Fluid Dynamics Analysis Research Articles

Numerical Analysis on The Aerodynamic Performance of A High-speed Train Operating on Various Embankment Heights Under The Influence of Crosswinds

Given the unavoidable geographical surface, railings must be raised above ground level in some cases, which is known as an embankment. It was discovered that the height of the embankment had a significant influence on the slipstream on the train's leeward side especially during crosswind conditions. The primary objectives of this study were to investigate the impact of varying embankment heights on the aerodynamic characteristics of a high-speed train under different crosswind conditions using computational fluid dynamics (CFD) analysis. The German Aerospace Center DLR's Next-Generation High-speed Train (NG-HST) model has been used for this study. The yaw angles (ψ) are ranging from 10° to 50° in 10° increments. The Reynolds number based on the model's height and freestream velocity at the computational domain is 1.3 x 106. In the results, it shows that embankment height and crosswind ψ has a significant impact on the aerodynamic characteristics. Essential aerodynamic parameters that have a significant impact on train stability, such as the drag, lift, and side force coefficients, as well as the roll, yaw, and pitch moment coefficients, revealed that the higher the ψ, which included 40° and 50°, produced poor results compared to the lower ψ, which included 10°, 20°, and 30°. In terms of visual appearance, rising of crosswind angles have a greater impact on the formation of vortices on the leeward side of the train body and embankment. Thus, it can be concluded that the embankment heights and crosswind angles are crucial in determining train safety operations.

Quantitative Measurements in the Exhaust Flow of a Rotating Detonation Combustor Using Rainbow Schlieren Deflectometry

Abstract This study employs Rainbow Schlieren Deflectometry (RSD) to characterize the unsteady, supersonic/subsonic exhaust plume of a Rotating Detonation Combustor (RDC). Firstly, RSD images are analyzed to quantify the frequency and strength of flow oscillations and their relationship to the detonation wave. Secondly, a 3D tomographic algorithm is used to obtain the local 3D density field across the whole region of interest (ROI). The tomographic analysis relies upon wave rotation to infer projection data of the 3D exhaust plume at multiple view angles using a single RSD/camera system and was previously validated using phantom data from computational fluid dynamics analysis of an RDC. The annular RDC operated on methane and 2/3 O2 - 1/3 N2 oxidizer mixture is equipped with a converging nozzle to pressurize the combustion chamber. The product flow exiting the nozzle throat expands across an unoptimized conical aerospike attached to the center body of the RDC. RSD images provide a temporal resolution of 369 ns and spatial resolution of 100 ?m in a 6.4 high and 25.6 mm wide ROI of the exhaust plume. A rainbow filter is calibrated to convert hue in color schlieren images into deflection angle data. This data is used to characterize the unsteady flow oscillations that show excellent agreement with PCB pressure probe measurements acquired inside the combustion chamber. Tomographic analysis yields a 3D local density field that shows distinct features, consistent with published numerical simulations of the RDC exhaust plume.

A Pseudo-Spectral Method for Wall Shear Stress Estimation from Doppler Ultrasound Imaging in Coronary Arteries.

The Wall Shear Stress (WSS) is the component tangential to the boundary of the normal stress tensor in an incompressible fluid, and it has been recognized as a quantity of primary importance in predicting possible adverse events in cardiovascular diseases, in general, and in coronary diseases, in particular. The quantification of the WSS in patient-specific settings can be achieved by performing a Computational Fluid Dynamics (CFD) analysis based on patient geometry, or it can be retrieved by a numerical approximation based on blood flow velocity data, e.g., ultrasound (US) Doppler measurements. This paper presents a novel method for WSS quantification from 2D vector Doppler measurements. Images were obtained through unfocused plane waves and transverse oscillation to acquire both in-plane velocity components. These velocity components were processed using pseudo-spectral differentiation techniques based on Fourier approximations of the derivatives to compute the WSS. Our Pseudo-Spectral Method (PSM) is tested in two vessel phantoms, straight and stenotic, where a steady flow of 15mL/min is applied. The method is successfully validated against CFD simulations and compared against current techniques based on the assumption of a parabolic velocity profile. The PSM accurately detected Wall Shear Stress (WSS) variations in geometries differing from straight cylinders, and is less sensitive to measurement noise. In particular, when using synthetic data (noise free, e.g., generated by CFD) on cylindrical geometries, the Poiseuille-based methods and PSM have comparable accuracy; on the contrary, when using the data retrieved from US measures, the average error of the WSS obtained with the PSM turned out to be 3 to 9 times smaller than that obtained by state-of-the-art methods. The pseudo-spectral approach allows controlling the approximation errors in the presence of noisy data. This gives a more accurate alternative to the present standard and a less computationally expensive choice compared to CFD, which also requires high-quality data to reconstruct the vessel geometry.

