  We derive an expression for the velocity profile of a pressure-driven
yield-stress fluid flow-ing around a two-dimensional concentric annulus. This
result allows the prediction of the effects of channel curvature on the
pressure gradient required to initiate flow for given yield stress, and for the
width of the plug region and the flux through the channel at different
curvatures. We use it to validate numerical simulations of the flow from a
straight channel into a curved channel which show how the fluid first yields
everywhere before reaching the predicted velocity profile.
