Simulation Of Flow Research Articles

Stokes-dependent droplet collection efficiency on a NACA 0012 airfoil from droplet-informed simulations with statistical overloading.

Accurate modelling of ice accretion on aircraft wings requires analysing droplet impingement on the surface to optimize the design of ice-protection systems. We perform Euler-Lagrange simulations of a droplet-laden flow impinging on a NACA 0012 airfoil. Our study includes water droplets with eight discrete sizes ranging from 1 to 160 microns. We vary the free-stream velocity of the incoming airflow in the range [Formula: see text] m s-1 and the chord length of the airfoil in the range [Formula: see text] m. Due to the dilute nature of supercooled clouds, one-way coupling is used in the simulations. The effects of droplet breakup and collision are also neglected. To reduce the computational cost, we employ statistical overloading of droplets, allowing us to simulate millions of impinging droplets in a time span on the order of milliseconds. Our results show that the droplet collection efficiency, which measures the likelihood of droplet impingement on the airfoil surface, increases with droplet size and free-stream velocity but decreases with airfoil size. We demonstrate that collection efficiency, impingement velocity and impingement angle are primarily dictated by a single non-dimensional parameter, the droplet Stokes number. We also identify a critical stagnation-streamline Stokes number below which impingements do not occur and use it to estimate the minimum droplet size for impingement. In addition, we observe droplet behaviour to become Stokes number independent at large values of the Stokes number.This article is part of the theme issue 'Heat and mass transfer in frost and ice'.

A High-Efficient Modeling Method for Aerodynamic Loads of an Airfoil with Active Leading Edge Based on RFA and CFD

For the airfoil in freestream, the pressure difference between the upper and lower surfaces and the variations in pressure gradients are significant at its leading edge area. Under reasonable deflections, the active leading edge can effectively change airfoil aerodynamic loads, which helps to improve the rotor aerodynamic performance. In this paper, a modeling method for an airfoil with an active leading edge was developed to calculate its aerodynamic loads. The pitch motion of the rotor blade and the leading edge deflections were taken into account. Firstly, simulations of steady and unsteady flow for the airfoil with an active leading edge were conducted under different boundary conditions and with different leading edge deflection movement. Secondly, the rational function approximation (RFA) was employed to establish the relationship between aerodynamic loads and airfoil/active leading edge deflections. Then, coefficient matrices of the RFA approach were identified based on a limited number of high-fidelity computational fluid dynamics (CFD) results. Finally, an aerodynamic model of the airfoil with an active leading edge was developed, and its accuracy was validated by comparing it to the high-fidelity CFD results. Comparative results reveal that the developed model can calculate the aerodynamic loads of an airfoil with an active leading edge accurately and efficiently when applied appropriately. The modeling method can be used in aerodynamic load calculations and the aeroelastic coupling analysis of a rotor with active control devices.

Anticipating Future Hydrological Changes in the Northern River Basins of Pakistan: Insights from the Snowmelt Runoff Model and an Improved Snow Cover Data

The water regime in Pakistan’s northern region has experienced significant changes regarding hydrological extremes like floods because of climate change. Coupling hydrological models with remote sensing data can be valuable for flow simulation in data-scarce regions. This study focused on simulating the snow- and glacier-melt runoff using the snowmelt runoff model (SRM) in the Gilgit and Kachura River Basins of the upper Indus basin (UIB). The SRM was applied by coupling it with in situ and improved cloud-free MODIS snow and glacier composite satellite data (MOYDGL06) to simulate the flow under current and future climate scenarios. The SRM showed significant results: the Nash–Sutcliffe coefficient (NSE) for the calibration and validation period was between 0.93 and 0.97, and the difference in volume (between the simulated and observed flow) was in the range of −1.5 to 2.8% for both catchments. The flow tends to increase by 0.3–10.8% for both regions (with a higher increase in Gilgit) under mid- and late-21st-century climate scenarios. The Gilgit Basin’s higher hydrological sensitivity to climate change, compared to the Kachura Basin, stems from its lower mean elevation, seasonal snow dominance, and greater temperature-induced melt exposure. This study concludes that the simple temperature-based models, such as the SRM, coupled with improved satellite snow cover data, are reliable in simulating the current and future flows from the data-scarce mountainous catchments of Pakistan. The outcomes are valuable and can be used to anticipate and lessen any threat of flooding to the local community and the environment under the changing climate. This study may support flood assessment and mapping models in future flood risk reduction plans.

