Hydrodynamic Research Articles

Study on Prediction of Explosion Hazard Area and Correlation of Major Factors through Computational Fluid Dynamics Analysis

Study on Prediction of Explosion Hazard Area and Correlation of Major Factors through Computational Fluid Dynamics Analysis

Impact of water based nanofluids in heat exchanger type active solar PV cooling systems: A comparative CFD analysis

Solar photovoltaic technology is a fast growing form of renewable energy with many positive factors such as low cost, environmental friendliness, energy independence, etc. But, one of the major drawbacks of solar photovoltaic technology is the less efficiency compared to other forms of renewable energy technologies. There are many factors affecting the efficiency of a solar PV system such as temperature, solar irradiance, material quality, reflection losses, cell design etc. Researchers are focusing on different aspects to control the above factors to improve the efficiency of solar PV systems. Solar photovoltaic cooling system is one such solution which can be used to control the operating temperature of solar photovoltaic cells. The most common coolant used in these systems is water due to its superior thermo physical properties. In this research we are focusing on improvement of the thermophysical properties of water using nanotechnology. This article presents a CFD (Computational Fluid Dynamics) analysis conducted for a heat exchanger type solar PV cooling system integrated with a solar photovoltaic panel for water based nanofluids mainly focusing on three metal oxide nanoparticles Al2O3, CuO, and TiO2. Initially the heat exchanger model was developed using Solid Edge 2022 software and the thermo physical properties were simulated using Ansys 2019 software for different water based nanofluids. The obtained results were analyzed comparatively with the performance of water as a coolant in the same heat exchanger system. The results conclude that metal oxide/water based nanofluids have comparatively better thermal properties than water and can be suggested as possible alternatives for water in closed loop heat exchanger applications.

High-Fidelity CFD Simulation of Mixed Convection and Forced Convection in a Pebble Bed Test Reactor Core

The Hermes low-power [35-MW(thermal)] reactor will be built and operated by Kairos Power LLC (KP) to demonstrate its fluoride salt–cooled high-temperature reactor (FHR) technology. In the KP FHR, the reactor core is composed of randomly packed pebbles with TRISO fuel particles inside with FLiBe flow upward through the core acting as a coolant. Previous numerical and experimental studies have been limited to either a small-size bed or to a lack of detailed measurements for heat transfer. To address the lack of high-fidelity heat transfer data in a real-size FHR core, in this study, we simulated a pebble bed core with 34 374 pebbles randomly packed, similar to the Hermes reactor’s size. The core radius was 14 times that of the pebble diameter, while the core height was 45 times. In this work, we were particularly interested in a mixed convection regime, where buoyancy is important. Therefore, we performed several large-eddy simulations at different Reynolds numbers (160 to 1000) with gravitational force included. The spectral element computational fluid dynamics code NekRS with graphics processing unit acceleration was used for this study. The low-Mach number approximation was applied to address property changes in the FLiBe and to account for buoyancy. A pure hexahedral mesh with 60 million elements was generated by the Voronoi cell method. At the polynomial order of 5, the total degrees of freedom was 7.5 billion. The developed case in this work is the first of its kind in terms of size and complexity. The local numerical data across the domain were obtained and compared with empirical correlations. After examining the data, we found the following conclusions. For pressure drop, the Reger correlation predicted less than a 5% error. On the other hand, for heat transfer, the Wakao correlation outperformed the others. Based on our findings, we recommend the use of the Wakao correlation for the Nusselt number calculation, and for pressure drop, the KTA (Kerntechnischer Ausschuss) correclation, among the available experimental correlations. The Reger direct numerical simulation–driven correlation for pressure drops should also be considered, given its best agreement with our calculations.

