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Numerical simulation of the pressure pulses produced by a pressure screen foil rotor Feng, Monica Mei

Abstract

Pressure screening is the most industrially efficient and effective means of removing contaminants that degrade the appearance and strength of paper and of fractionating fibres for selective treatments and use in specialty products. A critical component of a screen is the rotor which induces a tangential velocity in the suspension and produces pressure pulses on the screen cylinder surface to keep the screen apertures clear. To understand the effect of the key design and operating variables for a NACA foil rotor, a computational fluid dynamic (CFD) simulation was developed using FLUENT, and the numerical results were compared with experimental measurements. All the experimental measurements for negative pressure peak were 50% larger than the numerical results over a wide range of foil tip-speeds, clearances, angles of attack and foil cambers. In addition, it was shown that the magnitude of the pressure pulse peak increases linearly with the square of tip-speed for all the angles of attack studied. The maximum negative pressure pulse occurred for NACA 0012 and 4312 foils at 5 degrees angle of attack and NACA 8312 at 0 degrees. The stall angle of attack was found to be approximately 5 degrees for NACA 8312, 10 degrees for NACA 4312 and 15 degrees for NACA 0012. The positive pressure peak at the screen cylinder surface near the leading edge of the foil was eliminated for foils operating at a positive angle of attack. The magnitude of the negative pressure peak increased as clearance decreased. Increased camber increases both the magnitude and the width of the pressure pulse. In addition to, and more important than, these specific results, we have shown that CFD is a viable tool for the optimal design and operation of rotors in industrial pressure screens.

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