Examination of Flow Response to Vent Shape Modification

During volcanic eruptions, the vent profile evolves due to high pressure and shear from ejected gases and particulates. The basic process has been considered numerically, but there are few experimental studies of this process. Recently, a laboratory-scale study was conducted, using a compressed air jet directed through an erodible powder sample. Initial experiments demonstrated that the erosion process was quasi-steady, indicating that the system could be further studied using rigid samples with appropriate vent contours. Therefore, a series of tapered solid vents have been fabricated, with dimensions corresponding to key phases in the erosive process studied previously. Air is directed vertically through these samples at a moderate overpressure ratio of K ~ 3, and particle image velocimetry (PIV) is used to measure the flow velocities near the exit. These velocities are used to determine the time-dependent response of the flow structure and overall mass flow rates, which may provide a baseline for further computational simulations.