Simulation of the fluid flow pattern and property estimation for bio-diesel plant design

The fluid flow pattern that occurs in the bio-diesel production process is related to viscosity, flow velocity, and pressure. Fluid flow is a paramount cause of failure in pipes in several industries. The heat transfer cause across pipes needs to be analyzed to avoid failure during operation. The simulation and visualization of fluid flow in the plant pipes were developed for the pressure drop along with the length of the pipe. Flow patterns was analyzed using a Computational Fluid Dynamics model approach (CFD). The CFD within the ANSYS environment has three important stages, namely pre-processing, finding solutions, and post-processing. Mesh was generated and the material properties were assigned. The boundary conditions were stipulated, and the process analyzed to ensure convergence of the solution in a stable state. High density of the blend was observed for 40% bio-diesel blend and low density at 5% bio-diesel blend. The results of the correlation analysis shows that density is directly proportional to bio-diesel content. The density-composition depict a uniform increasing density value with percentage bio-diesel mixture content. The viscosity slightly increases with bio-diesel content. There is a clear trend of viscosity increasing proportional to bio-diesel content. The simulation ensures that the parameters for the design and fabrication of the bio-diesel reactor as obtained from the simulation results is optimal.

Soliton solutions of the (2 + 1)-dimensional Jaulent-Miodek evolution equation via effective analytical techniques

In this study, we investigate the -D Jaulent-Miodek (JM) equation, which is significant due to its energy-based Schrödinger potential and applications in fields such as optics, soliton theory, signal processing, geophysics, fluid dynamics, and plasma physics. Given its broad utility, a rigorous mathematical analysis of the JM equation is essential. The primary objective of this work is to derive exact soliton solutions using the Modified Sub-Equation (MSE) and Modified Auxiliary Equation (MAE) techniques. These solutions are computed using Maple 18, and encompass a variety of wave structures, including bright solitons, kink solitons, periodic waves, and singular solitons. The potential applications of these solutions span diverse domains, such as nonlinear dynamics, fiber optics, ocean engineering, software engineering, electrical engineering, and other areas of physical science. Through numerical simulations, we visualize the physical characteristics of the obtained soliton solutions using three distinct graphical formats: 3D surface plots, 2D contour plots, and line plots, based on the selection of specific parameter values. Our results demonstrate that the MSE and MAE techniques are not only efficient but also straightforward in extracting soliton solutions for the JM equation, outperforming other existing methods. Furthermore, the solutions presented in this study are novel, representing contributions that have not been previously reported in the literature.

Duodenogastric Reflux in Health and Disease: Insights from a Computational Fluid Dynamics Model of the Stomach.

The stomach is responsible for physically and chemically processing the ingested meal before controlled emptying into the duodenum through the pyloric sphincter. An incompetent pylorus allows reflux from the duodenum back into the stomach, and if the amount of reflux is large enough, it could alter the low pH environment of the stomach and erode the mucosal lining of the lumen. In some cases, the regurgitated contents can also reach the esophagus leading to additional complications. In this work, "StomachSim", an in-silico model of the fluid dynamics of the stomach, is used to study the mechanism of duodenogastric reflux. The effects of variations in food properties and motility disorders on reflux are investigated. The simulations show that the primary driver of reflux is the relaxation of the antrum after a stomach contraction terminates near the pylorus. The region of the stomach walls exposed to the regurgitated contents depends significantly on the density of the stomach contents. For stomach contents of higher viscosity, the increased pressure required to maintain gastric emptying reduces the amount of duodenogastric reflux. Concomitant stomach motility disorders that weaken the relaxation of the walls also affect the amount of reflux. The study illustrates the utility of in-silico models in analyzing the factors at play in gastrointestinal diseases.

Self-assembled Gap-Rich PdMn Nanofibers with High Mass/Electron Transport Highways for Electrocatalytic Reforming of Waste Plastics.

Innovating nanocatalysts with both high intrinsic catalytic activity and high selectivity is crucial for multi-electron reactions, however, their low mass/electron transport at industrial-level currents is often overlooked, which usually leads to low comprehensive performance at the device level. Herein, a Cl-/O2 etching-assisted self-assembly strategy is reported for synthesizing a self-assembled gap-rich PdMn nanofibers with high mass/electron transport highway for greatly enhancing the electrocatalytic reforming of waste plastics at industrial-level currents. The self-assembled PdMn nanofiber shows excellent catalytic activity in upcycling waste plastics into glycolic acid, with a high current density of 223 mA cm-2@0.75 V (vs RHE), high selectivity (95.6%), and Faraday efficiency (94.3%) to glycolic acid in a flow electrolyzer. Density functional theory calculation, X-ray absorption spectroscopy combined with in situ electrochemical Fourier transform infrared spectroscopy reveals that the introduction of highly oxophilic Mn induces a downshift of the d-band center of Pd, which optimizes the adsorption energy of the reaction intermediates on PdMn surface, thereby facilitating the desorption of glycolic acid as a high-value product. Computational fluid dynamics simulations confirm that the gap-rich nanofiber structure is conducive for mass transfer to deliver an industrial-level current.

