Experimental investigation of entrapped air pocket in a partially full water pipe

Abstract

The effect of air pocket during rapid filling of partially full pipe with dead end is investigated experimentally. The air–water flow patterns are observed with a high-speed camera. Pressure histories synchronously recorded are also presented to illustrate the relations between the air–water phase evolutions and the pressure oscillation patterns. Experiments indicate that tailwater is beneficial to reduce air pressure surge. Having the same air volume, the case with thinner or no tailwater can result in the larger pressure surge. The highest pressure fluctuates dramatically with the increase of initial air volume (involved in changing air length and tailwater depth). However, the trends of measured results show the maximum air pressure first increases and then decreases if initial air pocket volume increases at a given initial tailwater depth or air length. Moreover, the ratio of the maximum pressure to upstream inlet pressure increases as upstream inlet pressure increases.