Cerebrospinal Fluid Dynamics Analysis Using Time-Spatial Labeling Inversion Pulse (Time-SLIP) Magnetic Resonance Imaging in Mice.

Background/Objectives: Abnormalities in cerebrospinal fluid (CSF) dynamics cause diverse conditions, such as hydrocephalus, but the underlying mechanism is still unknown. Methods to study CSF dynamics in small animals have not been established due to the lack of an evaluation system. Therefore, the purpose of this research study is to establish the time-spatial labeling inversion pulse (Time-SLIP) MRI technique for the evaluation of CSF dynamics in mice. Methods: We performed the Time-SLIP technique on 10 wild-type mice and 20 Tiptoe-walking Yoshimura (TWY) mice, a mouse model of ossification of the posterior longitudinal ligament (OPLL). We defined the stir distance as the distance of CSF stirring and calculated the mean ± standard deviation. The intraclass correlation coefficient of intraobserver reliability was also calculated. Furthermore, in TWY mice, the correlation coefficient between stir distance and canal stenosis ratio (CSR) was calculated. Results: The stir distance was significantly lower in TWY mice at 12 weeks and 17 weeks of age (1.20 ± 0.16, 1.21 ± 0.06, and 1.21 ± 0.15 mm at 12 weeks and 1.32 ± 0.21, 1.28 ± 0.23, and 1.38 ± 0.31 mm at 17 weeks for examiners A, B, and C). The intrarater reliability of the three examiners was excellent (>0.90) and there was a strongly negative correlation between stir distance and CSR in TWY mice (>-0.80). Conclusions: In this study, we established the Time-SLIP technique in experimental mice. This technique allows for a better understanding of CSF dynamics in small laboratory animals.

A study on a physical based manoeuvring mathematical model for submarines

The manoeuvrability of submarines is one of the important factors from mission and safety points of view. In particular, manoeuvring motions with a large drift angle and/or angle of attack in both the horizontal and the vertical planes have different motion parameters compared to the normal manoeuvring motions. To evaluate the manoeuvrability during these types of particular motions of submarines, especially at the initial design stage, the manoeuvring hydrodynamic derivatives that are related to various manoeuvring motions must be identified.Karasuno model, which is termed a physical based model, has the advantages that it needs only model experiments for drift motion and it can provide greater accuracy under motion with large angles. Despite these advantages, this model has not been applied to other vessels excluding fishing vessels. The applicability of this method to submarines therefore should be examined. The applicability of Karasuno model for submarines is validated through a computational fluid dynamics (CFD) analysis and comparisons with experimental data in this work. The findings contribute to identifying the manoeuvring hydrodynamic forces for submarines and evaluating their manoeuvring performance. Through rigorous validation, the potential of the proposed model as a reliable tool for predicting and analyzing submarine maneuvering motions is demonstrated.