Prediction model and real-time diagnostics of hydraulic fracturing pressure for highly deviated wells in deep oil and gas reservoirs

It is a common occurrence in the fracture processes of deep carbonate reservoirs that the fracturing construction pressure during hydraulic fracturing operation exceeds 80 MPa. The maximum pumping pressure is determined by the rated pressure of the pumping pipe equipment and the reservoir characteristics, which confine the fracture to the target area. When the pump pressure exceeds the safety limit, hydraulic fracturing has to reduce the construction displacement to prevent potential accidents caused by overpressure. Therefore, real-time prediction of the fracturing construction pressure and diagnosis of abnormal fluctuations during hydraulic fracturing of highly deviated wells are indispensable. Based on the well trajectory, pumping process, and string structure of highly deviated wells, a movement interface model for the fracturing fluid at different stages within the wellbore has been established, using the method of computational fluid dynamics. This model analyzes the fluid movement behavior with diverse properties at various fracturing times and determines the relationship between the pressure changes at the leading and trailing edges of fluid movement in each section of the wellbore over time by combining different string structures and preset pumping procedures. The frictional pressure within the wellbore fluid, the hydrostatic fluid pressure, and the near-well friction drags have been calculated and predicted. A real-time prediction model for diagnosing pumping fracturing has been constructed to further comprehend “abnormal” fracturing construction pressures in highly deviated wells. This offers a theoretical foundation for the correct diagnosis and decision-making regarding hydraulic fracturing in highly deviated wells while guiding its smooth implementation in real time.

Observations of Cherenkov-Like Radial Wake in Water Waves.

Cherenkov radiation (CR) is a fascinating phenomenon that occurs not only in electromagnetic (EM)waves but also in water waves. The V-shaped wake formed by a moving object on the water surface results from the constructive interference of water waves of different wavelengths, similar to CR. We designed and fabricated a one-dimensional (1D) water wave crystal to analogize the behavior of moving particles in water waves. This crystal exhibits a band structure with both positive (positive group velocity) and negative slopes (negative group velocity), exciting and directing the water waves to produce forward and backward radiating wakes through a mechanism similar to CR. Notably, the radiation angle is easily adjustable. This method of regulating water wave wakes holds potential applications in scattering cancellation-based wake stealth, navigation technology, and fluid dynamics for future offshore vessels.

Computational fluid dynamics analysis and experimental study of artificially ventilated temperature sensors for meteorological observations

Computational fluid dynamics analysis and experimental study of artificially ventilated temperature sensors for meteorological observations

Wave structures and its evolution modeled by variant Mikhailov-Novikov-Wang equation

Abstract In this study, we first transform the variant Mikhailov-Novikov-Wang equation into a corresponding dynamical system using the traveling wave transform. In order to derive the Gaussian soliton solutions of the equation, the generalized trial equation method is employed. We employ the complete discrimination system for polynomial method for qualitative analysis and concluded the existence of periodic and soliton solutions of the equation by exploring the relationship between the roots and coefficients of the polynomials without explicitly solving the solutions. Further quantitative analysis verifies these conclusions by presenting the corresponding solutions. Sensitivity evaluation is conducted via multiple situations using numerical simulations, which demonstrate how the initial conditions influence the evolution of the system. Additionally, chaotic phenomena are also discovered by introducing a perturbation term, confirming the presence of chaotic behavior. To the best of our awareness, this study is the first to explore the sensitivity and chaotic properties of this equation. Considering the significances of the equation in plasma physics and fluid dynamics, that we obtained can have the practical applications in the real-physical world.

