Abstract
The flow through an abrupt expansion pipe has a large annular vortex region just after the expansion. The negative pressure in this region causes a large flow resistance, drag. Some flow control is needed to reduce the flow resistance. In this study, the reduction of the flow resistance by mounting a small ring shaped obstacle on the downstream pipe wall is newly proposed and examined. The backward flow in the vortex region was decreased by mounting the obstacle. The optimum combination of height and location of obstacle is h/H = 0.8 and L/H = 2.07 (h: height of obstacle, L: distance between obstacle and expansion, H: step height of expansion part), respectively. In this case, the flow resistance is reduced by 26% than a normal abrupt expansion pipe, and it is nearly equivalent to the 30 degree diffuser. This is a simpler method than using diffuser, particularly for a large scale pipe or duct system.
