Experimental scanning for simplifying the model of a stirred-tank flow

Abstract

 Velocity measurements by two-component laser Doppler velocimetry (LDV) and laser sheet visualizations were used to analyze the 3D turbulent flow field in a stirred tank, for the purpose of reducing the intricacy of the hydrodynamics to more simple models. We first deal with the mean flow field measured, and the instantaneous visualized patterns, to appreciate the deviation from steadiness and predict the dispersion of particles from the mean motion alone. The study then focuses on the discharge flow from the agitator (Rushton turbine). The jet at the exit from the turbine is modeled in mean values. The flow instability as shown experimentally indicates that the Reynolds number plays no part in this phenomenon. A study based on dynamical system theory, considering a frequency modulation of the flow, shows the possibility of describing rather simply the deterministic component in the velocity fluctuation due to the blades.