Wall Boundary Research Articles

A deep learning upscaling framework: Reactive transport and mineral precipitation in fracture-matrix systems

Pore-scale modeling has limited applicability at large scales due to its high computational cost. One common approach to upscale pore-scale models is the use of effective medium theories, which homogenize small-scale features in a porous structure and characterize the medium by macroscale properties (e.g., permeability) and equations (e.g., Darcy’s law). However, there are classes of physical processes for which effective medium approximations may become inaccurate, e.g., mineral precipitation and clogging during reactive transport. We have developed a deep learning upscaling framework, in which pore-scale modeling is directly employed in macroscale systems, without relying on effective medium approximations. The upscaling framework is first developed for general multiscale systems and then applied to modeling reactive transport with mineral precipitation in the altered layer in fracture-matrix structures. Solute transport from the fractures to the matrix is modeled as a wall boundary condition for the fractures, which, in turn, is predicted by recurrent neural networks using the concentration histories at the fracture-matrix boundary. Specifically, we consider a meter-scale fracture network embedded in sandstones, where the smallest feature is at the micron scale. The proposed framework allows us to span five orders of magnitude in length scales by capturing mineral precipitation in the altered layer of the rock matrix at the pore scale across the entire meter-scale fracture network.

The view from Mathura: nationalist projections in local perspective

ABSTRACT Following the Indian Supreme Court's verdict allowing the construction of a Rām Mandir at the site of the former Babri Masjid in 2019, Hindu nationalists have put renewed pressure on the North Indian city of Mathura. There, the seventeenth-century Shahi Idgah shares a boundary wall with a temple complex associated with the birth site of the deity Kṛṣṇa. Between 2019 and 2023, at least nine court cases were filed to remove the idgah from the vicinity of the Kṛṣṇa Janmabhūmi. With the future of a contentious religious site unfolding in the courts, I adopt an ethnographic perspective to assess the consequences of political stake claiming in the name of religion within the city of Mathura. I argue that the very threat of transforming a religiously plural landscape into a distinctively Hindu territory has had material consequences for those who live in Mathura. This situation demonstrates how rhetorical and spatial erasure mutually reinforce one another within contemporary Hindutva projects, whereby Muslim sacred territory in India becomes progressively more difficult to access, both conceptually and on the ground.

Vertex-Centered Mixed Finite Element–Finite Volume scheme for 2D anisotropic hybrid mesh adaptation

The scope of this paper is to propose an appropriate numerical strategy to extend the Mixed Finite Element–Finite Volume (MEV) scheme to adapted meshes composed of both triangular and quadrangular elements, called hybrid meshes (Kallinderis and Kavouklis, 2005; Ito et al., 2013) (also named mixed-element meshes (Marcum and Gaither, 1999; Mavriplis, 2000)). Convective, diffusive and source terms require specific gradient discretization to maintain a global second-order accuracy. The major contributions of this paper concern the specification of these gradients, the convective fluxes’ discretization and an innovative framework for anisotropic metric-based adaptation on hybrid meshes. Particularly, the V4 scheme, traditionally developed for triangular elements, is extended to quadrilateral elements. This method maintains the same order of accuracy as the baseline version when upwind/downwind quadrilateral elements are aligned with the attached edge. Viscous fluxes are discretized using the APproximated Finite Element (APFE) method (Puigt et al., 2010), which is second-order accurate on regular quadrilaterals. Nodal gradients, which are considered at boundaries and for source terms, are discretized with a generalization of Clement’s L2-operator on hybrid meshes. The mesh adaptation relies on a specific metric gradation process to favor the clustering of structured elements at wall boundaries. The proposed scheme is validated on a set of CFD simulations.

