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Liquid hydrogen plays a critical role in large-scale hydrogen storage and long-distance transport. The primary cost associated with liquid hydrogen supply is attributed to the liquefaction consumption. The hydrogen turbo-expander, a pivotal component in industrial hydrogen liquefaction plants, is instrumental in determining liquefaction costs. Improving the efficiency of the expander offers a significant opportunity for cost reduction. This paper commences by validating the loss model employed to assess the hydrogen turbo-expander using numerical simulation results. Subsequently, a regional division model is introduced for the expander impeller passage to identify the locations of various losses. Under diverse operational conditions, the boundaries of regions are determined through a comparison between the loss model and numerical simulation. Finally, an examination of losses in the hydrogen turbo-expander is conducted using Computational Fluid Dynamics (CFD) results under varying operating conditions, yielding the following insights. With an increase in the expansion ratio of the hydrogen turbo-expander, the isentropic efficiency initially rises and then declines. Among the various losses observed under variable working conditions, incidence loss emerges as the most critical factor. When the expansion ratio is small, a negative attack angle forms at the impeller inlet, causing chaotic flow within the channel and an increase in passage loss. • Correlations in loss model are validated for hydrogen turbo-expanders. • The proposed regional division model enables a quantitative loss analysis. • Efficiency decays more severely with the expansion ratio lower than design value. • Incidence loss is the primary driver for efficiency decline far from design condition. [ABSTRACT FROM AUTHOR]

The consumption of aquaculture products and, in turn, the importance of the aquaculture industry are increasing with the depletion of global fishery resources. In the flow-through aquaculture systems used in Korea, olive flounders are overcrowded near the central outlet, causing stress, and the sharp central outlet hole injures the olive flounders. Therefore, in this study, we propose a central outlet cap that can prevent overcrowding and injuries in olive flounders near the central outlet in a flow-through aquaculture system. An L27(35) orthogonal array was constructed using five central outlet cap design variables, and computational fluid dynamics (CFD) analysis was performed for each experimental point. The pressure drop between the tank inlet and the central outlet was evaluated, and the experimental point with the highest pressure drop was identified. In addition, the internal fluid velocity of the experimental point with the highest pressure drop value was confirmed to be improved compared to the initial flow-through aquaculture system. The central outlet cap designed in this study is expected to be economically beneficial to aquaculture by reducing the overcrowding of olive flounder and preventing injury to olive flounder while improving the internal fluid velocity. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the critical suction velocity required for lifting sediment off the bed under hydrosuction. Flow characteristics below the suction pipe under unbound and bound conditions were studied experimentally and numerically, and the effects of various parameters on the critical suction velocity, such as suction pipe diameter, suction discharge, suction inlet height, and sediment size, were investigated. The results showed all the parameters significantly affect the critical suction velocity, with suction inlet height being the most influential. Unbound and bound conditions yielded divergent flow characteristics beneath the suction pipe, revealing distinct flow patterns. Interdependency among the parameters affecting critical suction velocity have been studied statistically, and empirical relations are developed to compute the critical suction velocity, its resultant centerline velocity, and the associated flow profile. A proposed relation for critical suction velocity showcased a ±10% error margin, while equations computed resultant centerline velocities and flow profiles with ±15% accuracy, representing satisfactory agreement. These findings can also be helpful in designing efficient suction systems in various sediment-laden water environments. Practical Applications: The current study on hydrosuction sediment removal presents practical solutions for addressing the persistent challenge of reservoir sedimentation. Hydrosuction is an efficient and cost-effective method of sediment removal with minimum disturbance to the connecting structures and surrounding ecosystem and aquatic life, ensuring sustainable reservoir management. The study focuses on providing detailed insight into the behavior of the flow below the suction pipe under varying conditions, which is responsible for sediment movement during hydrosuction. The study also investigates the minimum suction velocity required to lift the sediment off the bed surface. Applicability of hydrosuction is not limited to the desilting of a reservoir; it also holds potential for various applications in multiple fields, such as river and canal restoration, dredging of navigational channels, irrigation canal cleaning, dewatering and slurry removal, contaminant cleanup, trench excavation, flood control, and wastewater management. [ABSTRACT FROM AUTHOR]

The long-term effects of the centrifugal force of water flow in a curved river channel result in the scouring of the concave bank and the silting of the convex bank. This phenomenon significantly impacts the stability of bank slopes and the surrounding ecological environment. A common hydraulic structure, the spur dike, is extensively employed in river training and bank protection. Focusing on a 180° bend flume as the research subject, this study examines the effects of spur dike placement on the concave bank side of the bend. To this end, a second-order accurate computational format in computational fluid dynamics (CFD) and the RNG k-ε turbulence model were employed. Specifically, the influence mechanism of the pick angle and the river-width-narrowing rate on the flow dynamics and eddy structures within the bend were investigated. The results indicated that both the river-width-narrowing rate and pick angle significantly influence the flow structure of the bend, with the pick angle being the more dominant factor. The vortex scale generated by a positive pick angle of the spur dike is the largest, while upward and downward pick angles produce smaller vortex scales. Both upward and positive pick angles have larger areas of influence, and the maximum value of turbulent kinetic energy occurs at the back of the secondary spur dike. In contrast, the downward pick angle has a smaller area of influence for turbulent kinetic energy, resulting in a smaller vortex at the back of the spur dike and leading to smoother water flow overall. In river-training and bank-protection projects, the selection of the spur dike angle is crucial for controlling scour risk. The findings provide valuable insights for engineering design and construction activities. [ABSTRACT FROM AUTHOR]

A coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach is used to calculate the interaction of a flexible rag transported by a fluid current with a fixed solid cylinder. More specifically a hybrid Eulerian-Lagrangian approach is used with the rag being modeled as a set of interconnected particles. The influence of various parameters is considered, namely the inlet velocity (1.5, 2.0, and 2.5 m/s, respectively), the angle formed by the initially straight rag with the flow direction (45°, 60° and 90°, respectively), and the inlet position (90, 100, and 110 mm, respectively). The results show that the flow rate has a significant impact on the permeability of the rag. The higher the flow rate, the higher the permeability and the rag speed difference. The angle has a minor effect on rag permeability, with 45° being the most favorable angle for permeability. The inlet position has a small impact on rag permeability, while reducing the initial distance between the rag an the cylinder makes it easier for rags to pass through. [ABSTRACT FROM AUTHOR]

