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The energy conversion capacity of wave energy conversion devices highly depends on the hydrodynamic characteristics of the energy-harvesting structure. To investigate the effect of hydrodynamic performance on the power conversion characteristics, a twin-buoy wave energy converter (WEC) was investigated by using a three-dimensional numerical wave pool based on the Computational Fluid Dynamics (CFD) method. Several factors are examined, including the elasticity coefficient of the anchor chain, the bottom configuration of the floating body, and the power take-off (PTO) damping coefficient. The heave displacement, heave velocity, and heave force of the converter are calculated under specific wave parameters, and the flow field cloud diagram during the heave motion is analyzed. The results indicate that a wave energy converter with a hemispherical floating body exhibits the best kinematic performance. The influence of the mechanical damping coefficient on the energy conversion performance of the device is studied. By appropriately reducing the mechanical damping coefficient, the energy capturing capability of the device can be increased to a certain extent. These findings can serve as a theoretical basis for the application of deep-water wave energy conversion in engineering and the optimization of future WEC designs. [ABSTRACT FROM AUTHOR]

Copyright of Firat University Journal of Experimental & Computational Engineering (FUJECE) is the property of Firat University Journal of Experimental & Computational Engineering (FUJECE) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As a crucial part in micro-electromechanical manufacture, local ultra-precision processing of highly ductile copper is expected to be realized by fluid jet polishing (FJP), which widely utilized in optical elements. Since copper exhibits different wear behavior from stiff and brittle material, there is currently no abrasive wear prediction model applicable for copper to investigate the polishing mechanism. This research reveals that the copper material removal is dominated by deformation wear rather than cutting wear through abrasive jet impact experiments and localized wear scars analysis. A three-dimensional gas-liquid-particle triphasic wear model for copper in FJP is developed by considering impact energy and wear mechanism simultaneously. Ultimately, validation assessments at various working pressures and impingement angles achieve the goodness-of-fit up to 0.92–0.97 in quantitative comparison between simulations and experimental measurements, which demonstrate the wear prediction ability of the proposed model. This investigation facilitates a better understanding of copper wear mechanism and provides theoretical guidance for FJP process optimization. [ABSTRACT FROM AUTHOR]

In this study, we present a comprehensive numerical analysis of blood flow within human left ventricle models, with particular emphasis on optimizing simulation conditions to enhance the realism and computational efficiency of heart flow dynamics. The objective is to determine the most effective mesh configurations, flow conditions, and boundary settings necessary for accurately capturing the formation and behavior of the vortex ring—a pivotal element in ventricular flow dynamics. Utilizing a computational fluid mechanics approach, we review the influence of both idealized and patient-specific geometries on simulation outcomes. It is imperative to consider the necessity of dynamic wall motion and the precise calibration of inlet and outlet boundary conditions, which must be designed to mimic physiological conditions as accurately as possible. These factors are of paramount importance in achieving a balance between computational resource demands and the fidelity of the simulations, thereby providing valuable insights for future cardiovascular modeling efforts. Tutorials explaining details of the simulations and the codes used are included in ModelFLOWs-app website [14].

Purpose: Tortuosity of the internal carotid artery (ICA) is associated with intracranial aneurysms (IAs). The siphon is the most curved segment of the ICA, but its morphology has controversial effects on IAs. This study aimed to explore the morphometric features of the siphon and the potential hemodynamic mechanisms that may affect C7 aneurysm formation. Methods: In this study 32 patients with C7 aneurysms diagnosed at Xiangya Hospital between 2019 and 2021 and 32 control subjects were enrolled after propensity score matching. Computed tomography angiography (CTA) images were acquired to measure morphologic features, and then, by combining clinical data, simplified carotid siphon models were constructed, and computational fluid dynamics (CFD) analysis was performed. Results: The presence of C7 aneurysms was associated with the height of the C4–C6 curved arteries (odds ratio [OR] 0.028, 95% confidence interval [CI] 0.003–0.201; P < 0.001). The heights of the C4–C6 curved arteries in the aneurysm group were significantly shorter than those in the control group. The CFD analysis revealed that shorter C4–C6 bends led to greater blood velocity and pressure in the C7 segment arteries. Conclusion: A shorter C4–C6 bend was associated with distal C7 aneurysm formation, and an elaborate hemodynamic mechanism may underlie this association. [ABSTRACT FROM AUTHOR]

Background: A percutaneous ventricular assist device (pVAD) is an effective method to treat heart failure, but its complications, mainly hemolysis and thrombus formation, cannot be ignored. Accurate evaluation of hemolysis and thrombus formation in pVAD is essential to guide the development of pVAD and reduce the incidence of complications. Methods: This study optimized the numerical model to predict hemolysis and thrombus formation in pVAD. The hemolysis model is based on the power law function, and the multi‐component thrombus prediction model is improved by introducing the von Willebrand factor. Results: The error between the numerical simulation and the hydraulic performance experiment is within 5%. The numerical results of hemolysis are in good agreement with those of in vitro experiments. Meanwhile, the thrombus location predicted by the numerical model is the same as that found in the in vivo experiment. Conclusion: The numerical model suggested in this study may therefore accurately assess the possible hemolytic and thrombotic dangers in pVAD, making it an effective tool to support the development of pVAD. [ABSTRACT FROM AUTHOR]

