The Role of Tip Leakage Flow in Spike-Type Rotating Stall Inception

Abstract

This paper describes the role of tip leakage flow in creating the leading edge separation necessary for the onset of spike-type compressor rotating stall. A series of unsteady multipassage simulations, supported by experimental data, are used to define and illustrate the two competing mechanisms that cause the high incidence responsible for this separation: blockage from a casing-suction-surface corner separation and forward spillage of the tip leakage jet. The axial momentum flux in the tip leakage flow determines which mechanism dominates. At zero tip clearance, corner separation blockage dominates. As clearance is increased, the leakage flow reduces blockage, moving the stall flow coefficient to lower flow, i.e., giving a larger unstalled flow range. Increased clearance, however, means increased leakage jet momentum and contribution to leakage jet spillage. There is thus a clearance above which jet spillage dominates in creating incidence, so the stall flow coefficient increases and flow range decreases with clearance. As a consequence, there is a clearance for maximum flow range; for the two rotors in this study, the value was approximately 0.5% chord. The chordwise distribution of the leakage axial momentum is also important in determining stall onset. Shifting the distribution toward the trailing edge increases flow range for a leakage jet dominated geometry and reduces flow range for a corner separation dominated geometry. Guidelines are developed for flow range enhancement through control of tip leakage flow axial momentum magnitude and distribution. An example is given of how this might be achieved.

Low pressure ratio transonic fan stall with radial distortion

“…As well as a lower total pressure ratio, low pressure ratio fans are distinguished by reduced rotor inlet relative Mach numbers, typically below 1.4 at the tip and with subsonic relative inflow towards the hub. Analysis of single-stage, low hub-to-tip ratio subsonic compressors (Pullan, et al, 2015;Hewkin-Smith, et al, 2019) and transonic compressors (Hah, et al, 2006;Kim, et al, 2019) observe spike-type stall inception, or the absence of significant low-frequency disturbance preceding stall. Hewkin-Smith, et al (2019) attributed the sudden drop in pressure rise from local sectors of the rotor row to either spillage of tip leakage flow ahead of the leading edge, or separation from the suction surface within the rotor passage.…”

Separated Flow Topology in Compressors

“…Hewkin-Smith et al in Ref. [11] showed how sweep and lean changes the distribution of the axial momentum in a tip leakage jet. By increasing the axial momentum of the jet or pushing its distribution rearward, it was possible to change the route to tip separation from a tip leakage dominated mechanism to a corner separation dominated mechanism.…”

“…Hewkin-Smith et al showed that the 3D design could change the route to tip separation in Ref. [11], but it cannot change the topology of the separation once it has occurred. Large discontinuities are still present in all of the designs, and so, cell behavior is always observed.…”

Momentum Transportation Analysis in Axial-slot Casing Treatment for Axial Compressors

“…The total momentum can be calculated by Equation 6and (7). Notice that the momentum here is not only on the slot openings, but also on the tip clearance plane.…”

“…(Nan, 2014) investigated the influence of circumferential grooves in Rotor 67 by analyzing the momentum of a specific control volume inside the grooves. Besides, the momentum distribution in the tip clearance is used as a criterion to evaluate the tip leakage flow strength (Cameron et al, 2013;Hewkin-Smith et al, 2019;Nan, 2014). For the circumferential grooves, the momentum flux makes the extension of stall margin linearly (Shabbir and Adamczyk, 2005;Ross et al, 2017).…”