Periodic Reporting for period 4 - TRUFLOW (TRansfers at tiny scales in tUrbulent multiphase FLOW)
Reporting period: 2024-12-01 to 2025-05-31
The project aims at predicting the behavior of natural and industrial systems and processes with a wide range of scales, for example ocean wave systems which combine long wavelengths of meters with tiny droplets and bubbles down to the micron size. Typically the simulation of such systems is extremely costly, as each small scale feature must be described by a computational cell. The number of computational cells required then surpasses any current of foreseeable capability on even the largest computing systems. To be nevertheless able to predict the behavior of such systems and design new ones in the industrial case, one must solve so-called multiscale mathematical problems. The computational methods that are developed for this aim are called subgrid-scale methods. Another problem addressed in the project as it uses similar methodology is the propagation of respiratory viruses and notably the Covid virus.
The realization of computational capabilities for systems with wide ranges of scales is of central importance for the energy transition which requires the design of new industrial process or the adaptation of old ones to replace greenhouse-gas producing processes by carbon-neutral processes. Such processes are for example the production of iron by direct reduction and the pyrolysis of methane, plastics and organic waste. Most of the relevant industrial processes for the energy transition, such as electrochemical processes, involve multiphase flows with a range of scales. For example the secondary refinement of metals in bottom blown ladles involves regions of mass transfer, called boundary layers, that can become extremely thin. The redesign of metallurgical processes to adapt them to avoid carbon emissions will require accurate simulation of such boundary layers by the multiscale methods that are the main topic of the TRUFLOW project. Simpler processes that also have huge impact for society are the diffusion of carbon dioxide to and from small bubbles, a process that again involves very thin boundary layers. Through the design of industrial processes using the multiscale approach of the project, and thanks to the better understanding of natural processes such as the ocean-atmosphere carbon dioxide exchange the project is of wide and major importance. As for the propagation of respiratory diseases, it is a very important problem as its resolution allows both to validate the science of propagation and to design public health regulations.
The objectives of the project, accordingly, are the multiscale treatment of very thin boundary layers occurring in industrial processes such as bottom-blown ladles or rising gas bubbles, the prediction of the formation of very small droplets in processes that lead to liquid mass breakup such as atomization, and the treatment of another small scale process known as the dynamic contact line, where liquid-gas interfaces meet a solid. This process is also important for heat and mass transfer and extremely costly computationally. The multiscale treatment also has the objective of simulating heat transmission processes such as boiling and spray cooling in which a solid surface is cooled by the projection of a spray formed by an atomizing jet, and nucleate boiling where heat transfer is achieved by the localized vaporization of water. For respiratory disease propagation the objective is to predict the droplet size distributions in atomizing films modelling the mucous-salivary films in the human respiratory duct.
The realization of computational capabilities for systems with wide ranges of scales is of central importance for the energy transition which requires the design of new industrial process or the adaptation of old ones to replace greenhouse-gas producing processes by carbon-neutral processes. Such processes are for example the production of iron by direct reduction and the pyrolysis of methane, plastics and organic waste. Most of the relevant industrial processes for the energy transition, such as electrochemical processes, involve multiphase flows with a range of scales. For example the secondary refinement of metals in bottom blown ladles involves regions of mass transfer, called boundary layers, that can become extremely thin. The redesign of metallurgical processes to adapt them to avoid carbon emissions will require accurate simulation of such boundary layers by the multiscale methods that are the main topic of the TRUFLOW project. Simpler processes that also have huge impact for society are the diffusion of carbon dioxide to and from small bubbles, a process that again involves very thin boundary layers. Through the design of industrial processes using the multiscale approach of the project, and thanks to the better understanding of natural processes such as the ocean-atmosphere carbon dioxide exchange the project is of wide and major importance. As for the propagation of respiratory diseases, it is a very important problem as its resolution allows both to validate the science of propagation and to design public health regulations.
The objectives of the project, accordingly, are the multiscale treatment of very thin boundary layers occurring in industrial processes such as bottom-blown ladles or rising gas bubbles, the prediction of the formation of very small droplets in processes that lead to liquid mass breakup such as atomization, and the treatment of another small scale process known as the dynamic contact line, where liquid-gas interfaces meet a solid. This process is also important for heat and mass transfer and extremely costly computationally. The multiscale treatment also has the objective of simulating heat transmission processes such as boiling and spray cooling in which a solid surface is cooled by the projection of a spray formed by an atomizing jet, and nucleate boiling where heat transfer is achieved by the localized vaporization of water. For respiratory disease propagation the objective is to predict the droplet size distributions in atomizing films modelling the mucous-salivary films in the human respiratory duct.
