Multi-Objective optimization of a novel swinging inlet strategy for Air-Cooled battery thermal management systems under Fast-Charging conditions in electrical vehicles

This study presents high-spatial-resolution two-component, two-dimensional particle image velocimetry (PIV) measurements of a self-similar adverse pressure gradient turbulent boundary layer (SS-APG-TBL) at the verge of separation. The experiments were performed in the LTRAC APG-TBL wind tunnel, where the flexible roof was adjusted to impose the pressure distribution required for self-similar development within the test section. The APG-TBL had a Reynolds number based on the boundary-layer thickness of R e δ = 7 . 9 × 1 0 4 , and the Clauser pressure-gradient parameter β = 18 . 8 was maintained throughout the measurement domain. A dual-camera 2C-2D PIV system was employed to capture both large-field and near-wall velocity fields, enabling accurate measurement of the flow adjacent to the wall. Calibration procedures, including lens-distortion correction and camera-overlap alignment, were performed to ensure sub-pixel accuracy in the velocity fields. The probability density and cumulative distribution functions of the instantaneous streamwise velocity adjacent to the wall are used to assess the wall-shear condition and demonstrate that the boundary layer is at the verge of separation. The probability density distribution peaks near zero and exhibits positive skewness, indicating a near-zero mean with intermittent high-velocity events. The results confirm a low-skin-friction state consistent with incipient separation, with nearly constant wall-shear stress across the measurement stations. Furthermore, the mean-velocity defect and Reynolds stresses collapse when expressed in self-similar variables, providing strong experimental evidence of a self-similar APG-TBL at moderate Reynolds number. The present database establishes an experimental benchmark, extending the study of SS-APG-TBLs beyond direct numerical simulation and to higher Reynolds numbers, and offers a new reference for turbulence modelling and theoretical analyses of self-similar adverse pressure gradient turbulent boundary layers. • Self-similar APG-TBL at the verge of separation created with a contoured tunnel roof. • Dual-camera 2C-2D PIV combined high spatial resolution with a large field of view. • Near-zero wall shear stress confirmed by near-wall velocity PDF. • Mean-defect and Reynolds stresses collapse under self-similar scaling. • Experimental database at β ≈ 20 . 3 and Re δ ≈ 7 . 9 × 1 0 4 for SS-APG-TBL studies.

In Brazil, coronary angioplasty with stent implantation is a primary intervention for cardiovascular diseases, yet in-stent restenosis remains a significant complication. Recent proposals suggest transitioning from traditional cylindrical stents to conical geometries to better align with vascular physiology. This study aims to compare the performance of cylindrical and conical stents and investigate the influence of varying strut thicknesses on hemodynamic parameters. The study employed computational modeling using both Fluid-Structure Interaction (FSI) and Computational Fluid Dynamics (CFD) simulations to quantify hemodynamic parameters including Time-Averaged Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), and Relative Residence Time (RRT). A total of 12 simulations were performed (6 FSI and 6 CFD) on models of cylindrical and conical arteries with stent strut thicknesses ranging from 0.1 mm to 0.3 mm. The finite volume method was used for the fluid domain, while the finite element method was applied to the solid domain (arterial wall and stent). Blood was modeled as a non-Newtonian fluid using the Carreau model, with Reynolds numbers from 251 to 381 and Womersley numbers from 2.23 to 3.78. Quantitative analysis revealed that rigid-wall CFD consistently underestimates the risk of restenosis compared to FSI. Specifically, FSI predicted areas of critical Time-Averaged Wall Shear Stress (TAWSS ≤ 1 Pa) that were 12% to 46% larger than those predicted by CFD. Strut thickness emerged as a dominant factor; increasing thickness to 0.3 mm resulted in WSS values approximately three times lower than the 0.1 mm models, significantly expanding recirculation zones. Regarding geometry, while cylindrical stents exhibited concentrated high Oscillatory Shear Index (OSI) at the distal edge, conical stents demonstrated a more distributed OSI pattern and a markedly improved Relative Residence Time profile, reducing peak RRT at the distal edge by approximately 60% compared to cylindrical models (12.25Pa-1 vs. 29.94Pa-1), thereby mitigating stagnation and potential edge restenosis. The findings confirm that neglecting arterial compliance (CFD only) leads to a substantial underestimation of hemodynamic risk. Both stent geometry and strut thickness are critical; while conical stents offer better risk distribution, thicker struts can negate these benefits. Optimizing these parameters is essential for next-generation stent designs.

