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Research Papers: Flows in Complex Systems

# A Numerical Investigation into the Effectiveness of Multi-Element Pressure Screen Rotor Foils

[+] Author and Article Information
Sean Delfel, James Olson

Pulp and Paper Centre and Department of Mechanical Engineering, The University of British Columbia, 2385 East Mall, Vancouver, BC, V6T 1Z4, Canada

Carl Ollivier-Gooch

Department of Mechanical Engineering, The University of British Columbia, 2324 Main Mall, Vancouver BC, V6T 1C4, Canada

J. Fluids Eng 131(1), 011101 (Nov 26, 2008) (12 pages) doi:10.1115/1.2979002 History: Received October 05, 2007; Revised July 06, 2008; Published November 26, 2008

## Abstract

Pressure screening is an efficient way to remove unwanted debris from a pulp stream, which improves the quality of the end product paper. Past work has found that increased foil camber and angle-of-attack improve the performance of pressure screen foil rotors by increasing the magnitude and width of the negative pressure pulse on the screen cylinder while at the same time reducing the magnitude of the positive pressure pulse on the screen cylinder. Too large an angle-of-attack or too much camber leads to separation of the flow over the foil and a loss in rotor performance, however. This study therefore investigates, using computational fluid dynamics, the ability of multi-element rotor foils to delay stall over the foil and improve upon the performance of an existing pressure screen rotor foil. In this study, the effect of foil angle-of-attack, flap angle, the geometry of the trailing edge of the main foil, and the positioning of the flap relative to the main foil were studied. A multi-element foil was developed based on the NACA 8312, a foil used in industrial pressure screen rotors. In general, stall was delayed and a larger angle-of-attack was obtained than the single-element foil, and increased camber was added to the foil by deflecting the flap. Positive pressure pulse on the screen cylinder approached a negligible value with both increasing angle-of-attack and increasing flap angle, while the negative pressure pulse increased in magnitude with both increasing angle-of-attack and flap angle before the foil began to separate and the suction was lost. The $x$-positioning of the flap was shown to have less of an effect on the foil performance than the $y$-positioning. All told, the magnitude of the negative pressure pulse was increased by 15% while at the same time eliminating the positive pressure pulse.

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## Figures

Figure 7

Pressure traces on the screen cylinder for a multi-element foil at varying angles-of-attack. The flap is at δ=7 deg for all cases.

Figure 8

(a) Maximum wall pressure coefficient on the screen cylinder and (b) minimum wall pressure coefficient on the screen cylinder versus foil angle-of-attack. The flap is at δ=7 deg for all cases.

Figure 6

Pressure contours and streamlines for a multi-element foil at (a) α=0 deg, (b) α=2 deg, (c) α=4 deg, (d) α=5 deg, (e) α=7 deg, and (f) α=10 deg. The flap is at δ=7 deg for all cases.

Figure 5

Pressure traces on the screen cylinder for a multi-element foil with varying main foil trailing edge lip lengths. The foil is at α=0 deg and the flap is at δ=7 deg for all cases.

Figure 4

Pressure contours and streamlines for a multi-element foil with varying main foil trailing edge lip lengths: (a) l=0.10c, (b) l=0.25c, and (c) l=0.50c. The foil is at α=0 deg and the flap is at δ=7 deg for all cases.

Figure 9

Pressure contours and streamlines for a multi-element foil at (a) δ=7 deg, (b) δ=15 deg, (c) δ=22 deg, (d) δ=29 deg, and (e) δ=36 deg. The foil is at α=7 deg for all cases.

Figure 10

Pressure traces on the screen cylinder for a multi-element foil at varying flap angles. The foil is at α=0 deg for all cases.

Figure 11

(a) Maximum wall pressure coefficient at the screen cylinder and (b) minimum wall pressure coefficient at the screen cylinder versus flap angle for various angles-of-attack

Figure 12

Surfaces of (a) maximum wall pressure coefficient and (b) minimum wall pressure coefficient versus foil angle-of-attack and flap angle

Figure 3

Multi-element rotor foil with specific foil parameters defined

Figure 2

Experimental and numerical results for pressure traces on the screen cylinder for a NACA 8312 rotor foil at Re=5×105, an angle-of-attack of α=0 deg, a chord of c=4 cm, and a gap of g=3 mm

Figure 1

Computational domain and a typical mesh

Figure 13

Pressure contours and streamlines for a multi-element foil with varying x-positions for the flap leading edge. The flap leading edge is at (a) x=0.00c, (b) x=−0.02c, (c) x=−0.03c, (d) x=−0.05c, (e) x=−0.06c, and (f) x=−0.08c. In all cases, the flap leading edge is at y=−0.05c, α=1 deg, and δ=15 deg.

Figure 14

Pressure contours and streamlines for a multi-element foil with varying y-positions for the flap leading edge. The flap leading edge is at (a) y=−0.04c, (b) y=−0.05c, (c) y=−0.07c, (d) y=−0.09c, and (e) y=−0.11c. In all cases, the flap leading edge is at x=0.04c, α=1 deg, and δ=15 deg.

Figure 15

Surfaces of (a) maximum wall pressure coefficient and (b) minimum wall pressure coefficient versus flap leading edge x- and y-positions. The foil is at α=1 deg, and δ=15 deg for all cases.

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