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Academic Paper

Investigating Turbulent Properties at the Base of a Stirred Vessel with LES

Time Scales and Turbulent Spectra Above the Base of Stirred Vessels from Large Eddy Simulations

Flow, Turbulence and Combustion (2020)

Jason J. Giacomelli, Harry E. A. Van den Akker

Many industrial processes carried out in a stirred vessel involve the suspension of solid particles and can underperform if the solid phase is not adequately suspended. In this paper, Philadelphia Mixing Solutions, Ltd. explores the turbulent properties at the base of a stirred vessel.

Industrial processes – such as crystallization, leaching and slurry transport – underperform if the solid phase is not adequately suspended within the stirred vessel. In order to continuously mobilize and suspend particles, the vessel impeller needs to convey energy to the particles. This paper investigates the mechanics that dominate this energy, including spatial resolution, tank size and time scales.

Though each process varies, in general, all particles must be in motion at the base of the vessel, and no particle can be stagnant for more than one to two seconds. So, what happens in a highly turbulent system with large particles that settle to the base relatively quickly? That’s the question this research aims to solve for engineers who are trying to confidently size agitation equipment.

Large Eddy Simulations (LES) are uniquely suited to predict a large fraction of the turbulent energy in the stirred vessel. Compared to Direct Numerical Simulations, Reynolds Averaged Navier-Stokes (RANS) simulations and experimental data, LES resolves most of the turbulence. This research leverages the lattice-Boltzmann approach—a computationally more efficient method—to complete all LESs.

­Through this method, the researchers were able to gain an understanding of the time scales of turbulent flow filed existing above the base of the vessel at minimum required energy levels.

The full paper:

  1. Outlines the LES modeling approach and discusses velocities, spectra and time scales.
  2. Details the simulation, including vessels, impellers and probes.
  3. Computes energy spectra, temporal autocorrelations, Taylor time scales and integral time scales.

To learn more about the development of the approach and see the results, read the full paper here.