Double-pipe heat exchangers (DPHEs) are vital in industrial applications, and improving their performance is crucial for sustainability. This study uses three-dimensional Computational Fluid Dynamics (CFD) simulations to investigate the impact of passive flow modifications, specifically geometrically spaced and perforated ring inserts, on heat transfer and pressure drop in a DPHE. The research involved developing a 3D numerical model whose accuracy was ensured through a comprehensive mesh independence study and rigorous validation against established empirical correlations and experimental data. Subsequent simulations explored the influence of geometric spacing ( G -factor) and the number of perforations per ring. Results demonstrated that for unperforated rings P = 0 , uniform spacing maximised heat transfer, reaching a Nusselt number of 177.4 at a Reynolds number of 12,000. In contrast, strongly biased configurations exhibited superior overall performance by balancing thermal enhancement with hydraulic losses. These biased cases achieved a Performance Evaluation Criterion (PEC) of 1.065, equivalent to a 6.5% improvement compared with the uniform arrangement. The introduction of perforations significantly altered performance; a four-hole configuration with G = 1 . 00 consistently achieved the highest heat transfer and overall performance, with the Nusselt number rising to 195.8 and the PEC reaching 1.176, indicating an optimal balance between fluid mixing and flow resistance. By comparison, increasing the number of perforations further to eight reduced the pressure drop from 171 . 9 Pa for solid rings to 132 . 0 Pa , but had a less pronounced positive impact on heat transfer performance. For this configuration, the Nusselt number remained close to that of the unperforated case. Analysis of both turbulent kinetic energy (TKE) and velocity vector fields provided critical insights into the underlying mechanisms, illustrating how ring geometry and perforations disrupt boundary layers and generate beneficial turbulence. Furthermore, regression-based multivariate correlations for both the Nusselt number and friction factor were formulated as functions of Reynolds number, G -factor, and porosity. Validation against the full set of 75 CFD simulation cases demonstrated high accuracy, with 96% of the correlation-predicted Nusselt numbers deviating by less than ± 5 % from the corresponding CFD results, and the equivalent friction factor values deviating by less than ± 10 % . • Non-uniform ring spacing significantly affects DPHE thermo-hydraulic behaviour. • Four-hole perforated rings provide the best heat-transfer and pressure balance. • Strongly biased ring spacing yields higher overall PEC than weakly biased layouts. • CFD reveals mixing patterns driven by combined spacing and perforation effects. • Correlations predict Nusselt number and friction factor for 75 DPHE cases.

A dynamic iterative method for hydrodynamic coefficients of flexible netting and its numerical validation

Effect of bleeding on aerodynamics of non-slender delta wing in ground effect

Heat transfer enhancement in Darcy–Forchheimer Jeffrey–Hamel flow of a partially ionized power-law nanofluid under Hall and ion-slip effects

Gust response alleviation via wingtip bending freely with fluid-structure interaction approach based on dynamic modal rotation method

• A rigorous two-stage DNS framework is developed to provide high-quality reference data for shock-turbulence-flame interactions in supersonic reacting shear layers using a moderately complex hydrocarbon fuel. • The flow is shown to be remarkably robust to variations in mean scalar dissipation rate, with reaction rates governed by localized regions of high scalar dissipation, implying accurate modelling is possible at lower grid resolutions than traditionally expected. This study examines critical aspects of Direct Numerical Simulations (DNS) of ethylene-air combustion for hypersonic propulsion applications. A combustion mechanism was selected based on a comparative analysis of multiple models, balancing chemical fidelity and computational cost. Detailed configurations of two DNS cases are presented, focusing on high-speed reacting turbulent shear layers including interactions with an oblique shock wave ( M s = 1.3 , inflow angle 5 ∘ ). A lower and standard Reynolds number case are employed to ensure mesh convergence while maintaining computational feasibility. Although most statistical quantities exhibit strong convergence trends, full convergence was not achieved for the scalar dissipation rate. This study investigates the underlying physical mechanisms responsible for this behaviour and demonstrates their limited impact on all other key variables. These results advance the understanding of turbulence-combustion interactions and will be used to guide new developments in numerical modelling for next-generation air-breathing hypersonic propulsion systems.