On a holistic investigation of implicit/explicit/semi-implicit GS4-I framework and time step control for unsteady fluid dynamics

Purpose This paper aims to design and analyze implicit/explicit/semi-implicit schemes and a universal error estimator within the Generalized Single-step Single-Solve computational framework for First-order transient systems (GS4-I), which also fosters the adaptive time-stepping procedure to improve stability, accuracy and efficiency applied for fluid dynamics. Design/methodology/approach The newly proposed child-explicit and semi-implicit schemes emanate from the parent implicit GS4-I framework, providing numerous options with flexible and controllable numerical properties to the analyst. A universal error estimator is developed based on the consistent algorithmic variables and it works for all the developed methods. Applications are demonstrated by merging the developed algorithms into the iterated pressure-projection method for incompressible Navier–Stokes equations. Findings The child-explicit GS4-I has improved solution accuracy and stability properties, and the most stable option is the child explicit GS4-I(0,0)/second-order backward differentiation formula/Gear’s methods, which is new and novel. Numerical tests validate that the universal error estimator emanating from implicit designs works well for the newly proposed explicit/semi-implicit algorithms. The iterative pressure-correction projection algorithm is efficiently fostered by the error estimator-based adaptive time-stepping. Originality/value The implicit/explicit/semi-implicit methods within a unified computational framework are easy to implement and have flexible options in practical applications. In contrast to traditional error estimators, which work only on an algorithm-by-algorithm basis, the proposed error estimator is universal. They work for the entire class of implicit/explicit/semi-implicit linear multi-step methods that are second-order time accurate. Based on the accurately estimated local error, balance amongst stability, accuracy and efficiency can be well achieved in the dynamic simulation.

Parametric Analysis of the Factors Impacting the Spatial Distribution of Particles in a Bus Environment

This study presents a parametric analysis of the factors impacting particle distribution within a bus environment using computational fluid dynamics (CFD) simulations, with a primary focus on the relative concentration (RC) of particles. The Novel Relative Concentration (RC) metric, which measures the deviation from a return concentration, was used to assess the effects of ventilation rates, the number and spatial arrangement of particle emitters, and thermal conditions. Our investigation reveals that increasing air changes per hour (ACHs) from 5.74 h⁻1 to 28.66 h⁻1 reduces the overall particle concentration by approximately 45%, but localized high concentration zones persist, with maximum RC values observed at 1.57. Scenarios with evenly distributed emitters achieved near-uniform particle distribution, with RC values averaging around 0.95, while clustered emitters resulted in localized high concentrations, with RC values exceeding 2.0. Thermal conditions were found to have a minimal effect on RC, with average values of 1.664 for cooling and 1.588 for heating, showing only a 4.68% difference. The RC metric provided clear insights into the non-uniformity of particle distribution, highlighting areas prone to higher concentrations, with some zones reaching RC values of 2.5, indicating concentrations 2.5 times higher than the well-mixed average. These findings underscore the importance of optimizing ventilation systems for both overall air exchange and uniform air distribution, offering practical implications for improving air quality and reducing the risk of airborne pathogen transmission in public transportation systems. Future research should explore real-time ventilation adjustments based on passenger load, the effects of different particle types, and the development of models incorporating human behavior and movement patterns.

Analytical simulation of mixed convective Williamson nanofluid flow above a stretched Riga plate considering viscous dissipation effects

This work examines, accounting for viscous dissipation, an analytical simulation of mixed convection heat transfers in a Williamson blood base nanofluid flow on a stretched Riga plate (RP). The Lorentz force, which influences fluid dynamics, is produced by the alternating magnetic fields that comprise the RP. The flow characteristics are further complicated by the blood base Williamson nanofluid’s (WN) non-Newtonian behavior. The governing partial differential equations (PDEs) for momentum and energy are transformed into a set of nonlinear ordinary differential equations (NODEs) by similarity transformations. We solve these equations analytically using the homotopy analysis method (HAM). We investigate in detail how the temperature and velocity profiles (VPs) are affected by significant parameters as the Williamson parameter (WP), viscous dissipation, volume friction of nanoparticles, modified Hartmann number (MHN), heat generation parameter and Biot number (BN). The findings show that the thermal conductivity (TC) of nanoparticles is increased, improving the efficiency of heat transfer. Moreover, a Lorentz force generated by the RP considerably alters the temperature and flow fields. With regard to the design and optimization of thermal systems utilizing complex boundary conditions (BCs) and non-Newtonian nanofluids, this work offers significant new insights.

