Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Investigation of the Pseudo-Isotropic Approximation of a Turbulent Flow in a Stirred Tank
Submission Author:
Aline Gallo De Mitri , SP
Co-Authors:
Mateus Portella, Aline Gallo De Mitri, Helder Moura, Rodrigo de Lima Amaral, José Roberto Nunhez, Guilherme Castilho
Presenter: Mateus Portella
doi://10.26678/ABCM.COBEM2021.COB2021-0996
Abstract
The fluid dynamics study of the turbulent flow in a stirred tank is significantly relevant for optimizing the agitation system, reducing operation costs and improving products, especially in large-scale tanks. In this context, one of the hypotheses generally used for analyzing the turbulence is the pseudo-isotropic approximation, which considers the flow velocity components independent of the evaluation direction. However, the vortices generated by the impeller have a clearly defined orientation, which makes the assumption inconsistent with the phenomena. This work aims to analyze the flow in a stirred tank from the three velocity components (axial, radial and tangential) to investigate the applicability of the pseudo-isotropic approximation. The turbulent flow of water in a tank stirred by a 45º down-pumping pitched-blade turbine operated at 660 rpm using the Stereoscopic-PIV technique was evaluated. Angle-resolved measurements were taken at the fixed blade positions of 0º, 30º and 60º and the results are shown in terms of time-averaged velocity components and turbulent kinetic energy fields. The highest velocities were obtained in the axial direction and the lowest in the radial direction. All the velocities in different angle-resolved fields exhibited substantial velocity fluctuations in the trailing vortices and the discharge regions, especially in the case of the tangential component. It was concluded that the pseudo-isotropic approximation is questionable in the impeller vicinity due to the velocity variations and the vortices formation. However, when the region of interest is located far from this area, the approximation is acceptable.
Keywords
Pseudo-isotropic approximation, Stirred tank, Pitched blade turbine, Turbulent kinetic energy
