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PIV measurements of flow through forming fabrics Peng, Haiya


Three-dimensional velocity fields in the single phase approach flow to a multiple layer woven forming fabric were measured using Particle Image Velocimetry (PIV). The measurements were conducted on a scale model of a forming fabric in a water/glycerin flow loop. Each strand on the paper side of the model forming fabric had a filament diameter around 15.4mm, and the loop test section was 310mm squared, permitting the measurement of detailed velocity distributions over multiple strands of the fabric. The flow speed in the loop test section were varied to achieve screen Reynolds numbers (Res), calculated based on paper side filament diameter (d), between 15 and 65. PIV measurements showed that the normalized ZD velocity deviation decreases from 19.7% at a plane 0.25d upstream from the forming fabric to 4.2% at a plane 1.5d upstream. The normalized CMD velocity deviation decreases from 15.3% at a plane 0.25d upstream from the forming fabric to 1.9% at a plane 1.5d upstream. The normalized MD velocity deviation decreases from 14.5% at a plane 0.25d upstream from the forming fabric to 2.3% at a plane 1.5d upstream. The highest ZD velocity is about 3.3 times higher than the lowest ZD velocity at a plane 0.25d above the fabric. This ratio decreases to 1.2 at a plane 1.5d above the fabric. These findings show that the flow non-uniformity caused by the fabric weave is restrained to a short distance above the fabric. However, even this non-uniformity is not particularly felt by fibers, whose length scale results in an averaging of the local velocity field. CFD simulations of the same flow were consistent with the PIV measurements.

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