Olfactory sampling volume for pheromone capture by wing fanning of silkworm moth: a simulation-based study

Odours used by insects for foraging and mating are carried by the air. Insects induce airflows around them by flapping their wings, and the distribution of these airflows may strongly influence odour source localisation. The flightless silkworm moth, Bombyx mori, has been a prominent insect model for olfactory research. However, although there have been numerous studies on antenna morphology and its fluid dynamics, neurophysiology, and localisation algorithms, the airflow manipulation of the B. mori by fanning has not been thoroughly investigated. In this study, we performed computational fluid dynamics (CFD) analyses of flapping B. mori to analyse this mechanism in depth. A three-dimensional simulation using reconstructed wing kinematics was used to investigate the effects of B. mori fanning on locomotion and pheromone capture. The fanning of the B. mori was found to generate an aerodynamic force on the scale of its weight through an aerodynamic mechanism similar to that of flying insects. Our simulations further indicate that the B. mori guides particles from its anterior direction within the ~ 60° horizontally by wing fanning. Hence, if it detects pheromones during fanning, the pheromone can be concluded to originate from the direction the head is pointing. The anisotropy in the sampling volume enables the B. mori to orient to the pheromone plume direction. These results provide new insights into insect behaviour and offer design guidelines for robots for odour source localisation.

Design, analysis and development of a proton exchange membrane in fuel cell

This research presents the design and fabrication of a Proton Exchange Membrane fuel cell (PEMFC) utilising open pore cellular metal foam as the material for the flow plate. Efficient housing designs are suggested for both the hydrogen and oxygen sides, achieved by implementing. The study identifies the flow regime via the open pore cellular metal foam flow plate using Computational Fluid Dynamic (CFD) modelling and analysis techniques. Energy, environmental and economic analyzes (4E) and multi-objective optimization of a PEM fuel cell equipped with coolant channels Energy analysis of a proton exchange membrane fuel cell (PEMFC) with an open-ended anode using agglomerate model: A CFD study A transient heat and mass transfer CFD simulation for proton exchange membrane fuel cells (PEMFC) with a dead-ended anode channel. This research can provide appropriate references and recommendations for future Proton Exchange Membrane Fuel Cell (PEMFC) flow channel designs. The performance improvements of flow channel designs become significant at elevated current density, and with the output voltage increasing to 25.8 %. The estimated performance power of the fuel cell was 6 W, meaning that it was unlikely that the 10 W target would be achieved. In reality, the designs proved to have an excellent open circuit voltage of over 0.9 V, however, the maximum current achieved was below the target, and thus limiting the power to only about 2.1 Watts. The purpose of this paper is to give a general theoretical guidance for current and future relevant R&D activities aiming at high-performance, durable, and low-cost fuel cells as well as a thorough overview of the issues, advancements, and perspectives of the flow-field designs for bipolar plates in PEMFC.

Comprehensive analysis of the effect of structural parameters on erosion wear, structural stress, and deformation of high-pressure double-elbow in shale-gas fracturing

In field hydraulic fracturing operation of shale gas development, the high pressure and large displacement liquid-particle two-phase fracturing fluid can be forced to change direction many times through high-pressure double-elbow, and be transported from the outlet pipeline of the fracturing pump to the main pipeline. The high-pressure double-elbow is prone to be affected by erosion wear and Fluid-Structure Interaction (FSI), resulting in perforation and fracture, posing a potential safety threat to field operation. In this study, we conducted the erosion wear experiments on 35CrMo steel used for high-pressure double-elbow in shale-gas fracturing. The erosion rates under different impact angles and flow velocities were obtained, and proposed a novel model of erosion prediction for high-pressure double-elbow. Then the numerical investigation was employed to conduct a comprehensive analysis of erosion wear, structural stress and deformation by the coupling of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA). The effects of structural parameters such as connection straight pipe length, pipe inner diameter and fluid turning direction were discussed. The results indicate that with the increase of connection straight pipe length, the flow erosion decreases first then varies little, and the deformation gradually increases. Slight erosion wear but large structural stress and deformation in major inner diameter pipe. And the minimum degree of erosion and flow-induced deformation present with the fluid turning direction of double-elbow as 0°. The study can provide references for the design, installation and detection of high-pressure double-elbow and ensure safety in the process of shale gas fracturing.

