Extending the authors' earlier investigations, transient flow associated with rapid filling of an open-ended pipeline is explored both experimentally and numerically. A crucial finding is that trapped air in an open-ended system makes it more prone to transient subatmospheric pressures. However, if only one air pocket is present, and there is a relatively substantial air pocket with a short blocking column, subatmospheric pressures are avoided. Once subatmospheric pressure arises, transient intensities would first increase and then decrease with an increase of the length ratio of blocking column to the air pocket, and then gradually diminish for relatively large length ratios. If two air pockets are present, the downstream air pocket and blocking column are beneficial for relieving the subatmospheric phenomenon associated with the upstream air pocket; however, the subatmospheric phenomenon typically persist in the downstream air pocket. An elastic model for open-end case is validated by experimental data.
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