Sensitivity of coronary hemodynamics to vascular structure variations in health and disease

Local hemodynamics play an essential role in the initiation and progression of coronary artery disease. While vascular geometry alters local hemodynamics, the relationship between vascular structure and hemodynamics is poorly understood. Previous computational fluid dynamics (CFD) studies have explored how anatomy influences plaque-promoting hemodynamics. For example, areas exposed to low wall shear stress (ALWSS) can indicate regions of plaque growth. However, small sample sizes, idealized geometries, and simplified boundary conditions have limited their scope. We generated 230 synthetic models of left coronary arteries and simulated coronary hemodynamics with physiologically realistic boundary conditions. We measured the sensitivity of hemodynamic metrics to changes in bifurcation angles, positions, diameter ratios, tortuosity, and plaque topology. Our results suggest that the diameter ratio between left coronary branches plays a substantial role in generating adverse hemodynamic phenotypes and can amplify the effect of other geometric features such as bifurcation position and angle, and vessel tortuosity. Introducing mild plaque in the models did not change correlations between structure and hemodynamics. However, certain vascular structures can induce ALWSS at the trailing edge of the plaque. Our analysis demonstrates that coronary artery vascular structure can provide key insight into the hemodynamic environments conducive to plaque formation and growth.

The Sub 2-h Official Marathon is Possible: Developing a Drafting Strategy for a Historic Breakthrough in Sports

BackgroundDrafting for drag reduction is a tactic commonly employed by elite athletes of various sports. The strategy has been adopted by Kenyan runner Eliud Kipchoge on numerous marathon events in the past, including the 2018 and 2022 editions of the Berlin marathon (where Kipchoge set two official world records), as well as in two special attempts to break the 2 h mark for the distance, the Nike Breaking2 (2017) and the INEOS 1:59 Challenge (2019), where Kipchoge used an improved drafting formation to finish in 1:59:40, although that is not recognized as an official record.ResultsIn this study, the drag of a realistic model of a male runner is calculated by computational fluid dynamics for a range of velocities. The formations employed in the past by Kipchoge, as well as alternative formations, are analyzed and systematically compared with respect to mechanical power. In a quest to show that running an official marathon in under 2 h is possible, the power analysis is extended to the pacers. We developed a simple drafting and pacing strategy that Kipchoge could have used to run the 2022 Berlin marathon in a surprising 1 h, 59 min and 48 s.ConclusionsElite marathon runners can make better use of the pacers to experience reduced drag in races. The associated energy reduction makes it possible to run faster, finishing the race in less time. Using a better drafting strategy and a positive splitting pacing strategy, Kenyan runner Eliud Kipchoge could have broken the sub 2 h barrier in both the 2018 and 2022 editions of Berlin Marathon.

Enhancing cardiac assessments: accurate and efficient prediction of quantitative fractional flow reserve

BackgroundObstruction within the left anterior descending coronary artery (LAD) is prevalent, serving as a prominent and independent predictor of mortality. Invasive Fractional flow reserve (FFR) is the gold standard for Coronary Artery Disease risk assessment. Despite advances in computational and imaging techniques, no definitive methodology currently assures clinicians of reliable, non-invasive strategies for future planning.MethodThe present research encompassed a cohort of 150 participants who were admitted to the Rajaie Cardiovascular, Medical, and Research Center. The method includes a three-dimensional geometry reconstruction, computational fluid dynamics simulations, and methodology optimization for the computation time. Four patients are analyzed within this study to showcase the proposed methodology. The invasive FFR results reported by the clinic have validated the optimized model.ResultsThe computational FFR data derived from all methodologies are compared with those reported by the clinic for each case. The chosen methodology has yielded virtual FFR values that exhibit remarkable proximity to the clinically reported patient-specific FFR values, with the MSE of 6.186e-7 and R2 of 0.99 (p = 0.00434).ConclusionThis approach has shown reliable results for all 150 patients. The results are both computationally and clinically user-friendly, with the accumulative pre and post-processing time of 15 min on a desktop computer (Intel i7 processor, 16 GB RAM). The proposed methodology has the potential to significantly assist clinicians with diagnosis.

