Flows in curved rectangular channels. (1st report Visualization of secondary flow in the developing region of laminar flow)

Laminar flows through curved rectangular channels were visualized at the entrance region by using incense smoke. The channels have the aspect rations 1 and 2, curvature ratios ranging from 5 to 8 and a width of 20 mm. Visualization was carried out at 12 positions from the inlet (θ=0°) to the outlet (θ=270°) of the curved rectangular channels. It was clarified that (1) the flow patterns were made by superimposing a constant velocity distribution of main flow and main secondary flow vortices. (2) the main secondary flow vortices were at both sides near the inner wall. (3) two pairs of the new type secondary flow vortices were set up at the position of θ=120° in the case of the aspect ratio of 2 and (4) the maximum velocity point of the main flow was shifted outward from the center and shifted again toward the center as the curved angle θ increased.