Hybrid Finite-Volume/Discontinuous Galerkin framework for the solution of Multiphysics problems using unstructured meshes

A hybrid FV/DG framework is developed for the simulation of compressible multispecies flows on unstructured meshes with a five-equation Diffuse-Interface Model [1]. The high order DG method is employed for the purpose of limiting the material interface smearing typical of the diffuse-interface models resulting from excessive numerical dissipation [2, 3]. In order to ensure high-order accuracy in smooth flow regions and non-oscillatory behaviour near shocks or material interfaces, the hybrid scheme resorts to the underlying FV method when invalid cells are detected by a troubled cell indicator checking the unlimited DG solution, and enables a highorder non-linear CWENOZ reconstruction [4,5] if the solution present oscillations. The CWENO and CWENOZ type reconstruction uses a high-order polynomial for the central stencil and a lower-order polynomial for the directional stencils enhancing robustness and efficiency of classic WENO schemes. To achieve consistency in advecting material interfaces at constant pressure and velocity, the source term from the non-conservative equation is discretised compatibly with the Riemann solver, following the work of Johnsen and Colonius [6]

High-order methods for diffuse-interface models in compressible multi-medium flows: a review

The diffuse interface models, part of the family of the front capturing methods, provide an efficient and robust framework for the simulation of multi-species flows. They allow the integration of additional physical phenomena of increasing complexity while ensuring discrete conservation of mass, momentum, and energy. The main drawback brought by the adoption of these models consists of the interface smearing, increasing with the simulation time, therefore, requiring a counteraction through the introduction of sharpening terms and a careful selection of the discretization level. In recent years, the diffuse interface models have been solved using several numerical frameworks including finite volume, discontinuous Galerkin, and hybrid lattice Boltzmann method, in conjunction with shock and contact wave capturing schemes. The present review aims to present the recent advancements of high-order accuracy schemes with the capability of solving discontinuities without the introduction of numerical instabilities and to put them in perspective for the solution of multi-species flows with the diffuse interface method.Engineering and Physical Sciences Research Council (EPSRC): 2497012. Innovate UK: 263261. Airbus U

Hybrid discontinuous Galerkin-finite volume techniques for compressible flows on unstructured meshes

In this paper we develop a family of arbitrarily high-order non-oscillatory hybrid Discontinuous Galerkin(DG)-Finite Volume(FV) schemes for mixed-element unstructured meshes. Their key ingredient is a switch between a DG method and a FV method based on the CWENOZ scheme when invalid solutions are detected by a troubled cell indicator checking the unlimited DG solution. Therefore, the high order of accuracy offered by DG is preserved in smooth regions of the computational domain, while the robustness of FV is utilized in regions with strong gradients. The high-order CWENOZ variant used has the same spatial order of accuracy as the DG variant, while representing one of the most compact applications on unstructured meshes, therefore simplifying the implementation, reducing the computational overhead associated with large stencils of the original WENO reconstruction without sacrificing the desirable non-oscillatory properties of the schemes. We carefully investigate several parameters associated with the switching between DG and FV methods including the troubled cell indicators in a priori fashion. For the first time in the literature, we investigate the definition of the bounds for an admissible solution, the frequency by which we use the troubled cell indicators, and the evolution of the percentage of troubled cells for unsteady test problems. The 2D and 3D Euler equations are solved for well established test problems and compared with computational or experimental reference solutions. All the methods have been implemented and deployed within the UCNS3D open-source high-order unstructured Computational Fluid Dynamics (CFD) solver. The present coupling has the potential to improve the shortcomings of both FV-DG in a computational efficient manner. The improved accuracy and robustness provided is a characteristic of paramount importance for industrial-scale CFD applications, and favours the extension to other systems of governing equations

High-order hybrid DG-FV framework for compressible multi-fluid problems on unstructured meshes

In this work we extend the hybrid Discontinuous Galerkin/ Finite Volume framework, introduced in V. Maltsev, D. Yuan, K. W. Jenkins, M. Skote, P. Tsoutsanis, “Hybrid discontinuous Galerkin-finite volume techniques for compressible flows on unstructured meshes, Journal of Computational Physics 473 (2023)” [1], to multi-species problems involving gas-gas and gas-liquid systems. The numerical scheme achieves high order accuracy in smooth flow regions thanks to the DG discretisation, yet avoiding oscillations at material interfaces and shocks thanks to a FV type reconstruction. This strategy, as typically represented in literature, makes use of the so-called troubled cell indicators for the detection of numerical oscillations generated by an unlimited high-order scheme in presence of discontinuities, and enables a more dissipative scheme in the troubled cells only in order to suppress the spurious oscillations. As will be shown in a series of increasingly challenging test-cases, when applied to multi-species flows in the context of diffuse-interface models, the hybrid framework is able to limit the excessive material interface dissipation, characteristic of these interface-capturing methods, allowing at the same time a control over the amount of dissipation necessary to solve stiffer problems

Data supporting: High-order hybrid DG-FV framework for compressible multi-fluid problems on unstructured meshes""

