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Numerical Simulation of Air-water Bubbly Jet Issuing from a Square Nozzle by a Vortex in Cell Method

Tomomi Uchiyama and Yusuke Kishimoto

A water jet entrained with small air bubbles is simulated. The Vortex in Cell method for bubbly flow proposed by the authors in a prior study is used for the simulation. The method discretizes the vorticity field into vortex elements and computes the time evolution of the flow by tracing the convection of each vortex element using the Lagrangian approach. The bubbly jet issues vertically upward from a nozzle of square cross-section. The Reynolds number based on the water velocity is 5000. The bubble diameter is 0.2 mm, and the bubble volumetric flow rate ratio at the nozzle is 0.0025. The bubbles increase the water turbulence intensity around the jet centerline. This makes the water momentum diffusion in the lateral direction larger at the initial region of the jet. The bubble effect lessens with increasing axial distance from the nozzle. These simulated results are favorably compared with existing measurements, demonstrating the validity of the current simulation method for bubbly jet. In the developed region, the water velocity decay is relaxed and the half-width reduces. This is because the water is accelerated by the bubbles, which have higher axial velocity due to the buoyant force.