On the Flow in a Circular Section Tube and the Loss due to a Sudden Enlargement : Effects of Drag Reducing Additives

Abstract

In the flow of water through a sudden enlargement in a circular section tube, effects of drag reducing additives on losses due to friction and sudden enlargement were studied experimentally. And, in the case that the drag reduction occured in the upstream of drag reduction reappears in the downstream of a sudden enlargement, it was found under a certain condition that the drag reduction reappears in the downstream of a sudden enlargement, the distance of pressure recovery in the rear of a sudden enlargement lengthens and the sudden enlargement factor decreases. From discussions of experimental results, we also found that the relationship between rate of drag reduction (D_r*) and wall shear stress at the onset point of drag reduction (τ_w*) in circular section tube flows prior to a sudden enlargement was useful in the characterization of above mentioned phenomena.