Experimental analysis of hydrodynamics in a radially agitated tank

A PIV technique is used to analyze the local hydrodynamics generated by a Rushton turbine. Different types of motion coexist in the tank: the mean flow (or global circulation), the periodic fluctuations (or trailing vortices) induced by the blade rotation in the impeller region, and the turbulent fluctuations (that dissipate the kinetic energy). These three kinds of motion can be estimated after experiments as soon as a triple decomposition of the velocity is performed. The mean velocity, the periodically induced stress, and the Reynolds stress are analyzed in the agitated tank, close to the impeller. These data are used for two purposes: to identify and quantify the transfer of kinetic energy between mean flow, periodic flow, and turbulence; and to estimate the dissipation rate of turbulent kinetic energy (TKE) from the balance of TKE, in which each term will be derived from experiments. Characteristics of turbulence are also presented and discussed.