GRANULAR-FLOW RHEOLOGY - ROLE OF SHEAR-RATE NUMBER IN TRANSITION REGIME

This paper examines the rationale behind the semiempirical formulation of a generalized viscoplastic fluid (GVF) model in the light of the R einer-Rivlin constitutive theory and the viscoplastic theory, thereby identifying the parameters that control the rheology of granular flow. The shear-rate number (N) proves to be among the most significant par ameters identified from the GVF model. As N --> 0 and N --> infinity, the GVF model can reduce asymptotically to the theoretical stress vers us shear-rate relations in the macroviscous and grain-inertia regimes, respectively, where the grain concentration (C) also plays a major ro le in the rheology of granular flow. Using available data obtained fro m the rotating-cylinder experiments of neutrally buoyant solid spheres dispersing in an interstitial fluid, the shear stress for granular fl ow in transition between the two regimes proves dependent on N and C i n addition to some material constants, such as the coefficient of rest itution. The insufficiency of data on rotating-cylinder experiments ca nnot presently allow the GVF model to predict how a granular flow may behave in the entire range of N; however, the analyzed data provide an insight on the interrelation among the relevant dimensionless paramet ers.