A corrected filtered drag model considering the effect of the wall boundary in gas-particle fluidized bed

The databases used to construct traditional mesoscale drag models is usually obtained from fine-grid simulation results in the full-periodic domains, ignoring the function of the wall boundary. In actual fluidized bed reactors, the presence of wall boundary can significantly affect the heterogeneous structures in near-wall areas, thereby affecting the drag force. Therefore, this work aims to further enhance the performance of the prediction results of existing filtered drag model by introducing the influence of the wall boundary. Based on the mesoscale drag force model published in previous literature, a correction coefficient considering the influence of the distance from the grid to the wall boundary is proposed. The applicability of the new corrected model is further enhanced by introducing the influence of solid volume fractions and slip velocities. Simple posteriori validations are systematically conducted in various common fluidized beds including the bubbling bed, the turbulent bed, and the fast bed to assess the predictive capability of the newly proposed correction drag model.

Fluctuation of the phase boundary in the six-vertex model with domain wall boundary conditions: a Monte Carlo study

We consider the six-vertex model with domain wall boundary conditions in a square lattice of dimension N × N. Our main interest is the study of the fluctuations of the extremal lattice path about the arctic curves. We address the problem through Monte Carlo simulations. At , the fluctuations of the extremal path along any line parallel to the square diagonal were rigorously proven to follow the Tracy-Widom distribution. We provide strong numerical evidence that this is true also for other values of the anisotropy parameter Δ (). We argue that the typical width of the fluctuations of the extremal path about the arctic curves scales as and provide a numerical estimate for the parameters of the scaling random variable.

A single-phase GPU-accelerated surface tension model using SPH

This paper presents an accelerated single-phase surface tension smoothed particle hydrodynamics (SPH) solver developed to run entirely on a graphics processing unit (GPU) capable of simulating millions of particles in three dimensions on a single GPU. The single-phase surface tension model is augmented with a contact line force to improve the prediction of the physics at the liquid-solid contact point. The surface tension model uses the modified dynamic boundary condition (mDBC) to impose no-slip conditions at the wall boundary. To enable simulations with millions of particles, the single-phase surface tension model has been implemented in the open-source SPH code DualSPHysics to exploit the GPU acceleration, paying special attention to the size of the kernel support and integration of the neighbour lists. The new scheme is validated using 2-D and 3-D test cases including drop deformation, drop oscillation, Rayleigh-Plateau instability and surface contact angles. The results show a good agreement with the analytical solutions with a standard spatial convergence behaviour. Profiling the new surface tension solver shows an additional computational complexity. The performance analysis shows that the new code has a speed up of up two orders of magnitude (x70-80) compared to the CPU-only code. Profiling the new CUDA kernels shows they have the near identical performance metrics with the main CUDA kernels in the original DualSPHysics solver.

A general smoothed particle hydrodynamics (SPH) formulation for coupled liquid flow and solid deformation in porous media

The method of smoothed particle hydrodynamics (SPH) has been recently developed to study the coupled flow-deformation problems in porous material and considerable success has been achieved comparing to traditional mesh-based method, especially for treating large deformation and post-failure. However, computational challenges remain for the hydro-mechanical boundary treatment as well as the accuracy and stability of the numerical scheme. It is shown that the use of conventional SPH operator for the solution of the coupled problem can lead to several issues including numerical instabilities, inaccuracies and unphysical particle clumping as well as particle disorders near the boundary. To address these issues, a general SPH scheme with enhanced accuracy for saturated/unsaturated porous material is proposed in this paper. An improved SPH formulation for seepage analysis is proposed to allow an accurate prediction of liquid flow in porous material. A new stabilisation technique that combines the use of a density diffusion term, a modified particle shifting algorithm, and a new viscous damping term is developed to further improve the accuracy, stability and robustness of the proposed method. The implementations of stress boundary conditions and hydraulic boundary conditions in SPH, such as confining stress, hydraulic head, infiltration/evaporation, and potential seepage face, using either wall boundary particles or free-surface domain particles, are discussed in detail. A range of benchmark examples is adopted to verify the validity of the present coupled framework. The proposed model is finally applied to simulate the failure process of embankment dam due to rapid drawdown. Results indicate that the methodology proposed herein can be a promising tool for the analysis of the coupled hydro-mechanical process in porous material involving large deformations.