With the continuous growth of energy demand, the advantages of nuclear power, such as high energy density, low emissions, and cleanliness, are gradually highlighted. However, the increasing capacity of the turbine generator in nuclear power plants has led to greater losses and critical heating issues. Designing an effective cooling system plays an important role in improving the rotor's heat dissipation ability, especially under the condition of limited rotor space. In this study, the cooling effects of the rotor using a radial straight-type cooling structure and a composited radial–axial–radial cooling structure are compared and analyzed for a 1555 MVA hydrogen-cooled nuclear turbine generator. Three-dimensional fluid thermal coupled models of the rotor with both cooling structures are established, and corresponding boundary conditions are provided. The models are solved using the finite volume method. The flow law of cooling hydrogen gas inside the rotor and the temperature distribution of various parts of the rotor are studied in detail. Compared with the radial straight-type cooling structure, adopting the composited radial–axial–radial cooling structure can reduce the average temperature of the rotor field windings by 4.5 °C. The research results provide a reference for the design and optimization of the rotor cooling system for large-capacity nuclear turbine generators. [ABSTRACT FROM AUTHOR]

Unlike uniform motion, when an object moves underwater with variable speed, it experiences additional resistance from the water, commonly referred to as added mass force. At present, several methods exist to solve this force, including theoretical, experimental, and simulation approaches. This paper addresses the challenge of determining the added mass force for irregularly shaped small objects undergoing variable speed motion underwater, proposing a method to obtain the added mass force through numerical simulation. It employs regression analysis and parameter separation analysis to solve the added mass force, added mass, viscous drag coefficient, and pressure drag coefficient. The results indicate that an added mass force exists during both the acceleration and deceleration of the object, with little difference between them. Under the same velocity conditions, significant differences exist in pressure drag forces, while differences in viscous drag forces are not significant. This suggests that the primary source of added mass force is pressure drag, with viscous drag having little effect on it. During acceleration, the surrounding fluid accelerates with the object, increasing the pressure drag with a high-pressure area concentrating at the object's front, forming an added mass force that is directed backward. By contrast, during deceleration, the fluid at the object's front tends to detach, and the fluid at the rear rushes forward, leading to a smaller high-pressure area at the front and a larger one at the rear, reducing the pressure drag and forming an added mass force that is directed forward. By comparing the added mass of a standard ellipsoid obtained from numerical simulation with theoretical values, the regression analysis method is proven to be highly accurate and entirely applicable for solving the added mass of underwater vehicles. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study of self-sustained processes excited in a Helmholtz resonator after a flow over its orifice. A comparative analysis of various approaches to the numerical modeling of this problem was carried out, taking into account both the requirements for achieving the required accuracy and taking into account the resource greediness of calculations, the results of which were verified by comparison with data obtained during a special experiment. The configuration with a spherical resonator with a natural frequency of 260 Hz and an orifice diameter (about 5 cm) in an air flow with a speed of 6 to 14 m/s was considered. A comparison of the calculation results with data obtained in experiments carried out in the wind tunnel demonstrated that the accuracy of calculations of the characteristics of the self-sustained mode using the simplest URANS class model tends to the accuracy of calculations within the large eddy simulation approach formulated in the WMLES model. At the same time, when using WMLES, it is possible to better reproduce the background level of pulsations. From the point of view of resource greediness, expressed in the number of core hours spent obtaining a solution, both models of the turbulence turned out to be almost equivalent when using the same grid models. [ABSTRACT FROM AUTHOR]

Aim: This article focuses on the use of artificial neural networks to mathematically describe the parameters that determine the size of a jet fire flame. To teach the neural network, the results of a horizontal propane jet fire, carried out experimentally and using CFD mathematical modelling, were used. Project and methods: The main part of the work consisted of developing an artificial neural network to describe the flame length and propane-air mixing path lengths with good accuracy, depending on the relevant process parameters. Two types of data series were used to meet the stated objective. The first series of data came from field tests carried out by CNBOP-PIB and from research contained in scientific articles. The second type of data was provided by numerical calculations made by the authors. The methods of computational fluid mechanics were used to develop the numerical simulations. The ANSYS Fluent package was used for this purpose. Matlab 2022a was used to develop the artificial neural network and to verify it. Results: Using the nftool function included in Matlab 2022a, an artificial neural network was developed to determine the flame length Lflame and the length of the Slift-off mixing path as a function of the diameter of the dnozzle and the mass flux of gas leaving the nozzle. Using Pearson’s correlation coefficient, a selection was made of the best number of neurons in the hidden layer to describe the process parameters. The neural network developed allows Lflame and Slift-off values to be calculated with good accuracy. Conclusions: Artificial neural networks allow a function to be developed to describe the parameters that determine flame sizes in relation to process parameters. For this purpose, the results of the CFD simulations and the results of the jet fire experiments were combined to create a single neural network. The result is a ready-made function that can be used in programmes for the rapid determination of flame sizes. Such a function can support the process of creating scenarios in the event of an emergency. A correctly developed neural network provides opportunities for the mathematical description of jet fires wherever experimental measurements are not possible. Solution proposed by the authors does not require a large investment in ongoing calculations, as the network can be implemented in any programming language. Keywords: computational fluid mechanics, artificial neural networks, jet fire