DESIGN AND OPTIMIZATION OF A COST-EFFECTIVE NET-ZERO ENERGY MOSQUE LOCATED IN A HOT AND DRY CLIMATE

ABSTRACT This research paper presents a comprehensive analysis to develop an energy-efficient and net-zero-energy (NZE) model for a proposed hypothetical mosque model located in Riyadh, Saudi Arabia. The study employs a sequential optimization analysis using BEopt software (Building Energy Optimization Tool) to explore various energy conservation measures (ECMs) from three main categories: HVAC, lighting, and building envelope. The ECMs are evaluated based on energy savings and life-cycle cost, with the most cost-effective options selected for the proposed energy-efficient design package. Furthermore, a passive downdraught evaporative cooling (PDEC) system is introduced as a passive cooling strategy to further reduce the cooling energy consumption. Computational fluid dynamics (CFD) analysis is utilized to optimize the airflow around the building and PDEC tower, determining the optimal PDEC dimensions for enhanced ventilation performance. The PDEC system is found to contribute 12% to cooling energy savings, which further enhances the energy efficiency of the proposed mosque. A rooftop solar PV system is incorporated into the optimal energy-efficient design to achieve a NZE mosque. The results demonstrate that the NZE model achieves 80% energy savings, with the remaining 20% offset by the solar PV system. Moreover, life-cycle cost analysis reveals that the NZE model offers the lowest cost, making it the most cost-effective design option. This research provides valuable insights into designing sustainable mosques in hot and dry climates, such as Riyadh, offering a comprehensive solution to significantly reduce energy end-use and promote sustainable building practices.

Role of aneurysmal hemodynamic changes in pathogenesis of headaches associated with unruptured cerebral aneurysms.

One symptom commonly associated with the presence of unruptured intracranial aneurysms is headache. In this study, the authors aimed to analyze factors associated with headaches among patients with intracranial aneurysms, with special consideration of hemodynamic parameters. The authors prospectively included 96 patients with 122 unruptured intracranial aneurysms. The authors obtained detailed medical history including current diseases and medications, as well as blood pressure values taken during hospitalization from the patients' medical records. The short-form McGill Pain Questionnaire was administered to each patient at admission and 3-6 months after the procedure to assess type and severity of headache. Based on imaging data, the authors obtained 3D reconstruction of each patients' aneurysm dome with feeding artery. The authors performed computational fluid dynamics analysis of blood flow through prepared models using OpenFOAM. Blood was modeled as Newtonian fluid, using the incompressible transient solver. Patient-specific internal carotid artery (ICA) blood velocity waves obtained with Doppler ultrasound were set as inlet boundary conditions. After performing simulation, the authors calculated the hemodynamic parameters of the aneurysm dome. A total of 30 patients (31.25%) reported having headaches. In multivariate logistic regression analysis, female sex (OR 2.81, 95% CI 2.51-4.86; p < 0.01), ICA aneurysm location (OR 7.93, 95% CI 5.51-8.52; p < 0.01), multiple aneurysms (OR 6.05, 95% CI 1.83-11.83; p = 0.02), mean dome blood velocity (OR 3.10, 95% CI 2.01-3.30; p < 0.01) and time-averaged wall shear stress (OR 1.18, 95% CI 1.47-2.72; p = 0.04) were independently associated with the presence of headache. Additionally, 17 patients (56.67%) reported complete relief of symptoms after the procedure. In multivariate logistic regression analysis, the mean blood flow in the ICA was independently associated with complete resolution of headaches after aneurysm treatment (OR 2.32, 95% CI 1.57-3.28; p < 0.01). Hemodynamic parameters of intracranial aneurysms might be associated with headaches and their relief after aneurysm treatment.

Influence of the Magnitude of the Taper Angle of Divergent and Convergent Tapered Annular Seals on the Stability of a Vertical Rotor-Seal System

