A Multi-Block Approach to Obtain Angle-Resolved PIV Measurements of the Mean Flow and Turbulence Fields in a Stirred Vessel

摘要

Two-dimensional Particle Image Velocimetry (PIV) measurements have been used to characterize the complex turbulent flow generated by a T/3 45° pitched-blade down-flow turbine, operated at Re ≈ 5 · 10~4, in a fully turbulent stirred vessel. To maintain high spatial resolution when viewing the whole vessel, a multi-block approach has been developed, which combines data from different fields of view into a composite flow map. Using 500 measurements of instantaneous u and v velocity fields, angle-resolved mean velocity maps and turbulence properties, such as the RMS velocities and the turbulence kinetic energy, have been estimated near to the blade, as well as in the bulk of the vessel, at a spatial resolution of between 1 and 2 mm. Vorticity maps have also been calculated to help visualize the trailing vortex structures close to the impeller blades and integral length scales have been estimated from the two-dimensional spatial auto-correlation function. It is shown than the common assumption that the integral length scale is about half the blade width is an overestimate close to the impeller and an underestimate far from the impeller.