Power Flow Simulation and Thermal Performance Analysis of Electric Vehicles Under Standard Driving Cycles

This paper presents a simulation framework for evaluating power flow, energy efficiency, thermal behavior, and energy consumption in electric vehicles (EVs) under standardized driving conditions. A detailed Simulink model is developed, integrating a lithium-ion battery, inverter, permanent magnet synchronous motor (PMSM), gearbox, and a field-oriented control strategy with PI-based speed and current regulation. The framework is applied to four standard driving cycles—UDDS, HWFET, WLTP, and NEDC—to assess system performance under varied load conditions. The UDDS cycle imposes the highest thermal loads, with temperature rises of 76.5 °C (motor) and 52.0 °C (inverter). The HWFET cycle yields the highest energy efficiency, with PMSM efficiency reaching 92% and minimal SOC depletion (15%) due to its steady-speed profile. The WLTP cycle shows wide power fluctuations (−30–19.3 kW), and a motor temperature rise of 73.6 °C. The NEDC results indicate a thermal increase of 75.1 °C. Model results show good agreement with published benchmarks, with deviations generally below 5%, validating the framework’s accuracy. These findings underscore the importance of cycle-sensitive analysis in optimizing energy use and thermal management in EV powertrain design.

Integrated Maintainability in the Structural and System Design of Fixed-Wing UAVs

This paper introduces an overall design approach to a fixed-wing unmanned aerial vehicle (UAV) with an emphasis on the incorporation of maintainability into structural and system-level designs. Conceptual design was established using CAD software, following which aerodynamic performance was analyzed by external flow simulations based on the finite volume method. The outcome of the above analyses was used to finalize the external shape, resulting in detailed structural and layout designs. Mechanical behavior of critical structural components was analyzed through finite element analysis (FEA) to determine stress distribution, deformation, and vibration characteristics under simulated operational loading conditions. A distinctive feature of this research is the prioritization of maintainability as a primary design criterion from the outset. The inner arrangement of components; batteries, electric ducted fan motors, avionics, and control surfaces, was carefully planned to provide maintainability access for both personnel and tools. Sensor and control systems were also embedded with the aim of facilitating condition-based and predictive maintenance over UAV’s operational life. This involved choosing sensor points of attachment and providing access to areas expected to need regular inspection, adjustment, or replacement. The completed UAV prototype optimizes aerodynamics, structural strength, and maintainability. The design strategy not only satisfies performance and production demand but also helps to reduce maintenance downtime and lifecycle costs. This maintainability-driven design philosophy serves to increase the UAV's viability for actual world deployment in environments in which reliability, serviceability, and operational readiness are vital.

Flow dynamic differences between Kawasaki Disease patients with coronary artery aneurysms and ectasia.

Flow dynamic differences between Kawasaki Disease patients with coronary artery aneurysms and ectasia.

Simulations for Casson nanofluid flow with mass flux zero nanoparticle aspect across an exponentially elongated permeable sheet

ABSTRACT The potential applications of nanofluid in enhancing heat transfer performance in industrial and energy-related processes, including the design of more efficient cooling systems and solar energy absorbers, have inspired many studies on magneto-nanofluid. The principal goal of this investigation is to examine the magneto-Casson fluid flow through an exponentially stretched surface incorporating the Buongiorno nanofluid model along with different effects like heat and Ohmic dissipation, heat source and chemical reaction. The thermal flow analysis of radiative heat and viscous dissipation for the system is done. The variety of partial differential equations (PDEs) in the mathematical framework is simplified to ordinary differential equations (ODEs) with appropriate dimensionless variables, and approximate computational solutions are attained through a modified weighted residual scheme. The impression of different influential parameters on flow fields was examined via plotted graphs. Graphs illustrate the significant parameter’s impacts on each profile and exhibit relevant dynamical quantities, including the Skin friction, heat gradient, and mass gradient. As noticed, the flow rate profile decreased by about 3.82%, arising from the combined influences of the magnetic, viscous Casson and porosity terms with varied suction values. Also, the thermal distribution is enhanced by 4.28% with rising values of the radiation and Eckert number. The current viscoelastic nanofluid model is being investigated to determine whether it possesses superior energy storage efficiency compared to conventional nanofluid.

