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UBC Theses and Dissertations

Characterization of design parameters for a free foil rotor in a pressure screen Gonzalez, Jaime Arturo


This thesis experimentally examined the pressure pulses produced by a NACA foil rotor. For this purpose, an experimental apparatus representing a cross section of a small industrial pulp pressure screen was used. The Cross Sectional Screen (CSS) was fitted with high frequency pressure sensors and an optical position encoder to record the pressure pulses created by the rotor on the inside of the screen basket and the effect of foil operation and design on the pulse shape and magnitude was determined. From this study, it was shown that: (1) the magnitude of pressure increases with the square of rotor tip speed, i.e., the dimensionless pressure coefficient was independent of rotor tip speed. (2) The magnitude of the pressure pulse increased exponentially as the clearance of the foil and the screen plate decreased. (3) The magnitude of the pressure pulse decreased with increasing pulp consistency. (4) The magnitude of the positive pressure peak increases with foil thickness; this is particularly important for thicknesses greater than 12%. The magnitude of the negative pressure peak and the shape of the pulse in general do not change significantly due to foil thickness. (5) For the foils tested (0%, 4% and 8% camber) the magnitude of the suction peak increased with increasing camber at zero angle of attack. (6) Angle of attack significantly changed the shape and magnitude of the pressure peak. In particular, it was noted that the maximum negative peak occurs at angles of attack between 5° and 15°, depending on the type of foil and experimental conditions. For positive angles of attack, the positive pressure peak seemed to be negligible. This suggests the optimal angle of attack for a NACA0012 foil is in the vicinity of 10°. In general, it was established that the Cross Sectional Screen modified to measure pressure pulses together with CNC machining of rotor foils provide a powerful tool for designing improved foils and assessing the resulting pressure pulses.

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