical flow patterns inside propagating stall cells at various load are presented. Computed flow velocity ahead of and behind the rotor under design condition is compared with the measured data. Furthermore, computed force and moment acting on the blades under stalled condition are described. Blade Reynolds number and Mach number are 2.8×105 and 0.3, respectively, to meet the rig test conditions.