Role of curvature in controlling SWBLI behavior in a hypersonic double ramp flow

Hypersonic flows generate intense unsteady pressure and thermal loads, posing significant challenges for high-speed aerospace applications such as re-entry vehicles and hypersonic cruise systems. These extreme conditions necessitate effective flow control strategies to enhance aerodynamic performance and structural integrity. This study examines the influence of surface curvature on these loads in a double-wedge geometry, aiming to optimize flow control approaches. Unsteady Mach 7 flow simulations are conducted using a high-fidelity, time-accurate solver with third-order MUSCL as well as seventh-order WENO schemes, ensuring precise resolution of shock interactions and flow structures. A standard double-ramp configuration is analyzed alongside two smooth ramp configurations, where the faceted intersection of the front and aft wedges is replaced with different curvature levels. The computational results are validated against experimental heat-flux data to confirm the accuracy of the numerical approach. The findings reveal that the high-curvature geometry (curvature, κ=1.01) introduces only marginal variations in mean pressure and thermal loads. However, transient flow characteristics are notably altered. In contrast, the low-curvature configuration (κ=0.49) significantly reduces both pressure and thermal loads by 43% and 58%, respectively, while also minimizing the separation region. The reduced separation leads to a smoother and more stable flowfield, contributing to improved aerodynamic efficiency. Long-term analysis further indicates that the low-curvature configuration accelerates the decay of large-amplitude unsteady signals, suggesting enhanced flow stability over extended durations. These results underscore the potential benefits of surface curvature in mitigating aerodynamic heating and structural stresses in hypersonic flows, and therefore provide insights for the development of more efficient hypersonic vehicles with improved thermal management, enhanced vehicle survivability, and better overall performance in extreme flight conditions.

Numerical simulations of MHD Jeffrey fluid flows over curved geometry: non-similar analysis

Numerical simulations of MHD Jeffrey fluid flows over curved geometry: non-similar analysis

Investigating Turbulence Effects on Magnetic Reconnection Rates through 3D Resistive Magnetohydrodynamic Simulations

Abstract We investigate the impact of turbulence on magnetic reconnection through high-resolution 3D magnetohydrodynamic (MHD) simulations, spanning Lundquist numbers from S = 103 to 106. Building on the A. Lazarian & E. T. Vishniac theory, which asserts reconnection rate independence from ohmic resistivity, we introduce small-scale perturbations until t = 0.1 t A. Even after the perturbations cease, turbulence persists, resulting in sustained high reconnection rates of V rec/V A ∼ 0.03–0.08. These rates exceed those generated by resistive tearing modes (plasmoid chain) in 2D and 3D MHD simulations by factors of 5–6. Our findings match observations in solar phenomena and previous 3D MHD global simulations of solar flares, accretion flows, and relativistic jets. The simulations show a steady-state fast reconnection rate compatible with the full development of turbulence in the system, demonstrating the robustness of the process in turbulent environments. We confirm reconnection rate independence from the Lundquist number, supporting Lazarian and Vishniac’s theory of fast turbulent reconnection. Additionally, we find a mild dependence of V rec on the plasma–β parameter, decreasing from 0.036 to 0.028 (in Alfvén units) as β increases from 2.0 to 64.0 for simulations with a Lundquist number of 105. Lastly, we explore the magnetic Prandtl number’s (Pr m = ν/η) influence on the reconnection rate and find it negligible during the turbulent regime across the range tested, from Pr m = 1 to 60.

Numerical simulation of blood flow in 3D CT-based healthy and atherosclerosis carotid artery bifurcation models to compare the hemodynamics and biomechanics using FSI method under realistic boundary conditions

