Laminar Flow and Pressure Loss of Power-Law Fluids in Pipes with an Axisymmetric Sudden Contraction

摘要

A steady laminar flow of an incompressible non-Newtonian fluid (inelastic power-law fluid; n<1) in pipelines with an axisymmetric sudden contraction was studied by experiments on pressure drops and a theoretical analysis using the finite difference methods. The main results obtained are as follows:(1) The sudden contraction loss decreases with increase in Reynolds number. The effects of the power-law index and the diameter ratio are small in the laminar flow and within experimental error in the range of the present experiments.(2) The present numerical method based on Kawamura's finite difference scheme and curvilinear grid points developed by Thompson et al. is useful for the contraction pipe flow in the range of 102-103 of Reynolds number.(3) The pressure at pipe wall has a minimum right after the sudden contraction section and through the recovery process, it becomes to decrease monotonously. In this monotonous region, the pressure under the same Reynolds number increases with decrease of the power-law index.(4) The pressure at pipe axis varies approximately as the pressure at pipe wall does. As Reynolds number becomes sufficiently small, the minimum right after the sudden contraction section disappears.(5) The velocity profile does not have a monotonous shape in the corner region of upstream side and in the separation region of downstream, and the maximum velocity at non-axial position appears in the downstream side of contraction pipe.(6) The vortex region in the corner of upstream side becomes larger with increase in Reynolds number. As Reynolds number becomes sufficiently large, the separation vortex region appears in the downstream side.