抄録
The flow from a large space into a pipe has a large annular separated vortex region just after the pipe inlet. This vortex region makes the drag of pipe inlet extremely large. In order to reduce the drag of pipe inlet, the control and suppression of the separated vortex region at the pipe inlet are needed. Generally, bellmouth is mounted at the pipe inlet. But, in this study, the reduction of the flow resistance of pipe inlet on the wall of a large reservoir tank by a simpler method is newly shown and examined. In this new method, a small ring shaped obstacle (see, Fig.1) on the wall of tank at the pipe inlet. It is expected that the separated flow from the obstacle flows along the pipe wall and the vortex region at the pipe inlet is suppressed or minimized. We measured the pressure and velocity distribution in the directions of pipe axis, and visualized a flow pattern of the flow just after pipe inlet. The test section is made by transparent acrylic resin in order to visualized the flow pattern and has many pressure taps on the pipe along the axis. The velocity distribution is measured by Laser Doppler Anemometer (LDA). Flow visualization is made by water solution of fluorescence sodium dye and Laser light sheet method. We also examined the effect of ring shaped small obstacle on the drag reduction. We examined the effect of obstacle with several heights, widths and mounting position. It is made clear that the vortex region just after the pipe inlet is suppressed and then the inlet loss or drag is reduced by about maximum 90% by mounting a ring shaped small obstacle.