Kaplan turbines are widely utilized in low-head and large flow power stations. This paper employs Computational Fluid Dynamics (CFD) to complete numerical calculations of the full flow channel under different blade angles and various guide vane openings, based on 25 off-cam experimental working conditions. The internal flow characteristics of the runner blade and draft tube are analyzed, and a discriminant number for quantitatively assessing the flow uniformity of the draft tube is proposed. The results indicate that low-frequency and high-amplitude pressure pulsations occur on the high- and low-pressure edge of the blade when the opening is small, with pulsations decreasing as the opening increases. The inner flow line of the draft tube is disturbed when both the blade angle and opening are small. Additionally, the secondary frequency of the draft tube inlet is double that of the vane passing frequency. The discriminant number of the flow inhomogeneity approaches 0 under optimal flow conditions. The number increases continuously with the decrease in efficiency, and the flow in the three piers of draft tube becomes more nonuniform. The research results provide a reference for enhancing performance and ensuring the operational stability of Kaplan turbines. [ABSTRACT FROM AUTHOR]

The studies on vascular flows have increased in the last decade. In this work; we have focused on the effects of flow model and blood rheology on hemodynamics for a real-subject scan using Computed Tomography Angiography (CTA) during numerical solutions. Various vascular flow studies using Newtonian or non-Newtonian blood models were presented in the literature with laminar or turbulent flow assumptions. In this study; six different turbulent models (Realizable k- ε , Standard k- ε , SST k- ω , Standard k- ω , Transition k-kl- ω , Transition SST) were compared to laminar flow to show whether turbulent flow solution is necessary. Blood rheology was investigated by using five different non-Newtonian models (Carreau, Herschel–Bulkley, Carreau–Yasuda, Casson, Power-Law) in addition to Newtonian model to indicate whether non-Newtonian blood assumptions is necessary. The In vivo boundary conditions were utilized by the UDF code which defines the real-patient cardiac cycle obtained by Echocardiography (ECHO) to present hemodynamics in the study. The results show that laminar flow well matched with the four turbulent models and two models shows by 4.8% and 19.5% differences in Wall Shear Stress (WSS) according to laminar flow. When the blood rheology was investigated, results revealed significant differences in WSS by 25.7%, 8.7%, 22.4%, 12.3%, and 32.5% for the non-Newtonian models in the given order, respectively, compared to Newtonian assumption. It concluded that laminar flow solution could be effective instead of solving turbulent flows in terms of computational cost, however, non-Newtonian blood effects could be considered to determine critical hemodynamics levels in a normal aortic arc. [ABSTRACT FROM AUTHOR]

Injection mandrel is one of the key components to control the water injection rate of each layer in the layered injection process in the oilfield. The imbalance between the layers can be changed by an optimized injection mandrel to control the appropriate injection rate. This study introduces an approach to optimize water injection in oilfields, focusing on a new eccentric injection mandrel with adjustable flat nozzles. Firstly, computational fluid dynamics (CFD) simulations were carried out using FLUENT software to model and analyze the flow characteristics of the injection mandrel. The simulation results were validated through experimental comparisons, demonstrating excellent consistency. Secondly, the nozzle shapes were identified and optimized. The semicircle nozzle demonstrating superior regulation performance due to its smallest differential pressure and a robust linear relationship between flow rate and opening degree. Finally, orthogonal tests are designed for three influencing factors of the eccentric injection mandrel: number of injection holes, injection hole diameter, and nozzle shape. The simulation results show that the number of injection holes is 36, the diameter of injection holes is 3.2 mm, and the eccentric injection mandrel has relatively better performance. After optimization, the differential pressure between the inlet and outlet is reduced by 57.14%, and the average shear stress on the fluid is reduced by 3.88%. This innovative methodology, employing CFD simulations and orthogonal tests, offers precise water injection rate control, reducing water wastage, and optimizing energy consumption in water injection systems. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated that the flow characteristics of pressure waves in hydraulic experiments show two types of reflected waves: those with the same type pressure vibration trend and those with the opposite vibration trend, with the pressure amplitude equal to that of the original wave. Reflection characteristics in a simulation must be consistent with those found experimentally. To determine reasonable boundary conditions (BCs), the focus of this work was the simulation of pressure wave reflection under five combinations of BCs using computational fluid dynamics. Three three-dimensional simulation models were developed based on the k–ε turbulence model. Reflection characteristics were obtained under the different BCs. The results showed that the pressure boundary in the pipe simulated the reflected waves correctly. The reservoir was found to be more accurate than the pressure boundary, which reflected the slight fluctuation in the reflected wave. Both the wall boundary and the velocity boundary could be used to simulate valve operation. However, if intercepting part of the pipeline, the reflected wave showed phase advance and pressure amplitude attenuation compared with that at the same position in the original pipeline. This study is helpful for setting reasonable BCs in pressure wave simulations. [ABSTRACT FROM AUTHOR]

The Savonius hydrokinetic turbine (SHT) is widely used for generating electricity from running water. However, most optimization work has been carried out on conventional blades with similar concave and convex profiles. This study aims to enhance SHT performance by modifying the rotor blades' outer surface radius (0.079, 0.087 and 0.095 m) to create a semi-elliptical shape, thus reducing opposing forces. The tip speed ratio (TSR) varies from 0.5 to 1.3 with an interval of 0.1. A constant channel velocity of 0.8 m/s at Re = 2.25 x 105 is considered for the analysis. The flow field has been numerically investigated using the SST k - ω model. This study comprises the angular variation in the coefficients of power (Cp) and torque (Cm), performance curves of the rotor, and pressure distribution on the blade surface at different angular positions. It is observed that the rotor with a radius of 0.095 m has a maximum Cp value of 0.142, which is 7.57% and 18.33% higher than the Cp values of rotors with radii of 0.079 m and 0.087 m, respectively. The maximum power output of the rotor with a radius of 0.095 m is 2.32 W, whereas the power outputs of the rotors with radii of 0.087 m and 0.079 m are 2.16 W and 1.96 W, respectively. An increase in the instantaneous values of Cm between rotation angles 0° to 115° is observed, during which the returning blades mainly interact with the incoming stream. The pressure decreases as the radius of the semi-elliptical outer surface increases at rotor positions ranging from 0° to 225°, but it increases at rotor positions ranging from 270° to 315°. [ABSTRACT FROM AUTHOR]

The Savonius hydrokinetic turbine (SHT) is widely used for generating electricity from running water. However, most optimization work has been carried out on conventional blades with similar concave and convex profiles. This study aims to enhance SHT performance by modifying the rotor blades' outer surface radius (0.079, 0.087 and 0.095 m) to create a semi-elliptical shape, thus reducing opposing forces. The tip speed ratio (TSR) varies from 0.5 to 1.3 with an interval of 0.1. A constant channel velocity of 0.8 m/s at Re = 2.25 × 105 is considered for the analysis. The flow field has been numerically investigated using the SST k - ω model. This study comprises the angular variation in the coefficients of power (Cp) and torque (Cm), performance curves of the rotor, and pressure distribution on the blade surface at different angular positions. It is observed that the rotor with a radius of 0.095 m has a maximum Cp value of 0.142, which is 7.57% and 18.33% higher than the Cp values of rotors with radii of 0.079 m and 0.087 m, respectively. The maximum power output of the rotor with a radius of 0.095 m is 2.32 W, whereas the power outputs of the rotors with radii of 0.087 m and 0.079 m are 2.16 W and 1.96 W, respectively. An increase in the instantaneous values of Cm between rotation angles 0◦ to 115◦ is observed, during which the returning blades mainly interact with the incoming stream. The pressure decreases as the radius of the semi-elliptical outer surface increases at rotor positions ranging from 0◦ to 225◦, but it increases at rotor positions ranging from 270◦ to 315◦.