Abstract The rotordynamic (RD) fluid force generated in seals affects the stability of turbomachinery. RD coefficients have been determined using bulk-flow or computational fluid dynamics analyses, and the effect of seals on the stability has been evaluated. Plain annular seals and convergent tapered annular seals have been used to improve stability, and their dynamic characteristics have been studied. On the other hand, research has also been conducted on divergent tapered annular seals, because the seals can become divergent tapered due to operating conditions, pressure deformation, and manufacturing error. These studies do not provide a comprehensive picture of the effect of divergent tapered annular seals on stability, because some show that divergent tapered annular seals reduce stability, whereas others show that they may increase stability. This study analyses a plain liquid annular seal, divergent tapered annular seals, and convergent tapered annular seals to clarify the effect of the taper angle on the stability of a vertical rotor-seal system. The analysis was carried out by continuously changing the taper angle for both the divergent tapered and convergent tapered annular seals, the RD coefficients were calculated in each case, and the onset speed of instability (OSI) was calculated by eigenvalue analysis. The change in OSI, or stability, with a change in taper angle is then investigated. The change in OSI with a change in taper angle was investigated experimentally and compared with the analytical results to demonstrate the validity of the analytical results. The analytical and experimental results were in qualitative and quantitative agreement.

Can β-blockers prevent intracranial aneurysm rupture? - insights from Computational Fluid Dynamics analysis.

Hypertension is a risk factor for intracranial aneurysm rupture. We analyzed whether the intake of drugs from specific classes of anti-hypertensive medications affects hemodynamic parameters of intracranial aneurysm dome. We recorded medical history including medications and the in-hospital blood pressure values. We then obtained 3D reconstruction of each patients' aneurysm dome and the feeding artery. Using OpenFOAM software we performed Computational Fluid Dynamics analysis of blood flow through the modeled structures. Blood was modeled as Newtonian fluid, using the incompressible transient solver. As the inlet boundary condition we used the patient-specific Internal Carotid Artery blood velocity waves obtained with Doppler ultrasound. We calculated haemodynamic parameters of the aneurysm dome. All presented analyses are cross-sectional.We included 72 patients with a total of 91 unruptured intracranial aneurysms. The history of β-blocker intake significantly influenced hemodynamic parameters of aneurysm dome. The patients on β-blockers had significantly smaller aneurysm domes (5.09 ± 2.11 mm vs. 7.41 ± 5.89 mm; p = 0.03) and did not have aneurysms larger than 10 mm (0% vs 17.0%; p = 0.01). In the Computational Fluid Dynamics analysis, walls of aneurysms in patients who took β-blockers were characterized by lower Wall Shear Stress Gradient (1.67 ± 1.85 Pa vs. 4.3 ± 6.06 Pa; p = 0.03), Oscillatory Shear Index (0.03 ± 0.02 vs. 0.07 ± 0.10; p = 0.04) and Surface Vortex Fraction (16.2% ± 5.2% vs. 20.0% ± 6.8%; p<0.01). After controlling for covariates, we demonstrated difference of Surface Vortex Fraction (F[1, 48] = 4.36; p = 0.04) and Oscillatory Shear Index (F[1, 48] = 6.51; p = 0.01) between patients taking and not taking β-blockers, respectively. Intake of β-blockers might contribute to more favorable hemodynamics inside aneurysmal sac. Other antihypertensive medication classes were not associated with differences in intracranial aneurysm parameters.

Computational Fluid Dynamics Analysis of Slip Flow and Heat Transfer at the Entrance Region of a Circular Pipe

In the era of sustainable development goals (SDGs), energy efficient heat transfer systems are a must. Convective heat transfer within circular pipes is an important field of research on a rarely addressed limitation of fluid flows. Vacuum solar tubes is one of many applications that could benefit from the existence of nanoparticles, Al2O3, for example, to enhance the heating of air or water steam. The current research investigates the impacts of the Reynolds number (Re), Prandtl number (Pr), Knudsen number (Kn), aspect ratio (x/Dh), and volume fraction of Al2O3 nanoparticles (ϕ) on the Nusselt number (Nu) under constant wall heat flux conditions. An axisymmetric computational fluid dynamics (CFD) analysis of the nanofluid flowing at the entrance region of a circular pipe was conducted under a slip flow at steady-state developing laminar conditions using the Ansys-Fluent 2018 software package. A mesh sensitivity analysis was conducted, and a proper number of mesh elements was selected. The results showed that an increasing Re and/or ϕ would result in an increasing Nu. The dependance of Nu on Kn was strong due to the high slip values and temperature jump. An increasing x/Dh ratio resulted in reduced Nu values. The major impact was due to Kn, which caused a reduction of up to 40% in the Nu value due to slip conditions. However, there was an enhancement of 2.5% in the heat transfer due to the addition of nanoparticles, which was found at Re = 250, Kn = 0.1, and ϕ = 0.1 (Pr = 0.729). Finally, Nuavg, Nux, U/Um, and ReCf were corelated with Kn, Pr, Re, and x/Dh with proper coefficient of determination (R2) values.