This paper presents the results of a study of self-sustained processes excited in a Helmholtz resonator after a flow over its orifice. A comparative analysis of various approaches to the numerical modeling of this problem was carried out, taking into account both the requirements for achieving the required accuracy and taking into account the resource greediness of calculations, the results of which were verified by comparison with data obtained during a special experiment. The configuration with a spherical resonator with a natural frequency of 260 Hz and an orifice diameter (about 5 cm) in an air flow with a speed of 6 to 14 m/s was considered. A comparison of the calculation results with data obtained in experiments carried out in the wind tunnel demonstrated that the accuracy of calculations of the characteristics of the self-sustained mode using the simplest URANS class model tends to the accuracy of calculations within the large eddy simulation approach formulated in the WMLES model. At the same time, when using WMLES, it is possible to better reproduce the background level of pulsations. From the point of view of resource greediness, expressed in the number of core hours spent obtaining a solution, both models of the turbulence turned out to be almost equivalent when using the same grid models.

Minimally-invasive therapies are well-established treatment methods for saccular intracranial aneurysms (SIAs). Knowledge concerning fusiform IAs (FIAs) is low, due to their wide and alternating lumen and their infrequent occurrence. However, FIAs carry risks like ischemia and thus require further in-depth investigation. Six patient-specific IAs, comprising three position-identical FIAs and SIAs, with the FIAs showing a non-typical FIA shape, were compared, respectively. For each model, a healthy counterpart and a treated version with a flow diverting stent were created. Eighteen time-dependent simulations were performed to analyze morphological and hemodynamic parameters focusing on the treatment effect (TE). The stent expansion is higher for FIAs than SIAs. For FIAs, the reduction in vorticity is higher (Δ 35–75% case 2/3) and the reduction in the oscillatory velocity index is lower (Δ 15–68% case 2/3). Velocity is reduced equally for FIAs and SIAs with a TE of 37–60% in FIAs and of 41–72% in SIAs. Time-averaged wall shear stress (TAWSS) is less reduced within FIAs than SIAs (Δ 30–105%). Within this study, the positive TE of FDS deployed in FIAs is shown and a similarity in parameters found due to the non-typical FIA shape. Despite the higher stent expansion, velocity and vorticity are equally reduced compared to identically located SIAs. [ABSTRACT FROM AUTHOR]

The use of film cooling technology is one of the most effective ways to minimize the damage to wall materials caused by the high-temperature environment in a ramjet. Optimization of the design to achieve the highest film cooling efficiency on the hot wall is the focus of current research. Due to the large number of parameters affecting the film cooling efficiency and the interactions between them, an improved orthogonal design-of-experiments method is chosen to investigate the contribution of different parameters. Flat plate film cooling and transverse groove film cooling are simulated numerically. The results indicated that the contribution of each parameter is ranked as hole spacing (S/D) > incidence angle > blowing ratio for flat plate film cooling; hole spacing > transverse groove depth > blowing ratio > incidence angle for transverse groove film cooling. The film cooling efficiency is inversely proportional to the size of the flow field area affected by the vortex ring and directly proportional to the size of the vortex intensity. Transverse groove film cooling forms a more complete film in most cases, which is better than flat plate film cooling. Within the scope of this study, a complete film at S/D > 2.0 cannot be generated on the flat plate, which should not be used in ramjet. [ABSTRACT FROM AUTHOR]

With the continuous growth of energy demand, the advantages of nuclear power, such as high energy density, low emissions, and cleanliness, are gradually highlighted. However, the increasing capacity of the turbine generator in nuclear power plants has led to greater losses and critical heating issues. Designing an effective cooling system plays an important role in improving the rotor’s heat dissipation ability, especially under the condition of limited rotor space. In this study, the cooling effects of the rotor using a radial straight-type cooling structure and a composited radial–axial–radial cooling structure are compared and analyzed for a 1555 MVA hydrogen-cooled nuclear turbine generator. Three-dimensional fluid thermal coupled models of the rotor with both cooling structures are established, and corresponding boundary conditions are provided. The models are solved using the finite volume method. The flow law of cooling hydrogen gas inside the rotor and the temperature distribution of various parts of the rotor are studied in detail. Compared with the radial straight-type cooling structure, adopting the composited radial–axial–radial cooling structure can reduce the average temperature of the rotor field windings by 4.5 °C. The research results provide a reference for the design and optimization of the rotor cooling system for large-capacity nuclear turbine generators.

In the present two-dimensional numerical study, we investigate the roles of geometrical parameters of a hydrofoil (shape/curvature of the leading and trailing edges and thickness) and kinematic parameters (phase difference between heave and pitch (ϕ)) on the propulsive performance of different-shaped hydrofoils oscillating at maximum angles of attack up to α max = 30 ∘ . The study was carried out at a fixed non-dimensional maximum heave to chord ratio h ∘ / C = 0.75 , Strouhal number S t = 0.25 , and Reynolds number R e = 5000 . Our findings reveal that hydrofoil performance and stability improve with leading and trailing edge curvatures but decline as thickness increases. By analyzing the near-wake structure, we establish that even minimal flow separation increases power consumption while moderate flow separation enhances thrust. Over the range of different-shaped hydrofoils at different α max and ϕ , maximum propulsion efficiency occurs for those parameters for which there is a small degree of flow separation but with no roll-up of a separating vortex. In comparison, maximum thrust generation occurs when there is a moderately strong flow separation but without induction of a significant amount of fluid around the trailing edge. These insights offer valuable knowledge for understanding fish propulsion efficiency and have applications in designing autonomous underwater vehicles (AUVs) and micro-air vehicles (MAVs). [ABSTRACT FROM AUTHOR]

