• CFD was used to analyze the flow field characteristics, such as the velocity field, pressure field, viscous force field, and turbulent kinetic energy distribution. • As the angle of the sector-shaped opening in the meshing area decreases, the windage of the gear pair decreases. • The oil drainage groove should be designed at a position where the included angle between the side of meshing out and the meshing center of the gear pair is 45°. • When the sector-shaped opening of the groove was small, the windage of the gear was also small, and the windage loss was the smallest when the groove opening angle was 10°. To reduce the windage loss caused by hydrodynamic behavior, this study optimizes the parameters of the windshield based on the analysis of the drag reduction mechanism of the windshield. CFD was used to analyze the flow field characteristics to study the influence of the windshield on the motion state of the fluid around the gears and to clarify the drag reduction mechanism of the windshield. The control variable method is adopted to study the influence of the opening at the meshing area of the gear pair and the oil drainage groove on the drag reduction effect of the windshield to optimize the design parameters of the windshield. The research results show that: the drag reduction effect is optimal when the windshield covers the three surfaces of the spiral bevel gear, and the windage power loss is minimized when the gap between the windshield and the gear surface is 1 mm. Without affecting the meshing motion of the gear pair, the smaller the meshing opening, the smaller the windage of the gear pair. When an oil drainage groove with a 10° sector-shaped opening is designed at the position where the included angle between the meshing-out side of the gear pair and meshing center is 45°, the drag reduction effect of the windshield is the best.

Abstract The air-cooling system is an advantageous cooling method for battery modules due to its low cost, light weight, simple design, and no sealing required. In this study, the thermal performance of an air-cooled lithium-ion battery module was investigated through both numerical and experimental approaches, considering the influence of various design and operating parameters. The experimental investigation was conducted to examine the thermal behavior of an air-cooled lithium-ion battery module under specific operating conditions, providing temperature distribution data to validate the numerical model. Distinguishing itself from previous studies, this research replaces simplified assumptions with a high-accuracy approach by employing the mesh motion technique for dynamic airflow generation and an Equivalent Circuit Model (ECM) validated with experimental HPPC data. After the numerical model was validated against experimental data in terms of battery cell temperature, demonstrating high statistical reliability with an average R 2 of 0.979, comprehensive numerical analyses were conducted to investigate the effects of six critical design and operating parameters: fan speed, ambient temperature, discharge rate, air outlet and fan positions, and inter-cell spacing. The battery cells’ temperature inside the module decreased as the fan speed increased up to 4000 rpm, but no significant change in temperature was observed after this speed value. As the ambient temperature increased, cell temperatures and module voltage increased, and the maximum temperature difference between cells decreased. It was revealed that the cooling capacity of the system was insufficient for the 7C discharge rate. As the distance between cells increased, cell temperatures decreased, and a more homogeneous temperature distribution occurred. Lower cell temperatures and homogeneous temperature distributions occurred in the front-dual-side and top-dual-side fan positions, where three-dimensional air flow was provided with multiple fan placements. Among all configurations, when T ₘₐₓ and Δ T ₘₐₓ are evaluated together, the best thermal performance was achieved in the top-outlet configuration, with values of 36.75 °C and 6.78 °C, respectively. These findings provide significant contributions to the design optimization of air-cooled lithium-ion battery systems.

The behavior of highly flexible structures under Flow-Induced Vibrations (FIV) conditions, in certain flow regimes, is characterized by a strong coupling between the structural dynamics and fluid phenomena such as vortex shedding. This work presents selected results of ongoing research aimed at developing a fully open-source numerical framework to simulate the dynamic behavior of such structures immersed in complex fluid flows. The framework is based on a partitioned coupling approach of a fluid solver and a structural one, an Arbitrary Lagrangian-Eulerian mesh motion strategy, and Quasi-Newton Interface stabilization technique (IQN) that accounts for large displacements of the coupling interface. To illustrate the potential of such framework, we present strongly coupled Fluid-Structure Interaction (FSI) simulations of a thin flexible elastic plate subjected to FIV.

