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Research Papers

Effects of Fan Speed on Rotating Stall Inception and Recovery

[+] Author and Article Information
Minsuk Choi

Department of Mechanical Engineering, Imperial College London, London SW7 2BX, UKm.choi@imperial.ac.uk

Mehdi Vahdati

Department of Mechanical Engineering, Imperial College London, London SW7 2BX, UKm.vahdati@imperial.ac.uk

Mehmet Imregun

Department of Mechanical Engineering, Imperial College London, London SW7 2BX, UKm.imregun@imperial.ac.uk

J. Turbomach 133(4), 041013 (Apr 21, 2011) (8 pages) doi:10.1115/1.4003243 History: Received September 12, 2010; Revised October 20, 2010; Published April 21, 2011; Online April 21, 2011

An implicit, time-accurate 3D compressible Reynolds-averaged Navier-Stokes (RANS) solver is used to simulate rotating stall inception and recovery, the so-called rotating stall hysteresis, in the case of a modern fan geometry. In the first instance, rotating stall was simulated for 70%, 80%, and 90% fan speeds using a whole-annulus fan model with a variable-area nozzle downstream. As the fan speed is increased, the stall cells also increase in size but their number decreases. One large stall cell is predicted to rotate along the annulus at 80% and 90% speeds, while there are three smaller cells at 70% speed. In all cases, the reverse flow is confined to the near-tip region and the rotating stall does not develop into a full-span stall because of the fan blade’s high-aspect ratio. To simulate stall recovery, the nozzle area was increased gradually at 70% and 90% speeds and the flow was seen to recover from rotating stall to reach an unstalled operating condition. The recovery process was found to be affected by the fan speed. At 70% speed, the large disturbances decay first to form almost symmetric stall cells. Thereafter, the stall cells shrink into smaller ones as the mass flow rate increases further. At 90% fan speed, a single stall cell rotates along the annulus, the disappearance of which results in recovery. An attempt has been made to explain the dependence of the stall inception and recovery patterns on the fan speed.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Computational geometry

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Figure 2

Hysteresis curves: (a) schematic representation and (b) computed

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Figure 3

Static pressure time history at four numerical sensors located 40% chord upstream of the fan: (a) 70% fan speed, (b) 80% fan speed, and (c) 90% fan speed

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Figure 4

Static pressure distribution at 40% chord upstream of the fan in the rotating frame at stall inception: (a) 70% fan speed (2 rev, 4 rev, 5.5 rev, and 6.5 rev), (b) 80% fan speed (2 rev, 3 rev, 4 rev, and 5 rev), and (c) 90% fan speed (2 rev, 4 rev, 5 rev, and 6 rev)

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Figure 5

Instantaneous stream lines and normalized radial velocity distributions inboard of tip for 70% fan speed: (a) 0.2 rev and (b) 1.0 rev

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Figure 6

Static pressure distribution near tip (99% span) at 1.0 rev for 70% fan speed

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Figure 7

Static pressure distribution (left) and reverse flow region (right) upstream of the fan in the rotating frame after 20 rev: (a) 70% fan speed, (b) 80% fan speed, and (c) 90% fan speed

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Figure 8

Blockage variations during stall development

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Figure 9

Static pressure time history during stall recovery: (a) 70% fan speed and (b) 90% fan speed

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Figure 10

Static pressure distribution upstream of the fan during recovery process at 70% fan speed: (a) 25 rev, (b) 40 rev, (c) 50 rev, and (d) 55 rev

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Figure 11

Static pressure distribution upstream of the fan during recovery process at 90% fan speed: (a) 25 rev, (b) 45 rev, (c) 53 rev, and (d) 58 rev

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Figure 14

Sketch for stall propagation at different shaft speeds: (a) small stall and (b) large stall

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Figure 13

Flow angle distribution along span during stall development

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Figure 12

Sketch for stall propagation

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