Laminar Secondary Flow in Square Bends

Abstract

The laminar secondary flow in square bends was studied by the flow visualization technique.
Axial and secondary velocities were measured by using the hydrogen bubble method, and it was observed that the position of maximum axial velocity moved along the plane of symmetry away from the center of curvature.
To express quantitatively the secondary flow which characterizes the bend flow, the intensity of secondary flow is newly defined as the circulation, and its axial distribution was obtained experimentally.
The intensity of secondary flow was related to the deflection angle from the bend inlet, the radius of curvature and the Dean number. It was found that the circulation has its maximum value near the bend inlet and almost disappears at the bend outlet.