Numerical Simulation and Experimental Measurement of Pressure Pulses Produced by a Pulp Screen Foil Rotor

Abstract

Pressure screening is an efficient means of removing various contaminants that degrade the appearance and strength of paper. A critical component of a screen is the rotor, which induces a tangential velocity to the suspension and produces pressure pulses to keep the screen apertures clear. To understand the effect of key design and operating variables for a NACA foil rotor, a computational fluid dynamic (CFD) simulation was developed using FLUENT, and the results were compared to experimental measurements. Comparing the pressure pulses obtained through CFD to experimental measurements over a wide range of foil tip speeds, clearances, angles of attack, and foil cambers, general trends of the pressure pulses were similar, but the overall computed values were 40% smaller than the measured values. The pressure pulse peak was found to increase linearly with the square of tip speed for all the angles of attack studied. The maximum magnitudes of negative pressure pulse occurred for the NACA 0012 and 4312 foils at a 5 deg angle of attack and for the NACA 8312 foil at 0 deg. The stall angle of attack was found to be ϳ5 deg for NACA 8312, ϳ10 deg for NACA 4312, and ϳ15 deg for NACA 0012. The positive pressure peak near the leading edge of the foil was eliminated for foils operating at a positive angle of attack. The magnitude of the negative pressure coefficient peak increased as clearance decreased. Increased camber increases both the magnitude and width of the negative pressure pulse.

Experimental study of a time‐varying turbulent cross‐flow near a two‐dimensional rough wall with narrow apertures

“…[13,27,24,29] The CSS has a depth of 50 mm and the partially-slotted cylinder has an inside diameter of 290 mm. The experiments were conducted with a Phantom high-speed video camera using a crosssectional screen (CSS).…”

“…The experiments were conducted with a Phantom high-speed video camera using a crosssectional screen (CSS). This angle minimizes the positive component of the pressure pulse according to Feng et al, [27] which is desirable since the positive pressure pulse component is not thought to help clear the aperture, but may instead jam the slot with trapped fibres and force deformable contaminants through the aperture. [13,27,24,29] The CSS has a depth of 50 mm and the partially-slotted cylinder has an inside diameter of 290 mm.…”

“…Feng et al [27] simulated the pressure pulse using CFD and compared the results to experimental measurements over a wide range of foil tip speeds, clearances, angles-of-attack, and foil cambers. The pressure pulse peak was found to increase linearly with the square of tip speed for all angles-of-attack studied.…”

“…The figures show a reduction in vortex size as slot velocity increases, consistent with Gooding. [27] Figure 8 shows the effect of velocity ratio (i.e.,V s /V u ) on vortex size. This agrees with Mokamati et al; [16] however, the present study suggests a stagnation point closer to the slot entry than they found, which may be a consequence of differences in the channel geometry and the type of particles used in the studies.…”

“…When rotor speed is reduced (Figure 18b), the flow reversal is seen to disappear when slot velocity is increased from 1 to 4 m/s. [24,26,29,33,34] Theoretical studies, using computational fluid dynamics [27,35,36,37] have also shown that the acceleration of flow under the foil gives rise to a suction pulse, but these studies were done either with a solid or highly-simplified model of the porous cylinder wall. Note that the v component is applied through a ROI that is 2.75 mm wide versus the 0.15 mm slot width where V s is calculated.…”