Pulsatile flows of a bingham plastic in circular pipes

Pulsatile flows of a Bingham plastic through a circular pipe have been investigated numerically. The unsteadiness in the studied flow phenomenon is due to a sinusoidal varying pressure gradient component superimposed on a non-zero mean value. These time periodic flows are typical of many pumping operations and manufacturing processes of highly viscous Newtonian and non-Newtonian fluids. Pulsating the flow of a non-Newtonian Bingham plastic leads to time-averaged flow rates that are higher than the ones obtained under steady state conditions. The influence of the governing non-dimensional parameters, i.e. the yield, Reynolds and Strouhal numbers, on both the flow rate enhancement as well as the extra power required to maintain the flow pulsations is investigated. The presented results identify two asymptotic flow regimes. The first is a quasi-steady state one encountered at low frequencies. The other limiting regime, found at the high end of the studied frequency spectrum, leads to time-averaged characteristics identical to those of the steady state case.