Séminaire LMFA - Ins and outs of weak volcanic erupting plumes

The behavior of wind-bent plumes is important to a wide variety of fields, including volcanic plume modeling. Current models predict the mixing of ambient air through application of closure arguments known as entrainment coefficients, yet there still exists substantial uncertainty within these models. By understanding the fundamental physics involved in the mixing of a round jet in cross-flow, models predicting the concentration of volcanic ash can be improved by identifying the role of turbulence and wind speed on the rate of entrainment within the plume. Jets of air are ejected orthogonally into a closedloop wind tunnel with varying cross-flow velocities. Mean flow statistics are collected using particle image velocimetry (PIV) to identify the edges of the shear layer to perform control volume analysis to understand the transfer of momentum and energy. The incorporation of both inertial and Reynolds stress contributions allows for inclusion of turbulence, an effect ignored in current models. Here, we show the largest contributor to entrainment of momentum and energy is located on the lee-side of the jet, where cross-flow moving around the jet is recirculated and entrained. By quantifying the large entrainment, general understanding of wind-bent plumes can be enhanced by accounting for highly turbulent interactions.