Numerical investigation of Reynolds number effects on scaled wind turbine rotors

• Flame stability with heat transfer and NOx pathways of ultra-lean NH 3 /H 2 blends. • Hydrogen enrichment extends ammonia’s lean flammability limit. • Radical pool strength (H, O, OH) increases with Re and ϕ. • Intermediate species (NH 2 , NH, HO 2 , HNO) exhibit distinct equivalence-ratio trends. Ammonia’s narrow flammability and low reactivity limit its use in micro-combustors, but hydrogen enrichment offers a pathway to stable ultra-lean operation. Hydrogen enrichment has been proposed as a viable strategy to overcome these limitations, yet systematic mapping of lean NH 3 /H 2 flames under micro-scale confinement remains scarce. In this work, a two-dimensional numerical study was conducted on a planar micro-combustor fuelled with an NH 3 /H 2 blend (10/90 vol%) to quantify flame stability, heat transfer, and NOx chemistry over a broad range of Reynolds numbers Re = 191–1330 and ϕ = 0.65–0.20. Hydrogen addition extends the lean limit from ϕ = 0.65 to ϕ = 0.2, with ultra-lean flames ( ϕ = 0.20–0.25) stabilized only at Re = 572 and 381, respectively. Outlet temperatures rise with Re and approach adiabatic values, while heat loss ratio ( Q loss /HoR) reduces below 0.065 once Re exceeds 953 across the entire equivalence ratio range. Radiative coupling provides an additional stabilizing effect, with incident radiation increasing from 3.6 × 10 4 W/m 2 ( ϕ = 0.20, Re = 572) to 76 × 10 4 W/m 2 ( ϕ = 0.65, Re = 1330). Radical pool analysis revealed that H, O, and OH intensify with both Re and ϕ , sustaining chain branching and flame anchoring, while intermediate species showed distinct behaviours. Kinetic pathway analysis confirmed that NO formation is dominated by HNO decomposition and NO 2 reduction, whereas consumption proceeds mainly through reactions with HO 2 and HNO cycling. The findings provide the first integrated stability–heat transfer–reaction pathway analysis of NH 3 /H 2 micro-planar flames, demonstrating how hydrogen extends ammonia’s lean limit to ultra-lean regimes while reshaping the NO/N 2 O distribution through radical-driven chemistry.

• First application and demonstration of two implicit time-stepping schemes on industrial geometries using high-order spectral/hp element discretization • Both schemes reduce computational cost up to 14.7 × less than a reference using community standard semi-implicit scheme • Timestep sensitivity analysis, verification with reference, and validation with experiments • Guidelines for leveraging these schemes for scale-resolving industrial simulations High-fidelity modeling approaches such as implicit Large Eddy Simulations are increasingly used for analyzing complex, unsteady flow phenomena in industrial geometries at realistic Reynolds numbers. However, their computational cost prevents wider adoption as a suitable tool in developing aerodynamic devices. One solution available to most commercial tools is to increase the simulation timestep, beyond the CFL limit of commonly adopted semi-implicit scheme, by employing fully implicit time discretization. Two implicit time-stepping techniques for solving the incompressible Navier-Stokes equations in a segregated manner using the high-order Spectral/hp element method were examined in this study. Our objectives were to explore the practical timestep limit for each scheme, assess the impact of timestep on accuracy, and evaluate the potential speed-up. The Imperial Front Wing (IFW) industrial benchmark was considered for these purposes. Even for this challenging geometry, both schemes successfully allowed for an increased simulation timestep, resulting in a considerable reduction in the total computation time. This work outlines the characteristics of each scheme, compares them with existing literature on canonical flows, and highlights the trade-offs between accuracy and computational efficiency.