A Numerical Test Rig for Turbomachinery Flows Based on Large Eddy Simulations With a High-Order Discontinuous Galerkin Scheme—Part III: Secondary Flow Effects

Abstract In this final paper of a three-part series, we apply the numerical test rig based on a high-order discontinuous Galerkin scheme to the MTU T161 low-pressure turbine with diverging end walls at off-design Reynolds number of 90,000, Mach number of 0.6, and inflow angle of 41 deg. The inflow end wall boundary layers are prescribed in accordance with the experiment. Validation of the setup is shown against recent numerical references and the corresponding experimental data. Additionally, we propose and conduct a purely numerical experiment with upstream bar wake generators at a Strouhal number of 1.25, which is well above what was possible in the experiment. We discuss the flow physics at midspan and in the end wall region and highlight the influence of the wakes from the upstream row on the complex secondary flow system using instantaneous flow visualization, phase averages, and modal decomposition techniques.

Chiral domain dynamics and transient interferences of mirrored superlattices in nonequilibrium electronic crystals

Mirror symmetry plays a major role in determining the properties of matter and is of particular interest in condensed many-body systems undergoing symmetry breaking transitions under non-equilibrium conditions. Typically, in the aftermath of such transitions, one of the two possible broken symmetry states is emergent. However, synthetic systems and those formed under non-equilibrium conditions may exhibit metastable states comprising of both left (L) and right (R) handed symmetry. Here we explore the formation of chiral charge-density wave (CDW) domains after a laser quench in 1T-TaS2 with scanning tunneling microscopy. Typically, we observed transient domains of both chiralities, separated spatially from each other by domain walls with different structure. In addition, we observe transient density of states modulations consistent with interference of L and R-handed charge density waves within the surface monolayer. Theoretical modeling of the intertwined domain structures using a classical charged lattice gas model reproduces the experimental domain wall structures. The superposition (S) state cannot be understood classically within the correlated electron model but is found to be consistent with interferences of L and R-handed charge-density waves within domains, confined by surrounding domain walls, vividly revealing an interference of Fermi electrons with opposite chirality, which is not a result of inter-layer interference, but due to the interaction between electrons within a single layer, confined by domain wall boundaries.

Comprehensive Construction of the Interface Structure and Pathways for Building a Sound Relationship between Government and Business

The comprehensive and close relationship between government and business is a distinctive social connection where contemporary political power, administrative resources, and commercial activities interweave. This relationship is a requirement outlined in Article 25 of the 2023 "Opinions of the CPC Central Committee and the State Council on Promoting the Development and Growth of the Private Economy." The comprehensive and close relationship between government and business directly influences the national political and business ecology. This relationship manifests a significant interface structure and a boundary constraint system. The boundary consists of a boundary wall, boundary gate, permeability, and the law of boundary exchange. The boundary constraint system possesses specific functions and value pursuits. Power is the boundary, and interests are the shell; seeking profits through power, defending rights through interests. Power and rights form the interface structure of the political ecology of the comprehensive and close relationship between government and business; public and private interests constitute the boundary in the business ecology of this relationship; the integration of politics and business is reflected in permeability and the law of boundary exchange. The balance between power and interests forms the boundary in the political ecology of the comprehensive and close relationship between government and business. The expansion of private interests and the abuse of public power are boundaries; the exercise of power and its supervision are shells; profitability and gains are the boundary in the political ecology of the business ecology. Profitability and profits are boundaries; to be or not to be is the shell; political, legal, and business integration form the foundational construction of the comprehensive and close relationship between government and business, and it is also the path that structures the boundary system of this relationship. Constructing a boundary system for the comprehensive and close relationship between government and business can enhance the governance capabilities and levels of both the entire political and business ecologies. Political thinking, legal thinking, and business thinking constitute the thinking principles of an integrated government-business boundary system. Compliance, legality, and legitimacy form the integrated boundary structure path for the comprehensive and close relationship between government and business. Rules, systems, and culture can eliminate "politicking without principles and rules" and "business without moral and legal bottom lines." An integrated government-business boundary system can optimize the political-business ecology, creating a fair, transparent, and rule-of-law development environment and fostering a favorable atmosphere for the healthy growth of businesses.