The article presents experimental and numerical studies of the torque of a Rushton turbine impeller operating in a cylindrical tank without partitions. The analyses were carried out on a laboratory scale for one system geometry and five impeller rotational speeds. Numerical calculations were performed using the Multiple Reference Frame (MRF) and Sliding Mesh (SM) methods in combination with the Volume of Fluid (VoF) model, with an analysis of the influence of mesh density performed prior to the main calculations. The simulations were performed in the ANSYS Fluent environment, while the experimental measurements were performed using the IKA EUROSTAR 60 control drive. The results obtained showed good qualitative agreement of the torque characteristics as a function of rotational speed, with simultaneous quantitative discrepancies consisting in obtaining higher torque values in numerical simulations compared to the experiment. These discrepancies may result from the limitations of the RANS approach in mapping global vortex motion and free surface deformation of the liquid, as well as from measurement uncertainties, which indicates further directions for research.

Fluid-structure interaction (FSI) is a key phenomenon in various engineering applications, characterized by the mutual influence of motion and forces between the fluid and the solid domains. Numerical simulations of FSI problems using the Finite Element Method (FEM) often face stability and convergence challenges in the solution of the fluid dynamics problem, such as spurious oscillations in the velocity field in convection-dominated regimes and pressure instabilities in incompressible flows. Furthermore, in high Reynolds number flows, the presence of turbulence can make it difficult for numerical schemes to converge to stable solutions, demanding discretizations that significantly increase the computational cost of simulations. To address these challenges while maintaining representative results, several stabilizing techniques and turbulence modeling strategies have been proposed in the literature. This work presents a comparative analysis of consistent stabilized formulations for incompressible flows with vorticity interacting with flexible structures. It includes the Streamline-Upwind/Petrov-Galerkin (SUPG), Pressure-Stabilized Petrov-Galerkin (PSPG), and Variational Multiscale (VMS) techniques. The influence of incorporating the Large-Eddy Simulation (LES) turbulence model is also investigated. The fluid flow is described within the Arbitrary Lagrangian-Eulerian (ALE) framework and coupled to a large displacement structural mechanics solver in a strong partitioned way. Time discretization is carried out using the generalized-α method, and fluid mesh movement is governed by the Laplace equation. The results show that VMS formulation yields slightly more accurate results than the SUPG/PSPG approach. Furthermore, the inclusion of the LES turbulence model improves the solution quality, particularly for high Reynolds number flows.

Aircraft interacts with the ground through landing gear system, while taxiing down the runway.Under rain or snow conditions, water film splashed by aircraft tires during taxiing on water-covered runways adheres to the landing gear, leading to ice accretion under low-temperature conditions, which may directly compromise aircraft takeoff and landing safety. Due to the substantial resource consumption required for experimental investigation of this problem, numerical simulation was employed to model the phenomenon.The water film icing process can be divided into two main stages: the formation of water film on the landing gear caused by tire spray, and the subsequent icing and heat transfer process of the splashed water film on the landing gear, this study conservatively simplifies the tire spray phenomenon as a typical liquid-solid two-phase coupling problem. A Finite Volume Model simulating water accumulation dynamics on landing gear tires was developed in Fluent software, based on extreme runway water accumulation conditions and extreme navigation weather scenarios during takeoff of a domestic civil aircraft model. The model incorporates coupled tire-water film-landing gear interactions. The VOF (Volume of Fluid) model and mesh motion are employed to calculate the water film thickness on the landing gear. A conservative thermodynamic equilibrium equation is then constructed based on boundary conditions to estimate the ice accretion thickness. The article analyzed the influence of external factors (aerodynamic drag, gravitational force, etc.) on water film thickness. The calculation results indicate that a conservative estimation of ice accretion derived from water film thickness does not compromise takeoff and landing safety, thereby validating that under rainy or snowy weather conditions with water accumulation on the runway, the conservative maximum icing thickness resulting from wheel spray water and landing gear water accumulation during aircraft taxiing will not exceed a level sufficient to pose a threat to aircraft takeoff and landing safety.

