new simplified method to evaluate levels of local anisotropy of turbulence in mixing vessels has been proposed. The method has been tested both in a baffled and an unbaffled tank stirred with a Rushton turbine, by means of a detailed comparison with levels of local anisotropy of turbulence determined with the analysis of the invariants of the anisotropy stress tensor. In both configurations three-dimensional laser Doppler anemometry measurements have been performed throughout the whole vessel. The results indicated that turbulence deviates significantly from the isotropic state not only in the impeller region but also near the bottom of the vessel, for both baffled and unbaffled configurations. Larger regions with high local anisotropy of turbulence are present in the unbaffled vessel with respect to the baffled vessel. Finally, the simplified method was also tested and applied to a magnetically driven impeller that has been poorly investigated in the published literature but largely employed for industrial mixing processes. The flow field generated by this impeller is also shown. Advantages, drawbacks, and applicability of the simplified method are discussed.

Screening tool to evaluate the levels of anisotropy of turbulence in stirred vessels

BRUNAZZI, ELISABETTA;GALLETTI, CHIARA;PINTUS, SANDRO
2005

Abstract

new simplified method to evaluate levels of local anisotropy of turbulence in mixing vessels has been proposed. The method has been tested both in a baffled and an unbaffled tank stirred with a Rushton turbine, by means of a detailed comparison with levels of local anisotropy of turbulence determined with the analysis of the invariants of the anisotropy stress tensor. In both configurations three-dimensional laser Doppler anemometry measurements have been performed throughout the whole vessel. The results indicated that turbulence deviates significantly from the isotropic state not only in the impeller region but also near the bottom of the vessel, for both baffled and unbaffled configurations. Larger regions with high local anisotropy of turbulence are present in the unbaffled vessel with respect to the baffled vessel. Finally, the simplified method was also tested and applied to a magnetically driven impeller that has been poorly investigated in the published literature but largely employed for industrial mixing processes. The flow field generated by this impeller is also shown. Advantages, drawbacks, and applicability of the simplified method are discussed.
Brunazzi, Elisabetta; Galletti, Chiara; Paglianti, A.; Pintus, Sandro
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/205208
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