Direct imposition of the wall boundary condition for weakly compressible flows in three-dimensional smoothed particle hydrodynamics simulations

This study introduces a novel method for imposing wall boundary conditions in smoothed particle hydrodynamics (SPH). SPH is a particle method based on the Lagrangian approach, primarily employed in fluid analysis as a part of numerical computation methods. Due to its ability to discretize space using particles, SPH excels in handling analyses of free surface flow or multiphase flow with intricate boundary surfaces. However, there is a drawback in modeling wall boundaries using particles, as resolving the particle deficiency problem necessitates multi-layered boundary particles to be arranged behind the wall boundary. This leads to difficulties in implementing complex shapes and adds computational expense. To address this issue, this study suggests the use of boundary segments for wall boundary modeling and specifically employs triangular segments for three-dimensional expansions. For robust application of boundary conditions, a method considering both Poisson's equation and geometric configurations is proposed. The proposed method is independent of the segment density, which facilitates efficient and flexible modeling. In addition, by imposing accurate boundary conditions from the wall, the stability and accuracy of the solution are enhanced. The performance of the proposed method is validated through numerical examples, compared with various analytical and experimental results.

Actual Shear Rate Prediction Associated with Wall Slip Phenomenon Using Radial Basis Function Network

Wall slip can be defined as a phenomenon where the particles in a suspension moving away from the wall boundary, leaving a thin liquid-rich layer adjacent to the boundary. Such a phenomenon may induce a significant impact on rheological measurements, particularly to viscosity, shear stress, and shear rate. Suspension has wide applications such as food processing, personal care products, pharmaceuticals, paints, medicine, and agrochemical. The traditional technique for the actual shear rate prediction is challenging yet difficult and non-favourable from the perspective of time and cost-effectiveness. Therefore, development of a mathematical computational model which has the ability to perform the prediction task with an acceptable level of accuracy is highly in need. Since radial basis function network (RBFN) has the ability to perform input-output mapping in a highly accurate manner, both of the approaches are employed to generate the actual shear rate prediction model. Through the model evaluation using a series of statistical analyses, it was found that RBFN model V is the best model as it shows the highest coefficient of determination (0.9998), lowest mean squared error (0.001058) and root mean squared error (0.001447), most negative Akaike information criterion (-18426.5) and Bayesian information criterion (-18415.5), and the smallest percentage error.

Global exact controllability of the viscous and resistive MHD system in a rectangle thanks to the lateral sides and to distributed phantom forces

We consider the 2-D incompressible viscous and resistive magnetohydrodynamics (MHD) system in a rectangle, with controls on the lateral sides. The velocity satisfies Dirichlet boundary conditions, while the magnetic field follows perfectly conducting wall boundary conditions on the remaining, uncontrolled part of the boundary. We extend the small-time global exact null controllability result of Coron et al. in [Ann PDE 5(2):1-49, 2019] from Navier-Stokes equations to MHD equations, with a little help of distributed phantom forces, which can be chosen arbitrarily small in any given Sobolev spaces. Our analysis relies on Coron’s return method, the well-prepared dissipation method, long-time nonlinear Cauchy-Kovalevskaya estimates and Badra’s local exact controllability result.

Numerical study of airfoil used for helicopter rotor tip to investigate the enhancement in the aerodynamic characteristics using active flow control at forward flight conditions

Helicopter forward flight is the most important state of flight due to time spent in this mode during the complete helicopter trip. In this study, a main rotor blade tip airfoil was simulated to obtain the effect of applying active flow control on the tip part of the rotor blade. A blowing excitation jet is applied to the leading edge of the airfoil just before the separation point with small momentum and high frequency to enhance the near wall boundary layer characteristic. This jet is used with different amplitude, frequency and excitation location from a leading edge to study the effect of this parameter. A numerical model is used to solve two different angles of attack and all results are compared with NACA report that used the same helicopter hub and airfoil. Results show good agreement with the experimental results and the chosen excitation parameter gives good enhancement to the performance of the airfoil used in the tip part of the helicopter blade in this mode of flight. Performance represented in lift and drag and lift to drag ratio shows improvement, reaching about 10% increase in lift and 30% decrease in drag, which means more than 50% change in lift to drag ratio. Furthermore, this study gives a good estimation of the best excitation location that is required for real application on the helicopter blade to improve of forward flight performance.