Blended-wing–body (BWB) has emerged as a potential concept to replace the traditional tube and wing (TAW) configuration. As with traditional flying wings, the BWB is prone to the wing-rock phenomenon but with a different triggering mechanism, which causes significant flight stability and control challenges. This paper aims to investigate the wing-rock characteristics of a BWB unmanned combat aerial vehicle and further evaluate the efficacy of active flow control techniques for its suppression. A validated computational framework has been developed based on rigid-body single-degree-of-freedom (single-DOF) dynamic mesh motion and forced roll sliding mesh motion employing the unsteady Reynolds-averaged Navier–Stokes equations. Free-to-roll simulations have predicted the onset angle of attack and various wing-rock characteristics. Jet blowing was influential in suppressing wing-rock amplitude and mean roll angles within a specific range of angles of attack, after which its momentum coefficient has to be increased. Liutex-based flow analysis revealed complex tip-separated flow interactions and the coalescence of multiple vortex systems as the primary causes of wing-rock initiation. The developed framework can be extended to multi-DOF analyses, flow-adaptive blowing, or to investigate other dynamic instabilities.

CFD modeling of sloshing-induced pressure drop inside LH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si11.svg" display="inline" id="d1e632"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> storage tanks used in maritime applications

Abstract With global warming enhancing the navigability of Arctic routes, the accurate prediction of ice resistance during navigation is of great engineering significance for the design and performance evaluation of polar ships. This study proposes a high-fidelity numerical simulation method that combines image recognition with CFD–DEM coupling and a six-degree-of-freedom (6-DOF) dynamic model to predict ship resistance in pack ice conditions. Using ice images from the CEHINAV towing tank experiments in Spain, the watershed image segmentation algorithm was applied to extract the spatial distribution and size information of ice blocks. A digital ice field was then reconstructed by surface injection of ice fragments of various sizes, thereby achieving consistency with the physical ice field. In the fluid–structure interaction simulations, a dynamic overset mesh and 6-DOF motion model were introduced to realistically reproduce the ship’s motion and the ship–ice interactions in the pack ice zone. Numerical simulations under different speeds and ice concentrations show that the average deviation from experimental data remains within 10%, thus confirming the accuracy and reliability of the proposed method. The results indicate that the bow region is the main area of ice loading and resistance concentration, with resistance increasing significantly as the ice concentration rises. The resistance curves exhibit evident nonlinear fluctuations and unloading phenomena. Further regional analysis reveals that the transverse resistance distribution along the hull gradually decreases from the midship toward both sides, while local regions exhibit transient fluctuations, a finding that highlights the complex and unsteady characteristics of ship–ice interactions.

We develop a numerical method for the Keller-Segel chemotaxis system that is designed to(i) preserve the model’s fundamental structural properties (positivity / bound preservation, mass conservation, and energy dissipation),(ii) efficiently and accurately resolve the near-singular dynamics associatedwith spike formation and finite-time blow-up.Our approach combines a linear, positivity-preserving scalar auxiliary variable (SAV) scheme (following the framework in [15]) with a Fourier spectralspatial discretization and an moving-mesh PDE-based method. The SAV reformulation provides a convenient platform for stable, linear time steppingwhile maintaining energy dissipation; the Fourier spectral discretization delivers high accuracy in smooth regions; and the moving-mesh PDE mesh redistribution concentrates collocation points in regions of large gradients so thatsharp, localized structures can be resolved without prohibitive cost. We show that the proposed moving mesh SAV scheme inherits positivity preservation, mass conservation, and discrete energy dissipation provided the mesh motion avoids element overlap. Two-dimensional tests demonstrate the method’s ability to capture fine spike profiles and estimate blow-up times with substantially reduced computational effort; the formulation extends straightforwardly to three spatial dimensions. Numerical results show that the proposed method is a practical and effective method for accurate simulation of chemotactic aggregation.

