Large Channel Width Research Articles

Stress-Birefringent Patterns of a Viscoelastic Fluid at a Sharp-Edged Entrance

Stress-birefringent patterns were determined for a viscoelastic fluid (14 wt-% polystyrene in Aroclor) flowing into a sharp-edged channel entrance. The final data are point-by-point shear stresses and differences in normal stresses. Independent shear and normal stress data were obtained on the Weissenberg Rheogoniometer. In developed straight channel flow, the experimental shear stresses are in quantitative agreement with those calculated from the rheogoniometer data; the normal stresses are of the correct magnitude but the agreement is not quantitative. Very good detail of the stresses at the corners and in the entrance region is available. The entrance regions are of the order of one large channel width upstream and one small channel width downstream, as judged by the approach of the stresses to within a few per cent of their developed values. The accelerating region upstream of the entrance was treated theoretically with a simplified version of the theory of Bernstein, Kearsley, and Zapas, using the model of radial, plug flow. Although a reasonably good prediction of the normal stresses along the centerline is obtained, the predominance of the Newtonian term does not make the check a sensitive one.