Laser Doppler measurements of turbulent parameters in different multiple-propeller systems

In this study, laser Doppler anemometry (LDA) measurements in the r-z plane are obtained in two stirred tanks equipped with two downward pumping prope llers in the turbulent and the transient flow domains. A new approach of th e hydrodynamics generated by this system consists of determining the one-di mensional energy spectrum and the autocorrelation coefficient function at d ifferent locations in each vessel. In the turbulent flow, the integral scal es, the Taylor microscales, and the Kolmogorov microscale have been determi ned. The dissipation rate is obtained with two methods: from the semi-empir ical expression epsilon = A k(3/2)/D and from the frequency spectrum. Resul ts show the influence of the rheological properties on the flow patterns, t he influence of the blade passage frequency on the frequency spectrum, and the apparition of a low frequency characterizing the production of macro-in stabilities. Comparison of the turbulent characteristics with the values re ported in the literature shows that our combination of propellers produces larger eddies than a Rushton turbine.