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Research Papers: Flows in Complex Systems

Aerodynamic Performance of Blade Tip End-Plates Designed for Low-Noise Operation in Axial Flow Fans

[+] Author and Article Information
Alessandro Corsini, Franco Rispoli

Dipartimento di Meccanica e Aeronautica, “Sapienza” University of Rome, Via Eudossiana 18, I00184 Rome, Italy

A. G. Sheard

 Fläkt Woods Limited, Axial Way, Colchester CO4 5AR, UK

J. Fluids Eng 131(8), 081101 (Jul 07, 2009) (13 pages) doi:10.1115/1.3026723 History: Received July 25, 2007; Revised October 03, 2008; Published July 07, 2009

This study assesses the effectiveness of modified blade-tip configurations in achieving passive noise control in industrial fans. The concepts developed here, which are based on the addition of end-plates at the fan-blade tip, are shown to have a beneficial effect on the fan aeroacoustic signature as a result of the changes they induce in tip-leakage-flow behavior. The aerodynamic merits of the proposed blade-tip concepts are investigated by experimental and computational studies in a fully ducted configuration. The flow mechanisms in the blade-tip region are correlated with the specific end-plate design features, and their role in the creation of overall acoustic emissions is clarified. The tip-leakage flows of the fans are analyzed in terms of vortex structure, chordwise leakage flow, and loading distribution. Rotor losses are also investigated. The modifications to blade-tip geometry are found to have marked effects on the multiple vortex behaviors of leakage flow as a result of changes in the near-wall fluid flow paths on both blade surfaces. The improvements in rotor efficiency are assessed and correlated with the control of tip-leakage flows produced by the modified tip end-plates.

FIGURES IN THIS ARTICLE
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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Test fan rotor blades and tip end-plates (not to scale)

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Figure 2

Chordwise distributions of tip-leakage-vortex rotation number Ro under design operating conditions (dashed line: data fan; solid line: TF fan; solid-line-symbols: TFvte fan)

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Figure 7

Comparison of SPL far-field cross spectra (dashed lines: data fan; solid lines: TF fan; line-symbols: TFvte fan; dashed-dotted line: TF_step fan; dashed-dotted line-symbols: TFvte_step fan)

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Figure 8

Comparison of experimental specific noise level Ks in the operating range (dashed lines: data fan; solid lines: TF fan; line-symbols: TFvte fan; dashed-dotted line: TF_step fan; dashed-dotted line-symbols: TFvte_step fan)

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Figure 9

Normalized helicity contours and leakage-vortex streamlines: (a) data fan, (b) TF fan, (c) TFvte fan, (d) TF_step fan, and (e) TFvte_step fan

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Figure 10

Tip leakage-vortex TLV1 trajectories: (a) line-squares: data; line-circles: TF; line-triangles: TFvte, (b) line-squares: data, line-circles: TF_step; line-triangles: TFvte_step

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Figure 11

Tip leakage flow: (a) velocity distribution; (b) skewing angle distribution

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Figure 12

Spanwise blade load analysis: (a) local diffusion factor (DFloc) profiles and (b) static-pressure coefficients (Cp) at the blade tip (dashed lines: data fan; solid lines: TF fan; line-symbols: TFvte fan; dashed-dotted line: TF_step fan; dashed-dotted line-symbols: TFvte_step fan)

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Figure 3

Comparison of characteristic curves: (a) static-pressure rise and pressure rise difference; (b) efficiency curves (dashed lines: data fan; solid lines: TF fan; line-symbols: TFvte fan)

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Figure 4

Far-field setup of the test rig (not to scale) for outlet measurements

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Figure 5

Computational grid of fan rotor

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Figure 6

SPL narrowband spectra: (a) up to 1 kHz; (b) 1–5 kHz (dashed lines: data fan; solid lines: TF fan; line-symbols: TFvte fan; dash-dotted line: TF_step fan; dashed-dotted line-symbols: TFvte_step fan)

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Figure 13

Powell’s (26) sound-source distributions in the tip gap at R=0.998: (a) data fan, (b) TF fan, (c) TFvte fan, (d) TF_step fan, and (e) TFvte_step fan

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Figure 14

Evolution of total pressure loss coefficient (ζ) inside the blade passage under design conditions: (a) data fan, (b) TF fan, (c) TFvte fan, (d) TF_step fan, and (e) TFvte_step fan

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