Drag reduction and velocity distribution in developing pipe flow

Abstract

Drag reduction and mean velocity measurements obtained for polymer injection into a developing axisymetric boundary layer in the inlet region of a pipe are reported. Experiments were conducted in a 12-in. diam commercial steel pipe. Concentrated solutions of Polyox WSR 301 were injected into the pipe at 3.5 diam for the pipe entrance. Injection concentrations varied from 100 ppm to 2400 ppm with Reynolds number varying from 2.8x10 to fifth power to 3.0x10 to the sixth power. Data for the inlet and fully developed regions of this study indicate that high drag reductions can be obtained in the inlet region. Drag reduction was found to depend on polymer flow rate, wall shear stress, and distance, but not to depend significantly on injection velocity or injection concentration. A four-layer mean velocity model is shown to describe the velocity profile in the developing polymeric region. The polymer interactive layer is dependent on flow and polymer characteristics. The upward shift of the turbulent layer is directly related to the dimensionless drag reduction parameter (V/u)(hu sub p/hu sub w). The velocity profile in the outer flow of the developing region is described by a velocity defect law with a constant profile parameter.