The wide usage of guide parts makes it one of the most interesting research hot spots in the field of fluid machinery. To improve the flow field distribution of the vertical turbo air classifier, the guide holes in the air intake region are designed. The flow fields of the classifiers with and without guide holes are simulated using ANSYS‐FLUENT. The gas‐phase simulation results show that the guide holes have a 'diversion' effect on the airflow, decreasing the tangential velocity and increasing the radial velocity of the airflow. After the airflow passes through the guide holes, the small guide hole sizes cause the large radial velocity and the strong 'diversion' effect, which can improve the flow field distribution. The well‐distributed flow field of the elutriation region and annular region are obtained when the guide hole size is 7 mm × 7 mm. The discrete phase simulation results show that the cut size of the classifier without the guide holes is 9.1 μm. The cut size is 13.4 μm when the guide hole size is 7 mm × 7 mm. With the increase in the guide hole size, the cut size increases. However, when the guide hole size is larger than 10.5 mm × 10.5 mm, the cut size is almost kept unchanged, which is 22.9 μm. [ABSTRACT FROM AUTHOR]

The aim of this publication was to investigate the effects the blade count of a high-pressure centrifugal compressor's impeller has on the performance of the DGEN 380 turbine engine at take-off. The study began with the development of a zero-dimensional thermo-fluid model of the engine. The model was matched with experimental data from the WESTT CS/BV virtual test bench for the baseline count and then implemented to analyse the engine behaviour at alternative counts. The corresponding changes in the compressor pressure ratio and efficiency were modelled in a commercial 3D CFD software and transferred to the zero-dimensional model with proper scaling. The results proved that the baseline design lied in the optimal range of thrust-specific fuel consumption. The increase in the blade count led to a crisis of the aerodynamic loading at the splitters, so that no further rise in the pressure ratio could be achieved. The results of the study could be implemented by mechanical engineers while solving the tasks of the maintenance and modernisation of gas turbines with radial compressors. [ABSTRACT FROM AUTHOR]

Copyright of Safety & Fire Technology (2657-8808) is the property of Centrum Naukowo-Badawcze Ochrony Przeciwpozarowej and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Unlike uniform motion, when an object moves underwater with variable speed, it experiences additional resistance from the water, commonly referred to as added mass force. At present, several methods exist to solve this force, including theoretical, experimental, and simulation approaches. This paper addresses the challenge of determining the added mass force for irregularly shaped small objects undergoing variable speed motion underwater, proposing a method to obtain the added mass force through numerical simulation. It employs regression analysis and parameter separation analysis to solve the added mass force, added mass, viscous drag coefficient, and pressure drag coefficient. The results indicate that an added mass force exists during both the acceleration and deceleration of the object, with little difference between them. Under the same velocity conditions, significant differences exist in pressure drag forces, while differences in viscous drag forces are not significant. This suggests that the primary source of added mass force is pressure drag, with viscous drag having little effect on it. During acceleration, the surrounding fluid accelerates with the object, increasing the pressure drag with a high-pressure area concentrating at the object’s front, forming an added mass force that is directed backward. By contrast, during deceleration, the fluid at the object’s front tends to detach, and the fluid at the rear rushes forward, leading to a smaller high-pressure area at the front and a larger one at the rear, reducing the pressure drag and forming an added mass force that is directed forward. By comparing the added mass of a standard ellipsoid obtained from numerical simulation with theoretical values, the regression analysis method is proven to be highly accurate and entirely applicable for solving the added mass of underwater vehicles.

Attention to photovoltaic (PV) cells to convert solar irradiation into electricity is significantly growing for domestic usage and large-scale projects such as solar farms. However, PV efficiency decreases on hot days. This paper proposes an effective cooling technique consisting of a 2% nano encapsulated phase change material (NEPCM) slurry and impinging jets (IJs) in a PV system. The impact of five influencing parameters on PV efficiency is studied using a multi-phase volume of fluid (VOF) model encompassing the effects of solar irradiation, latent heat, mass flow rate, number of nozzles, and jet-to-surface distance. The maximum efficiency of 15.82% is achieved under irradiation of 600 W/m2. The latent heat shows a slight improvement at the low particle concentration. Increasing the mass flow rate to 0.12 kg/s enhances the PV output power by 17.32%. While the PV performance is shown to be improved over the increment of the number of nozzles, the jet-to-surface spacing of 5.1 mm records a remarkable PV surface temperature reduction to 33.8 °C, which is the ideal operating temperature for the PV panel.

