The Effect of Aperture Geometry on the Steady Flow Through Narrow Apertures in a Cross Flow: Experimental Study, 2007 TAPPI Papermakers and PIMA International Leadership Conference

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Turbulent flow over a rough surface with suction or blowing is a common fluid mechanics problem that has many practical applications including pulp screening. To better understand the complex hydrodynamics at the critical region near the screen surface, the mean velocity and turbulent intensity profiles above a contoured surface in a steady cross flow with suction, similar to that in a pulp pressure screen, was experimentally determined for a range of contour geometries and flow velocities. The mean velocity profiles were shown to be log linear with an offset from the classical flow over a smooth plate and were a function of contour height, wire width, suction velocity and cross flow velocity. The mean velocity decreased with contour height and increased with wire width. Wires with similar ratios of contour height and wire width had similar mean velocity profiles. The mean velocity increased as suction velocity increased and the boundary layer was pulled through the apertures. A correlation for mean velocity and wall shear stress on the cylinder was determined for all variables tested. The turbulent intensity profile in the cross flow direction was also determined. The near wall turbulence was a strong function of contour geometry and flow velocities. The maximum turbulence intensity near the wall was shown to increase with contour height and to decrease with wire width and suction velocity.