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Research Papers

Origins and Structure of Spike-Type Rotating Stall

[+] Author and Article Information
G. Pullan

Visiting Associate Professor
Gas Turbine Laboratory,
Massachusetts Institute of Technology,
77 Massachusetts Avenue,
Cambridge, MA 02139

A. M. Young, I. J. Day

Whittle Laboratory,
University of Cambridge,
1 JJ Thomson Avenue,
Cambridge CB3 0DY, UK

E. M. Greitzer, Z. S. Spakovszky

Gas Turbine Laboratory,
Massachusetts Institute of Technology,
77 Massachusetts Avenue,
Cambridge, MA 02139

This speed is measured in the same (absolute) frame of reference as the stalling blade row. For stall inception occurring in a rotor, a spike travelling at 80% of wheel speed in the absolute frame has a speed of 20% in the relative frame.

Vortex lines cannot end in a fluid, and what we have drawn is a section of a vortex tube. The vortex lines within the tube continue in thin layers on the casing and on the rotor (at these surfaces they must be tangential to the surface) rather than in the form of a discrete vortex. For simplicity, we have not drawn the vortex lines outside of the section of the tube that is shown.

These times correspond to the computations in Figs. 14(a), 14(b), and 14(c), as will be described.

1Present address: Whittle Laboratory, University of Cambridge, 1 JJ Thomson Avenue, Cambridge CB3 0DY, UK.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 9, 2014; final manuscript received August 11, 2014; published online November 18, 2014. Editor: Ronald Bunker.

J. Turbomach 137(5), 051007 (May 01, 2015) (11 pages) Paper No: TURBO-14-1202; doi: 10.1115/1.4028494 History: Received August 09, 2014; Revised August 11, 2014; Online November 18, 2014

In this paper, we describe the structures that produce a spike-type route to rotating stall and explain the physical mechanism for their formation. The descriptions and explanations are based on numerical simulations, complemented and corroborated by experiments. It is found that spikes are caused by a separation at the leading edge due to high incidence. The separation gives rise to shedding of vorticity from the leading edge and the consequent formation of vortices that span between the suction surface and the casing. As seen in the rotor frame of reference, near the casing the vortex convects toward the pressure surface of the adjacent blade. The approach of the vortex to the adjacent blade triggers a separation on that blade so the structure propagates. The above sequence of events constitutes a spike. The computed structure of the spike is shown to be consistent with rotor leading edge pressure measurements from the casing of several compressors: the centre of the vortex is responsible for a pressure drop and the partially blocked passages associated with leading edge separations produce a pressure rise. The simulations show leading edge separation and shed vortices over a range of tip clearances including zero. The implication, in accord with recent experimental findings, is that they are not part of the tip clearance vortex. Although the computations always show high incidence to be the cause of the spike, the conditions that give rise to this incidence (e.g., blockage from a corner separation or the tip leakage jet from the adjacent blade) do depend on the details of the compressor.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Spike stall inception in MHI single-stage axial compressor with rotor tip clearance of 1% span. (Data courtesy of Takasago R&D Center, MHI.)

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Fig. 2

Spike stall inception in the MIT single-stage axial compressor with tip shrouded rotor [6]

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Fig. 3

Spike stall inception in the vaned diffuser of a centrifugal compressor [7]

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Fig. 4

The vortical structure and propagation of the spike

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Fig. 5

The connection between spike structure and casing pressure trace

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Fig. 6

Vortex filament evolution from leading edge separation (left), and image system showing vortex ring (right). View is upstream along stagger angle.

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Fig. 7

Computed total-to-static characteristics for the E3 Rotor B

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Fig. 8

Spike stall inception in 2D E3 tip profile cascade computation

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Fig. 9

Blade loading perturbation caused by suction-surface separation in 2D E3 tip profile cascade

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Fig. 10

Spike caused by leading edge separation in 2D E3 tip profile cascade

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Fig. 11

Spike stall inception in E3 rotor computation, zero clearance

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Fig. 12

Blade loading perturbation caused by growth of corner separation in E3 rotor, zero clearance, 95% span

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Fig. 13

Spike caused by leading edge separation in E3 rotor, zero clearance, 95% span

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Fig. 14

Structure of the spike. Isosurface of the λ2 vortex criterion, E3 rotor zero clearance.

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Fig. 15

Circumferential interface line shown by time-averaged entropy (left); unsteady tip leakage flow shown by instantaneous radial vorticity (right). E3 rotor with tip clearance, last stable operating point before stall, 95% span.

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Fig. 16

Spike stall inception in E3 rotor computation, with tip clearance

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Fig. 17

Spike formation in E3 rotor, with clearance, 95% span

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Fig. 21

Spike caused by leading edge separations in the Cambridge compressor (t = 0.55 revs in the computation)

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Fig. 20

Earliest detection of leading edge separations in the Cambridge compressor (t = 0.39 revs in the computation)

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Fig. 19

Measured and computed casing static pressure traces at the leading edge plane for the Cambridge compressor

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Fig. 18

Measured and computed total-to-static pressure rise characteristics for the Cambridge compressor

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