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Research Papers: Flows in Complex Systems

Stall Inception Mechanism in an Axial Flow Fan Under Clean and Distorted Inflows

[+] Author and Article Information
Pramod B. Salunkhe

Department of Aerospace Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India

A. M. Pradeep

Department of Aerospace Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, Indiaampradeep@aero.iitb.ac.in

J. Fluids Eng 132(12), 121102 (Dec 03, 2010) (14 pages) doi:10.1115/1.4002921 History: Received December 08, 2009; Revised October 27, 2010; Published December 03, 2010; Online December 03, 2010

The present paper describes the use of Morlet wavelet transform in understanding the stall inception mechanism in a single stage axial flow fan. Unsteady pressure data from wall mounted sensors were used in the wavelet transforms. This paper was carried out under undistorted and distorted inflow conditions as well as for slow throttle closure and throttle ramping. It was observed from the wavelet transforms that the stall inception under clean inflow (undistorted) and counter-rotating inflow distortions (in the direction opposing the rotor rotation) incur through short length-scale disturbances and through long length-scale disturbances under static and co-rotating inflow distortions (in the same direction of rotor rotation). Modal activity was observed to be insignificant under clean inflow while under static inflow distortion, long length-scale disturbances evolved due to interaction between rotor blades and the distorted sector, especially near the trailing edge of the distortion screen. The presence of a strong mode was observed under both co- and counter-rotating inflow distortions. With throttle ramping, stall inception occurs through long and short length-scale disturbances under co- and counter-rotating inflow distortions, respectively. Some preliminary flow characteristics were studied using a seven hole probe. A significant increase in flow angle and decrease in axial flow coefficient close to the rotor tip were observed under co-rotating inflow distortion as compared with counter-rotating inflow distortion.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic representation of a single stage axial flow fan test rig

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Figure 2

Modified arrangement to incorporate the co- and counter-rotations of the distortion screen

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Figure 3

Variation in distortion coefficient with circumferential angle under dynamic inflow distortion

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Figure 4

Variation in axial flow coefficient, circumferential flow coefficient, and flow angle under co- and counter-rotating inflow distortions

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Figure 5

Fan performance under clean inflow with and without tip injection

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Figure 6

Unsteady pressure traces under clean inflow

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Figure 7

Wavelet analysis of unsteady data segment under clean inflow at sensor 6 from −6 to −1 rotor revolutions

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Figure 8

Wavelet analysis of unsteady data segment under static inflow distortion

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Figure 9

Unsteady pressure traces under co-rotating inflow distortion at various rotor revolutions prior the stall inception

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Figure 10

Wavelet analysis of data segment at sensor 1 under co-rotating inflow distortion

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Figure 11

Wavelet analysis for all six sensors under co-rotating inflow distortion

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Figure 12

Static pressure traces from unstall to full stall under counter-rotating inflow distortion

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Figure 13

Wavelet analysis of data segment for sensor 6 under counter-rotating inflow distortion

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Figure 14

Wavelet analysis for all six sensors under counter-rotating inflow distortion

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Figure 15

Unsteady pressure traces from unstall to full stall under co-rotating inflow distortion with throttle ramping

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Figure 16

Unsteady data segment and corresponding wavelet power spectrum under co-rotating inflow distortion with throttle ramping

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Figure 17

Unsteady pressure traces from unstall to full stall under counter-rotating inflow distortion with throttle ramping

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Figure 18

Wavelet analysis for data segment of sensor 1 under counter-rotating inflow distortion with throttle ramping

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