Periodic Reporting for period 1 - MULTIPIR (Multiscale modelling of migration of pollutant particles in rivers)
Reporting period: 2020-12-01 to 2022-11-30
River pollution from fine-grained sediment (FGS) is an unsolved challenging environmental problem. A thorough understanding of FGS migration in rivers is critical in improving water quality in rivers and river management. To achieve this, a hybrid discrete element method (DEM) and lattice Boltzmann method (LBM) are firstly employed to systematically analyse transportation of FGS. The effects of fluid inertia, particle density and cavity size on the trap efficiency in the cavity are systematically investigated. The results show that three distinctive regimes can be identified using a dimensionless trap number: a resuspension regime, a fully trapped regime, and a continuous circulating regime. To investigate the migration behavior of FGS particles under higher Reynolds number, a discrete phase model (DPM) coupled with computational fluid dynamics (CFD) is also developed. The influence of particle properties, operating parameters, and various flume configurations on the flow status and migration behaviour is systematically analysed. Flume tests are performed to validate the developed models and further explore the migration behaviour of particles. The infiltration rate of the FGS particles dramatically increases when the particle density increases or fluid velocity decreases. Moreover, the shape of the cavity is found to have less effect on the infiltration rate. It is also found that the resuspension rate increases linearly with the growth of inlet velocity and decreases dramatically with the rise of the particle size and density. A GPU-enhanced DEM approach is also developed to explore the transportation behavior of shaped particles. It is found that the transportation of spherical particles involves the smallest particle retention number, mean residence time, and power consumption, while shaped particles lead to the larger particle retention number and higher power consumption. The combined numerical and experimental investigations provide a step-change in process understanding and model development underpinning future river pollution control initiatives.
MULTIPIR employs an interdisciplinary approach to understand the fundamental mechanisms of migration behaviour of pollutant particles and to develop predictive computational modelling of the infiltration and resuspension process of the fine-grained sediment (FGS) in a river. During the two years, significant progress in research and personal development is made and summarized below.
1) DEM-LBM MODELLING OF PARTICLE MIGRATION OVER CAVITY
We employed a hybrid discrete element method (DEM) and lattice Boltzmann method (LBM) to systematically investigate the transportation and entrapment of a dilute suspension in a microchannel flow over a rectangular cavity. The effects of fluid inertia, particle density and cavity size on the trap efficiency in the cavity are systematically investigated. The results show that decreasing the Reynolds number and increasing the length and depth of the cavity all lead to an increase in the trap efficiency. A close examination of the trajectory of particles reveals three distinct dynamic behaviours in the cavity flow: i) resuspension, ii) circulation in the central vortex and iii) deposition near the tailing edge of the cavity. Three distinctive regimes were then identified using a dimensionless trap number Tp: a resuspension regime with Tp<1, a fully trapped regime with Tp>2.5 and a continuous circulating regime in between. The obtained results would provide insight for the sedimentation behaviour. Based on this work, one paper has been published on Powder Technology, which is a top journal in the field of particle-based science and technology.
2) DPM-CFD MODELLING OF PARTICLE MIGRATION IN WATER
A discrete phase model (DPM) coupled with computational fluid dynamics (CFD) is developed to investigate the migration behavior of FGS particles. In order to simulate the flow field and particle motion, the commercial CFD software, ANSYS FLUENT, is used, and the discrete phase model is implemented. A flume with an inverted trap configuration is modelled to study the migration of particles. The influence of particle properties (particle size, particle density), operating parameters (fluid velocity), and various flume configurations (cavity shape) on the flow status and migration behaviour is then systematically analysed. To ensure accurate simulations, it is essential to validate the numerical models. Therefore, flume tests are performed to validate the developed models and further explore the migration behaviour of particles in this study. An experimental setup to measure the migration behaviour of particles is developed. The infiltration and resuspension behaviour of FGS particles is also explored. It is shown that the infiltration rate of the FGS particles dramatically increases when the particle density increases or fluid velocity decreases. Additionally, the shape of the cavity is found to have less effect on the infiltration rate. It is also found that the resuspension rate increases linearly with the growth of inlet velocity and decreases dramatically with the rise of the particle size and density. Evolutions of velocity and position along the cavity during particle migration are examined. The velocity distribution at plane Y=0 along the cavity width is affected by the vortex. Velocity magnitude shows an ‘M’ shape, and the X velocity shows an ‘N’ shape distribution. Based on this work, one paper is under preparation for submission to a journal.