The plunger valve has an important role in a large compressor system as its operating characteristics directly affect the aerodynamic boundary condition of the compressor equipment. In this study, dynamic modeling and analysis method of the plunger valve are proposed for an accurate control of the system. By considering the interaction between the dynamic flow in the valve and actuator action, a lumped parameter model for the fluid-structure interaction force and multibody dynamic model of the actuator are developed based on intrinsic correlation parameters. A combination analysis to simultaneously predict valve flow and actuator dynamic characteristics is proposed. The predicted results are in a good agreement with experimental data, which validates the proposed model and analysis method. The analysis results show that the coupling effect between the valve flow and actuator is significant and has an important role in valve control, particularly when the valve opening is smaller. Compared to the experimental data and computational fluid dynamics results, the presented methods are accurate for valve control and effective for prediction of flow rate. [ABSTRACT FROM AUTHOR]

The rotor of a high-power water-filled submersible motor rotates at high speed in liquid during operation. while working motor internal air gap fluid flow in complicated cases, fluid flow characteristics is not only directly affect the water of the rotor friction loss, also affect the submersible motor cooling effect. In this paper, the fluid field in the inner cavity of submersible motor is deeply studied. The air-gap fluid grid model was established according to computational fluid dynamics, and the influence of air-gap on fluid velocity of submersible motor was studied based on ANSYS and FLUENT software. The results show that the pressure decreases linearly after the cooling water enters the motor air gap, the maximum pressure is located at the air gap inlet and the minimum at the air gap outlet; the outlet and inlet pressure of the air gap fluid grows with the increase of the air gap inlet fluid flow rate, and the growth rate tends to decrease in different degrees. The research results provide a basis for the design of submersible motor and the determination of the reasonable flow of fluid in the motor. [ABSTRACT FROM AUTHOR]

Microchannels are small-scale channels with unique properties that make them useful in various fields, such as electronics, biomedical engineering, and chemical engineering. This research paper investigates the effect of microchannel geometry on fluid flow behavior at different values of the Reynolds number. A rectangular microchannel with a pattern of obstructions and water as the working fluid was used in this study. Computational fluid dynamics (CFD) simulations were used to investigate the impact of different channel geometrical configurations and different values of the Reynolds number on fluid flow behavior. The results showed that the channel geometrical configuration and the Reynolds number significantly affect fluid flow behavior. A geometry with increasing obstruction heights led to higher values of pressure drop than the geometry with decreasing obstruction heights. This study provides valuable insights into microchannel flow behavior and can be used for the development of optimized microchannel designs for diverse applications. [ABSTRACT FROM AUTHOR]

In order to promote the development of new power systems and the consumption of clean energy, pumped storage hydropower stations tend to become increasingly larger in capacity and higher in head height. In this paper, a three-dimensional model of the full channel of a high-head pump turbine is established, and the influence of the gap thickness between the runner crown and the headcover on the internal flow field characteristics, pressure fluctuation characteristics and axial water thrust are studied by means of computational fluid dynamics (CFD). The results indicate that the area where the pressure and velocity vary greatly in the flow field of the crown clearance is at the seal of the labyrinth ring. In addition, the pressure balance pipe has a greater impact on the pressure and flow rate of the water passing through the clearance, and the crown clearance near the pressure balance pipe generates a vortex, resulting in energy loss. Decreasing the thickness of the clearance has no obvious effect on the pressure on the flow-passing components, and increasing the thickness of the clearance has a great change in the pressure values at the upper crown inlet, in front of the labyrinth ring of the crown and in front of the labyrinth ring of the band. The upper part of the vaneless area, the crown inlet and the lower ring inlet are close to the runner; hence, the interference from the rotating parts is the strongest. The effect of increasing the thickness of the crown clearance on the axial water thrust is greater than that of decreasing the thickness of the crown clearance. The pulsation frequency of the axial thrust on the crown, band and blade and the resultant force of the axial thrust increase with the increase in the crown clearance thickness. [ABSTRACT FROM AUTHOR]

The flow parameters through complex-type bridge piers configured in various geometries were explored and compared in this work using dye visualisation and computational fluid dynamics (CFD) methods. The Detached Eddy Simulation (DES) technique based on the SST k omega model has been chosen to investigate the flow characteristics around complex bridge piers, and time-averaged normalised mean streamwise velocity, time-averaged normalised mean cross-stream velocity, time-averaged normalised mean pressure, time-averaged normalised mean Reynolds shear stress, time-averaged normalised mean y vorticity, time-averaged normalised mean z vorticity, and drag coefficient have been selected as parameters for this study. According to the study's findings, when the time-averaged normalised mean streamwise velocity component of all complex bridge piers was examined, the pile sections had the highest values. Drag coefficients have been sorted from low to high when comparing complex bridge piers in all geometries such as elliptical, circular, rectangular, and square. Article Highlights Flow characteristics around complex bridge piers Dye visualisation experiments and CFD method with DES based on the SST k omega model Drag Coefficients of complex bridge piers [ABSTRACT FROM AUTHOR]

In this paper, the flow characteristics induced by a cubic artificial reef with diversions (DCAR) were investigated using computational fluid dynamics (CFD). The results showed that the design of a DCAR can greatly improve the flow field range compared to typical cubic artificial reefs. The upwelling volume of the DCAR was more than 16 times that of a typical cubic artificial reef. The flow field effect produced the best results when the cut-opening ratio (COR) was 0.1–0.2 with constant flow. The parameters of the upwelling and back vortex increased with an increase in the flow velocity, and it decreased with an increase in the COR. The drag coefficient was less affected by the flow velocity, which remained between 1.32 and 1.44. The new type of artificial reef can improve the flow characteristics around the reefs. [ABSTRACT FROM AUTHOR]

