Simulating Stall Inception in a High-Performance Fan

Abstract

Abstract Aircraft engine performance and stability is limited by the onset of flow instabilities, such as rotating stall or surge. Although much research has been conducted on the subject, the mechanisms by which spike-type stall inception occurs in highspeed machines are still not well understood. This paper investigates the mechanisms of stall inception in a highly-loaded transonic fan rotor using full-annulus Unsteady Reynold’s-Averaged Navier-Stokes (URANS) simulations. Comparisons are made between the flow phenomena at the near-stall operating point and as stall inception occurs. The mechanisms of stall inception are shown to be interactions between the detached bow shock and the tip leakage vortex. These interactions result in two vortices within the blade passage near the rotor tips. The location and strength of these vortices affect leading edge spillage in the adjacent blade row. At the near-stall operating point, the vortices impact the pressure surface of the adjacent blade and then convect downstream. Stall inception occurs when the bow shock has moved far enough upstream to allow the resultant passage vortices from the shock/tip leakage vortex interaction to pass in front of the leading edge of the adjacent blade. After this, radial vortical structures are seen at the blade tips, much like what is observed in low-speed compressors. Understanding the mechanisms of stall inception in high-speed fans will allow for appropriate steps to be taken to delay stall inception and extend the stable operating range of the fan.