This article deals with a thermal energy storage system in the form of a water tank with a thermocline. The well-known thermocline phenomenon is modeled using computational fluid dynamics (CFD). However, the reservoir model proposed in this article is zero-dimensional. This is due to the fact that the aim of this article is to build a mathematical model that will be more useful in mathematical models of complex energy systems in which a hot water tank is one of many elements of the system. In such a zero-dimensional mathematical model, the hot water tank will be modeled using equations describing heat transfer, and the thermocline itself will be treated as a heat transfer surface with known dimensions and heat transfer coefficient. A novelty of this paper is that it addresses heat loss across the thermocline as defined in this manner. A CFD model of a thermal storage tank is created, validated with available experimental data, and used to obtain the heat transfer coefficient U. The resulting value is then analyzed quantitatively and qualitatively and the changes in the thickness of the thermocline are accounted for in the equation. The results from this groundbreaking work can be used to analyze heat storage in the form of thermocline water tanks at the level of system modeling, e.g., for the purpose of configuring the structure of other devices and control systems. [ABSTRACT FROM AUTHOR]

The use of film cooling technology is one of the most effective ways to minimize the damage to wall materials caused by the high-temperature environment in a ramjet. Optimization of the design to achieve the highest film cooling efficiency on the hot wall is the focus of current research. Due to the large number of parameters affecting the film cooling efficiency and the interactions between them, an improved orthogonal design-of-experiments method is chosen to investigate the contribution of different parameters. Flat plate film cooling and transverse groove film cooling are simulated numerically. The results indicated that the contribution of each parameter is ranked as hole spacing (S/D) > incidence angle > blowing ratio for flat plate film cooling; hole spacing > transverse groove depth > blowing ratio > incidence angle for transverse groove film cooling. The film cooling efficiency is inversely proportional to the size of the flow field area affected by the vortex ring and directly proportional to the size of the vortex intensity. Transverse groove film cooling forms a more complete film in most cases, which is better than flat plate film cooling. Within the scope of this study, a complete film at S/D > 2.0 cannot be generated on the flat plate, which should not be used in ramjet.

The aim of this work was to investigate the reshaping mechanisms of a reshaping berm breakwater (BB) by assessing the results of a two-dimensional numerical model in OpenFoam. The flow inside and outside the breakwater was numerically simulated. The initial and reshaped form of the breakwater was modelled using the Darcy–Forchheimer equation and k–ϵ closure model. The numerical model was calibrated with and validated against experimental data of wave-induced pressure and water-level fluctuations inside and outside the breakwater. Both the initial and reshaped BB were evaluated for calibration and validation processes. The results show that the minimum run-down level on the breakwater slope is a critical area for armour instability due to outward driving forces caused by the critically synchronised outward flow and excess pressure gradient. Moreover, parallel downward flow occurs during a wave run-down, which can push the displaced armour down the slope. After reshaping, the breakwater profile has a milder slope than the initial profile, and the outward forces due to the excess pressure gradient are reduced to less than one-half of their initial amount, a result of the change in breaker type. Accordingly, the reshaped profile is modified to harmonise with the new flow field conditions. [ABSTRACT FROM AUTHOR]

Attention to photovoltaic (PV) cells to convert solar irradiation into electricity is significantly growing for domestic usage and large-scale projects such as solar farms. However, PV efficiency decreases on hot days. This paper proposes an effective cooling technique consisting of a 2% nano encapsulated phase change material (NEPCM) slurry and impinging jets (IJs) in a PV system. The impact of five influencing parameters on PV efficiency is studied using a multi-phase volume of fluid (VOF) model encompassing the effects of solar irradiation, latent heat, mass flow rate, number of nozzles, and jet-to-surface distance. The maximum efficiency of 15.82% is achieved under irradiation of 600 W/m2. The latent heat shows a slight improvement at the low particle concentration. Increasing the mass flow rate to 0.12 kg/s enhances the PV output power by 17.32%. While the PV performance is shown to be improved over the increment of the number of nozzles, the jet-to-surface spacing of 5.1 mm records a remarkable PV surface temperature reduction to 33.8 °C, which is the ideal operating temperature for the PV panel. [ABSTRACT FROM AUTHOR]

In this paper, the gas-liquid flow is comprehensively analyzed under different inlet gas void fractions, and the effect of tip leakage vortex (TLV) on the gas flow pattern in multiphase pumps is revealed. The results show that the gas flow pattern in an impeller is closely related to the centrifugal force, low-pressure region, and vortex motion. Most gas is present near the hub and suction surface of the blade as well as in the TLV. The two- and three-dimensional spatiotemporal evolution of the gas is presented, and the gas motion during the inception, development, and dissipation of TLV is revealed. It is reflected that the gas volume fraction is the highest at the TLV core and gradually weakens along the radial direction with the vortex core at the center. Additionally, the TLV energy dissipation is closely related to the gas and pressure difference, and strong energy dissipation occurs in the jet-wake flow. [ABSTRACT FROM AUTHOR]

In the present two-dimensional numerical study, we investigate the roles of geometrical parameters of a hydrofoil (shape/curvature of the leading and trailing edges and thickness) and kinematic parameters (phase difference between heave and pitch (ϕ)) on the propulsive performance of different-shaped hydrofoils oscillating at maximum angles of attack up to αmax=30∘. The study was carried out at a fixed non-dimensional maximum heave to chord ratio h∘/C=0.75, Strouhal number St=0.25, and Reynolds number Re=5000. Our findings reveal that hydrofoil performance and stability improve with leading and trailing edge curvatures but decline as thickness increases. By analyzing the near-wake structure, we establish that even minimal flow separation increases power consumption while moderate flow separation enhances thrust. Over the range of different-shaped hydrofoils at different αmax and ϕ, maximum propulsion efficiency occurs for those parameters for which there is a small degree of flow separation but with no roll-up of a separating vortex. In comparison, maximum thrust generation occurs when there is a moderately strong flow separation but without induction of a significant amount of fluid around the trailing edge. These insights offer valuable knowledge for understanding fish propulsion efficiency and have applications in designing autonomous underwater vehicles (AUVs) and micro-air vehicles (MAVs).

