Drag Reduction of T-junction Pipe Flow by Small Obstacles

Abstract

Flows in the T-junction of a counter-flow pipe are run counter to each other and they usually flow out vertically together. A flow separated from the junction corner forms separated vortex regions and they reduce the effective cross-sectional areas of the pipe, and this increases flow resistance, i.e., drag (pressure loss). The corner of the junc-tion is generally rounded to prevent the flow from separating and to reduce drag. This method can reduce drag by 30% with a rounded radius of 0.1D (D: pipe inner diame-ter), but some process is needed to remove the corners. We propose a simple method of reducing drag in the flows of T-junction pipes by mounting two small weir-shaped obstacles on the upstream of the walls of the two pipes beside the junction corners. This method is a simple way of reducing drag without having to use a removal process. The pressure distribution along the pipes was measured and the drag in a T-junction pipe was derived. The flow pattern was visualized with a tracer method and this was evaluated to confirm the separation of flow from the corners. As a result, we clarified that drag in a T-junction could be reduced by a maximum of about 30% by mounting small obstacles at heights of 0.30D and 0.47D from the upstream of the corners.