Periodic Reporting for period 2 - TRUFLOW (TRansfers at tiny scales in tUrbulent multiphase FLOW)
Okres sprawozdawczy: 2021-12-01 do 2023-05-31
The project aims at making scientific breakthrough in the prediction of heat and mass transfer across fluctuating fluid interfaces. It is a considerable challenge in terms of computation. Mass and heat transfer is not only a ubiquitous part of industrial processes, but also a critical component of the global climate system through ocean-atmosphere interactions. Sustainable development and greenhouse gas emission containment will require an overhaul of already knowledge-intensive processes. TRUFLOW thus aims at enabling the quantitative prediction of the heat and mass transfer in fluid flow using simulation, high performance computation and both multiphysics and multiscale methods.
The TRUFLOW Project uses and develops cutting edge simulation methods, including interface tracking and subgrid scale methods to investigate a range of critical processes, allowing for example industry to plan for improved carbon capture processes such as rotating packed beds, new processes such as hydrogen-based metallurgy to replace carbon based metallurgy and so reduce carbon dioxide emissions, heat and mass transfer in hydrogen fuel cells, boiling and cavitation simulation and CO2 transfer across the wavy ocean surface. The key limiting factor in the success of simulation in this domain is the considerable range of scales expected, with slowly diffusing chemicals creating boundary layers that are orders of magnitude smaller than the typical fluid structures, bubbles or droplets. Critical heat fluxes in boiling and interface motion at the microscale are determined by contact line motion, which involves tiny molecular scales. The project aims to bridge these various extreme length scale gaps using boundary layer theory and numerical methods based on it.
The final objective of TRUFLOW is to couple simulation with analysis of existing experimental data. It also involves analysis of the performance of reduced order models of flows with tiny scale transfers, and a systematic use of these models in industrial or natural configurations.
The TRUFLOW Project uses and develops cutting edge simulation methods, including interface tracking and subgrid scale methods to investigate a range of critical processes, allowing for example industry to plan for improved carbon capture processes such as rotating packed beds, new processes such as hydrogen-based metallurgy to replace carbon based metallurgy and so reduce carbon dioxide emissions, heat and mass transfer in hydrogen fuel cells, boiling and cavitation simulation and CO2 transfer across the wavy ocean surface. The key limiting factor in the success of simulation in this domain is the considerable range of scales expected, with slowly diffusing chemicals creating boundary layers that are orders of magnitude smaller than the typical fluid structures, bubbles or droplets. Critical heat fluxes in boiling and interface motion at the microscale are determined by contact line motion, which involves tiny molecular scales. The project aims to bridge these various extreme length scale gaps using boundary layer theory and numerical methods based on it.
The final objective of TRUFLOW is to couple simulation with analysis of existing experimental data. It also involves analysis of the performance of reduced order models of flows with tiny scale transfers, and a systematic use of these models in industrial or natural configurations.
We created a number of reference cases by direct numerical simulation. A large number of such simulations were performed for mass transfer from rising bubbles and in a model of three-phase flow applied to ladle metallurgy. We also retrieved and analyzed *experimental* data for the same problem. A direct diagnosis of the validity of simulations can be obtained from comparison of the experimental open eye data with the simulation. We obtained partial agreement with experiment for the open-eye area and are still investigating the causes of the discrepancy. The numerical simulation results for mass transfer were also compared to experiment with good agreement within the error bars of the prediction. This case should benefit from future use of the boundary layer approach.
Another reference case was obtained for moving contact lines by comparing molecular dynamics, volume of fluid (VOF) and phase field methods for the problem of a droplet sheared between two plates separated by a distance of 50 nanometers. This study has led to a trove of new modelling approaches for the contact line. The classical problem of hydrodynamic assist and curtain coating was revisited. In order to improve the modelling at very small, nanoscopic scales, a diffuse interface method using the van der Waals equation was developped.
Preliminary simulations of nucleate boiling were performed. A major first step was obtained when the mechanisms leading to the formation of the microlayer, a thin layer of liquid appearing in nucleate boiling, were elucidated.