Numerical simulations of the wind flow around isolated stockpiles of bulk material are performed to assess the emission potential (P) of particulate matter (PM) from the pile surfaces exposed to wind erosion (i.e., industrial wind erosion). The analysis is focused on two metal sulphides (lead and zinc sulphides), which are typically stored in the open yards of industrial plants that operate in the commodity sector for the production of non-ferrous metals. The EPA methodology is applied to the numerical simulated flow fields to quantify the effect of the wind stress over the erodible surfaces of the two ores. Two alternative open bay geometries and different volumes of material stocked within the enclosing walls are considered. Moreover, the protective effect of the walls is assessed by comparing the same pile configurations without walls. This is found to be highly dependent on the wind direction, as well as to the pile configuration. A methodology that can be easily customized to specific industrial sites is proposed to define the best storage configuration for PM emission prevention and control. [ABSTRACT FROM AUTHOR]

The calculation of aerodynamic force and aerodynamic heating for flight vehicles round trip to Earth􀆳s atmosphere （over different flow regimes） is one of the challenges and hotspots in computational fluid dynamics. Since the flow scenarios faced by such vehicles are no longer purely continuous flow or rarefied flow， neither the Navier-Stokes equations’ solver nor the direct simulation Monte Carlo （DSMC） method can obtain accurate results. In recent years ，based on the Boltzmann model equation， which is independent of the continuity hypothesis， various numerical approaches have been developed to simulate fluid flow problems in all flow regimes by discretizing this equation in both physical space and velocity space. This paper reviews and analyzes the research progress of this kind of algorithm， including the gas kinetic unified algorithm （GKUA），the unified gas kinetic scheme （UGKS） and the improved discrete velocity method （IDVM）. It focuses on the basic ideas and the implementation of these methods and pays attention to their current progress and applications. At the same time， the IDVM is further extended to simulate the unsteady flows in all flow regimes. Finally， some problems existing in this kind of algorithm are discussed and the prospect for work in the future is proposed. [ABSTRACT FROM AUTHOR]

The aim of this publication was to investigate the effects the blade count of a high-pressure centrifugal compressor’s impeller has on the performance of the DGEN 380 turbine engine at take-off. The study began with the development of a zero-dimensional thermo-fluid model of the engine. The model was matched with experimental data from the WESTT CS/BV virtual test bench for the baseline count and then implemented to analyse the engine behaviour at alternative counts. The corresponding changes in the compressor pressure ratio and efficiency were modelled in a commercial 3D CFD software and transferred to the zero-dimensional model with proper scaling. The results proved that the baseline design lied in the optimal range of thrust-specific fuel consumption. The increase in the blade count led to a crisis of the aerodynamic loading at the splitters, so that no further rise in the pressure ratio could be achieved. The results of the study could be implemented by mechanical engineers while solving the tasks of the maintenance and modernisation of gas turbines with radial compressors.

In order to clarify and enhance the work performance of the threshing and cleaning machine for plot-bred wheat and further reduce the grain retention in all working areas in the machine, in this study, a discrete element model for the threshing material of plot-bred wheat and a gas-solid coupling simulation model for the machine were established by ensuring all the harvesting criteria for the machine. Then numerical simulation was completed on the movement process of the threshing material in the threshing and cleaning machine for plot-bred wheat, the movement law and motion trajectory of all components of the threshing material were explored, and the impact forms of unreasonable work parameters on the separating and cleaning process were analyzed. First, four working areas were divided in the threshing and cleaning machine for plot-bred wheat. Under gas-solid flow coupling effect, the number variation of threshing material in each working area was analyzed under the effect of gas-solid coupling, and the operation characteristics of "no retained seeds and convenient cleaning" of the threshing machine for plot-bred wheat were further improved. The verification test results showed that, when the feeding amount of wheat was 0.30 kg/s, the rotation speed of the shaft of the tooth-type threshing cylinder was set to 1350 r/min, the rotation speed of the winnower was set to 500 r/min, the rotation speed of the residue absorption fan was set to 1000 r/min, the average total loss rate in threshing of the sample machine was 0.56%, and average impurity rate of the threshing material was 5.26%, average damage rate in threshing was 0.68%. In the test, the status of material discharged from the residue absorption fan outlet and bottom of the cyclone separator was similar to that of the simulation results, showing that it was feasible to use the method of gas-solid coupling to simulate the movement law of threshing material in the threshing and cleaning machine for plot-bred wheat. [ABSTRACT FROM AUTHOR]

Numerical modeling of turbulent impinging swirling jets involve complex flow physics that make their computation still very challenging. Thus, the literature on computational modeling of these nanofluid jets is really scarce, with most works on laminar impinging nanofluid jets or turbulent swirling/non-swirling air or water-only jets. In this paper a computational analysis of different configurations in the application of $ {\rm Al}_2{\rm O}_3 $ nanoparticles to submerged high-Reynolds turbulent jet flows for cooling purposes is developed. Six volume fractions have been investigated ( $ \phi = 0, 2, 4, 6, 8 $ and $ 10\% $ , which correspond to a Prandtl number of the nanofluid within the range $ Pr_{nf} \in [7, 14.4] $ ) along with two nozzle-to-plate distances ( $ H/D=2 $ and 4) and several swirl numbers ( $ S=0 $ , $ 0.16 $ , $ 0.27 $ , $ 0.45 $ , $ 0.77 $ and $ 0.83 $ ). The jet regime is fixed at a Reynolds number $ Re=35{,}000 $ . The computational study shows that the application of nanoparticles enhances forced convection for all the simulations carried out. However, the influence of swirl number and nozzle-to-plate distance is not that clear. Variations cause different effects on the performance. For instance, to vary the swirl intensity at large nozzle-to-plate separation has different effect than in short separations. Also, some ranges of variation of swirl may enhance heat transfer whilst others may worsen it.

