Large Eddy Simulation of the influence of solids on macro instability frequency in a stirred tank

The mixing flow in a cylindrical tank stirred with a PBT was simulated with a LES model with Eulerian-Lagrangian approach, in order to study the effect of varying amounts of suspended solids on the frequency and amplitude of macro instabilities (MI). The dispersed phase was reassembled solid glass particles of two different sizes (1 mm, 2 mm) and varying concentrations (up to 3% by volume). The continuous phase velocities were sampled at 18 different locations and were evaluated with the Lomb algorithm to obtain frequency spectra of the flow. The results showed that the MI could be detected in all suspensions and that the frequency is not influenced by the addition of solids. However, the MI became less prominent with increasing number of particles. A periodic fluctuation of the baffle jet could be observed with identical frequency. All results compare fairly well to previously obtained experimental data.