Atherosclerosis, a primary cause of cardiovascular diseases, arises from intricate interactions between hemodynamic factors and vascular biology. This condition is characterized by a reduction in luminal cross-sectional area, which consequently impairs blood supply. In this study, patient-specific models of a stenosis carotid artery and its digitally-created healthy counterpart were reconstructed from CT scans. Employing the finite element method and a two-way fluid-structure interaction (FSI) coupling approach, non-Newtonian simulations of pulsatile and laminar blood flow were performed. The arterial wall was modeled as a linear, elastic, isotropic, and homogeneous material. The presence of plaque led to an approximately two-fold increase in peak velocity within the stenotic region, rising from approximately 0.3 m/s in the healthy model to 0.7 m/s, directly attributable to the reduced luminal area. The maximum shear stress of the wall at the location of the plaque reached 40 Pa. Furthermore, the maximum wall displacement increased from 1.5 mm in the healthy artery to 1.7 mm in the stenosis artery. While pressure results indicated minor localized increases and decreases before and after the plaque site, respectively, these changes did not significantly affect the total arterial pressure. Examination of blood flow streamlines revealed flow recirculation regions in the carotid sinus bulb of both arteries. In the stenosis artery, an additional and more pronounced flow recirculation region formed distal to the plaque, owing to the post-stenotic expansion. This phenomenon led to a substantial increase of approximately 240% in the oscillatory shear index (OSI) within the internal carotid artery branch. The relative residence time (RRT) remained relatively constant in the common carotid artery and the bifurcation region. However, RRT decreased by approximately 40% in the carotid branches, predominantly in the external carotid artery. Comparison of hemodynamic parameters and biological indices between healthy and stenosed arteries suggests that atherosclerotic plaques significantly alter local hemodynamics, potentially creating novel regions susceptible to atherosclerosis that are absent in healthy artery. In the healthy artery, about 8.3% of the vessel area was at risk for disease (TAWSS < 0.4 Pa), but this increased to 20% in the stenosed artery due to plaque accumulation, a 2.4-fold expansion. Regarding RRT, an increase was observed; areas with RRT > 10 expanded by approximately 1.6 times in the stenosed artery (from 3.1% in healthy to 5% in diseased).

Large-Eddy Simulation of Low Reynolds Number Flow Around Airfoils with Suction and Ejection Slits

Large-Eddy Simulation of Low Reynolds Number Flow Around Airfoils with Suction and Ejection Slits

Hybrid Nanofluid Thin-Film Dynamics of [PVA/MoS2+Cu]HNF: Synthesis, Characteristics and 3D Electromagnetic Flow Simulation via Variant Thickness Surface

This work aims to study the thermal features of three-dimensional hybrid nanofluid flow in the electromagnetic radiative flow of [PVA/MoS2+Cu]HNF via surface with variant thickness. Microporous structure thin films are fabricated from [PVA/MoS2+Cu]HNF via a physical vapor deposition (PVD) methodology. This study considered the existence of slippery speed and jumping heat constraints. Copper and molybdenum disulfide nanoparticles are suspended in polyvinyl alcohol (PVA) to form a hybrid nanofluid. Controlling equations are streamlined to ordinary differential equations and are resolved numerically by utilizing the NDSolve function in Mathematica. The implications of various parameters like nanoparticle volume size, radiative parameter and magnetic force are investigated, and outcomes are graphically provided. Studio 7.0 application with TDDFT/DMol3 is utilized to analyze molecular structures and conduct frequency computations for crystal modes and isolated molecules. DFT-Gaussian09W vibration values are juxtaposed with the experimental data about either the structural or optical aspects. The main outcomes are indicated by the isolated molecule of the polymer [PVA]iso and composite [PVA/MoS2+Cu]iso exhibiting a bandgap of 5.415 eV and 1.772 eV, respectively. The magnetic field reduces hybrid nanofluid flow velocity owing to the Lorentz force, which opposes fluid motion. A surge in radiative heat flux (RHF) significantly raises the nanofluid temperature.

Numerical Studies of Advanced Methane Drainage Employing Underground Long-Reach Directional Drilling

This paper presents the procedures and results of the numerical modelling and simulations performed to analyse an innovative method of advanced methane drainage employing underground long-reach directional drilling (LRDD) technology. The analysis involved the implementation of geomechanical and dynamic reservoir models to simulate processes in coal seams and the surrounding rocks during coal mining and concurrent methane drainage, in accordance with the proposed technology. The analysis aimed to quantitatively assess the effectiveness of the technology, evaluate its sensitivity to the geological and geomechanical properties of the rocks, and identify the potential for optimisation of its technological and operational parameters in the proposed strategy. The works presented in this paper include the following key tasks: the construction of a system of geological, geomechanical, and dynamic simulation models; the analysis of the geomechanical effects of various types and regions of occurrence; the implementation of the correlation between the geomechanical states of the rocks and their transport properties; and the performance of the effectively coupled geomechanical and reservoir fluid flow simulations. The proposed approach was applied to the specific conditions of the multi-seam Murcki–Staszic Coal Mine operated by Jastrzębska Spółka Węglowa, Poland.

