arXiv subjects

Ehsan Amani

Publications and source records attributed to Ehsan Amani.

6 recordsLinked to original sources

arXiv2026

cfdmfFTFoam: A front-tracking solver for multiphase flows on general unstructured grids in OpenFOAM

The Front-Tracking Method (FTM) is a promising approach for numerical solution of multiphase flows, considering a trade-off between accuracy and computational cost. The existing open-source open-access software for FTM is scarce, due to complexity of the coding and algorithms, and is limited to structured Cartesian grids or connectivity-free front mesh hybrid FTMs. To provide a pure FTM solver on general unstructured grids, the Ftc3D FTM code has been integrated into the OpenFOAM CFD software by implementing necessary front mesh to Eulerian grid communication and front nodes advection algorithms, applicable to unstructured grids and for both serial and parallel runs. The new FTM package, called cfdmfFTFoam, has been further equipped with a variety of FTM sub-algorithms, including the front volume correction, remeshing, surface tension computation, indicator function construction, etc. Assessments and validations of the new solver are provided against several standard multiphase flow benchmarks. It is anticipated that cfdmfFTFoam would facilitate future research on and algorithm improvement in the field of FTM.

physics.flu-dyn↗

arXiv2026

A Novel Explicit Filter for the Approximate Deconvolution in Large-Eddy Simulation on General Unstructured Grids: A posteriori tests on highly stretched grids

Explicit filters play a pivotal role in the scale separation and numerical stability of advanced Large Eddy Simulation (LES) closures, such as dynamic eddy-viscosity or Approximate Deconvolution (AD) methods. In the present study, it is demonstrated that the performance of commonly used explicit filters applicable to general unstructured grids highly depends on the grid configuration, specifically the cell aspect ratio, which can result in poor filter spectral properties, ultimately leading to large errors and even solution divergence. This study introduces a novel, efficient explicit filter for general unstructured grids, addressing this shortcoming through a combination of a face-averaging technique and recursive filtering. The filter parameters are then determined through a constrained multi-objective optimization, ensuring desirable spectral properties, including high-wavenumber attenuation, filter-width precision, filter stability and positivity, and minimized dispersion and commutation errors. The AD-LES of turbulent channel flow benchmarks using the new filter demonstrate a noticeable improvement in turbulent flow predictions on highly stretched boundary-layer-type grids, particularly in reducing the log-layer mean velocity profile mismatch, compared to simulations using conventional filters. The analyses show that this enhancement is mainly attributed to the sufficient level of attenuation near the Nyquist wavenumber achieved by the new filter in all spatial directions across various grid configurations, among others. The new filter was also successfully tested on unstructured prism grids for the 3D Taylor-Green vortex benchmark.

physics.flu-dyn↗

arXiv2025

A front-tracking study of retinal detachment treatment by magnetic drop targeting

We investigate the Ferrofluid Drop Targeting (FDT) for the treatment of the Retinal Detachment (RD), considering, for the first time, the real 3D geometry of an eye and magnets configurations as well as the viscoelastic rheology of the medium, i.e., the Vitreous Humor (VH). A Front-Tracking Method (FTM) is extended to handle a general 3D unstructured Eulerian grid and strong wall effects. The challenges include the accuracy and robustness of the solver when the drop spreads on the retina under the effect of a magnetic field, which necessitates the design of a multi-region Eulerian grid and defining a threshold distance between the front and wall, along with the choice of an effective front smoothing and volume correction FTM sub-algorithms near the walls. After model validations, the effect of different design parameters on important objectives, such as the travel time, settling time, retinal coverage area, and impact compressive stress, are studied. The results reveal that, in addition to the magnetic Bond number, the ratio of the drop-to-VH magnetic permeabilities plays a key role in the terminal shape parameters, like the retinal coverage. Additionally, simultaneously increasing these two parameters, significantly increase the total FDT force, coverage area, and stress concentration, while decreasing the drop-VH surface tension can mitigate the stress concentration on the retina.

physics.flu-dyn↗

arXiv2025

Novel mixed approximate deconvolution subgrid-scale models for large-eddy simulation

