Particle Image Velocimetry Experiments and Large Eddy Simulations of Merging Flow Characteristics in Dual Rushton Turbine Stirred Tanks

Abstract

The merging flow characteristics in dual Rushton turbine stirred tanks were investigated using particle image velocimetry (PIV) experiments and large eddy simulation (LES) methods. The velocity and turbulent kinetic energy (TKE) were carefully measured with a high resolution PIV system. The regions with high TKE levels are affected by the movement of the trailing vortices generated behind the blades of the two turbines. The effects of the blade arrangements between the upper and lower turbines on the flow characteristics were discussed, but they are negligible for the phase-averaged flow fields. However, the phase-resolved data are totally different under various blade arrangements. The LES results of velocity, TKE, and trajectories of the trailing vortex cores were quantitatively compared with the PIV experiments and the laser Doppler velocimetry (LDV) data in the literature. Both the phase-averaged and phase-resolved LES results are in good agreement with the PIV experimental data and are better than the simulation results of the k−ε model. The good agreement between LES simulations and PIV experiments shows that the LES method has great potential for predicting complex flow fields in stirred tanks.

Evaluation and accuracy of the local velocity data measurements in an agitated vessel

“…The width of baffles was b = 0.1T . The measurements were carried out with impeller speed 300 rpm, when Reynolds number was 5.0·10 4 , which represents turbulent regime (Re > 10 4 ) for agitated vessel. In turbulent regime the mean velocity and fluctuations are dependent only on impeller tip speed V tip and geometry.…”

“…Although the development of mixing processes is nowadays based mostly on CFD (Computational Fluid Dynamics) where the LES (Large Eddy Simulation) approach is commonly used e.g. [1], [2], [3], [4], [5], the DNS (Direct Numerical Simulation) approach is also under development [6]. The large part of published results in this field were summarised in [7], [8].…”

Stereo‐PIV experiments and large eddy simulations of flow fields in stirred tanks with Rushton and curved‐Blade turbines

“…Based on our previous LES studies using totally hexahedral cells, [39][40][41] a slightly finer grid consisting of approximately two million unstructured, nonuniformly distributed hexahedral cells was used for the current LESs of stirred tank with RT impeller. The impeller discharge region was discretized by finer cells than those used in other regions of the tank, and the averaged cell sizes in these two regions were about 1.5 and 4 mm, respectively.…”

Study of fluid flow in baffled vessels stirred by a Rushton standard impeller

“…The grid cell size in the impeller region was in a range 0.003-0.012 D. The time step was 0.0005 s that corresponds to 0.6°of the impeller movement. The initial computational time was 24 s, which is sufficient for the flow development [14,21]. The computed velocity field was transformed to the cylindrical coordinates (r, θ , z).…”