Abstract
Pressure transients in a rapidly filling pipe with an entrapped air pocket are investigated analytically. A rigid-plug elastic water model is developed by applying elastic water hammer to the majority of the water column while applying rigid water analysis to a small portion near the air-water interface, which avoids effectively the interpolation error of previous approaches. Moreover, another two simplified models are introduced respectively based on constant water length and by neglecting water elasticity. Verification of the three models is confirmed by experimental results. Calculations show that the simplification of constant water length is feasible for small air pockets. The complete rigid water model is appropriate for cases with large initial air volume. The rigid-plug elastic model can predict all the essential features for the entire range of initial air fraction considered in this study, and it is the effective model for analysis of pressure transients of entrapped air.