Suddenly expanding annular pipe flows of a shear-thinning non-Newtonian fluid were numerically investigated within the steady laminar flow regime. The power-law constitutive equation is used to model the rheology of interest. A parametric study is performed to reveal the influence of annular diameter ratio, k, and power-law index, n, over the following range of parameters: k = {0, 0.5, 0.7} and n = {1, 0.8, 0.6}. Flow separation and entrainment, downstream of the expansion plane, creates two recirculation regions. The first is a central recirculation region between the expansion plane and the flow stagnation point along the centerline. A second, corner recirculation region forms between the expansion plane and the flow reattachment point along the wall. The results demonstrate impact of the investigated geometrical and rheological parameters on the extent and intensity of both flow recirculation regions, the wall shear stress distribution, and the evolution and redevelopment characteristics of the flow downstream the expansion plane.

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