Experimental and numerical investigation of wavelength and resolution dependency of dynamic optical coherence tomography signals

The wavelength and system-resolution dependencies of dynamic optical coherence tomography (DOCT) are investigated experimentally and numerically. Experimental investigations demonstrate significant wavelength dependency for the DOCT values but no marked resolution dependency. Numerical simulations were performed using diffusion, random-ballistic motion, and mono-directional flow-based motion models. Diffusion and random-ballistic motion-based simulations show significant wavelength dependency. Additionally, these simulations revealed a small but certain resolution dependency. Mono-directional flow simulations did not show wavelength dependency but did demonstrate resolution dependency. The DOCT value is sensitive to both tissue dynamics and the OCT system specification. These effects should be considered when interpreting DOCT images.

Calibration of parameters in microscopic traffic flow simulation models considering micro-meteorological information.

Different micro-meteorological conditions can affect a driver's judgment of road conditions, leading to changes in following behavior. On rainy days, water films on the road reduce traction, increasing the likelihood of hydroplaning and traffic accidents. While there are existing following models under various weather conditions, research on the specific impact of micro-meteorological factors is insufficient. To achieve fine management in intelligent transportation and real-time monitoring of vehicle states, it's essential to study following behavior under different micro-meteorological conditions and establish corresponding models. This paper focuses on the Intelligent Driver Model (IDM) and the Wiedemann99 model, considering the impact of micro-meteorological conditions. By incorporating a driver's judgment factor, λ, the IDM and Wiedemann99 models are improved, leading to the development of new models: I-IDM and I-Wiedemann99. Simulation validation is used to choose speed and following distance as performance indicators for parameter calibration of the I-IDM and I-Wiedemann99 models, with the sum of Root Mean Square Percentage Error (RMSPE) as the goodness-of-fit function. Comparisons are made between the driving paths, speeds, and accelerations of following vehicles before and after calibration, verified through simulations. The conclusions are as follows: the average error and standard deviation of the improved I-IDM model are smaller than those of the I-Wiedemann99 model, with the maximum Root Mean Square Percentage Error (RMSPE) for I-IDM model parameter calibration being 0.4568 and the minimum being 0.1324. For the I-Wiedemann99 model, the maximum RMSPE is 0.4613 and the minimum is 0.1376. The parameter calibration results of the I-Wiedemann99 model are more dispersed compared to those of the I-IDM model, indicating that the I-IDM model simulates following behavior more effectively than the I-Wiedemann99 model. The findings of this study can provide a reference for further improving the theory of following behavior, and offer a theoretical basis and IoT technology support for refined traffic management under rainy conditions.

Blood flow simulations in a cerebral aneurysm secured by a Flow Diverter stent.

Objective: The objective of this research was to show a potential use of computational fluid dynamics tools in supporting the medical personnel by offering objective data regarding the hemodynamic changes in the aneurysm caused by implanting different models of the stent. Methods: The authors reconstructed patient-specific model of the cerebral arteries with diagnosed aneurysm. Then, four virtual models of the Flow Diverter stent (with varied nominal diameters) were prepared. During the numerical analyses, the Immersed Solid Method was used to model the presence of the stent wirebraid. After performing steady state and transient simulations of non-Newtonian blood flow in pre- and post-treatment models, changes in numerous hemodynamic parameters were analysed. Results: The results confirmed that stent porosity influences hemodynamic changes inside the aneurysm (for presented case studies). The less porous the stent, the more it promotes the possible intrasaccular thrombosis. This could be concluded by observing larger regions of stagnant blood with higher viscosity. Additionally, the denser the stent, the lower and more uniform the stress exerted on the aneurysm wall. Conclusions: Numerical simulations can provide valuable insight into phenomena occurring inside the blood flow after implanting the stent. This can support selecting optimal stent configuration for the particular patient and, consequently, can help in planning the endovascular procedure.

