Patrick J. Frawley

Comparison of Lagrangian and Eulerian Simulations of Slurry Flows in a Sudden Expansion

From a review of technical literature, it was not apparent if the Lagrangian or the Eulerian dispersed phase modeling approach was more valid to simulate dilute erosive slurry flow. In this study, both modeling approaches were employed and a comparative analysis of performances and accuracy between the two models was carried out. Due to an impossibility to define, for the Eulerian model already implemented in FLUENT , a set of boundary conditions consistent with the Lagrangian impulsive equations, an Eulerian dispersed phase model was integrated in the FLUENT code using subroutines and user-defined scalar equations. Numerical predictions obtained from the two different approaches for two-phase flow in a sudden expansion were compared with the measured data. Excellent agreement was attained between the predicted and observed fluid and particle velocity in the axial direction and for the kinetic energy. Erosion profiles in a sudden expansion computed using the Lagrangian scheme yielded good qualitative agreement with measured data and predicted a maximum impact angle of 29 deg at the fluid reattachment point. The Eulerian model was adversely affected by the reattachment of the fluid phase to the wall and the simulated erosion profiles were not in agreement with the Lagrangian or measured data. Furthermore, the Eulerian model under-predicted the Lagrangian impact angle at all locations except the reattachment point.

Combination of CFD and DOE to analyse solid particle erosion in elbows

Solid particle erosion is a major concern in the engineering industry, particularly where transport of slurry flow is involved. Such flow regimes are characteristic of those in alumina refinement plants. The entrainment of particulate matter, for example sand, in the Bayer liquor can cause severe erosion in pipe fittings, especially in those which redirect the flow. The considerable costs involved in the maintenance and replacement of these eroded components led to an interest in research into erosion prediction by numerical methods at Rusal Aughinish alumina refinery, Limerick, Ireland, and the University of Limerick. The first stage of this study focused on the use of computational fluid dynamics (CFD) to simulate solid particle erosion in elbows. Subsequently an analysis of the factors that affect erosion of elbows was performed using design of experiments (DOE) techniques. Combining CFD with DOE harnesses the computational power of CFD in the most efficient manner for prediction of elbow erosion. An analysis of the factors that affect the erosion of elbows was undertaken with the intention of producing an erosion prediction model.

A 2D Computational Fluid Dynamics Analysis of Wells Turbine Blade Profiles in Isolated and Cascade Flow

This paper deals with the application of Computational Fluid Dynamics (CFD) to the analysis of the aerodynamic characteristics of symmetrical airfoil blades in 2-Dimensional flow. The CFD model was used to compare blades of varying profiles to analyse the aerodynamic forces and the compressibility effects and to compare the differences in modelling the blades in isolated and cascade flow. The model was validated using correction factors with published results for the NACA 0015 blade profile, which show that the model gives good results for the aerodynamic forces. The differences in the predicted aerodynamic characteristics, such as low angle of incidence drag, as well as normal and tangential forces are compared for the isolated and cascade cases. The validated model was then used to compare proposed blade profiles for a Wells Turbine. The paper presents the results of the numerical investigation along with the analysis and comparison of the different profiles.Copyright

Application of the Lagrangian CFD Approach to Modelling of Crystallization in Stirred Batch Reactors Using the Smoothed Particle Hydrodynamics Method

Abstract Crystallization phenomena in stirred reactors are influenced by local hydrodynamic conditions and these must be taken into account for successful process scale-up and optimization. In this work, the available state of the art grid-based CFD methods and advantages and disadvantages of their application to mathematical modelling of batch crystallization processes were analyzed. The benefits of the Langrangian meshfree methods were discussed and the Smoothed Particle Hydrodynamics method proposed as an efficient method for a rapid prediction of the global mean flow in stirred reactors. Various aspects of the simulation results were assessed: quality of the fluid prediction, computational requirements, existence of numerical problems and availability of crystal size distribution. The developed Smoothed Particle Hydrodynamics CFD model was successfully coupled with discretised population balance equations to model a cooling batch crystallization process. It has been shown that 200 additional transport equations resulting from the discretisation of the population balance leads to only 50% decrease in computational performance while the same problem is still almost intractable from the computational point of view using the grid-based CFD methods.

A 3D Computational Fluid Dynamics Analysis of the Wells Turbine

This paper deals with the application of Computational Fluid Dynamics (CFD) to the performance comparison of some proposed blade designs for the Well’s Turbine. The turbines were modelled at typical Reynolds numbers for full scale rigs and the results were found to correlate well with scale predictions from experimental data. Three different turbine designs were analysed, one a 4-bladed rotor and the other two 8-bladed rotors. The only difference between the two 8-bladed rotors was the addition of forward sweep to one. The addition of forward sweep was shown to have little effect on the overall performance of the 8-bladed rotor. The 4-bladed rotor was shown to have the highest efficiency and pressure drop at low flow rates, however it was also shown to have a much smaller operating range than the 8-bladed rotors.© 2002 ASME

A Computational Fluid Dynamics Comparison of Wells Turbine Blades in 2D and 3D Cascade Flow

This paper deals with the application of Computational Fluid Dynamics (CFD) to the analysis of the aerodynamic characteristics of symmetrical airfoil blades in 2-Dimensional cascade flow. Theoretical two dimensional cascade analyses of Wells Turbines blade profiles have been used in the past to predict the performance of three-dimensional turbines. The use of two-dimensional cascade models is beneficial as it allows the analysis and optimisation of the blade profile with approximately one tenth the computational requirements of a three-dimensional model. The primary objective of this work was to provide further validation of the use of two dimensional cascade models by comparing the computational predictions with traditional theoretical calculation results and also with three-dimensional turbine results. A secondary objective was to use the two dimensional cascade models to better understand the blade interaction effects that occur in the Wells Turbine. The model was used to analyse and compare three different blade profiles at different cascade settings. This paper presents the results of the numerical investigation, the validation of the results and the subsequent analysis.Copyright