In this paper, an improved RSM-CFD method is used to optimally design a mixed turbine of non-equilibrium condensing steam (NECS) and hydrogen (H2), of which the response surface method (RSM) and computational fluid dynamics (CFD) are coupled to take into account the effects of the wet steam non-equilibrium condensation process of the multimixed working fluid. A single-stage H2/Steam (NEC)-mixed turbine was developed based on the improved RSM-CFD, and the effect mechanism of the H2 component ratio (ωH2) on the flow characteristics, internal power, and isentropic efficiency within the turbine stage were investigated. The results show that the isentropic efficiency (η) increases with the increase in the hydrogen component ratio (ωH2), since hydrogen, as a non-condensable component, can inhibit the nucleation and growth of steam, reducing the pressure pulsation on the blade surface; furthermore, it accelerates the transport and diffusion of liquid droplets, inhibits the flow separation, and reduces the flow loss in the flow channel. However, the internal power of the turbine (P) tends to decrease with increasing ωH2, since the increase in hydrogen reduces the pressure difference on the blade and lowers the torque of the fluid acting on the blade, and at the same time, the vortex and radial flow intensify, and the enthalpy drop inside the stage decreases. On this basis, the optimum operating conditions are found where the hydrogen component ratio (volume percent) ωH2 = 53%. Accordingly, the hydrogen component ratio should be maintained in the range of 38–68%, considering the work capacity and hydrogen yield of the mixed working fluid. [ABSTRACT FROM AUTHOR]

The hydraulic and anti-clogging performance of irrigation emitters are mainly governed by the internal flow characteristics in the flow channel. Computational fluid dynamics (CFD) and experiments were used to analyse internal flow characteristics and determine the key structural parameters of a stellate labyrinth channel irrigation emitter. Through experimental verification, the realisable k - ε model provided the best results for simulating the flow field. Five structural parameters of stellate labyrinth channel emitter were selected to study the influence on the flow characteristics inside the flow channel comprehensively. The velocity fields and profiles are presented along the stellate labyrinth channel. Turbulence properties and turbulent kinetic energy of flow inside the stellate labyrinth channel are analysed and discussed. The vortex zones consume energy and promote the deposition of particles. The swirling motion zone in stellate labyrinth channel emitter flow channel must be described to analyse flow characteristics. The advanced Q -criterion method was applied to identify and characterise the vortex zones in the stellate labyrinth flow channel. Through analysis results of the influence of different structural parameters on velocity fields, turbulence properties, and swirl characteristics, it was shown that a , r , h , and θ are main structural parameters that affect the flow characteristics in stellate labyrinth channel irrigation emitter. The results of this study provide references for the design theory of the new types of flow channel emitter. • The Realisable k - ε model provides best result for simulation. • Velocity fields and profiles are presented along the stellate labyrinth channel. • Turbulence properties of flow inside are analysed and discussed. • An advanced method is applied to identify and characterise the vortex zones. • The main structural parameters that affect flow characteristics are determined. [ABSTRACT FROM AUTHOR]

This editorial discusses the importance of Advanced Fluid Machinery in the sustainable development of energy. Fluid machinery is crucial in many engineering applications, including aerospace, civil, mechanical, and chemical engineering. This Special Issue, entitled "Optimization and Flow Characteristics in Advanced Fluid Machinery", features several research articles exploring flow characteristics and optimization in fluid mechanics. The authors present innovative ideas, methodologies, and techniques to advance the field of fluid mechanics. The papers cover a wide range of topics, including computational fluid dynamics (CFD), turbulence modeling, heat transfer, multiphase flow, and fluid–structure interactions. The articles featured in this Special Issue also investigate the relevant hydrodynamic attributes of turbomachinery, high-pressure jets, marine propulsion systems, and internal combustion engines to a considerable extent, significantly expanding the scope of research within the Special Issue. [ABSTRACT FROM AUTHOR]

Accurate prediction of the flow characteristics in low-permeable porous media is of great importance for achieving efficient geo-energy development as well as gas geological storage practices. Due to the microscale and complex geometry of the formation structures, mechanistic studies on the flow behavior in low-permeable porous media have arisen as a challenging research topic. In this paper, a pore-scale numerical study is carried out concerning the seepage characteristics in the low-permeable Berea core. After extracting the complex pore structure from the high resolution CT images, a novel methodology is proposed to screen the simulation representative elementary volume (REV), on which the fluid flow characteristics in the low-permeable pore media are scrutinized with help of the comprehensive Computational Fluid Dynamics (CFD) software. The roughness effect, which becomes significant in microscale pore channels, is taken into account for the permeability result corrections. Based on good agreement between the pore-scale simulation and the macroscale measurement results, the capability of the proposed CFD workflow on the study of the seepage characteristics in low-permeable porous media is well demonstrated. [ABSTRACT FROM AUTHOR]

The aerodynamic forces on road vehicles and flow structures around them result from complex interactions between fluid and structure. Ahmed body is a simplified car model created to demonstrate and simplify the flow around real-size ground vehicles. In this study, the flow structure on the wake region of Ahmed body with different slant angles (ϴ=15°, 25°, and 35°) was investigated. Experimental studies were conducted in a water channel by Particle Image Velocimetry (PIV). The freestream velocity was set to 0.2 m/s, and the Reynolds number defined by the characteristic length of the Ahmed body was 4.16×104 for Computational Fluid Dynamics (CFD) and PIV experiments. CFD simulations were performed using three different turbulence models: realizable k-ϵ, RNG k-ϵ, and SST k-ω, and the results were compared to experiments. The results are presented with different flow features such as time-averaged velocity vectors and velocity contours, streamline topology, vorticity, and Turbulence Kinetic Energy. The closest results to the experiments were obtained by the SST k-ω turbulence model for all slant angles of the Ahmed body. In addition, the drag coefficient is found to be 0.37 for all slant angles analyzed by SST k-ω turbulence models, which are also close to the results in the literature. [ABSTRACT FROM AUTHOR]

In situ pressure-preserved coring (IPP-Coring) is one of the most efficient methods for identifying the scale of the oil and gas content. However, the differential motion assembly of the IPP-Coring system often undergoes ball and ball seat seal failure and sticking due to surface erosion, and a greater pressure drop may unexpectedly trigger the assembly. This paper addresses these issues by improving the hydraulic structure of an assembly based on a deep understanding of the flow characteristics in the assembly, thus increasing the success rate of the IPP-Coring. Computational fluid dynamics (CFD) was employed to investigate flows in a differential motion assembly. The effects of the diameter and outlet structure of the ball seat on the fluid status, velocity, and pressure distribution were thoroughly analyzed. When the ball seat diameter increased from 30 to 40 mm, the maximum velocity and pressure drop decreased to 0.55 and 0.2 times their original values, respectively. There was a severe vortex area in the differential motion assembly due to the presence of the ball seat, but changing the outlet structure in the ball seat to an arc structure decreased the length of the vortex area and the fluid velocity near the wall to 0.7 and 0.4 times, respectively, compared with those with the original right-angled structure. In addition, the pressure drop decreased to 0.33 times the original value. Thus, the hydraulic structure of the assembly was improved, and a 40 mm diameter ball seat and an arc-shaped ball seat outlet were selected. Particle trajectory and erosion calculation results showed that the improved structure has a lower particle velocity and less impact on the wall, and the average erosion rate is only 0.42 times the value of the original structure. Due to the better erosion resistance and smaller pressure drop, the improved structure shows promise for field performance. [ABSTRACT FROM AUTHOR]

