A high resolution computational fluid dynamics model is used to simulate a steady air entraining laboratory scale hydraulic jump. A detailed examination of shear layer instabilities reveals the dynamic relationship between spanwise vortices, free surface fluctuations, and air–water spatial patterns. Spanwise vortices generated at the toe roll-up under a variable depth roller, creating large free surface fluctuations through high velocity water ejections in the roller. The mean shear layer elevation and free surface elevations periodically alternate between positive and negative correlation throughout the roller, driven by dynamic vortex transport. Vortices descending towards the lower wall create an upwelling of non-bubbly fluid into the shear layer that contributes to regions of decreased bubble concentration between vortices. The position of a strong shear layer at the location of maximum air entrainment, directly above the jump toe, leads to highly aerated vortices that influence bubble behavior. Bubbles breakup quickly after entrainment at the toe and bubble clusters are observed most frequently below and at the end of the roller where bubble breakup and energy dissipation are diminished. The dominant separation angle of clustered bubbles is independent of downstream distance and aligns closely with the direction of initial shear, suggesting bubble clustering is a remnant of bubble breakup.
Bibliographical noteFunding Information:
This research was supported by funding from the U.S. Department of Energy and its Office of Energy Efficiency and Renewable Energy Water Power Program, through a graduate research fellowship awarded and managed by the Hydro Research Foundation , and from the University of Minnesota through the Department of Civil Engineering's Sommerfeld Fellowship (grant no. DE-EE0002668). This work was carried out in part using computing resources at the University of Minnesota Supercomputing Institute. The authors would like to thank Dr. Frédéric Murzyn for providing experimental data.
- Air entrainment
- Bubble cluster
- Hydraulic jump
- Multiphase simulations
- Shear layer