This dataset contains binary output in Tecplot format for the test problems analysed in the "High-order hybrid DG-FV framework for compressible multi-fluid problems on unstructured meshes" JCP paper. Test cases included are: - Gas-water isolated material interface advection - 2D and 3D helium bubble interaction with shock wave - 2D shock driven air bubble collapse in water - 2D and 3D shock driven air bubble array collapse in water - 2D underwater explosionMulti-Physics Modellin

Data supporting: "High-order hybrid DG-FV framework for compressible multi-fluid problems on unstructured meshes"

This dataset contains binary output in Tecplot format for the test problems analysed in the "High-order hybrid DG-FV framework for compressible multi-fluid problems on unstructured meshes" JCP paper. Test cases included are: - Gas-water isolated material interface advection - 2D and 3D helium bubble interaction with shock wave - 2D shock driven air bubble collapse in water - 2D and 3D shock driven air bubble array collapse in water - 2D underwater explosion</p

Multi-fidelity aerodynamic methods for the analysis of propeller wing interaction

The propeller-wing aerodynamic interaction is investigated with multi-fidelity methods including Lifting Line Method (LLM), Surface Panel Method (SPM), and Vortex Particle Method(VPM). High-fidelity results from in-house unsteady RANS computations and experiments are used as a reference. Two open-source codes Flow Unsteady and DUST are used to carry out lowto mid fidelity simulations. For the computations performed with FlowUnsteady, the lifting surfaces are modeled using actuator line model or actuator surface model, while the propeller wake and wing wake are modeled using a reformulated VPM. With DUST, the lifting surfaces are modelled using surface panels and the wake is modelled by classic VPM. A clean wing, an isolated beaver propeller and a wing-mounted propeller are used as benchmarks for comparing the performance of the faster methods with uRANS and experiments. For simpler test cases such as the clean wing, a comparable accuracy is found for the prescribed wake and VPM wake, while the simulation time of the former is orders of magnitude lower than the latter. For the isolated propeller, the LLM that couples with VPM wake can predict thrust coefficient in the order of 10 minutes with less than 5% deviation compared to experiment data, while with high fidelity uRANS, more than 20 hours are needed. When the wing wake and propeller wake interaction is expected to have an impact on lift, drag and pressure distribution, the middle-fidelity VPM recovers much of the physics lost with lower fidelity methods, yet providing a good compromise between computational costs and accuracy

The Study of Co-Cu Heterogeneous Alloy Thin Films by NMR Method

В данной работе обсуждаются результаты, полученные при исследовании структуры магнитных слоев в мультислойных пленках Co/Cu со сверхтонкими магнитными слоями, приготовленных методом магнетронного ионно-плазменного распыления, методом ЯМР на ядрах 59Co (эффективная толщина слоя Co составляла dCo ≈ 3.5 и 4.5A). Несмотря на столь малые зна- чения эффективной толщины слоев, было обнаружено, что спектры ЯМР представляли собой суперпозицию двух пиков с центральными частотами f1=190−196МГц и f2=208−213МГц, которые, очевидно, соответствовали атомам кобальта, имеющим 0 и 1 атом меди в ближай- шем окружении. Данный факт указывает на то, что кобальт главным образом организуется в крупные кластеры, включающие большое число атомов.In the present work we discuss the structure of magnetic layer in magnetron sputtered Co/Cu multilayers with ultrathin magnetic layers ( effective layer thicknesses dCo ≈ 3.5 and 4.5A) obtained by means of 59Co NMR method. In spite of such a small effective thicknesses of sputtered layers it has been found that the NMR spectra are the superposition of two peaks with central frequencies f1=190-196MHz and f2=208- 213MHz which obviously correspond to Co-atoms which have 0 and 1 Cu-atom in the nearest-neighbor shell indicating that cobalt preferably forms clusters with large number of atoms involved

Chronic Administration of Non-Constitutive Proteasome Inhibitor Modulates Long-Term Potentiation and Glutamate Signaling-Related Gene Expression in Murine Hippocampus

Proteasomes degrade most intracellular proteins. Several different forms of proteasomes are known. Little is known about the role of specific proteasome forms in the central nervous system (CNS). Inhibitors targeting different proteasome forms are used in clinical practice and were shown to modulate long-term potentiation (LTP) in hippocampal slices of untreated animals. Here, to address the role of non-constitutive proteasomes in hippocampal synaptic plasticity and reveal the consequences of their continuous inhibition, we studied the effect of chronic administration of the non-constitutive proteasome inhibitor ONX-0914 on the LTP induced by two different protocols: tetanic stimulation and theta-burst stimulation (TBS). Both the tetanus- and TBS-evoked potentiation contribute to the different forms of hippocampal-dependent memory and learning. Field-excitatory postsynaptic potentials (fEPSPs) in hippocampal slices from control animals and animals treated with DMSO or ONX-0914 were compared. LTP induced by the TBS was not affected by ONX-0914 administration; however, chronic injections of ONX-0914 led to a decrease in fEPSP slopes after tetanic stimulation. The observed effects correlated with differential expression of genes involved in synaptic plasticity, glutaminergic synapse, and synaptic signaling. Obtained results indicate that non-constitutive proteasomes are likely involved in the tetanus-evoked LTP, but not the LTP occurring after TBS, supporting the relevance and complexity of the role of specific proteasomes in synaptic plasticity, memory, and learning