A Study of Oscillatory Flow in the Entrance Region of a Curved Pipe. Secondary Flow Visualization and Its Characteristics.

Abstract

A visualization study has been made to investigate the secondary flow induced in an oscillatory laminar flow in the entrance region of a curved pipe with a curvature ratio of 9.8. The experiments were performed under the condition of a moderate Womersley number a=10, which is a physiologically interesting nondimensional frequency. and a Dean number D=300. The secondary flow motion was rendered visible by means of a tracer method using nylon particles, and photographs were taken at four phases in one cycle and at axial locations from the upper stream tangent to the downstream in the curved pipe. The instantaneous velocity vectors and profiles of the secondary flow and its intensity were obtained from the photographs. We discuss the secondary flow characteristics in the entrance region of the curved pipe. Development of the secondary velocity field can be quite well explained from the axial flow field. The secondary flow pattern changes with the phase at the inlet region are complicated, especially at Ω=20∼50°around the curved turn. The intensity of the secondary flow is high during the inflow term of one cycle in the curved pipe, and is high during the outflow term in the upper stream tangent. The inlet length according to the information regarding the secondary flow agrees with the length evaluated from the amplitude of the axial flow velocity in our previous work given by the reference (7).