Thermal management is essential to improve the overall performance of photovoltaic (PV) cells. This study presents a comprehensive numerical study on a PV panel to achieve economic efficiency cooling system. A nanofluid jet impingement cooling (JIC) system with different configurations is developed and integrated into the PV panel to control the surface temperature. A three-phase mixture model shows a satisfactory agreement between the simulation and measurement values. Then, the simulations are conducted to understand the importance of different influencing parameters, including inlet temperature (20–40 °C), number of nozzles (8−24), mass flow rate (0.045–0.12 kg/s), jet-to-surface distance (5.1–55 mm), and nozzle diameter (1 and 2 mm). Numerical results demonstrate that uncooled PV temperature reaches 68.5 °C, while using the JIC system reduces that by 36.4 °C. Lower inlet temperatures and larger mass flow rates result in higher PV efficiency. The number of nozzles affects the surface temperature and its uniformity. Small jet-to-surface distances enhance the turbulence kinetic energy and the heat transfer rate. For the nozzle diameters of 1 and 2 mm, the maximum power increment increases to 20.36% and 20.19%, respectively. However, the nozzle diameter of 1 mm increases the pumping power with a coefficient of energy of 1.18. [ABSTRACT FROM AUTHOR]

In this study, the most widely used Rushton turbine in the industry was discussed, and the effect of different blade angles on the mixture was investigated numerically. As a standard model, 6 bladed propellers were used and 4 baffles were placed in the stirred tank. The selected tank model is in the form of a flat bottom cylindrical container. Flow characteristics were obtained by giving angles (10°, 20°, 30°, 40°, 50°, 60°) to the propeller blades used in the straight model. The obtained results were compared with each other. In addition, analyzes were repeated at different rotation speeds (600 rpm, 750 rpm, 1000 rpm) for each model at each angle. ANSYS Fluent 18 commercial software, which is the most preferred CFD program in the literature, was used for this numerical study. The analyzes were provided in the standard k-epsilon (ε) turbulence model. The Multiple Reference Frame (MRF) approach was used to simulate impeller rotation. The velocity profiles obtained from the simulations have been shown to be in consistent with the experimental estimates and the results of previous studies. As a result, it has been revealed that the best mixing balance is provided by the impeller blade at 40 and 50 degrees. [ABSTRACT FROM AUTHOR]

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Heat exchangers are multi-benefit thermal-devices, of wide use, as their structure varies with their scope of application. The development of channel configurations contained in these exchangers, and evaluation of their performance is the goal of many recent numerical and experimental achievements. Because of the high cost of such devices, many researchers had to follow CFD based computational methods instead of using experimental techniques. In this study, the hydrothermal structure of a finned channel heat exchanger is evaluated using the finite-volume based Ansys Fluent. Due to the complex structure of these channels, which contain overlapping transverse vortex generators, the flow develops into a turbulent structure that strongly influences the enhanced heat transfer. In this sense, various turbulence models are simulated to assess their numerical effect on the performance of the exchanger. Five different models are under experimentation which are (i) standard-, (ii) RNG- and (iii) realizable-case k-ε type models as well as (iv) standard- and (v) SST-case k-ω type models. As highlighted, the highest performance is reached with the SST-type k-ω, while the lowest one is that with the realizable-type k-ԑ.

This article deals with a thermal energy storage system in the form of a water tank with a thermocline. The well-known thermocline phenomenon is modeled using computational fluid dynamics (CFD). However, the reservoir model proposed in this article is zero-dimensional. This is due to the fact that the aim of this article is to build a mathematical model that will be more useful in mathematical models of complex energy systems in which a hot water tank is one of many elements of the system. In such a zero-dimensional mathematical model, the hot water tank will be modeled using equations describing heat transfer, and the thermocline itself will be treated as a heat transfer surface with known dimensions and heat transfer coefficient. A novelty of this paper is that it addresses heat loss across the thermocline as defined in this manner. A CFD model of a thermal storage tank is created, validated with available experimental data, and used to obtain the heat transfer coefficient U. The resulting value is then analyzed quantitatively and qualitatively and the changes in the thickness of the thermocline are accounted for in the equation. The results from this groundbreaking work can be used to analyze heat storage in the form of thermocline water tanks at the level of system modeling, e.g., for the purpose of configuring the structure of other devices and control systems.