Parabolic trough solar collector technology using TiO2 nanofluids with dimpled tubes

Nanoparticle concentrations have recently attracted attention as a means to increase the effectiveness of parabolic trough solar collectors (PTSC). Computational fluid dynamics (CFD) study has recently gained popularity for evaluating the performance of PTSC with Dimpled Tubes using a nanofluid made of TiO2 nanoparticles distributed in deionized water (DI-H2O). The effect of using Dimpled Tubes with varied turbulent flow rates, from 0.5 kg/minto 2.5 kg/min, is studied via a battery of tests and computational fluid dynamics simulations. TiO2nanofluid performance is compared to water, the “base fluid,” in this study.This study investigates the utilization of TiO2 nanofluids in enhancing the heat transfer performance of parabolic trough solar collector (PTSC) technology, particularly when integrated with dimpled tubes.The importance of this research lies in the quest for improving the efficiency of solar thermal systems, which is crucial for sustainable energy production.Variables such as solar collector efficiency, Reynolds number, and Nusselt number are tracked as the inquiry progresses. When TiO2 nanofluids are added to the base fluid within the dimpled tube, the convective heat transfer coefficient increases by an astonishing 34.25 percent.This improvement is most pronounced at a mass flow rate of 2.5 kg/min and a volume concentration of TiO2 nanofluid of 0.3 %. Parabolic trough solar collectors have recently been the focus of attempts to improve efficiency via nanoparticle concentrations. The paper uses Computational Fluid Dynamics analysis to investigate how well Dimpled Tubes work with TiO2/DI-H2O nanofluid. The significant increase in the convective heat transfer coefficient was clarified by experimental and CFD calculations that considered fluctuations in turbulent flow rates. The improvement is particularly striking at a mass flow rate and a volume concentration of TiO2 nanofluid.Findingsindicate a significant improvement in heat transfer rates when TiO2 nanofluids are used, particularly in conjunction with dimpled tubes. The combined effect leads to a notable thermal efficiency enhancement, representing the potential of nanofluid-based improvements in optimizing PTSC performance.

Applying Machine Learning Techniques: Uncertainty Quantification in Nonlinear Dynamics Characters Predictions via Gated Recurrent Unit-Based Reduced-Order Models

The development of reduced-order models has been a pivotal advancement in the computational analysis of fluid dynamics, substantially simplifying the complexity and boosting the efficiency of simulations. The accuracy and practicality of these models largely depend on the reduction techniques applied and the inherent characteristics of the fluid dynamics systems they represent. In this paper, we introduce an innovative machine-learning framework for assessing model uncertainty in computationally intensive reduced-order models. By combining subspace construction methods with advanced Bayesian inference techniques, our approach effectively captures the posterior distribution of model parameters, thereby providing an accurate representation of uncertainty in aerodynamic performance predictions. We employ the NACA0012 airfoil as a case study to validate our method’s ability to enhance the efficiency of reduced-order models and precisely measure the uncertainty inherent in predictions made by recurrent neural networks. It is important to note that our approach is influenced by specific constraints and variables that significantly impact the mean and variability of the predicted final lift coefficient distribution. Our findings indicate that setting the goodness of fit (R2) threshold above 0.985 markedly improves the correlation between Computational Fluid Dynamics (CFD) outcomes and model predictions, increasing from 72.2% to 97.9% as the interval amplification factor adjusts from 1.5 to 3. However, this adjustment causes a considerable expansion of the confidence interval, from 0.0737 to 0.1282, an increase of over 70%. Despite these challenges, our machine learning-based methodology provides essential insights into the further development of reduced-order modeling and uncertainty quantification in fluid dynamics. This highlights the need for ongoing research into the model parameters, especially in applications concerning aircraft control systems, to meet design specifications and ensure system reliability.

