Rigid-plug elastic-water model for transient pipe flow with entrapped air pocket

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 columns while applying rigid-water analysis to a small portion near the air–water interface. The proposed model is validated by the full elastic-water model and experimental data. It effectively avoids the interpolation error of the method of characteristics reducing its complexity when tracking the air–water interface. Moreover, the current model has the same accuracy as the full elastic-water model.