Abrupt expansions are a very frequent geometry in mechanical engineering systems, i.e. in combustion chambers, valves, heat exchangers or impinging cooling devices. However, despite the large number of devices that use this geometry, the expanded flow behaviour still needs further research to understand and predict the full system performance. This paper presents the application of the non-uniform finite difference approximation method developed in Sanmiguel et al. for the numerical characterisation of a confined swirling laminar jet discharging with a large expansion ratio. This investigation can be considered an extension of previous work by Revuelta, but now a swirling flow is generated by a rotating pipe upstream the expansion. The structures found when a fully-developed rotating Hagen-Poiseuille flow discharges into a much larger pipe section are summarised in a bifurcation diagram, whose coordinates are the Reynolds number of the jet (Rej) and the swirl parameter (L), for which the time-dependent, axisymmetric and incompressible Navier-Stokes equations are integrated numerically. For values of the jet Reynolds number below 200, there is a critical value of the swirl parameter above which stable vortex breakdown appears. For values of the Reynolds number above 200, three different behaviours are observed, and each performance appears for a critical value of the swirl parameter. When increasing the swirl parameter from zero, the flow becomes axisymmetrically unstable, showing an oscillatory behaviour. If further increasing the swirl intensity, the oscillatory flow coexists with a vortex breakdown bubble and, finally, a steady vortex breakdown is reached. The expansion ratio ε considered in all the simulations is 1 / ε = 20. In previous literature, the exactness of the limiting critical Rej and L values that define these behaviours has been found to be influenced by the variability in the inlet profile conditions, which affects the expanded flow. This enhances the importance in the present investigation to accurately simulate the discharge pipe inlet profiles. [ABSTRACT FROM AUTHOR]

The goal of the present work was to explore student perspectives about a course module designed with cognitivist and constructivist learning theories, the cognitive apprenticeship instructional model, and a T-shaped design, specifically the first module of a Computational Fluid Mechanics curricular unit within a Master of Computational Mechanics program. This module was redesigned accordingly after the professor participated in a faculty development course, Engineering Education Theory and Practice, at the Faculty of Engineering, University of Porto. Student perspectives on the efficacy of the redesigned course were solicited, along with those from students who had previously taken the course. Students who participated in the revised course module reported higher levels of satisfaction than students from the previous iteration of the course and were more likely to recognize the value of specific instructional activities. This paper describes the revision of the course module and a comparison of the student feedback before and after those revisions. [ABSTRACT FROM AUTHOR]

This study presents the first results of a new turbulence model implementation in our compressible finite volume CFD solver. The k - kL turbulence model is one of the newest two-equation models, and it is based on the ideas of Rotta's two-equation model. Various research groups progressively develop the model, and it is maturing rapidly. Reports suggest that the k - kL turbulence model provides superior results compared to the other twoequation turbulence models in specific problems. The improved solutions are observed mainly for the flows with high adverse pressure gradients, the blunt-body wakes and jet interactions. We have implemented the k - kL model (with the standard designation of k-kL-MEAH2015) in our solver, and we are testing it rigorously. This paper presents our results on standard turbulence test cases: subsonic flat plate and subsonic wall-mounted bump. The results compare well with the reference study previously presented and published by model developers. The design of the k - kL model prevents excessive production of turbulence and dissipation; hence it preserves vortices significantly better than the other two-equation models. The implemented model is also tested with a transonic fin trailing vortex case to support this statement. Results show that the k - kL model yields considerably better results than the SST turbulence model in cases including vortices. [ABSTRACT FROM AUTHOR]

Numerical modeling of turbulent impinging swirling jets involve complex flow physics that make their computation still very challenging. Thus, the literature on computational modeling of these nanofluid jets is really scarce, with most works on laminar impinging nanofluid jets or turbulent swirling/non-swirling air or water-only jets. In this paper a computational analysis of different configurations in the application of A l 2 O 3 nanoparticles to submerged high-Reynolds turbulent jet flows for cooling purposes is developed. Six volume fractions have been investigated ( ϕ = 0 , 2 , 4 , 6 , 8 and 10 % , which correspond to a Prandtl number of the nanofluid within the range P r n f ∈ [ 7 , 14.4 ]) along with two nozzle-to-plate distances ( H / D = 2 and 4) and several swirl numbers ( S = 0 , 0.16 , 0.27 , 0.45 , 0.77 and 0.83). The jet regime is fixed at a Reynolds number R e = 35,000. The computational study shows that the application of nanoparticles enhances forced convection for all the simulations carried out. However, the influence of swirl number and nozzle-to-plate distance is not that clear. Variations cause different effects on the performance. For instance, to vary the swirl intensity at large nozzle-to-plate separation has different effect than in short separations. Also, some ranges of variation of swirl may enhance heat transfer whilst others may worsen it. [ABSTRACT FROM AUTHOR]

In this paper, the gas-liquid flow is comprehensively analyzed under different inlet gas void fractions, and the effect of tip leakage vortex (TLV) on the gas flow pattern in multiphase pumps is revealed. The results show that the gas flow pattern in an impeller is closely related to the centrifugal force, low-pressure region, and vortex motion. Most gas is present near the hub and suction surface of the blade as well as in the TLV. The two- and three-dimensional spatiotemporal evolution of the gas is presented, and the gas motion during the inception, development, and dissipation of TLV is revealed. It is reflected that the gas volume fraction is the highest at the TLV core and gradually weakens along the radial direction with the vortex core at the center. Additionally, the TLV energy dissipation is closely related to the gas and pressure difference, and strong energy dissipation occurs in the jet-wake flow.