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The study focuses on heat transfer performance and flow structure associated with swirling jet on a flat target surface. The analysis is carried out with helicoid inserts of swirl number S = 1.3 by varying the number of vanes with Reynolds number between 11200 and 35600. The comparison of swirling jet with circular jet is carried out on its heat transfer performance. The heat transfer and flow structure are visualized using thermo-chromic liquid crystal sheet and oil film technique respectively. The numerical simulation is also performed at Re = 24700 for H/D distance between 1 and 4 using computational fluid dynamics. The heat transfer results reveal that the presence of axial recirculation zone at Re = 29800 and 35600 for the triple helicoid affects the uniformity of heat transfer distribution at 0 < X/D < 1.5 at H/D = 3. The axial component of velocity with respect to swirling jet is less than zero in the stagnation area and it increases at 0.57 < r/D < 0.97 for single vane and 0.63 < r/D < 0.97 for double and triple vanes. While the steep increase in tangential velocity of the triple vane jet is apparent at 0 < r/D < 0.5 at H/D = 2 and 3, the maximum value of point radially shifts inward towards the jet. The location of maximum turbulent kinetic energy approaching the surface at about r/D = 0.9 - 1.2 which characterizes the swirling jet at H/D = 2. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) computational fluid dynamics (CFD) approach is developed to elaborate the water-hammer pipe flow and 3D detailed dynamic characteristics of a closing ball valve. The proposed CFD approach considers the water compressibility and the viscous sublayer, which are sometimes neglected in previous studies. Comparisons of the CFD results, the measured pressures and the one-dimensional results, demonstrate that the current 3D CFD approach better reproduces the experimental pressure oscillations while helping to visualize the associated physical processes and to further explore the 3D transient characteristics. The mean velocity distributions in the radial direction significantly change as the pipe transient progresses, which is closely associated with transient shear stress. Mean velocity variations at the valve during the closing process undergo three distinct stages: slight change, then drastic reduction, and finally slowing down. Head loss coefficient and discharge coefficient of the valve change as the valve closing time shortens. HIGHLIGHTS The 3D dynamic flow characteristics in pipe transients are studied systematically.; Further analysis of the ball-valve characteristics under static and dynamic conditions carried out by 3D CFD simulations.; The effects of closure time on head loss coefficient and discharge coefficient are investigated.;

Currently, computational fluid dynamics has become the primary method for analyzing the fluid flow state inside the machine. Herein, the Ansys Fluent software is used to design a more effective oil‐field device, namely, a gas–liquid cylindrical cyclone (GLCC)‐horizontal combined separator. The characteristics of gas–liquid mixed flow, fluid turbulence intensity, and phase volume fraction distribution are analyzed, and the factors affecting the gas–liquid separation efficiency are evaluated under various working conditions. The results show that low gas–liquid separation efficiencies are obtained at inlet liquid ratios (liquid proportion in fluid) of both 30% and 70% in GLCC. After the fluid enters the separator, the maximum level of turbulence in the collision area increases from 2.458 to 3.033 m2/s2 as the inlet liquid ratio is increased from 30% to 70%, with the generation of oil–water and gas–liquid stratification at the back. Furthermore, the maximum gas holdup in the liquid outlet increases from 7% to 12% to 25% as the liquid ratio is increased from 30% to 50% to 70%. With throttling at a liquid ratio of 70%, the maximum gas holdup is again close to 14%. [ABSTRACT FROM AUTHOR]

In this research, the impermeable spur dike combined with grouped piles were arranged as two spur dike patterns (L and T), and the corresponding flow and turbulence characteristics in a rectangular open channel flow were investigated using a computational fluid dynamics (CFD) numerical approach based on the standard k - ε model. The patch lengths of the grouped pile were varied between 0.2 and 0.6 m around the impermeable spur dike, and the flow and turbulence behavior near the spur dike tip, in the mainstream, and on both banks of the channel were observed. When the patch length of grouped pile increased to 0.6 m, the increasing trend of mean streamwise velocity at the downstream was reduced up to 5% in the left bank, 52% in the right bank, and 8% in the mainstream. The tip of the spur dike turbulence intensity (T.I), turbulence kinetic energy (TKE), and mean streamwise velocity reduction were 19%, 35%, and 12%, respectively. The results revealed that both the spur dike patterns (L and T) are useful to protect the riverbanks and the spur dike tip suffering from higher velocities and turbulence effects comparing with the typically impermeable spur dike. [ABSTRACT FROM AUTHOR]

• Reducing decreasing JPCR's area ratio, HC intensity can be effectively enhanced. • A greater area ratio in JPCRs extends the operating range with a higher limit ratio. • In disinfection and algae control field, JPCR has a broad application prospect. Hydrodynamic cavitation (HC) has emerged as a promising technology for water disinfection. Interestingly, when subjected to specific cavitation pressures, jet pump cavitation reactors (JPCRs) exhibit effective water treatment capabilities. This study investigated the cavitation flow and vorticty transport in a JPCR with various area ratios by utilizing computational fluid dynamics. The results reveal that cavitation is more likely to occur within the JPCR as the area ratio becomes smaller. While as the area ratio decreases, the limit flow ratio also decreases, leading to a reduced operational range for the JPCR. During the cavitation inception stage, only a few bubbles with limited travel distances are generated at the throat inlet. A stable cavitation layer developed between the throat and downstream wall during the limited cavitation stage. In this phase, the primary flow carried the bubbles towards the outlet. In addition, it was found that the vortex stretching, compression expansion, and baroclinic torque terms primarily influence the vorticity transport equation in this context. This work may provide a reference value to the design of JPCRs for water treatment. [ABSTRACT FROM AUTHOR]

In this study, Computational Fluid Dynamics software (ANSYS Fluent) is used to investigate the turbulence and flow characteristics around spur dike in an open channel. After validating the numerical model with the experimental results, the spur dike was made permeable by providing staggered pores of varying permeabilities (22%, 37%, and 52%). Additionally, the pores angle was also varied (0°, 15°, 30°, and 60°) in order to elucidate the extent of flow diversion from the spur dike field towards the main channel. The flow characteristics around permeable spur dike are compared, including velocity distribution, reattachment length, roughness coefficient (n), turbulence kinetic energy (TKE), turbulence intensity (T.I), and wall shear stress. The results of turbulence and flow characteristics showed an improvement in the use of permeable spur dikes (0°) compared to impermeable spur dikes. The efficiency and controlled range of these results were further enhanced and achieved, while the permeability with increasing pore angles is used. When pore angle of spur dike increased to 60°, the increasing trend of mean streamwise velocity at the downstream (d/s) was reduced up to 25% and at the tip of the spur dike TKE, T.I, and mean streamwise velocity reduction were 22%, 15%, and 4%, respectively. This research recommends that a permeable spur dike with pores angle is ideal for protecting the tip of spur dike, riverbanks, and aquatic habitat during extreme floods. It also reduces reattachment length (br) and roughness coefficient (n). [ABSTRACT FROM AUTHOR]

