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.
Accurate prediction of the consequence of fire is crucial for fire safety analysis and assessment of designs for fire protection measures. Based on the previous study, a fully-coupled large Eddy simulation (LES) has been carried out to simulate the temporal combustion behavior of a large-scale buoyant pool fire. Although the pulsation effect of fire was properly captured, a single chemical reaction was adopted which could pose inappropriate interpretation of instantaneous heat release rate and vorticity generation. Combustion of fire involves hundreds of chemical reactions where the embedded kinetics plays a predominant role of the resultant heat release rate and species concentrations. Due to its complexity and intensive computational requirement, combustion kinetics simulations were used to be limited for combustion in laboratory scale. Most the existing fire models (e.g. Fire Dynamics Simulator -FDS) therefore only consider one or just few chemical reactions in simulation. With advancement of computer technology, integrating kinetics in fire modelling has become feasible. To investigate the influence of chemical kinetics on the vortical structures of fire, a LES model coupled with detailed chemical kinetics has been developed based on laminar flamelet approach. The flamelet library was evaluated based on the chemical mechanism for C1-C2 hydrocarbons combustion with soot formation. Numerical predictions are then compared and validated against previous numerical predictions and experimental data. Based on the preliminary results, the predicted time-averaged velocity and temperature profile has been found to be in good agreement with the experimental data whilst the temporal fluctuation of temperature and velocity are better captured in comparison to previous results with single step reaction.Hu et al., Modelling of temporal combustion behaviour in a large-scale buoyant pool fire with detailed chemistry consideration 1.
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