The Behavior of Tip Clearance Flow at Near-Stall Condition in a Transonic Axial Compressor Rotor

Abstract

It is known that the tip clearance flow is dominant and very important flow phenomena in axial compressor aerodynamics because the tip clearance flow has a great influence on the stability as well as aerodynamic loss of compressors. Our goal is to clarify the behavior of tip clearance flow at near-stall condition in a transonic axial compressor rotor (NASA Rotor 37). In the present work, steady and unsteady RANS simulations were performed to investigate vortical flow structures and separated flow field near the tip for several different clearance cases. Boundary layer separation on the casing wall and blade suction surface was investigated in detail for near-stall and stall condition. In order to understand such complicated flow field, vortex cores were identified using the critical point theory and a topology of the three-dimensional separated and vortical flows was analyzed. In the nominal clearance case, the breakdown of tip leakage vortex has occurred at a near-stall operating condition because of the interaction of the vortex with the shock wave, leading to a large blockage and unsteadiness in the rotor tip. On the other hand, the calculation with no clearance suggested that the separation on the suction surface was different from that with the nominal clearance. Since the shock wave induced the boundary layer separation on the blade suction surface in the transonic axial compressor rotor, focal-type critical points appeared on the suction surface near the tip at near-stall condition.

URANS analysis of the effect of realistic inlet distortions on the stall inception of a centrifugal compressor

“…is adequate to represent the main phenomena characterizing the near stall conditions, a preliminary analysis was performed for a geometry presenting a similar behavior to the compressor in study. For a transonic unshrouded compressor with axial inlet and pronounced tip gap in fact, the onset of unsteady disturbances at low mass flow is likely to be generated at the leading edge of the inducer, by the breakdown of the tip leakage vortex interacting with the passage shock [22]. In some circumstances, this leads to a local increase of blockage, which rotates within the annulus [7,8].…”

Numerical analysis of the tip leakage flow field in a transonic axial compressor with circumferential casing treatment

“…It rolls-up into a tip leakage vortex that disturbs the main flow, especially at highly loaded operating points. Indeed, several experimental and numerical studies have shown that the tip leakage vortex interacts with the endwall boundary layer and the shock wave in the passage [1,2,3] . The abrupt change of the core vortex downstream the shock wave somewhat corresponds to a "vortex breakdown" which blocks the passage flow near the tip gap region.…”

Numerical investigation of the unsteady tip leakage flow and rotating stall inception in a transonic compressor

“…They also proposed that tip leakage vortex breakdown as a possible cause of stall inception in a transonic compressor rotor. Yamada [7][8] numerically examined that the tip leakage vortex breakdown occurred near-stall condition in a transonic compressor. This vortex breakdown resulted in the rotating disturbance.…”