Abstract
This paper uses the advanced Delayed-Detached Eddy Simulation (DDES) of turbulence to simulate rotating stall inception of NASA Rotor 67. The rotor is a low-aspect-ratio transonic axial-flow fan with a tip speed of 429 m/s and a pressure ratio of 1.63. A full annulus simulation was employed with the time accurate compressible Navier-Stokes code in order to accurately capture the the formation of long-length disturbance and a short-length inception (spike). The validation for all numerical methods used in this study was accomplished by the comparisons of the CFD solutions with the test data in advance of unsteady simulations. Self-induced rotating stall development is simulated holding the same back pressure at the near stall experiment without any throttling. Spike type rotating stall occurs and rotates at roughly 50% of rotor speed counter to the rotation. After spike onset, rotating stall fully develops approximately within 2 rotor revolutions. Two distinct characteristics that can advance the mechanism of spike type rotating stall are observed. First, the passage shock is fully detached from rotor and decays during the spike inception. Consequently the shifted sonic line at the upstream of rotor allows stalling flow to propagate to the neighboring passage. Second, the trailing edge back flow contributes to the build up of a fully developed stall cell by pushing tip clearance flow toward blade leading edge and inducing tip spillage flow. Tip vortex originated from the leading edge dies out during spike inception as the swirl angle of incoming tip flow decreases, while in the unstalled passages it develops without breakdown. DDES challenge for the complete blade row reflects well the sequence of rotating stall and its unsteady behavior.