High‐resolution numerical simulations of polymer injection molding: Analysis of mesh size and refinement

AbstractAccurate and high‐resolution numerical simulations are crucial for preventing manufacturing defects during polymer injection molding. However, achieving efficient and precise simulations in this field remains a subject of ongoing research. In this study, we develop a macro‐scale numerical model to describe the behavior of melted polymer during the filling phase. Employing our in‐house finite‐element solver, XNS, we simulate the polymer and air flows as a two‐phase flow using the level‐set method. This formulation involves significant discontinuities across the interface, therefore a high mesh resolution along the interface becomes necessary. Furthermore, to accurately capture the polymer behavior along the wall, we apply a variable Navier slip condition that is dependent on the mesh size. To assess the impact of mesh size on the solution, we compare the results obtained with different levels of mesh refinement. Additionally, we investigate the effects of localized mesh refinement at the wall boundary and conclude that refinement in the interior of the channel is also required. Through our analysis, we highlight the importance of high‐resolution meshing and appropriate wall boundary conditions in achieving accurate simulations of polymer injection molding. This research contributes to the ongoing efforts in improving the understanding of the complex phenomena involved in this manufacturing process.

Experimental Study on Optimum Design of Aircraft Icing Detection Based on Large-Scale Icing Wind Tunnel

Icing detection is the premise and basis for the operation of aircraft icing protection system, and is the primary issue in flight safety assurance. At present, there is a lack of research methods and design reference for the layout optimization of ice detectors. Therefore, in order to simulate the real icing environment encountered by the aircraft more accurately, a large-scale icing wind tunnel was used to carry out experimental research on the icing characteristics of the sensor probes. A closed-loop experimental method including the typical condition selection, sensor array interference examination and ice shape repeatability verification was initially proposed. A stepwise optimization process and a sensitivity analysis on ambient conditions were combined to determine the optimal distribution for sensor installation. It is found that the water collection coefficient on the cylinder surface of the probe first increases and then decreases along the axial direction, reaching the extreme value at a certain position. The height of this extreme point will gradually increase with the development of the wall boundary layer, showing a variation range of 2~30 mm. Improper design may cause the sensor probe to fail to capture the point with the maximum icing thickness, affecting the sensitivity of icing detection. In addition, each probe position has different sensitivity to changes in flow parameters; the points with larger icing mass and lower sensitivity to changes in attack angle will have better detection effect. The measured data and analysis in the present work can provide a basis for the accurate design of icing sensor probes.

Large Eddy Simulation of a Low-Pressure Turbine Cascade with Turbulent End Wall Boundary Layers

We present results of implicit large eddy simulation (LES) and different Reynolds-averaged Navier–Stokes (RANS) models of the MTU 161 low pressure turbine at an exit Reynolds number of 90000\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$90\\,000$$\\end{document} and exit Mach number of 0.6. The LES results are based on a high-order discontinuous Galerkin method and the RANS is computed using a classical finite-volume approach. The paper discusses the steps taken to create realistic inflow boundary conditions in terms of end wall boundary layer thickness and freestream turbulence intensity. This is achieved by tailoring the input distribution of total pressure and temperature, Reynolds stresses and turbulence length scale to a Fourier series based synthetic turbulence generator. With this procedure, excellent agreement with the experiment can be achieved in terms of blade loading at midspan and wake total pressure losses at midspan and over the channel height. Based on the validated setup, we focus on the discussion of secondary flow structures emerging due to the interaction of the incoming boundary layer and the turbine blade and compare the LES to two commonly used RANS models. Since we are able to create consistent setups for both LES and RANS, all discrepancies can be directly attributed to physical modelling problems. We show that both a linear eddy viscosity model and a differential Reynolds stress model coupled with a state-of-the-art correlation-based transition model fail, in this case, to predict the separation induced transition process around midspan. Moreover, their prediction of secondary flow losses leaves room for improvement as shown by a detailed discussion of turbulence kinetic energy and anisotropy fields.

