Transition from supercritical to subcritical regime in free surface flow of yield stress fluids

Characteristics of the transition from supercritical to subcritical regime (hydraulic jump) in laminar flow of a Herschel-Bulkley fluid on an horizontal plane are examined. The set of equations governing the flow is presented, recovering earlier results for a Bingham fluid. The determination of the flow conditions downstream, given those upstream, involves solution of a nonlinear algebraic system in three unknowns; an approximate analytical formula for conjugate depths is derived since no exact solution can be obtained in closed form. The relative error thus introduced is then evaluated numerically; its maximum value is shown to be less than a few percent. The behavior of flow depth, bottom shear stress and critical depth are established and illustrated as function of the flow behavior index; the critical depth and the ratio of conjugate depths increase with the behavior index and until the bottom shear stress exceeds a certain value, and then decrease afterwards.