To improve the flow characteristics of diesel engines with twin intake ports, this study evaluates the installation of guide vanes of varying lengths, heights and angles in front of the intake runner of a CA4DD diesel engine. Considering the interference among various parameters of the guide vane, the parameters were studied with uniform design. To study the effect of guide vanes on the twin-intake diesel engine during the intake stroke, 9 guide vane models, where the vane lengths were 30–70 mm, the vane heights were 1.5-13.5 mm, and the vane angles were 4-36°, were compared with a base model without a guide vane. CATIA was used to build a simulation model, and XFLOW was used to run a three-dimensional (3D) computational fluid dynamics (CFD) simulation. Simulation of different valve lifts of 2–10 mm in steps of 2 mm showed that the guide vane slightly affected the flow coefficient and obviously affected the swirl ratio. Furthermore, designs 4, 5 and 6 had different performance improvements under different valve lifts. The velocity and vorticity of the in-cylinder were evaluated. Moreover, 9 guide vane models were fabricated and tested on a steady-flow test bench. The experimental results show that the swirl ratio average increase of the guide vane models compared to the base model is 21%. The maximum increase is 39% when the guide vane height is 6 mm, the length is 65 mm, and the angle is 24°; when the guide vane height is 7.5 mm, the length is 50 mm, and the angle is 20°, the average increase is 27%. The flow coefficient is less affected and fluctuates at approximately 2%. Hence, the experiments and simulations in this work yield consistent results, and the application of guide vane models compared to a base model can improve the performance of diesel engines.

Low-aspect ratio wing planforms, such as delta wings, experience the predominance on their aerodynamic characteristics of large-scale leading-edge vortices separating around the leading edges. Due to their important application for highly maneuverable aircraft, the physical and aerodynamic understanding related to the vortex flow is of primary relevance. The investigation process is routinely performed with numerical simulations employing Reynolds-averaged Navier-Stokes equations. As the vortex grows in intensity, the limitation of ordinary models reduces the accuracy grade. Scale-resolving or more complex turbulence models can increase the accuracy, but the computational cost prohibits the application to a large envelope of cases. In the context of this work, the enhancement of a one-equation eddy-viscosity model is employed. The model is improved by formulating additional vortex source terms exclusively active inside the vortex-flow region and by employing a calibration procedure that is integrated into an iterative automated process where experimental data are used as targets for optimizing the model. The accuracy is enhanced for a cluster of cases around the calibration target, and it shows the potential of the application to large datasets that include several geometric and flow condition variations. [ABSTRACT FROM AUTHOR]

In situ pressure-preserved coring (IPP-Coring) is one of the most efficient methods for identifying the scale of the oil and gas content. However, the differential motion assembly of the IPP-Coring system often undergoes ball and ball seat seal failure and sticking due to surface erosion, and a greater pressure drop may unexpectedly trigger the assembly. This paper addresses these issues by improving the hydraulic structure of an assembly based on a deep understanding of the flow characteristics in the assembly, thus increasing the success rate of the IPP-Coring. Computational fluid dynamics (CFD) was employed to investigate flows in a differential motion assembly. The effects of the diameter and outlet structure of the ball seat on the fluid status, velocity, and pressure distribution were thoroughly analyzed. When the ball seat diameter increased from 30 to 40 mm, the maximum velocity and pressure drop decreased to 0.55 and 0.2 times their original values, respectively. There was a severe vortex area in the differential motion assembly due to the presence of the ball seat, but changing the outlet structure in the ball seat to an arc structure decreased the length of the vortex area and the fluid velocity near the wall to 0.7 and 0.4 times, respectively, compared with those with the original right-angled structure. In addition, the pressure drop decreased to 0.33 times the original value. Thus, the hydraulic structure of the assembly was improved, and a 40 mm diameter ball seat and an arc-shaped ball seat outlet were selected. Particle trajectory and erosion calculation results showed that the improved structure has a lower particle velocity and less impact on the wall, and the average erosion rate is only 0.42 times the value of the original structure. Due to the better erosion resistance and smaller pressure drop, the improved structure shows promise for field performance.

In this research, heat transfer of fuel oil flow through the buried pipeline in three regimes, turbulent, transition, and laminar conditions are investigated. A large-scale laboratory set-up is designed for this purpose and numerical modeling was also performed to study the effect of different parameters. The simulation is based on the fluid's thermophysical properties and the results are validated using experimental data. Due to the strong dependence of viscosity and density of fuel oil on the temperature, regime changes along the pipeline happens which complicate the calculation of friction factor. Using the experiment results and choosing different numerical methods, the acceptable model of friction factor in the transition zone for the experimental pipe and the real pipeline was achieved. Numerical simulation was performed on a 107 km pipeline using a powerful computer network to achieve the results. The approach which is used to simulate laminarization shows just a 3% discrepancy with experimental data. For the real pipeline, about 30 percent of the length is in transition mode from turbulent to laminar. The diameter of 26" is chosen as the most optimal size to transform 180000 barrels per day (BPD). According to the design thickness, diameter, and length of the pipeline, the maximum safe stop time (MSST) of the pipeline is 41 hours which is the most important data in the pipeline's maintenance period. Based on the present experimental data and simulation results, the optimal depth for the least heat loss from this pipeline is 0.9 to 2.7 meters. [ABSTRACT FROM AUTHOR]

The forming of helical coils using a rolling process results in geometrical irregularities (wrinkles and ovality) that are likely to influence the hydrodynamic behaviour of the flow field inside the coil in applications such as air generators. In this study, the above behaviour was investigated by experimental and numerical analyses considering the heat exchanger used in dry air generators. In experimental analysis, a three-turn copper helical coil with wrinkles and ovality was investigated to estimate the global hydrodynamic characteristics inside the helical coil. The results were compared with that of the ideal geometry of a coil without wrinkles and ovality. The effect of wrinkles was assessed through friction factor, and the corresponding equivalent surface roughness was found to increase by 5.7 times, owing to the presence of wrinkles in the helical coil. Numerical simulation was conducted to determine the pressure distribution, velocity distribution, and secondary flow inside the helical coil; the results were validated with experimental data. A critical portion of the helical coil with multiple wrinkles was considered for numerical simulation to investigate the localized effects of wrinkles on the flow field behaviour. The analysis in the vicinity of wrinkles revealed negative pressure development during flow, which in turn would cause re-circulation and cavitation that are undesirable. [ABSTRACT FROM AUTHOR]

