Comparison of Numerical Models for the Interaction of a Fluid Transient with an Offline Air Pocket

Effective modeling of pipe network anomalies can supplement fluid transient diagnostic techniques. This study focuses on comparing modeling approaches for predicting the transient response due to air pockets entrapped outside the main flow path (offline), in particular testing the assumption that the flow inside the cavity can be predicted based on a lumped element. This assumption has been consistently made in previous modeling investigations in the time and frequency domains. The results are compared to a system frequency response model without the lumped inertia assumption by quantifying timing and signal frequency distribution errors. It is found that removing the lumped inertia assumption improved the prediction of the reflected and transmitted pulse frequency distributions by averages of 50% and 30%-35%, respectively.