Approximate Deconvolution (AD) has emerged as a promising closure for Large-Eddy Simulation (LES) in complex multi-physics flows, where the conventional pure Dynamic Eddy-Viscosity (DEV) models experience issues. In this research, we propose novel improved mixed hard-deconvolution or secondary-regularization models and compare their performance with the existing standard mixed AD-DEV and penalty-term regularizations. For this aim, five consistency criteria, based on the properties of the modeled sub-filter-scale stress in limit conditions, are introduced for the first time. It is proved that the conventional hard-deconvolution models do not adhere to a couple of important primary criteria. Furthermore, through a priori and a posteriori analyses of Burgers turbulence and turbulent channel flow, it is manifested that the inconsistency with the primary criteria can result in larger modeling errors, the over-prediction and pile-up of kinetic energy in eddies of a length scale between the explicit filter width and grid size, and even the solution instability. On the other hand, the favorable characteristics of the new mixed models, in terms of the consistency criteria, significantly improve the accuracy of the predictions, the solution stability, and even the computational cost, particularly for one of the new models called mixed Alternative-DEV (A-DEV).

physics.flu-dyn↗

arXiv2025

Wall-Modeled Large-Eddy Simulation of Turbulent Non-Newtonian Power-Law Fluid Flows

For high-fidelity predictions of turbulent flows in complex practical engineering problems, the Wall-Modeled (WM) Large-Eddy Simulation (LES) has aroused great interest. In the present study, we prove that the conventional Wall-Stress Models (WSMs) developed for WMLES of Newtonian fluids fail to predict the shear-thinning-induced drag reduction in power-law fluids. Therefore, we propose novel algebraic, integrated, and Ordinary-Differential-Equation (ODE) WSMs, for the first time, for WMLES of power-law Non-Newtonian (NN) fluids and assess their performance against reference Wall-Resolved (WR) LES solutions. In addition, the effects of the key model parameters, including the WSM type, sampling height, sampling cell, and axial grid resolution are explored, and it is revealed that turbulent NN flow predictions have a much higher sensitivity to the choice of WSM, compared to their Newtonian counterparts. It is manifested that, in contrast to WRLES, accurate modeling of the mean apparent and subgrid-scale NN viscosities in the NNODE model can improve the predictions considerably. Therefore, closures with lower uncertainties on coarse WMLES grids are sought for these terms. Finally, the best performance for the present test cases is obtained via the integrated NN WSM, sampling at the lower edge of the log layer within the third off-the-wall grid cell. Nevertheless, the new NNODE WSM can have an advantage in the presence of non-equilibrium effects in more complex problems.

physics.flu-dyn↗

arXiv2024

Systematic Benchmarking of Macrosegregation: The Performance of a Modified Hybrid Model

Recently, a new alloy solidification benchmark, called AFRODITE, with well-defined setups and state-of-the-art measurements has emerged, enabling a thorough assessment of MacroSegregation (MS) solvers, particularly in terms of their ability to predict different features of MS maps. In this research, we first develop an analytical solution for the alloy-solidification Stefan problem, which involves melt, solid, and mushy regions. This new analytical solution extends a previous solution (S. Cho and J. Sunderland, "Heat-conduction problems with melting or freezing", J. Heat Transfer, vol. 91, pp. 421-426, 1969) by incorporating a linear microsegregation law as a function of temperature in place of spatial coordinate. Then, we adopt this solution to verify an OpenFOAM MS solver in a limiting condition, where only heat diffusion is present. Subsequently, to capture the MS map of the Sn-3%Pb AFRODITE benchmark, the solver is incorporated using the standard Blake-Kozeny-Carman permeability law and one of its hybrid variants, slightly modified in this work to better align with physics by ensuring a continuous transition of characteristics from the slurry to the porous regions of the mush. It is demonstrated that the hybrid model predicts the main features of the MS map, including the channel segregates morphology and peak segregation degree due to the pile-up effect, in much finer agreement with the experimental observation. Careful analyses of the results reveal that these improved predictions stem from the hybrid model's more accurate estimation of the re-melting, melt flow advection parallel, and advection normal to the solidification front.

physics.flu-dyn↗