Thermal efficiency evaluation in shell-and-tube heat exchangers: A CFD-based parametric study

In this study, a novel approach was employed to enhance the performance of a Bowman brand EC-2028 shell-and-tube heat exchanger (STHE) by introducing perforated plates. The heat exchanger was first tested in a real system within a laboratory environment to establish baseline performance data. Computational fluid dynamics (CFD) analysis revealed that flow velocities in the middle tubes were higher due to their alignment with the main flow direction, resulting in decreased heat transfer efficiency. To address this issue, a perforated plate with concentric circles was introduced at the cold fluid entry. This plate, devoid of central holes, featured circles with radii of 9, 18, 27, 36, 45, 54, and 63 mm, each containing 6, 10, 17, 24, 30, 36, and 42 equidistant holes, respectively. The introduction of the perforated plate led to a decrease of approximately 0.33°C in the hot outlet temperatures, indicating an improvement in heat transfer efficiency. To further enhance performance, various configurations were tested by progressively closing holes from the innermost to the outermost circles. Eight different configurations, including the control, were evaluated under counterflow conditions. The CFD model was validated with experimental data before introducing the perforated plates, ensuring the accuracy of the simulations. The findings demonstrated significant improvements in heat transfer efficiency, with the optimized perforated plate configurations leading to more uniform flow distribution and reduced pressure drops. This study's novel approach of using perforated plates to modulate flow and enhance thermal performance highlights a new avenue for optimizing STHE designs, contributing to more efficient thermal management solutions in industrial processes.

Investigation of the Filling of a Spherical Pore Body with a Nonwetting Fluid: A Modeling Approach and Computational Fluid Dynamics analysis

AbstractUnderstanding the dynamics of the filling process of a pore body with a nonwetting fluid is important in the context of dynamic pore network models and others. It can justify many of the assumptions behind the different rules that describe how the network behaves during imbibition and drainage processes. It also provides insight into the different regimes pertinent to this system. The filling process starts with the contact line pinning at the pore entrance. Three regimes can be identified during the filling process that is related to how the contact line advances. In the first two regimes, the contact line pins at the pore entrance while the emerging droplet develops, and in the third one, the contact line departs the entrance of the pore and advances along the pore surface. During the first regime, which is brief, the curvature of the meniscus increases, and likewise, the corresponding capillary pressure, while in the other two regimes, the curvature decreases and so does the capillary pressure. Such behavior results in the rate at which the nonwetting fluid invades the pore to change. It initially decreases, then increases as the meniscus advances. The radius of curvature of the meniscus, eventually, increases to infinity for which the interface assumes a flat configuration. A one-dimensional modeling approach is developed that accounts for all these regimes. The model also considers the two immiscible fluids over a wide spectrum of contrast in viscosity. Information about the mean velocity of the invading fluid, the location of the contact line, the radius of curvature of the meniscus, the volume of the emerging droplet, and several others are among the details that the model provides. A computational fluid dynamics (CFD) simulation has also been considered to confirm the proposed fates of the interface and to provide a framework for comparisons. The results of the validation process show, generally, a very good match between the model and the CFD analysis.

Determination of Ambient Air Vaporizers’ Performance Based on a Study on Heat Transfer in Longitudinal Finned Tubes