Two-step multi-resolution reconstruction-based compact gas-kinetic scheme on tetrahedral mesh

This paper presents the development of a third-order compact gas-kinetic scheme (GKS) for compressible Euler and Navier-Stokes solutions, constructed particularly for an unstructured tetrahedral mesh. The scheme utilizes a time-dependent gas distribution function at a cell interface to not only calculate the fluxes needed for updating the cell-averaged flow variables but also to evaluate the flow variables at the cell interface. This leads to the evolution of cell-averaged gradients of flow variables. The success of this scheme heavily relies on the initial data reconstruction techniques, with an emphasis on their application to the tetrahedral mesh. Employing a conventional second-order unlimited least-square reconstruction directly on the cell-averaged flow variables of von Neumann neighbouring cells can introduce linear instability into the scheme. However, by using the updated cell-averaged gradients, the GKS with a third-order compact smooth reconstruction remains linearly stable under a large CFL number when applied to a tetrahedral mesh. To enhance the robustness of the high-order compact GKS for capturing a discontinuous solution, we propose a novel two-step multi-resolution weighted essentially non-oscillatory (WENO) reconstruction. This innovative approach overcomes the stability issues associated with a second-order compact reconstruction by incorporating a pre-reconstruction step. Additionally, it simplifies the third-order non-linear reconstruction process by adding a single large stencil to those used in the second-order one. A high-order wall boundary condition is achieved by fusing the constrained least-square technique with the WENO procedure, where a quadratic element is used in the reconstruction for cells with a curved boundary. Numerical tests involving both the second-order and third-order compact GKS are presented, encompassing both inviscid and viscous flows at both low and high speeds. The results demonstrate that the proposed third-order compact scheme possesses robustness in high-speed flow computation and exhibits excellent adaptability to meshes with complex geometrical configurations.

Improved Delayed Detached Eddy Simulation of Combustion of Hydrogen Jets in a High-Speed Confined Hot Air Cross Flow II: New Results

The improved delayed detached Eddy simulation (IDDES) approach used in the part I of this investigation to study the self-ignition and combustion of hydrogen jets in a high-speed transverse flow of hot vitiated air in a duct is extended in the following directions: (i) the wall boundary conditions are modified to take into account the optical windows employed in the experiments; (ii) the detailed chemical kinetic model with 19 reactions is used; (iii) a nonlinear turbulence model is implemented in the code to capture the secondary flows in the duct corners; (iv) the wall roughness model is adapted; (v) the synthetic turbulence generator is imposed upstream of the fuel injection. As a result of improving the mathematical and physical problem statements, a good agreement between the simulation and the experimental database obtained at the LAERTE workbench (ONERA) is achieved.

Near-fault ground motion characteristics and its effects on a collapsed reinforced concrete structure in Hatay during the February 6, 2023 Mw7.8 Kahramanmaraş earthquake

Ground motion in the vicinity of fault rupture produces pulse-type loading that may impose severe lateral displacement demands on structures due to forward-directivity effects. The Mw7.8 Kahramanmaraş Earthquake on February 6, 2023 created very high amplitude ground motions in the city of Hatay with distinct near-fault characteristics. In the city of 400,000 inhabitants, 33 % of the building stock was severely damaged or collapsed. Among the collapsed buildings, it was observed that there were new buildings built according to the latest seismic regulations. The seismic characteristics of the ground motion in Hatay were examined, the fault rupture, ground conditions and earthquake source characteristics affecting the engineering demand parameters were determined. Then, the seismic behavior and the reasons for the collapse of a 13-story reinforced concrete building, which is thought to be earthquake resistant with its structural system and material quality, were investigated using acceleration time-series recorded at a station very close to the building location. It has been understood that in shear wall systems, wall position and seismic detailing can impart significant damage (total destruction) on these elements under the effect of large displacement and high axial load demand by limiting the required ductility. Wall boundaries require more stringent confinement detailing than stated by the code under near-fault effects.