Choosing an appropriate computational domain for moving vehicles with strong fluid-structure interaction (FSI) is a challenging task. Typically, the vehicle follows a very long trajectory (compared to its size) in the longitudinal direction, but it can also experience significant lateral displacements, or even changes in direction, due to the fluid's action. If a fixed, earth-bound domain is used, it would need to be excessively large, demanding substantial computational effort. In this article, we propose a strategy to have a computational domain that follows the body, while keeping the lateral boundaries as streamlines so that standard slip boundary conditions can be applied there. Standard Arbitrary Lagrangian-Eulerian (ALE) terms are added to account for the mesh movement. This approach allows for the consideration of very complex vehicle movements with a computational cost roughly similar to that of a standard FSI problem. Note that ALE terms must be included anyway due to the body's movement caused by the FSI. Details of the numerical implementation of the streamlined boundaries are discussed, and several numerical examples are presented

Large eddy simulations (LES) of a side channel pump are conducted at different operating conditions, including best efficiency point (BEP) and off-design conditions. To address the numerical challenges of this LES, a high-quality mesh consisting of 116 million cells is generated for the impeller and casing parts. These parts are connected by three mesh interfaces, allowing for mesh motion at 3,450 RPM. The impeller with 72 staggered blades embedded in the side channel cavity transfers momentum to the flows in flow rates in the range of Q / Q BEP ∈ [ 0.8 − 1.2 ] , where Q is the volumetric flow rate. The validation shows a 5.1% efficiency deviation at the off-design condition of 0.8 Q BEP , where the flow is more unsteady than at other flow rates. The results reveal the state of turbulence, the pressure fluctuations and the vortical structures at the impeller periodic frequencies. The turbulence intensity of about 40% increases exponentially as the flow progresses around the impeller, driven by the interaction between the impeller blades and the radial discharge from the casing. The study illustrates that the state of turbulence is homogeneous in circumferential locations as θ ∈ [ π / 2 − 3 π / 2 ] of the casing, while the inlet and outlet ports change the state of turbulence. The six large structures generated by the impeller are related to the pressure fluctuations. The pumped outflow illustrates a moderate level of swirl while retaining extreme turbulence intensity in all conditions. The highest level of outflow swirl and turbulence is reported in 0.8 Q BEP . The study provides a comprehensive understanding of the complex vortical patterns and recirculation zones, which contribute to potential design improvements for enhanced, pump performance.

A unifying moving mesh method is developed for general $m$-dimensional geometric objects in $d$-dimensions ($d \geq 1$ and $1 \leq m \leq d$) including curves, surfaces, and domains. The method is based on mesh equidistribution and alignment and does not require the availability of an analytical parametric representation of the underlying geometric object. Mathematical characterizations of shape and size of $m$-simplexes and properties of corresponding edge matrices and affine mappings are derived. The equidistribution and alignment conditions are presented in a unifying form for $m$-simplicial meshes. The equation for mesh movement is defined based on the moving mesh PDE approach, and suitable projection of the nodal mesh velocities is employed to ensure the mesh points are not moved out of the underlying geometric object. The analytical expression for the mesh velocities is obtained in a compact matrix form. The nonsingularity of moving meshes is proved. Numerical results for curves $(m=1)$ and surfaces $(m=2)$ in two and three dimensions are presented to demonstrate the ability of the developed method to move mesh points without causing singularity and control their concentration.