Using perforated tube in exhaust mufflers is known to improve transmission loss (TL) by improving their sound pressure level (SPL) at the orifice. The perforated tube should affect the muffler performance analogous to a shell-and-tube heat exchanger. To the authors' knowledge, there are few previous assessments reported in literature of the effects that the perforated tube configuration has on acoustic response and pressure drop predicted. The effects of (i) the perforated tube length, (ii) the diameter of tube holes, and (iii) flow through perforated tube were investigated. To assess the perforated tube effect on flow, the SOLIDWORKS 2017 based on Computational Fluid Dynamics (CFD) tool was utilized using real walls approach model with a surface roughness of 0.5 micrometres (AISI 316 cold rolled stainless steel sheet (ss) Ra =0:5 μm). Perforated tube was found to cause back pressure which may increase SPL about 10%. [ABSTRACT FROM AUTHOR]

• The mathematical model of fluid–solid coupling is used for numerical calculation. • The distribution of the parameters of the annular fuel element with double-sided cooling is studied. • Analysis of flow heat transfer parameters for the annular fuel element flow channel. • Suitability analysis for existing empirical flow and heat transfer equations. • Development of new empirical relations for the friction factor and Nusselt number for the annular fuel element. Compared with conventional rod fuel elements, ring fuel elements have the advantage of high core power density and low fuel temperature. The study of their thermal and hydraulic characteristics is of significant importance. In this paper, computational fluid dynamics (CFD) is used to simulate the flow boiling in the annular fuel element based on the mathematical model of fluid–solid coupling. Parameters such as velocity field, temperature field and heat transfer coefficient of the flow channel were analyzed. The results show that the surface temperature of the solid fuel rod varies in a 90° cycle at the same position in the axial direction along the circumference. The heat transfer coefficient shows regular fluctuations along the flow direction. A new empirical equation for the heat transfer in the flow of the annular fuel element is also proposed, and the error of the predicted data is controlled within ± 3 %. [ABSTRACT FROM AUTHOR]

Ventricular assist devices or total artificial hearts can be used to save patients with heart failure when there are no donors available for heart transplantation. Blood pumps are integral parts of such devices, but traditional axial flow blood pumps have several shortcomings. In particular, they cause hemolysis and thrombosis due to the mechanical contact and wear of the bearings, and they cause blood stagnation due to the separation of the front and rear guide wheel hubs and the impeller hub. By contrast, the implantable axial flow, maglev blood pump has the characteristics of no mechanical contact, no lubrication, low temperature rise, low hemolysis, and less thrombosis. Extensive studies of axial flow, maglev blood pumps have shown that these pumps can function in laminar flow, transitional flow, and turbulent flow, and the working state and performance of such pumps are determined by their support mechanisms and flow channel. Computational fluid dynamics (CFD) is an effective tool for understanding the physical and mechanical characteristics of the blood pump by accurately and effectively revealing the internal flow field, pressure–flow curve, and shear force distribution of the blood pump. In this study, magnetic levitation supports were used to reduce damages to the blood and increase the service life of the blood pump, and a conical impeller hub was used to reduce the speed, volume, and power consumption of the blood pump, thereby facilitating implantation. CFD numerical simulation was then carried out to optimize the structural parameters of the conical axial maglev blood pump, predict the hemolysis performance of the blood pump, and match the flow channel and impeller structure. An extracorporeal circulation simulation platform was designed to test whether the hydraulic characteristics of the blood pump met the physiological requirements. The results showed that the total pressure distribution in the blood pump was reasonable after optimization, with a uniform pressure gradient, and the hemolysis performance was improved.

This paper takes a pump-turbine as the research subject and, based on the Computational Fluid Dynamics (CFD) numerical method and combined with test data, investigates the pressure fluctuation characteristics in the pump mode and analyzes the pressure fluctuation characteristics at 0.75 Qd, 1.0 Qd and 1.25 Qd when the guide vane opening is 17.5°. The results showed that the protruding frequencies of pressure fluctuation in the bladeless region were mainly 5 fn, 10 fn and 20 fn, and the main frequencies in the runner area and near the outlet wall of the draft tube were 16 fn and 5 fn, respectively. At different heights for the guide vanes, the pressure fluctuation in the bladeless region had significant differences, and the pressure fluctuation near the bottom ring was the most intense. The amplitude of the rotor–stator interaction frequency continuously attenuates from the bladeless region to the outlet of the stay vanes, and the amplitude attenuation of each frequency is mainly concentrated in the area of the guide vanes. In this paper, the influence of different flow rates on the pressure fluctuation in the pump mode is analyzed, which provides a theoretical reference for the stability and further study of pump-turbines. [ABSTRACT FROM AUTHOR]

• The flow characteristics in the two-stage series cyclone separator were simulated. • The separation performance was interpreted by analyzing particle distribution. • The two-stage cyclone separator was optimized using response surface methodology. Cyclones are generally operated in series when the efficiency of a single cyclone is not sufficient for the process. This study firstly used computational particle fluid dynamics (CPFD) to simulate the gas-solid two-phase flow characteristics in a two-stage series cyclone separator. The separation efficiency and distribution of energy consumption was interpreted by analyzing particle distribution characteristics. Secondly, the structure of the two-stage cyclone separator was optimized via response surface methodology (RSM) to make up for the disadvantage that the distribution of the separation load was non-uniform. The results showed that the grade efficiency for 3 μm of the first-stage cyclone separator was increased from 45.408% to 59.932% compared to the original model. The pressure drop of the first-stage cyclone separator is about 2.147 kPa while the second-stage cyclone separator is about 2.774 kPa. It can be seen that the overall optimized two-stage cyclone separator has the advantages of high efficiency, low energy consumption and load-balanced separation performance. [ABSTRACT FROM AUTHOR]

We investigated the flow characteristics in a tank of H/T = 1.5 stirred by a novel multi‐blade combined agitator (MBC) by using time‐resolved particle image velocimetry and large eddy simulation approach. The predictions were assessed by Y+ values, Taylor microscale and power spectrum analysis, as well as experimental validation of velocity distributions. Results demonstrate that the MBC agitator can load the energy into the system effectively with a power number of 12.5 in a turbulent regime, resulting in improved axial and radial mass exchange. The upper and lower short blades produce an axial down‐flow in the top half and an axial up‐flow in the bottom half, respectively. Part of axial flows change to radial flows by the radial pumping of the long blades, meanwhile, the impingement of two axial flows improves the axial mass exchange. These flow characteristics lead to an obvious improvement in the turbulent kinetic energy distribution uniformity with higher turbulent intensity. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of water–sediment inrush during coal mining, the characteristics of water–sediment flow in rock fractures were quantitatively analyzed by computational fluid dynamics (CFD). Based on the two-phase flow theory, a resistance model of water–sediment flow in fractures was established and verified by a laboratory-scale test. The results showed that: (1) With increases sediment particle diameter, volume fraction, and initial water phase velocity, the resistance of sediment particles grows gradually. (2) The drag force of sediment particles is mainly generated from the collision of the water phase and fracture wall. The velocity distribution of sediment particles can be divided into three stages, i.e., continuous increase, rapid decrease, and slow fluctuation. (3) The numerical model was shown to have high predictive accuracy by comparison with the test results. The model's predictive accuracy decreases with increased water phase velocity and decreases of the sediment particle diameter and volume fraction. (4) The smaller the fracture width, the larger the inclination and bending angles, and the greater the resistance of the two-phase flow in the fracture. Collisions between the particles and fracture wall cause velocity attenuation of the sediment particles. We propose water–sediment inrush prevention and control technology based on the numerical analysis results. [ABSTRACT FROM AUTHOR]