Ambient air vaporizers (AVVs) are the most commonly used type of heat exchanger for cryogenic regasification stations. The transfer of heat from the environment for heating the liquefied gas and its vaporization is a cost-free and efficient method. Designing ambient air vaporizers for regasification or fueling stations requires accepting the size and related thermal power of the AVV considering the operating conditions and the type of liquefied gases to be vaporized. The nominal capacity of the ambient air vaporizer depends on its design, the frosting of longitudinal finned tubes, and the airflow through the vaporizer structure. This paper presents the results of experimental studies and computational fluid dynamics (CFD) analysis on determining the heat output of AVV longitudinal finned tubes depending on their design. This experiment was conducted in order to establish a numerical model. The relation between the longitudinal finned tubes thermal power and the air flow velocity is demonstrated and the beneficial effect of forced convection is proved. The obtained results are used for verification calculations of ambient air vaporizers’ performance depending on the size of the AVV, the profile cross-section, and the airflow velocity for different liquefied gases. Under conditions of forced convection, profiles with 12 equal-height fins were discovered to be the most efficient for higher airflow velocity providing up to 7% higher heat rate than profiles with 8 equal-height fins. However, at low air velocity, profiles with 8 equal-length fins showed a comparable heat output to profiles with 12 equal-length fins. Profiles with 8 and 12 unequal high fins differ in average heat output by about 28%. The profile with 12 unequal high fins turned out to be the least effective when 2D airflow was considered in this analysis.

Applications of Finite-Time Lyapunov Exponent in detecting Lagrangian Coherent Structures for coastal ocean processes: a review

Addressing the threats of climate change, pollution, and overfishing to marine ecosystems necessitates a deeper understanding of coastal and oceanic fluid dynamics. Within this context, Lagrangian Coherent Structures (LCS) emerge as essential tools for elucidating the complexities of marine fluid dynamics. Methods used to detect LCS include geometric, probabilistic, cluster-based and braid-based approaches. Advancements have been made to employ Finite-time Lyapunov Exponents (FTLE) to detect LCS due to its high efficacy, reliability and simplicity. It has been proven that the FTLE approach has provided invaluable insights into complex oceanic phenomena like shear, confluence, eddy formations, and oceanic fronts, which also enhanced the understanding of tidal-/wind-driven processes. Additionally, FTLE-based LCS were crucial in identifying barriers to contaminant dispersion and assessing pollutant distribution, aiding environmental protection and marine pollution management. FTLE-based LCS has also contributed significantly to understanding ecological interactions and biodiversity in response to environmental issues. This review identifies pressing challenges and future directions of FTLE-based LCS. Among these are the influences of external factors such as river discharges, ice formations, and human activities on ocean currents, which complicate the analysis of ocean fluid dynamics. While 2D FTLE methods have proven effective, their limitations in capturing the full scope of oceanic phenomena, especially in 3D environments, are evident. The advent of 3D LCS analysis has marked progress, yet computational demands and data quality requirements pose significant hurdles. Moreover, LCS extracted from FTLE fields involves establishing an empirical threshold that introduces considerable variability due to human judgement. Future efforts should focus on enhancing computational techniques for 3D analyses, integrating FTLE and LCS into broader environmental models, and leveraging machine learning to standardize LCS detection.

Evaluation of microclimate in dairy farms using different model typologies in computational fluid dynamics analyses

Ventilation plays a key role in the livestock buildings since it is important to guarantee a comfortable environment and adequate indoor air quality for the animals. Naturally ventilated barns are usually characterized by high variability in the ventilation conditions. Moreover, the ventilation efficiency can be very different in different areas of a barn because of the different presence of the animals. On the other hand, appropriate ventilation is an essential requirement to ensure animal welfare and efficient and sustainable production since a proper ventilation is the most efficient way to remove undesirable air pollutants and to obtain a comfortable microclimate for the welfare of the animals. In this regard, the computational fluid dynamic (CFD) simulations represent a powerful and useful tool because they can be used to assess ventilation and microclimate conditions. In this context, the present study has the object to assess whether different CFD modelling approaches (i.e. model with animals modelled as obstacles with closed volume and model enriched with cows modelled as obstacles capable of exchanging heat with the surrounding air volume) show differences in relation to the climatic conditions inside a naturally ventilated dairy barn. The comparison of the results, set in terms of indoor air temperature and air velocity contours of the two different models, arises that if a precise definition of the microclimatic features is necessary, in order to correlate them with production parameters or assess animal welfare indexes, thermal simplification is not acceptable since can lead to completely misleading conclusions and incorrect evaluations. Then, only adopting CFD models considering the animal thermal behaviour is possible to obtain effective information both for the proper barn system management and for the creation of useful tools driving the farmers' choices.