AMR Techniques Research Articles

Numerical Simulation of Droplet Splashing Behavior in Steelmaking Converter Based on VOF-to-DPM Hybrid Model and AMR Technique

Numerical Simulation of Droplet Splashing Behavior in Steelmaking Converter Based on VOF-to-DPM Hybrid Model and AMR Technique

Modeling investigation on transient behaviors of gaseous ammonia jet flow with direct injection

This study investigates the characteristics of gaseous ammonia jets under an injection pressure of 0.8 MPa and an ambient pressure of 0.1 MPa, using LES and RANS simulation approaches to inform applications of ammonia in internal combustion engines. A three-dimensional constant volume chamber model was established, and the Dynamic Structure model was applied in LES modeling with AMR techniques. The near-nozzle transient structures were successfully captured. Furthermore, a direct comparison between LES and RANS simulation was made, and main jet characteristics were investigated. LES outperforms RANS in predicting the instantaneous structures of ammonia jets and provides a more distinct visualization of oblique shock waves and diamond-like shock cells. RANS excels at displaying averaged features with a smoother distribution curve that represents self-similar characteristics. Additionally, the transient characteristics of ammonia and hydrogen jets were compared. The vortex formation and mixing process in ammonia jets occur at a much slower rate compared to hydrogen jets. Meanwhile, transient vortex ring behaviors were analyzed in detail, including their development tendencies regarding initial, secondary, and broken vortex formation. It is revealed that petal-like swirling movements are strongly correlated with the air–fuel mixing process.

CFD analysis of drop generation in cross-junction microchannel

The development of microfluidic devices, which handle small volumes of fluids for mechanical, chemical and medical purposes, is accelerating. Drop microfluidics is a booming field. This study aimed to attain a better understanding of drop generation in a cross-junction device. Hence, the generation of drops in the cross-junction microchannel was numerically and two-dimensionally simulated. For this purpose, the open-source code of Gerris was implemented. Also, the effect of Ca and We number on the drop generation process was evaluated. The AMR technique is utilized to simulate drop motion. Six distinct regimes are identified, namely, long alternating (LA), short alternating (SA), alternating with different sizes (ADS), small drops (SD), jetting (J) and parallel (P). In combination with (LA and SA) regimes, the size of one drop is larger than the hydraulic diameter and the other is smaller. In the large alternating regime, the length of the drops decreases when Weber numbers increase and the drop generation frequency increases as the We number increases. In each transition from one regime to another, the pinch-off location suddenly increases, and then in each regime, with the increment of the We number, the location of drop breakage decreases.

A numerical study on the interaction of droplet collisions and air flow impact in cross-impinging spray

The spray impingement method has been widely used to effectively achieve better atomization of liquid fuel. The factors influencing the formation of impinged spray are analysed using computational fluid dynamics (CFD) modelling. Free spray and impinging sprays with three impinging distances are simulated using the Eulerian-Lagrangian multiphase method. The results are validated with experimental data. Meanwhile, some advanced methods are employed to obtain better results of simulation such as the AMR technique and adaptive collision mesh method. The spray widths in different impingement distances are compared to analyse the distribution of spray droplets. Upon the binary collision theory, the distribution of discrete droplets is attributed to the collisions of huge amounts of particles. In the process of spray impingement, the impact of air flow, generated by gas entrainment of spray, also influences the spray. As a supplement to the collisions of discrete droplets, the impingement of continuous air flow and their interaction is mainly discussed. The impact waves observed in the flow field demonstrate that the impingement of entrained air flow is similar to jet impingement.

On the Small-scale Turbulent Dynamo in the Intracluster Medium: A Comparison to Dynamo Theory* * Released on August, 19th, 2021.

We present non-radiative, cosmological zoom-in simulations of galaxy-cluster formation with magnetic fields and (anisotropic) thermal conduction of one massive galaxy cluster with M vir ∼ 2 × 1015 M ⊙ at z ∼ 0. We run the cluster on three resolution levels (1×, 10×, 25×), starting with an effective mass resolution of 2 × 108 M ⊙, subsequently increasing the particle number to reach 4 × 106 M ⊙. The maximum spatial resolution obtained in the simulations is limited by the gravitational softening reaching ϵ = 1.0 kpc at the highest resolution level, allowing one to resolve the hierarchical assembly of the structures in fine detail. All simulations presented are carried out with the SPMHD code gadget3 with an updated SPMHD prescription. The primary focus of this paper is to investigate magnetic field amplification in the intracluster medium. We show that the main amplification mechanism is the small-scale turbulent dynamo in the limit of reconnection diffusion. In our two highest resolution models we start to resolve the magnetic field amplification driven by the dynamo and we explicitly quantify this with the magnetic power spectra and the curvature of the magnetic field lines, consistent with dynamo theory. Furthermore, we investigate the ∇ · B = 0 constraint within our simulations and show that we achieve comparable results to state-of-the-art AMR or moving-mesh techniques, used in codes such as enzo and arepo. Our results show for the first time in a cosmological simulation of a galaxy cluster that dynamo action can be resolved with modern numerical Lagrangian magnetohydrodynamic methods, a study that is currently missing in the literature.