Assessment of future groundwater level using modflow code under different managerial scenarios in the Serres river basin, Greece

Given the lack of rainfall during the dry season in Greece and other countries, groundwater is important in meeting water needs for all uses. Reliable simulation of groundwater flow and predictions of groundwater levels under different management scenarios, in light of water crisis, are essential tools for the sustainable management of aquifers. In this paper, the MODFLOW code for simulating groundwater flow was applied to the Greek section of the transboundary Serres river basin in a complex aquifer system developed in alluvial deposits. The groundwater of the basin is critical for the fulfillment of both the irrigation requirements of an extensive local agricultural activity and the domestic needs of a significant population. Data necessary for model construction and simulation was provided by the relevant authorities and literature. The model calibration is considered successful as the simulated values show a statistically acceptable fit to the measured data. Sensitivity analysis shows that the aquifer’s storage coefficient change has the greatest impact on the groundwater level. In a management scenario where groundwater extraction is reduced by 5% over a ten-year period, the groundwater level is projected to rise by approximately 0.17 m. In contrast, in the worst-case scenario, where groundwater extraction increases by 6.5% reaching at a critical point regarding the sustainability of the groundwater resources in the area, the average groundwater level is expected to drop by 0.72 m, resulting in the reduction of aquifer reserves. The model serves as a valuable tool for mitigating and adapting to the impacts of the climate crisis, as well as for formulating policies that promote the sustainable management and rational use of the aquifer.

Predictive modeling and machine learning show poor performance of clinical, morphological, and hemodynamic parameters for small intracranial aneurysm rupture

Small intracranial aneurysms (SIAs) (< 5 mm) are increasingly detected due to advanced imaging, but predicting rupture risk remains challenging. Rupture, though rare, can cause devastating subarachnoid hemorrhage. This study analyzed 141 SIAs (101 unruptured, 40 ruptured) using semi-automatic morphological analysis and high-resolution, image-based blood flow simulations from 3D rotational angiography. Advanced morphological and hemodynamic parameters were extracted, with clustering applied to address multicollinearity. Univariate logistic regression identified cluster representatives, and forward selection highlighted the maximum height, Neck inflow rate, and Non-sphericity index as rupture predictors, though only the latter two were significant. Clinical variables like age, sex, and comorbidities were also assessed but failed to predict rupture risk. The full model showed overfitting, with a pseudo-R2 of 0.142 on the training set but only 0.032 on the test set. A simplified model using just Neck inflow rate and Non-sphericity index performed similarly poorly (pseudo-R2 of 0.034). Multiple machine learning classifiers were evaluated, with similar performance across models, supporting the model-independence of the results. Overall, neither morphological, hemodynamic, nor clinical variables reliably predicted rupture risk, highlighting the limitations of current methods and underscoring the need for prospective studies and multimodal approaches that integrate imaging biomarkers and compare small and large aneurysms for better risk stratification.

Necessary and Sufficient Conditions for Accurate Reduced Kinetic Mechanisms to Have Fidelity in Reactive Flow Simulations

ABSTRACT To date, there is still an inability to efficiently solve the Navier–Stokes equations for reactive flows in conjunction with lengthy and complex chemical kinetics describing oxidation of realistic fuels. Therefore, reduced kinetic mechanisms are sought that are as compact as possible, so as to reduce the number of species equations solved. However, there is a quandary for flow simulations as to whether compact reduced mechanisms could emulate hypothetical flow simulations using the template kinetics from which the reduced mechanism was obtained. In this study, necessary and sufficient conditions are derived for this emulation to occur. The proposed concepts, self-similarity and partitioning the ensemble of species into computed and non-computed species, are the building blocks of the chemical kinetic reduction in the Local Self-Similarity Tabulation method. It is shown that employing the same species partitioning concept for flow simulations must be accompanied by several conditions which must be satisfied for the simulation to be a good approximation of the hypothetical simulation using the template kinetic mechanism. These conditions represent the necessary and sufficient conditions criteria. There are indications from the literature that these criteria are not necessarily satisfied. A protocol is proposed for checking whether these conditions are fulfilled for any selected reduced mechanism. Several possibilities are advanced to palliate for lack of fulfillment of these criteria. Research gaps are identified that must be filled to enable successful utilization of reduced mechanisms in reactive flow simulations, and procedures to mitigate these gaps are outlined.