Atomisation is a major direction in TRUFLOW with the aim of understanding spray cooling and helping in the analysis of the transmission of respiratory diseases such as Covid. We retrieved and analyzed experimental data for some situations related to atomisation in human exhalations. The data allowed to evidence a Pareto law in droplet size distributions for violent exhalation and a log-normal law for more moderate exhalation.
We started developing subgrid models of various kinds. The study of contact lines has provided several new ideas. The breakup of thin sheets is now performed using a new model called "manifold death". This model is a major breakthrough obtained from TRUFLOW. For the first time, converged simulations of the statistics of an atomizing flow were obtained useing the manifold death method. This opens the possibility of statistically converged simulations in many fields related to atomization and breakup.
A new method for interfaces that facilitates the implementation of subgrid sheets and boundary layer methods, called Edge Based Interface Tracking has been developped, with first results obtained in the simple 2D kinematic case. This method is akin to front tracking but is closely tied to the Eulerian grids allowing for easier parallelisation and greater accuracy.
We are only starting to demonstrate the performance of the subgrid and reduced models we have developped for boundary layers. However for the simple case of diffusion from rising bubbles, accuracy comparable or superior to the state of the art was obtained.
Another reference case was obtained for moving contact lines by comparing molecular dynamics, volume of fluid (VOF) and phase field methods for the problem of a droplet sheared between two plates separated by a distance of 50 nanometers. This study has led to a trove of new modelling approaches for the contact line. The classical problem of hydrodynamic assist and curtain coating was revisited. In order to improve the modelling at very small, nanoscopic scales, a diffuse interface method using the van der Waals equation was developped.
Preliminary simulations of nucleate boiling were performed. A major first step was obtained when the mechanisms leading to the formation of the microlayer, a thin layer of liquid appearing in nucleate boiling, were elucidated.
Atomisation is a major direction in TRUFLOW with the aim of understanding spray cooling and helping in the analysis of the transmission of respiratory diseases such as Covid. We retrieved and analyzed experimental data for some situations related to atomisation in human exhalations. The data allowed to evidence a Pareto law in droplet size distributions for violent exhalation and a log-normal law for more moderate exhalation.
We started developing subgrid models of various kinds. The study of contact lines has provided several new ideas. The breakup of thin sheets is now performed using a new model called "manifold death". This model is a major breakthrough obtained from TRUFLOW. For the first time, converged simulations of the statistics of an atomizing flow were obtained useing the manifold death method. This opens the possibility of statistically converged simulations in many fields related to atomization and breakup.
A new method for interfaces that facilitates the implementation of subgrid sheets and boundary layer methods, called Edge Based Interface Tracking has been developped, with first results obtained in the simple 2D kinematic case. This method is akin to front tracking but is closely tied to the Eulerian grids allowing for easier parallelisation and greater accuracy.
We are only starting to demonstrate the performance of the subgrid and reduced models we have developped for boundary layers. However for the simple case of diffusion from rising bubbles, accuracy comparable or superior to the state of the art was obtained.
By the end of the project we expect to report the following
On the issue of three-phase flow and ladle metallurgy, we expect to elucidate the remaining uncertainties for open eye size, and to use the newly developped boundary layer techniques to predict mass transfer at very large Schmidt numbers.
On the issue of atomisation, we expect a large-scale use of the manifold death method to predict in statistically converged manner some reference atomising flows such as the pulsed jet.
On the contact line, we expect a new contact line simulation method, expanding the GNBC method with greater stability and accuracy.
We expect simulations of boiling compared in a satisfactory manner to experiments on rough surfaces.
On the issue of three-phase flow and ladle metallurgy, we expect to elucidate the remaining uncertainties for open eye size, and to use the newly developped boundary layer techniques to predict mass transfer at very large Schmidt numbers.
On the issue of atomisation, we expect a large-scale use of the manifold death method to predict in statistically converged manner some reference atomising flows such as the pulsed jet.
On the contact line, we expect a new contact line simulation method, expanding the GNBC method with greater stability and accuracy.
We expect simulations of boiling compared in a satisfactory manner to experiments on rough surfaces.