Study on the Fire Spread Characteristics of High-Rise Building Facades Under Strong Wind Conditions Based on the Combination of WRF and CFD

The spread of fires on the facades of high-rise buildings is highly influenced by atmospheric wind conditions, particularly in strong wind environments. A strong wind environment refers to the situation where the wind speed reaches level 6 or above, or the wind speed is between 10.8 m/s and 13.8 m/s. We conducted an in-depth study of the characteristics of flame spread on the facades of high-rise buildings under strong wind conditions. A nested coupling method based on WRF (Weather Research and Forecasting) and CFD (computational fluid dynamics) software (Ansys Fluent 2021) was used. The mesoscale meteorological simulation software WRF was utilized to obtain regional airflow variation data within a radius of 2 km around the high-rise building. Subsequently, these data were coupled with the CFD software (Ansys Fluent 2021) to simulate and obtain realistic wind field data within a 400 m range around the building. Finally, these realistic wind field data were used for FDS (Fire Dynamics Simulator) fire simulations and model experiments to accurately replicate building fire scenarios under strong wind conditions. The results indicate that using grid nesting for boundary condition division would help to improve the accuracy of fire spread characteristics on the facades of high-rise buildings under strong wind conditions. For a high-rise building, both headwinds and tailwinds promote vertical and horizontal flame spread, with a more significant impact on vertical flame spread speed. Side winds enhance horizontal flame spread but inhibit vertical flame spread. These findings provide a reference for the effective design of fire protection systems for the facades of high-rise buildings.

HEMODYNAMIC PERFORMANCE OF THREE FLOW DIVERTING STENTS FOR TREATMENT OF ABDOMINAL AORTIC ANEURYSM BASED ON A SIMPLIFIED PATIENT-SPECIFIC MODEL: A COMPARISON STUDY

In order to avoid aneurysm rupture, flow-diverting stents are deployed. This research presents a simplified patient-specific abdominal aortic model to test and assess the effects of three different not-covered flow-diverting stents (NCFDS): WALLSTENT™ is a commercially available NCFDS, while STENT BS and STENT PFS are numerically designed NCFDSs. Flow characteristics in abdominal aortic aneurysms (AAA) were studied using computational fluid dynamics (CFD) techniques on each stent before and after the procedure. We computed and compared the estimated flow structure, pressure, and wall shear stress (WSS) related indices between the three NCFDSs; these are crucial factors for evaluating aneurysm occlusion and rupture. The minimum estimated flow, pressure, and time average wall shear stress (TAWSS) and the maximum oscillatory shear index (OSI) and endothelial cell action potential (ECAP) are associated with using STENT PFS. Therefore, it may contribute to establishing a thrombus within the aneurysm sac and aneurysm shrinkage.

On the performance of highly aggressive inter compressor ducts

Abstract The enhancement of jet engine components may result in the expansion of the established design space. In particular, the trend towards short and therefore highly aggressive inter compressor ducts (ICD) extends the traditional design space. The potential for fuel savings resulting from a reduction in engine weight is in contrast to the emergence of a more complex flow field. Many studies consider the secondary flow system of highly aggressive ICDs at the design point, but there is a lack of off-design considerations. To fill this gap, the present study investigates in detail the off-design performance of the new German Aerospace Center (DLR) test case. Firstly, computational fluid dynamics (CFD) simulations of different typical operating points allow detailed considerations of the flow field under off-design conditions. Secondly, a variation of the inlet conditions describes the sensitivity of highly aggressive ICDs to different low-pressure compressor operating points. Finally, the comparison of the CFD stagnation pressure loss with the loss predicted by a preliminary off-design method validates the use of traditional off-design prediction during the preliminary design of highly aggressive ICDs.