BackgroundIntra-cerebrospinal fluid (CSF) drug delivery bypasses the blood-brain barrier, making it a promising route of delivery to treat central nervous system (CNS) diseases. Optimizing this delivery route is challenging because of complex interactions among drug kinetics, CSF flow dynamics and anatomical variations. Non-human primate (NHP) models provide an approximation to human physiology, making a suitable surrogate for studying intra-CSF drug dispersion. We present a NHP digital model for pharmacokinetic prediction of intra-CSF solute neuraxial dispersion that incorporates craniospinal compliance and other key physiological features.MethodsA 3D subject-specific digital model of the NHP CSF system was formulated using a 3D multi-phase computational fluid dynamics (CFD) approach with flow and geometric boundary conditions using animal-specific in vivo MRI data. Initial digital model drug dispersion predictions were carried out assuming rigid dura and pial surfaces and verified by comparison to a 3D-printed NHP bench-top model replicating the in vivo measurements utilizing fluorescein as a surrogate drug tracer. Once verified, the digital model was extended to mimic craniospinal compliance by incorporating a dynamic mesh to allow dura surface motion that replicated the non-uniform CSF flow along the neuroaxis. Results were quantified over a one-hour period after a 1 mL drug injection via lumbar puncture needle in terms of spatial-temporal drug dispersion along the neuroaxis for the rigid, compliant and bench-top models. Regional percent of injected dose was assessed across the lumbar, thoracic, cervical and cranial regions, while total exposure at each 1 mm section was calculated as the area-under-the-curve (AUC) along the neuroaxis.ResultsThe rigid digital model tracer dispersion predictions were verified through comparison with the NHP bench-top model, showing high spatial-temporal agreement (R² = 0.88). The introduction of dynamic mesh motion in the compliant digital model resulted in ~ 10X reduction in peak lumbar CSF flowrate compared with the rigid model (0.065 versus 0.65 mL/min). This decrease in peak CSF flowrate contributed to a reduction in the average Reynolds number along the neuroaxis, dropping from 250 in the rigid model to under 100 in the compliant model leading to decreased tracer dispersion in the lumbar region. At 1 h following injection, tracer distribution to the lumbar, thoracic, cervical and intracranial CSF was 91.9, 8.1, 0 and 0% of injected dose for the compliant model, while a model not including these physiological factors predicted 72.9, 20.4, 5.6 and 1.1%.ConclusionThe developed NHP-specific digital model, verified with NHP bench-top model simulations, provides a platform to understand and potentially improve intrathecal drug delivery protocols and devices. This study highlights the potentially important role of craniospinal compliance in CSF solute dispersion along the neuroaxis. Incorporating physiological factors such as compliance and varying flowrates into digital models of CSF transport can enhance the predictive capability of drug distribution within the CNS, aiding the design of more effective therapeutic strategies for CNS diseases.Clinical trial numberNot applicable.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12987-025-00723-z.

The excessive bristle deflection induced by applied high-pressure differential leads to brush seal failure. However, the mechanism of above failure is still unclear; it is essential to investigate leakage flow field within the deformed bristle pack. This study proposes a fluid–structure interaction (FSI) numerical method, achieving multi-physics coupling modeling of bristle bending and leakage flow through mesh motion technique, which breaks through the limitations of traditional static bristle assumptions. A realistic aerodynamic force distribution along the bristle length, extracted from a computational fluid dynamics (CFD) solution, was applied to the finite element (FE) model to calculate bristle bending and mechanical contacts. The results showed that leakage flow rates exhibit a significant reduction of 23.71%–42.91% by considering bristle deflection within pressure ratio of 1.5–3.0. There is a decrease of 11.21%–22.91% in axial aerodynamic force compared to ones without considering bristle deflection, which is due to increased flow resistance caused by reduced axial bristle spacing. The axial component of the aerodynamic force is 9.56–13.02 times of the circumferential and radial ones. The maximum axial deflection of the bristle pack is 6%–13.2% of its thickness. The axial bristle deflection gradually decreases in subsequent downstream rows due to closure of axial bristle spacing. Small deflection in the circumferential and radial direction is attributed to mechanical support caused by rotor. This work reveals the interaction mechanism between dynamic bristle deformation and leakage flow coupled both aerodynamic and mechanical loads, providing a critical theoretical basis for reducing leakage rates and extending service life in brush seal design.

An arbitrary Lagrangian–Eulerian finite element method and numerical implementation for curved and deforming lipid membranes is presented here. The membrane surface is endowed with a mesh whose in-plane motion need not depend on the in-plane flow of lipids. Instead, in-plane mesh dynamics can be specified arbitrarily. A new class of mesh motions is introduced, where the mesh velocity satisfies the dynamical equations of a user-specified two-dimensional material. A Lagrange multiplier constrains the out-of-plane membrane and mesh velocities to be equal, such that the mesh and material always overlap. An associated numerical inf–sup instability ensues, and is removed by adapting established techniques in the finite element analysis of fluids. In our implementation, the aforementioned Lagrange multiplier is projected onto a discontinuous space of piecewise linear functions. The new mesh motion is compared to established Lagrangian and Eulerian formulations by investigating a pre-eminent numerical benchmark of biological significance: the pulling of a membrane tether from a flat patch and its subsequent lateral translation.

