Effects of Stator Pressure Field on Upstream Rotor Performance

Abstract

Effects of stator pressure field on upstream rotor performance in a high pressure compressor stage have been assessed using three-dimensional steady and time-accurate Reynolds-averaged Navier-Stokes computations. Emphasis was placed on: (1) determining the dominant features of the flow arising from interaction of the rotor with the stator pressure field, and (2) quantifying the overall effects on time averaged loss, blockage, and pressure rise. The time averaged results showed a 20 to 40% increase in overall rotor loss and a 10 to 50% decrease in tip clearance loss compared to an isolated rotor. The differences were dependent on the operating point and increased as the stage pressure rise, and amplitude of the unsteady back pressure variations, was increased. Motions of the tip leakage vortex on the order of the blade pitch were observed at the rotor exit in all the unsteady flow simulations; these were associated with enhanced mixing in the region. The period of the motion scaled with rotor flow-through time rather than stator passing. Three steady flow approximations for the rotor-stator interaction were assessed with reference to the unsteady computations: an axisymmetric representation of the stator pressure field, an inter-blade row averaging plane method, and a technique incorporating deterministic stresses and bodyforces associated with stator flow field. Differences between steady and unsteady predictions of overall rotor loss, tip region loss, and endwall blockage ranged from 5 to 50% of the time average, but the steady flow models gave overall rotor pressure rise and flow capacity within 5% of the time averaged values.

Unsteady tip clearance flow in an isolated axial compressor rotor

“…Sirakov explained this performance changes by a mechanism that the timeaveraged double leakage flow through the rotor tip clearance was reduced by the interaction between the rotor tip clearance flow and the pressure pulses, induced on the rotor blade pressure surface by the upstream stator wakes. Besides Graf [13], the periodic unsteadiness of the tip clearance flow was also observed by Mailach et al t151 who performed a detailed experimental investigation on the time-resolved behavior of the flow in the rotor tip region in a four-stage low-speed axial compressor. The experiment results showed that the unsteady periodic fluctuating tip clearance flow induced the propagation of rotating instabilities.…”

Effects of injection frequency on the rotor stall margin

“…Graf [10] first discovered the periodic vibration of rotor tip flow field. Zhang [11] considered that the vibration of TLV was a dynamic balance between tip leakage flow and rotor tip loadings.…”

Numerical simulation of unsteady tip clearance flow in an isolated axial compressor rotor blades row

“…Graf et al, through their numerical analyses, investigated the effects of the downstream stator on the upstream rotor [16]. They found that the tip vortex of the rotor blade has a periodic behavior.…”