Stall inception in a transonic axial fan

Abstract

The current paper reports a numerical investigation of stall inception in a transonic compressor rotor, NASA Rotor-67, by using the whole flow passages in the computations. Surface roughness is added to one of the blades in order to trigger rotating stall. During stall inception, the tip clearance vortex moved away from the suction surface of the roughened blade's upper neighbour, leading to vortex breakdown. The stall cell was found to propagate opposite the direction of the blade rotation at about 30 per cent of rotational speed. The effect of air bleeding on stabilizing the compressor is also studied in this work. The mean mass flowrate removed from the bleed valves was 1.2 per cent of the mainstream flowrate. This amount of bleeding was found to effectively suppress the stalling disturbances.

Stall inception and control in a transonic fan, part A: Rotating stall inception

“…One way to relieve this condition is to allow the variation of exit static pressure to match with a desired mass flow rate. The relationship between the pressure variations and mass flow rate could be obtained using the conservation of mass through a downstream plenum chamber (like that used in [7] and [14]): A first order discretization of the above equation can be used to specify the average pressure at the outlet boundary at each numerical time step [14]. As the relation states, the larger the plenum chamber the slower the rate of pressure variations, which is confirmed by experiments (e.g., as found in [5], the reduction in the plenum pressure during stall inception is considerably slower for a big plenum chamber used to encounter deep surge, as compared to fully-developed rotating stall).…”

“…Therefore, as emphasized by in [9], "the debate about whether forward spillage occurs before or after stall onset is a topic of current interest which requires more numerical and experimental investigations". Some of the numerical studies reported on stall inception used part-span geometries to reduce the computational cost (e.g., [6][7][8] and [10]), whereas some others performed full-annulus computations (e.g., [11][12][13][14][15][16][17][18]). Hah et al [12] simulated spike-type stall inception in a transonic compressor rotor.…”

Numerical strategies for capturing rotating stall in fan

“…Rotating stall in a compressor is a local phenomenon whereby instabilities in blade passages propagate along the blade row in the circumferential direction. Due to modelling difficulties, most numerical studies for rotating stall are usually conducted using simplified or partial geometries and whole-annulus numerical simulations are relatively rare [1][2][3][4][5][6]. Vahdati et al [7,8] have recently studied aero-engine core compressor rotating stall using a hybrid single-passage whole-annulus model.…”

Full-Annulus Simulation of Non-Synchronous Blade Vibration of an Axial Compressor

“…Full-annulus simulations have been used to explain the flow mechanisms of stall inception since the flow has no circumferential periodicity [11][12][13][14][15]. Due to the unsteadiness of complex flow phenomena in turbomachines, the limitations brought by periodicity assumptions must be overcome in order to resolve more realistically flow structures.…”