Abstract Despite its applications, metal-assisted chemical etching (MACE) is still not well understood. To elucidate its underlying mechanism, MACE with micron-sized gold mesh was systematically carried out across a wide range of volume ratio R of HF acid to H2O2 solution. Slant wires were observed at room temperature over a broad range of parameters, which contradicts the well-established viewpoint that slantwise etching occurs only at elevated temperatures. Vertical wires form only in a narrow parameter space featuring a low R. The wide variation in observed slant angles indicates that the associated MACE processes do not exhibit a preferred etching direction. The observed R-dependent change of oxygen content in wires and of bubbling phenomena was explained by two competing mechanisms associated with direct and indirect Si dissolution. The high and low R regime is dominated by direct and indirect mechanism, respectively, whereas in the intermediate regime both mechanisms play an indispensable role. Slant wire formation is caused directly by the slantwise mesh movement. Although this movement is closely correlated with the direct mechanism, it cannot be fully explained by it. We hypothesize that hydrogen bubbling-induced flow has the potential to hydrodynamically drive the mesh slantwise and hence can be responsible directly for slant wire formation. To the best of our knowledge, this work not only reports a relatively novel phenomenon—slant wire formation by MACE at room temperature—but also provides, for the first time, a comprehensive understanding of its underlying complex mechanism.

An enriched immersed boundary method for Stefan problem with application to thermal modeling of additive manufacturing process

Abstract Spin-extrusion forming (SEF) is an innovative method for manufacturing thin-walled cylindrical rings with external cross ribs (TCRECR). The meshing motion between the feeding roll and the component shapes the rib, while the feed motion of the feeding roll causes the rib height to grow. The contour design of the feeding roll is critical, as an unsuitable design will produce motion interference, resulting in rib folding problems. This paper proposes two evaluation indices to characterize the rib folding defects, one is the rib aspect ratio, and the other is the relative error between the feeding roll's and the component's enclosed areas. Based on the reverse envelope motion experiments, mathematical models for evaluation indices are established, and the forming boundaries of SEF processing are determined through finite element (FE) simulations. A semi-analytic model for rib defect prediction is obtained, and its effectiveness is verified based on current experimental platforms. The plastic flow during SEF processing is analyzed, and the mechanism of external rib folding is systematically studied. When the relative area error exceeds a certain threshold, research indicates two causes for rib folding defects. One reason is that the growth rate on both sides of the rib will be greater than that in the middle due to an increase in the squeezing force of the feeding roll on both sides. Another reason is that the motion interference between the component and the feeding roll intensifies, and the material surrounding the center folds from both sides.

ABSTRACTIn this work, we first analyze the semiconservative direct discontinuous Galerkin (DDG) method for the Korteweg–de Vries (KdV) equations. The scheme achieves order accuracy in finite element approximation spaces with even degrees . Subsequently, we construct and analyze a nonconservative discrete scheme within the framework of the local discontinuous Galerkin (LDG) method. Moreover, this scheme can achieve a suboptimal convergence order of . For temporal discretization, we employ the implicit‐explicit additive Runge–Kutta method to achieve high‐order accuracy and efficiency. Finally, numerical experiments for the DDG and LDG methods are provided, including the accuracy of solitons, long‐term behavior, and conserved quantities. Given the potential for finite‐time soliton blowup phenomenon due to the presence of high‐order nonlinearity in this model, we also investigate the performance of some discontinuous Galerkin (DG) methods in simulating the instability of solitons while improving the accuracy and efficiency of blowup simulations through the incorporation of the arbitrary Lagrangian–Eulerian (ALE) method for adaptive mesh movement.