We present a theoretical and experimental analysis of the dam break of a viscoplastic fluid in a horizontal channel. A shallow, slow fluid model
based on the Herschel-Bulkley constitutive law allows one to characterize the early and late stages of the flow, the final state and the dependence
on yield stress and nonlinear viscosity. A particular diagnostic is advanced (time ratios based on the length of time required for the fluid to slump
certain distances from the broken dam) that may assist an experimentalist to unravel those dependences. Experiments are conducted with cornsyrup,
and aqueous suspensions of xanthan gum, kaolin, carbopol, cornstarch and apple puree. Cornsyrup xanthan gum and kaolin show fair quantitative
agreement with theory. Carbopol compares less favourably, due primarily to inertial effects which are missing from the theory. The results for
cornstarch confirm that it is shear thickening, but its detailed rheology remains unknown (and unexplored). Apple puree also appears to compare
well with theory, although repeating the dam break in a roughened channel leads to substantially different results, suggesting that fluid separation
can induce effective wall slip (a problem that also probably plagues the Bostwick device). Finally, theory is compared with Bostwick tests with
fruit puree, with limited success.
We present a theoretical and experimental analysis of the dam break of a viscoplastic fluid in a horizontal channel. A shallow, slow fluid modelbased on the Herschel-Bulkley constitutive law allows one to characterize the early and late stages of the flow, the final state and the dependenceon yield stress and nonlinear viscosity. A particular diagnostic is advanced (time ratios based on the length of time required for the fluid to slumpcertain distances from the broken dam) that may assist an experimentalist to unravel those dependences. Experiments are conducted with cornsyrup,and aqueous suspensions of xanthan gum, kaolin, carbopol, cornstarch and apple puree. Cornsyrup xanthan gum and kaolin show fair quantitativeagreement with theory. Carbopol compares less favourably, due primarily to inertial effects which are missing from the theory. The results forcornstarch confirm that it is shear thickening, but its detailed rheology remains unknown (and unexplored). Apple puree also appears to comparewell with theory, although repeating the dam break in a roughened channel leads to substantially different results, suggesting that fluid separationcan induce effective wall slip (a problem that also probably plagues the Bostwick device). Finally, theory is compared with Bostwick tests withfruit puree, with limited success.
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