We investigate the flow characteristics around step-up street canyons with various building aspect ratios (ratio of along-canyon building length to street-canyon width, and upwind building height to downwind building height) using a computational fluid dynamics (CFD) model. Simulated results are validated against experimental wind-tunnel results, with the CFD simulations conducted under the same building configurations as those in the wind-tunnel experiments. The CFD model reproduces the measured in-canyon vortex, rooftop recirculation zone above the downwind building, and stagnation point position reasonably well. We analyze the flow characteristics, focusing on the structural change of the in-canyon flows and the interaction between the in- and around-canyon flows with the increase of building-length ratio. The in-canyon flows undergo development and mature stages as the building-length ratio increases. In the development stage (i.e., small building-length ratios), the position of the primary vortex wanders, and the incoming flow closely follows both the upstream and downstream building sidewalls. As a result, increasing momentum transfer from the upper layer contributes to a momentum increase in the in-canyon region, and the vorticity in the in-canyon region also increases. In the mature stage (i.e., large building-length ratios), the primary vortex stabilizes in position, and the incoming flow no longer follows the building sidewalls. This causes momentum loss through the street-canyon lateral boundaries. As the building-length ratio increases, momentum transfer from the upper layer slightly decreases, and the reverse flow, updraft, and streamwise flow in the in-canyon region also slightly decrease, resulting in vorticity reduction. [ABSTRACT FROM AUTHOR]

As global environmental problems are worsening, the efficiency of storage systems for renewable energy are gaining importance. The redox flow battery (RFB), a promising energy storage system (ESS), is a device that generates or stores electricity through reduction–oxidation reactions between active materials constituting electrolytes. Herein, we proposed a flow frame design that reduces flow resistance in the flow path and causes uniform flow distribution in the electrode to develop an efficient redox flow battery. Through computational fluid dynamics (CFD) and experimental verification, we investigated the flow characteristics and flow uniformity inside the conventional redox flow battery cell. An analysis of the flow characteristics of the conventional flow frame revealed a non-uniform distribution of the flow discharged to the electrodes, owing to the complex (branched) flow path geometry of the inlet channel. To address this problem, we proposed a new flow frame design that removed and integrated bifurcations in the flow path. This new design significantly improved flow uniformity parameters, such as the symmetry coefficient ( C s y m ), variability range coefficient ( R i ), and maximum flow rate deviation ( D m ). Ultimately, we decreased the pressure drop by 15.3% by reducing the number of flow path bifurcations and chevron repositioning. [ABSTRACT FROM AUTHOR]

This paper considers a solution to the serious problem of hydraulic maladjustment in a dynamic flow balance valve for small diameter and low-pressure drop working conditions. The pressure drop compensation coefficient revising method was proposed to optimize the profile line of the valve core variable opening area. The flow rates of the valve before and after optimization under different displacements were simulated using Computational Fluid Dynamics (CFD) methods. The flow control accuracy of the balance valve before and after the optimization is compared and analyzed to the test values. At the same time, the influence of three key parameters: spring stiffness, the shell structure of the valve core, and geometry imperfections change due to machining burrs on the surface of the valve core for flow control accuracy was discussed. The results show that flow control accuracy after optimization satisfies the requirements of 5% flow rate control. Spring stiffness, the shell structure of the valve core and machining burrs on the surface of the valve core are shown to have an influence on the flow rate of the balance valve. This is especially true for machining burrs which has a larger effect with an average error of 10.1. [ABSTRACT FROM AUTHOR]

• Cryogenic throttle valves for superfluid helium system were developed and numerically simulated. • Influences of cone angle, unilateral minimum clearance, structure type and working medium type on flow field distribution and flow characteristics of valve are studied. • Increasing the cone angle and unilateral minimum clearance enhances valve flow capacity, with the cone angle having a more pronounced impact. • Altering the spool type significantly alters the flow characteristics, whereas changing the working fluid type only affects the velocity and pressure within the valve. As one of the important methods to obtain superfluid helium, throttling has been widely used due to its simple equipment. The cryogenic throttle valve, serving as a vital component in the throttling process, directly impacts the performance of the superfluid helium system. In this study, velocity and pressure field inside valve is numerically simulated by using computational fluid dynamics (CFD), and the flow characteristics of the valve are analyzed by theoretical calculations and experiments. Moreover, influences of cone angle, unilateral minimum clearance, structure type and working medium type on flow field distribution and flow characteristics of valve are studied by altering structural parameters of spool and working medium. The results demonstrate that increasing cone angle and unilateral minimum clearance can enhance flow capacity of valves, but influence of cone angle is more obvious. Changing the spool type will significantly alter the flow characteristics of the valve, while changing the working fluid type will only affect the velocity and pressure inside the valve. [ABSTRACT FROM AUTHOR]

Flow control is essential in high-pressure CO 2 systems. Flow regulators are widely used for flow adjustment in piping systems. In this paper, a novel combinational flow regulator is proposed, which contains four parallel branch channels, and each channel is arranged with a solenoid valve and an orifice plate. In order to analyze the internal flow characteristics of high-pressure CO 2 and flow adjustment performance of the proposed flow regulator, a numerical model of the regulator is established, and the validation of numerical model is verified by experimental results. Then, the pressure and velocity characteristics are studied numerically. Finally, the flow adjustment performance is investigated numerically and experimentally from three aspects: variation of flow rate with differential pressure, variation of the product of flow coefficient and throttling area, and dynamic variations of pressure, temperature and flow rate of the flow regulator. This paper serves as a valuable reference for researchers utilizing flow regulators to adjust the flow rate of CO 2 or other fluids. • Numerical model of a novel flow regulator is established, verified by experiments. • Pressure and velocity characteristics are discussed, CO 2 as working medium. • Variation of flow rate with differential pressure and flow area is analyzed. • Dynamic working situation of the regulator is investigated by experiments. [ABSTRACT FROM AUTHOR]