Flow and temperature fluctuation mechanism in a downward branch pipe with a closed end (5th. report, Investigation of fluctuation mechanism for penetration depth)

Abstract

Hot water in a main pipe flows into a branch pipe and forms a thermally stratified layer with cold water at a bent section. Fluctuation of the thermally stratified layer may initiates thermal fatigue crack in the branch pipe. The fluctuation mechanism of penetration depth induced by the main flow in the branch pipe with a closed end was investigated by experiments and numerical simulations. Three flow patterns were observed on the cross-section plane in the branch pipe. They were flow parallel to the cross section direction, flow consisted of small vortexes and a large swirl flow. Generation period of the large swirl flow at L/Db = 4.0 was nearly equal to fluctuation period of the penetration depth. It was shown the large swirl flow which generated periodically around L/Db = 4.0 moved downward in the branch pipe and caused the fluctuation of the thermal stratified layer.

Keywords

• cavity flow
• vertical branch pipe
• penetration depth
• thermal stratification
• swirling flow
• flow visualization
• numerical simulation