Numerical investigation of large-scale vortex evolution and hydrodynamic implications of a pitching axisymmetric body with appendages at Reynolds number 1000

This study investigates the dynamics of a single bubble rising in a quiescent liquid and impacting a fixed cylinder using a resolved two-fluid approach. The resolved two-fluid approach is validated against experimental data and compared with a one-fluid approach through 2D axisymmetric and 3D simulations across a wide range of Reynolds and Eötvos numbers, and density ratios. The two-fluid model accurately reproduces the bubble shape, terminal velocity, and impact dynamics, showing agreement with both experimental observations and the one-fluid approach. A detailed analysis on the impact force coefficient exerted by the bubble on the cylinder is conducted with the two-fluid approach by varying the bubble’s Reynolds and Eötvos numbers and the density, viscosity, and bubble-to-cylinder diameter ratios ( R e b ∈ [ 1 , 80 ] , E o ̈ ∈ [ 10 , 116 ] , ρ l / ρ g ∈ [ 25 , 1000 ] , μ l / μ g ∈ [ 10 , 100 ] , and d b / D c ∈ [ 0 . 5 , 1 . 0 ] ). This study reveals that, when varying one dimensionless number at a time, the bubble Reynolds number has the most significant influence on the impact force coefficient, followed by the bubble-to-cylinder diameter ratio and the Eötvös number, while the effects of viscosity and density ratios are weaker. A correlation on the impact force coefficient (associated to the force applied by the bubble on the cylinder at impact) is proposed and may be useful for Euler–Lagrange point-particle methods. • Numerical study of bubble impact on a cylinder across a wide range of dimensionless numbers. • Resolved two-fluid approach validated against experimental data and one-fluid simulations. • Two-fluid approach accurately capture bubble shape and terminal velocity. • Bubble Reynolds number found to have the strongest influence on the drag coefficient associated to the bubble impact on the cylinder. • Drag coefficient correlation proposed to improve impact predictions.

Three-dimensional wake dynamics of a square cylinder in oscillatory flows at low Reynolds numbers

• Comparison of flapping and rotating wings in compressible flows is presented. • Flexibility of flapping wing is considered. • Lift coefficient, lift-to-drag ratio and power factor are discussed. • Wing-wing interaction is discussed. Recently, flapping wings have been identified as a potential solution for future Martian unmanned aerial vehicles, due to their performance in low-Reynolds number and moderately compressible environments. This necessitates a comparison study between flapping wings, and proven rotary wing design for the unique, low-density Martian atmosphere. Here, such a comparison of equivalent flapping and rotating wing configurations is considered through numerical simulations, with an emphasis on lift generation and efficiency. In general, flapping wings generated sufficiently higher lift than their rotating counterparts at low Reynolds numbers, while rotating wings in general outperformed flapping wings in terms of the lift-to-drag ratio and power factor. However, there are exceptions to this: weakly flexible flapping wings at low aspect ratio ( Λ = 2 ) outperformed rotating wings in terms of lift generation and efficiency at Ma ≤ 1. Multi-rotating wing configurations are also considered to determine if wing-wing interactions have any improvement in the performance, finding that the average lift coefficient remains similar to the single rotating wing cases, despite significant changes in the temporal space. Overall, this study identifies that flapping wings have the ability to outperform their rotating counterparts in the Martian environment from an aerodynamic perspective.

Turbulent mixing and flame stability in a dual-swirler ammonia/methane co-flame burner: Reynolds number effects on NOx emissions