3) DEM MODELLING OF NON-SPHERICAL PARTICLES TRANSPORTATION
We develop a GPU-enhanced DEM approach to explore the transportation behavior of the non-spherical particles during twin screw granulation (TSG). Especially, a graphic processor units (GPUs) enhanced discrete element method (DEM) is adopted to examine the effect of particle shape on the conveying characteristics, e.g. particle retention number, residence time distribution, and power consumption. TSG with spherical particles gets the smallest particle retention number, mean residence time, and power consumption; while for Hexp shaped particles the largest particle retention number is obtained, and TSG with cubic particles requires the maximum power consumption. Furthermore, spherical particles exhibit a flow pattern closer to an ideal plug flow, while cubic particles present a flow pattern approaching a perfect mixing flow. The proposed GPU-enhanced DEM approach can simulate the complex TSG process with non-spherical particles. Based on this work, two papers have been published on the international journals, Particuology and Powder Technology.
1) DEM-LBM MODELLING OF PARTICLE MIGRATION OVER CAVITY
We employed a hybrid discrete element method (DEM) and lattice Boltzmann method (LBM) to systematically investigate the transportation and entrapment of a dilute suspension in a microchannel flow over a rectangular cavity. The effects of fluid inertia, particle density and cavity size on the trap efficiency in the cavity are systematically investigated. The results show that decreasing the Reynolds number and increasing the length and depth of the cavity all lead to an increase in the trap efficiency. A close examination of the trajectory of particles reveals three distinct dynamic behaviours in the cavity flow: i) resuspension, ii) circulation in the central vortex and iii) deposition near the tailing edge of the cavity. Three distinctive regimes were then identified using a dimensionless trap number Tp: a resuspension regime with Tp<1, a fully trapped regime with Tp>2.5 and a continuous circulating regime in between. The obtained results would provide insight for the sedimentation behaviour. Based on this work, one paper has been published on Powder Technology, which is a top journal in the field of particle-based science and technology.
2) DPM-CFD MODELLING OF PARTICLE MIGRATION IN WATER
A discrete phase model (DPM) coupled with computational fluid dynamics (CFD) is developed to investigate the migration behavior of FGS particles. In order to simulate the flow field and particle motion, the commercial CFD software, ANSYS FLUENT, is used, and the discrete phase model is implemented. A flume with an inverted trap configuration is modelled to study the migration of particles. The influence of particle properties (particle size, particle density), operating parameters (fluid velocity), and various flume configurations (cavity shape) on the flow status and migration behaviour is then systematically analysed. To ensure accurate simulations, it is essential to validate the numerical models. Therefore, flume tests are performed to validate the developed models and further explore the migration behaviour of particles in this study. An experimental setup to measure the migration behaviour of particles is developed. The infiltration and resuspension behaviour of FGS particles is also explored. It is shown that the infiltration rate of the FGS particles dramatically increases when the particle density increases or fluid velocity decreases. Additionally, the shape of the cavity is found to have less effect on the infiltration rate. It is also found that the resuspension rate increases linearly with the growth of inlet velocity and decreases dramatically with the rise of the particle size and density. Evolutions of velocity and position along the cavity during particle migration are examined. The velocity distribution at plane Y=0 along the cavity width is affected by the vortex. Velocity magnitude shows an ‘M’ shape, and the X velocity shows an ‘N’ shape distribution. Based on this work, one paper is under preparation for submission to a journal.
3) DEM MODELLING OF NON-SPHERICAL PARTICLES TRANSPORTATION
We develop a GPU-enhanced DEM approach to explore the transportation behavior of the non-spherical particles during twin screw granulation (TSG). Especially, a graphic processor units (GPUs) enhanced discrete element method (DEM) is adopted to examine the effect of particle shape on the conveying characteristics, e.g. particle retention number, residence time distribution, and power consumption. TSG with spherical particles gets the smallest particle retention number, mean residence time, and power consumption; while for Hexp shaped particles the largest particle retention number is obtained, and TSG with cubic particles requires the maximum power consumption. Furthermore, spherical particles exhibit a flow pattern closer to an ideal plug flow, while cubic particles present a flow pattern approaching a perfect mixing flow. The proposed GPU-enhanced DEM approach can simulate the complex TSG process with non-spherical particles. Based on this work, two papers have been published on the international journals, Particuology and Powder Technology.
In summary, both numerical and experimental approaches have been devoted to predicting the migration behaviour of pollutant particles. MULTIPIR takes an engineering approach that combined multiscale modelling and experimentation to explore infiltration and resuspension of FGS, aiming to provide a step-change in process understanding and theoretical development that will enable the creation of new predictive models underpinning the future river pollution control initiatives.