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Measurement of Trailing Vortices around a Hydrofoil Impeller with PIV and Large Eddy Simulation

The trailing vortices around a hydrofoil impeller were investigated in a 0.383 m i.d.stirred tank with a 0.188 m i.d.hydrofoil impeller using PIV and LES.The comparison between angle-averaged axial velocities by LES and PIV data was in very good agreement,verifying the validity and effectiveness of LES simulation.The presence of trailing vortices formed around the hydrofoil impeller blades were indicated by the mean velocity vectors near the edge of blades,the contours of turbulence levels and kinetic energy of turbulence.It was found that single trailing vortex formed around each blade.The vortex axis was identified to fall on the cylinder swept by the blade tip.The effect of trailing vortices on the turbulence structure was also discussed.The maximum normalized kinetic turbulence energy k/Vtip2 was about 0.04～0.06,which was located at 0.5Z/DT0.67 and 0.3r/R0.4.The research results could be used to improve the mixing process.