Bed roughness plays an important role in controlling flow resistance, turbulence and energy dissipation in open-channel flows, particularly in high-velocity hydraulic structures such as spillways. The influence of wart-type roughness elements on supercritical open-channel flow dynamics was investigated through controlled flume experiments, comparing smooth and rough ( S = 20 cm spacing) bed conditions. Velocity profiles, shear stress, and specific energy distributions were measured along the channel using point velocity measurements in a 7 m long, 0.5 m wide Plexiglas flume with a 2% slope at the Ujigawa Hydraulic Laboratory, Kyoto University. Results show that the rough configuration significantly reduces mean velocities compared to the smooth bed, with pronounced velocity deficits near the bed. Wall shear stress ( τ ) in the smooth case ranged from 2.92 to 3.04 Pa, showing a slight Reynolds number (Re) dependence, while the rough case exhibited lower τ (1.88–2.28 Pa) with greater variability, suggesting reduced drag due to flow separation. Non-dimensional shear stress ( τ/(ρv 2 )) was nearly constant for the smooth bed and fully constant for the rough bed, indicating a transition to a fully rough regime. The logarithmic law of the wall was validated, with a consistent von Kármán constant ( κ = 0.41) and reduced intercept ( A = 5.09 vs. 5.5) for the rough bed. Specific energy distributions revealed enhanced dissipation near the rough bed, impacting hydraulic efficiency. These findings are limited to S/K = 5.71 and Fr > 1.8, but highlight the potential of this specific wart-type roughness for energy dissipation and erosion protection in high-velocity structures.

The influence of Prandtl number on laminar mixed convective flow through a smooth, horizontal tube was investigated using ANSYS Fluent 22 to improve the understanding of the interaction between buoyancy and fluid viscosity on the thermohydraulic behaviour. Different propylene glycol concentrations (0%, 30%, 50%, 70%, 80%, and 90%) were considered for heat fluxes of 200-10 000 W/m 2 and Reynolds numbers of 250-2000. The tube had an inner diameter of 5.1 mm and a length of 10 m. It was found that as the Prandtl number increased, the buoyancy force increased up to 74% for the 90% propylene glycol concentration compared to pure water, resulting in higher vorticity and circulation strength. However, this was confined near the tube wall and when quantifying the buoyancy effects using the secondary flow strength, viscosity-induced damping was found to decrease buoyancy effects by up to 95%. Conversely, for low-Prandtl number mixtures such as 0% and 30% propylene glycol concentrations, increased secondary flow thinned the thermal boundary layer and enhanced heat transfer by 40% and 28%, respectively, compared to forced convective flow, despite a lower buoyancy force. Furthermore, secondary flow strength was quantified and grouped into three distinct regions: (1) developing region, (2) suppression region, and (3) enhancement region. When viscous effects dominated at higher Prandtl numbers (70% and 90%), the velocity profile became skewed above the tube's centre, and the merging position of the hydrodynamic boundary layers shifted upwards, which is the opposite of the trend seen in fluids with lower Prandtl number (0%, and 30%). Furthermore, as the Prandtl number increased, the hydrodynamic boundary layers along the axis merge closer to the tube inlet, while the thermal boundary layers merge further downstream. Hydrodynamic/thermal boundary layers and cross-sectional velocity/temperature profiles during forced/mixed convection for low/high Prandtl number fluids. • An increase in Prandtl number increased the buoyancy force but decreased buoyancy effects due to higher viscosities. • The vorticity magnitude increased with Prandtl number but was confined near the tube wall. • At high Prandtl numbers, the mixed convective velocity profile was skewed upward, shifting the peak velocity above the tube centre, while the opposite occurred at low Prandtl numbers. • The mixed convective temperature profile was skewed downward, causing the upper thermal boundary layer thickness to be greater than the bottom. • The hydrodynamic boundary layer merged earlier along the tube for increasing Prandtl number.

Abstract Conjugate heat transfer experiments to predict turbine component temperatures involve matching the Biot number of the experimental condition to that of the engine condition. Done properly, such an experiment could yield an overall effectiveness distribution that is relevant to the engine condition. However, the underlying theory suggests that the coolant warming factor χ, must also be matched to achieve the desired effect, and the requirements to do so have been neglected in the literature. Additionally, little success has been achieved in determining the theoretical requirements to match χ. In this work, we develop these requirements, apply them for when coolant flow is scaled by the Reynolds number ratio and advective capacity ratio, and test them by comparing computational results against experimental data. The findings from this study indicate a strong influence of the thermal conductivity of the coolant. Interestingly, a thermal conductivity inappropriately large will have opposite effects on the coolant warming factor depending on which coolant flow rate parameter is used to characterize the coolant flow. Knowledge of the subtle requirements to properly replicate the coolant warming factor in an experiment will allow turbine designers to achieve more accurate surface temperature predictions through properly designed experiments.