Studies on two-phase cross flow. Part II: Transition Reynolds number and drag coefficient

Abstract

A reduction of the transition Reynolds number from laminar separation to turbulent one of cross flow around a body is anticipated in a gas—liquid bubbly flow, since there exists intensive turbulence in the main flow. A decrease in the drag coefficient of the body can also be expected. This report was aimed to classify flow patterns of the two-phase wake flow behind a cylinder and to investigate quantitatively the change of the drag coefficient corresponding to the transition of the flow patterns. From measurements of the static pressure distribution on the cylinder surface and the drag coefficient of the cylinder, it was found that the flow pattern was sure to change finally into a new one similar to the transcritical type in the single-phase flow with an increase of the mean void fraction in the main flow. It was concluded that a large reduction of the upper transition Reynolds number occurred in a two-phase flow, because the transition could be realized by a little increase of the void fraction even below the lower transition Reynolds number in the case of a large cylinder diameter.