FLOW PATTERNS AND FRICTIONAL LOSSES IN AN OSCILLATING PIPE FLOW.

Abstract

Velocity distribution and pressure gradient in an oscillating pipe flow are measured over wide ranges of Reynolds numbers and dimensionless frequencies. Wall shear stress is determined by substituting experimental values of cross-sectional mean velocity and pressure gradient into an unsteady momentum integral equation. From these experimental quantities frictional losses and four characteristics parameters describing the flow pattern are calculated. They are well represented by the known laminar theory in a laminar regime and by the turbulent quasi-steady relations in a turbulent regime. Here, turbulent quasi-steady state is defined as the state in which relationship between cross-sectional mean velocity and wall shear stress for steady turbulent pipe flow holds at any moment in a cycle.