R-adaptive algorithms for supersonic flows with high-order Flux Reconstruction methods

The present paper addresses the development and implementation of the first r-adaptive mesh refinement (r-AMR) algorithm for a high-order Flux Reconstruction solver. The r-refinement consists on nodal re-positioning while keeping the number of mesh nodes and their connectivity frozen. The developed algorithm is based on physics-driven spring-analogies, where the mesh can be seen as a network of fictitious springs. While AMR increases the local mesh density, the high-order Flux Reconstruction method potentially provides a more accurate detection of complex flow features over relatively coarser mesh, when compared to low-order methods. In this work, a concise overview of the Flux Reconstruction method and spring-based AMR techniques will be given, followed by some promising results of r-AMR applied to benchmark high-order steady-state supersonic flow simulations.

Multi-scale flow simulation of automotive catalytic converters

The flow distribution within the automotive catalytic converter is an important controlling factor on the overall conversion efficiency. Capturing the flow features minimizing the computational cost is the first important step towards the solution of the complex full engineering problem. In this work we present a novel approach that combines physical and numerical multi-resolution techniques in order to correctly capture the flow features inside an automotive catalytic converter. While Adaptive Mesh Refinement techniques are optimized in order to minimize the computational effort in the divergent region, a novel subgrid model is developed to describe the flow inside the catalytic substrate placed between the convergent and divergent regions. The proposed Adaptive Mesh Refinement methods are tested for two test cases representative of the flow features found in the divergent region of a catalytic converter. The performance of the new subgrid model is validated against the non-uniformity index and the radial velocity profile data obtained by Benjamin et al. (2002). The effective coupling of AMR techniques and the subgrid model significantly reduces the error of the numerical predictions to 5–15% in conditions where the full simulation of the problem is out of current computational capabilities.

Development of a Computational Framework for Block-based AMR Simulations

AMR technique can provide efficient numerical calculation by adapting fine cells to regions where higher numerical resolution is required. However, it is generally difficult for users to implement the AMR technique in their generic simulation programs which use uniform ce lls. For the purpose of carrying out numerical simulations including the AMR technique, we developed a framework for blocked-structured AMR simulation by which we can easily convert a generic uniform-cell simu lation program to the one with the AMR treatment. In this paper we describe the developed framework and show the implementation of a simulation program into the framework by taking a two -dimensional advection simulation as an example.

Well-Balanced Adaptive Mesh Refinement for shallow water flows

Well-balanced shock capturing (WBSC) schemes constitute nowadays the state of the art in the numerical simulation of shallow water flows. They allow to accurately represent discontinuous behavior, known to occur due to the non-linear hyperbolic nature of the shallow water system, and, at the same time, numerically maintain stationary solutions. In situations of practical interest, these schemes often need to be combined with some kind of adaptivity, in order to speed up computing times. In this paper we discuss what ingredients need to be modified in a block-structured AMR technique in order to ensure that, when combined with a WBSC scheme, the so-called ‘water at rest’ stationary solutions are exactly preserved.

复杂地层注蒸汽热采稠油数值模拟的研究

本文对多孔介质中多相流动数值计算格式构造及复杂地层注蒸汽热采稠油自适应网格法方面的研究工作给予介绍。对于非均匀渗透率多孔介质中的流动问题，通过有限分析法构造数值格式，有效克服了网格结点附近渗流速度的奇点效应，和经典数值格式相比，计算效率得到了显著提高。从B-L方程出发，对于不可压缩两相流动，提出了数值模拟算法，该算法有效避免了两相渗流数值模拟的网格取向效应。对于复杂断层及复杂边界、渗透率空间分布不均匀、分布不同种类输运性质岩石或裂缝–孔隙双重介质等复杂地层中的注蒸汽热采稠油自适应网格法开展研究，大幅度提高了计算速度。在上述研究工作的基础上，自主开发了油藏数值模拟自适应网格法计算软件。 The works on the developments of the numerical scheme for multi-phase flows in porous media and the adaptive mesh refinement in numerical simulations of heavy oil thermal recovery by steam injection are introduced. First, a finite analytic method was developed to deal with a challenging problem in numerical simulations in the case of strong geological heterogeneity, which cause the upscaling permeability to have a rapid change cross the grid interfaces and therefore the nodal flow effects will lead the flow fingering to the high permeability region. With the traditional numerical scheme, refining the coarse grid enough is the only manner to describe the flow pattern accurately. Second, for the incompressible two-phase flows, a numerical scheme, which could avoid the grid orientation effects efficiently, was proposed. Next, the adaptive mesh refinement technique was applied to the numerical simulations for the processes of thermal recovery by steam injection, where the different heterogeneous cases of the reservoir were considered, like the reservoir with the permeability variations, the different rock-types, the fractured porous media, the complex faulted reservoir or complex boundary reservoirs. The proposed AMR technique is fast and can give good accuracy. At last, on the basis of above theoretical research, a software package for the reservoir simulations, where the AMR technique was included, was developed.

