Laminar non-Newtonian open channel flow: investigating velocity, wall shear stress and fluid depth

Abstract

Data for laminar non-Newtonian flow in various non-circular open channels can be described by a general relationship, f = K/ReH where f is the friction factor and ReH is the appropriate Haldenwang et al (1) Reynolds number corresponding to the rheological model used to describe the non-Newtonian behaviour exhibited by the test fluid. The K values were found to range from 14.6 to 17.6 depending on the channel shape used and to be similar to those reported for Newtonian flow (2). Despite the good agreement of f = K/ReH line with the data found for each channel shape, this paper outlines the concerns regarding the comparison of actual and predicted velocities, the comparison of measured and predicted wall stresses and the flow depth sensitivity. In terms of velocity, wall shear stress and flow depth prediction, the Haldenwang et al (1) model was found to hold reasonably well for power law fluids. However, this was not the case for Bingham plastic and Herschel-Bulkley fluids. A possible reason for these discrepancies may be due to the contribution of the yield stress not being properly accounted for in the flow modelling.