This paper shows the results of three-dimensional multi-passage numerical simulations on a transonic compressor, NASA compressor Rotor 37. The aim is to investigate the unsteady flow on the stall condition and elucidate the dynamic evolution mechanism of the rotating stall. Three-dimensional Reynolds-averaged Navier-Stokes equations with the Spalart-Allmaras turbulence model were solved to analyze the fluid flow in the transonic axial compressor. Before the study of the stall flow, grid independence and data correctness were well validated.
A new parameter B is defined to assess the blockage effect during the stall development. As shown in the results, with the development of the rotating stall, the blockage effect increases slowly before the 18th revolution in unsteady numerical simulation, and then increases dramatically in the following revolutions. Thus, the whole process of stall evolution can be divided into two stages, i.e. stall stage I and stall stage II. The stall stage I is the first 18th revolutions, while the stall stage II refers to the period after the18th revolution.
Further analyses of the instantaneous flow field show that the interaction between the tip leakage flow and the detached shock wave induces the breakdown of the leakage vortex. As the broken leakage vortex moves downstream, the low energy flow is rolled up. At the middle of the channel, the trajectory of the vortex core inclines to the PS of adjacent blade under the influence of the adverse pressure gradient, and an obvious new vortex is formed. During the development process of the rotating stall, the blockage is primarily induced by the tip leakage vortex and the new vortex. In the stall stage I, the evolution of the blockage area near the tip is periodic affected by the self-sustaineed process of tip leakage vortex. The self-sustained phenomenon will be illustrated in detail later. In the stall stage II, the whole passage is blocked at 99% blade span, and the spillage flow is observed throughout the whole stage. These flow charicteristics are regarded as signs of a rapid deterioration of the flow field. A vicious cycle is seen as the main reason for the rapid deterioration of the flow field, and the vicious cycle will be explained in detail later.