A major component of the work has been the study of a water model of a metallurgical bottom blown ladle. This part of the project is closely associated with the subgrid scale multiscale numerical method. The method has been conceptually developed, and followed by the writing of the associated computer code and its testing on the benchmark problem of ellipsoidal rising bubbles. The rising bubble case was treated both by direct numerical simulation, a brute force approach were sufficiently many cells are used to compute even thin (but not too thin, as such cases would be impossible on current computers) boundary layers and by the multiscale subgrid cell approach, with good agreement found between the two approaches, even when the boundary layers become much thinner than the grid cells. The method was then applied to the bottom-blown ladle case. Two different experiments were simulated, with numerical results for mass transfer that match the experiments. The successful application of the subgrid-scale mass-transfer method to such model experiments shows that they are ready to be exploited. The method is disseminated through a freely available dissertation, a paper in the second stage of reviewing, and talks at international conferences, as well as in several individual seminars given by the PI in China, India and the USA. It is also disseminated through the "sandbox" of the Basilisk platform, which provides the method as free code, and finally disseminated through collaboration on a benchmark with other research groups working on mass transfer.
Another major component of the work is the development of better multiphase flow methods, helping perform better atomization simulations. The EBIT method is a complete reworking of the Volume of Fluid (VOF) method existing at the beginning of the project. It allows to parallelize Front Tracking, a very rare feat. It has been disseminated through three scientific papers in top journals for the 2D version and in a submitted paper for the 3D version, at the latest ICTAM and ICMF and is through a sandbox as above. It is however not yet ready for exploitation. Another improvement in multiphase methods directly related to atomization is the ``manifold death'' method, disseminated through a scientific paper, and available through a sandbox. It has been exploited by several other research groups working on atomization, leading to publication in Journal of Fluid Mechanics, and exploited by the PI to study pulsed jet atomization, allowing to obtain better statistical convergence of the simulations upon grid refinement.
The third major component of the project is the study of dynamic contact lines. The PI has developed several new approaches, a Van der Waals diffuse interface method, a simplified model of localized bending in a VOF method mimicking the effect of interface bending and a Generalized Navier Boundary Condition method, all of which have been published and disseminated through papers, the sandbox, conferences and seminars.
A fourth major component is the study of nucleate boiling. We obtained a full simulation of the growth of a vapor bubble on a super-heated surface recovering a reference experiment in the literature. Spray cooling was also studied experimentally and numerically.
Another major component of the work is the development of better multiphase flow methods, helping perform better atomization simulations. The EBIT method is a complete reworking of the Volume of Fluid (VOF) method existing at the beginning of the project. It allows to parallelize Front Tracking, a very rare feat. It has been disseminated through three scientific papers in top journals for the 2D version and in a submitted paper for the 3D version, at the latest ICTAM and ICMF and is through a sandbox as above. It is however not yet ready for exploitation. Another improvement in multiphase methods directly related to atomization is the ``manifold death'' method, disseminated through a scientific paper, and available through a sandbox. It has been exploited by several other research groups working on atomization, leading to publication in Journal of Fluid Mechanics, and exploited by the PI to study pulsed jet atomization, allowing to obtain better statistical convergence of the simulations upon grid refinement.
The third major component of the project is the study of dynamic contact lines. The PI has developed several new approaches, a Van der Waals diffuse interface method, a simplified model of localized bending in a VOF method mimicking the effect of interface bending and a Generalized Navier Boundary Condition method, all of which have been published and disseminated through papers, the sandbox, conferences and seminars.
A fourth major component is the study of nucleate boiling. We obtained a full simulation of the growth of a vapor bubble on a super-heated surface recovering a reference experiment in the literature. Spray cooling was also studied experimentally and numerically.
On the issue of three-phase flow and ladle metallurgy, agreement with experiment in two experimental cases was obtained, which is considerable progress beyond the state of the art as such a DNS - experimental agreement was never observed before.
On the issue of atomization and the manifold death method, the statistical convergence, in the form of a converged particle size distribution is a major progress. ,
In nucleate boiling the full cycle of bubble formation and detachment was simulated for the first time.
On the contact line, we pushed simulations of reference flow to the unprecedented small scale of 50 nanometers.
On the issue of atomization and the manifold death method, the statistical convergence, in the form of a converged particle size distribution is a major progress. ,
In nucleate boiling the full cycle of bubble formation and detachment was simulated for the first time.
On the contact line, we pushed simulations of reference flow to the unprecedented small scale of 50 nanometers.