Numerical study on flame acceleration and DDT in an inclined array of cylinders using an AMR technique

Flame acceleration and deflagration-to-detonation transition in an inclined array of cylinders embedded in a H2–air gas are studied by solving the two-dimensional reactive Navier–Stokes equations with an AMR to resolve important events in the flow. The computations show three stages of flame acceleration and how they are affected by the inclination of the array. The initial stage is the flame acceleration due to the increase of the flame surface area by the flow around the cylinders. The entrainment of the flame in the wake of the cylinders contributes to the fastest flame acceleration for the inclination angle 0° at which the row of cylinders is parallel to the flame propagation. As the inclination angle varies, formation of funnels of unburned material in the wake becomes dominant, and the flame does not accelerate as quickly. In the second stage, shock-flame interactions are responsible for the flame acceleration. The high reaction rate in the shock-compressed material decreases the flame surface area, while sustaining the energy-release rate. The final stage is a quasi-steady state of supersonic propagation. Detonation ignited by a local explosion propagates as a quasi-detonation. For 0° inclination, the local explosion does not lead to detonation, and the flame propagates in the choking regime.

A cell-centered Lagrangian hydrodynamics scheme on general unstructured meshes in arbitrary dimension

We describe a cell-centered Godunov scheme for Lagrangian gas dynamics on general unstructured meshes in arbitrary dimension. The construction of the scheme is based upon the definition of some geometric vectors which are defined on a moving mesh. The finite volume solver is node based and compatible with the mesh displacement. We also discuss boundary conditions. Numerical results on basic 3D tests problems show the efficiency of this approach. We also consider a quasi-incompressible test problem for which our nodal solver gives very good results if compared with other Godunov solvers. We briefly discuss the compatibility with ALE and/or AMR techniques at the end of this work. We detail the coefficients of the isoparametric element in the appendix.

A comparison of anisotropy of magnetic remanence methods — a user’s guide for application to palaeomagnetism and magnetic fabric studies

Abstract Anisotropy of magnetic remanence (AMR) is increasingly being applied to palaeomagnetic and structural fabric studies. AMR techniques measure the anisotropy of the remanence carrying particles, and thus are directly relevant to palaeomagnetic studies concerned with computing the direction and intensity of the Earth’s ancient magnetic field from the natural remanent magnetization (NRM) recorded in anisotropic rocks. This paper provides a comparison of several AMR methods, including some of the less well-known techniques, and highlights the relative merits of each. Results from a strongly anisotropic rock and a pottery sherd are presented. The anisotropies of anhysteretic remanent magnetization (AARM) and isothermal remanent magnetization (AIRM) are currently the most commonly applied types of AMR, since they have provided reasonably good analogues of the anisotropy of thermoremanent magnetization (ATRM) acquired in the Earth’s field. They have also helped to correct for inclination shallowing of detrial remanent magnetization (DRM) in sediments. IRM anisotropy is the most rapid AMR technique, and is particularly useful for very low concentrations of remanence carrying particles. The gyroremanences, gyroremanent magnetization (GRM) and rotational remanent magnetization (RRM), are preferentially acquired by stable single-domain (SD) particles, and are thus directly relevant to the particles of major interest in palaeomagnetism. GRM anisotropy is the most sensitive AMR method. It is essentially the remanence equivalent of the anisotropy of magnetic susceptibility (AMS) delineator, since a single application of an alternating field will only produce a GRM in a sample containing an anisotropic distribution of particles. Static ARM methods need to take account of components of GRM that are simultaneously acquired.

이방성 자기저항측정을 이용한 NiO/NiFe 박막의 교환결합연구

We report an experimental evidence of coexistence of the strong and weak exchange couplings in unidirectional NiO/NiFe (antiferromagneticlferromagnetic) bilayer thin films. The exchange bias was measured by VSM and AMR techniques and then, analyzed into the strong and weak exchange couplings by means of a regression method. In NiO(60nm)/NiFe(10nm) film, the ratio of the weak exchange coupling field over the average exchange coupling field was found to be almost unchanged within it range from 0.2 to 0.4 irrespective to the strength of an applied field. However, the ratio increased among the samples with decreasing the average exchange coupling field due to the increment of the weak exchange coupling area.ጊ攀Ѐ㘱〻Ԁ䭃䑎䷙᜖ණ6ㄴ⸴㐻Ԁ䭃䑎䴀