Search

Reliable predictions of the flow rate and viscous dissipation in the melt conveying zone of single‐screw extruders are crucial for designing high‐quality and efficient extrusion processes. Full‐scale computational fluid dynamics simulations offer deep insights into the process, but they cover only specific use cases. Conversely, state‐of‐the‐art analytical approximation models suffer from a systematic error by neglecting channel curvature. To overcome these limitations, we employed a hybrid modeling approach that efficiently combines analytical, numerical, and data‐based techniques. First, the mathematical problem was formulated for a three‐dimensional, isothermal Stokes flow of power‐law fluids in curved channel segments of unit length, and the theory of similarity was applied to render it in a dimensionless form. Using the finite‐volume method, the flow problem was then solved numerically for a wide range of extrusion setups. Finally, by means of symbolic regression and genetic programming, three dimensionless approximation equations were derived from the numerical dataset. These regression models provide continuous and remarkably accurate predictions of both flow rate and viscous dissipation rate, and clearly outperform existing approximations due to the included effects of channel curvature. Implemented within screw design software, our novel regression models will enable faster progress in screw design and process troubleshooting. Highlights: Three‐dimensional flow of power‐law fluids in helical screw channelsGeneralized problem description using dimensional analysisMelt conveying simulations considering both curvature and flight effectsIntegration of process knowledge into symbolic regression modelingAnalytical screw characteristic curves with extended scope of validity [ABSTRACT FROM AUTHOR]

Introduction: In the circulatory system, the vessel branching angle may have hemodynamic consequences. We hypothesized that there is a hemodynamically optimal range for the renal artery's branching angle. Methods: Data on the posttransplant kinetics of estimated glomerular filtration rate (eGFR) were analyzed according to the donor and implant sides (right-to-right and left-to-right position; n = 46). The renal artery branching angle from the aorta of a randomly selected population was measured using an X-ray angiogram (n = 44). Computational fluid dynamics simulation was used to elucidate the hemodynamic effects of angulation. Results and Discussion: Renal transplant patients receiving a right donor kidney to the right side showed faster adaptation and higher eGFR values than those receiving a left donor kidney to the right side (eGFR: 65 ± 7 vs. 56 ± 6 mL/min/1.73 m2; p < 0.01). The average branching angle on the left side was 78° and that on the right side was 66°. Simulation results showed that the pressure, volume flow, and velocity were relatively constant between 58° and 88°, indicating that this range is optimal for the kidneys. The turbulent kinetic energy does not change significantly between 58° and 78°. Conclusion: The results suggest that there is an optimal range for the renal artery's branching angle from the aorta where hemodynamic vulnerability caused by the degree of angulation is the lowest, which should be considered during kidney transplantations. [ABSTRACT FROM AUTHOR]

This research evaluated permeability and hydraulic conductivity of Open Graded Friction Course (OGFC) in multiple directions. Using Computational Fluid Dynamics (CFD), Ansys Fluent was utilized to simulate the laminar flow model for twelve cubic specimens of OGFC with different geometry and various porosities. Reynolds number (Re), permeability (K), and hydraulic conductivity (k) were computed for each simulation horizontally and vertically. According to the study, the horizontal permeability measurements were greater than the vertical measurements. Moreover, the permeability of OGFC is governed by the percentage of the air voids, aggregate particle size, and the thickness of the specimens. As the diameter and percentage of air voids increased, the permeability increased. Specimens with large size of aggregates and larger thicknesses have the highest values of permeability, while specimens with the small size of aggregates have the lowest values of permeability. In addition, the velocity of the flow inside the voids decreased as the diameter and percentage of air voids increased, while the pressure increased, according to the study. [ABSTRACT FROM AUTHOR]

Aviation has wide aspects to challenge and discover, the ability to land and take off at slow speed, sudden increase in drag for short runway landings. This paper puts forth the solution by the use of adjustable multi slots configuration of an airfoil. In this case, the slots extend from the wing leading edge to trailing edge. This causes change in the chord, thereby changing the camber of unsymmetrical airfoil. An investigation was made to determine and compare the aerodynamic characteristics of multi slotted adjustable airfoil with un-morphed unsymmetrical airfoil at varied speeds and Angle of Attack (AoA). There are three slots distanced equally along the airfoil. The extension of these slots increases the chord length by 10% of total chord. The slotted and un-slotted airfoil profile are then studied using computational fluid dynamics of external flow over a body. The flow simulation is done at 10m/s, 20m/s, 30m/s, 40m/s and 50 m/s flow velocity and at 0, 3, 6, 9, 12, 15 AoA. The results were obtained for each case and the values for base and slotted model were compared. It was found that lift of slotted model is slightly higher than base model at low flow velocity. It was also seen that the use of slots at high speed causes a large amount of drag. This increased drag factor can be used in UAV's as spoilers during landing or for landing at shorter runways at lower speed, allowing a sudden decrease in aircraft speed and also to glide at a steeper angle over obstruction. [ABSTRACT FROM AUTHOR]

By exploring the effects of energy and velocity under different inlet speeds and abrasive concentrations, different inlet boundary conditions were selected for numerical analysis, and the intrinsic properties of the solid–liquid two-phase abrasive flow research and development calibre pipes were explored. The influence of law and process characteristics of solid–liquid two-phase abrasive flow is discussed. The fourth-order variable diameter pipe is taken as the research object. It is concluded that the inlet velocity is increased, the total energy and kinetic energy of the abrasive grains are also increased, and the total energy and kinetic energy are increased. The more intensely the abrasive grains collide with the workpiece wall, the more favourable is the effect of the abrasive flow on the wall surface finishing, and the increase of the abrasive concentration. The number of collisions of the disordered abrasive grains on the wall surface is increased, which is more conducive to the wall surface. The finishing process provides theoretical reference and technical support for the engineering application of solid–liquid two-phase abrasive flow.

Smoothed particle hydrodynamics (SPH) is a meshfree, Lagrangian, particle method, which combines the advantages of Euler and Lagrangian method and has special advantages in simulating violent non-linear fluid–structure interaction problems. In this study, an improved SPH method is used to simulate four fluid–structure interaction cases. Firstly, the violent flow in the mould filling process is simulated to validate that the SPH model can obtain accurate flow patterns with any complex solid boundaries. Secondly, the dam-break flow against a vertical wall is simulated, and the pressure curves are compared with the experiment. Then liquid sloshing problems under different external excitations are simulated, and the complex coupling characteristics can be captured. Finally, the interactions between fluid and floating bodies are researched. The obtained numerical results show good agreement with the results from other sources, and clearly demonstrate the effectiveness of the presented SPH method in modelling fluid–structure interaction problems.

The Reynolds‐averaged Navier–Stokes (RANS) method coupling with the actuator disc model (ADM) is considered as a promising numerical simulation technology of wind turbine wake, and it is widely utilised in the aerodynamics of wind turbines and optimal layout of wind farms. The k−ε turbulence model is widely adopted, among the RANS‐based turbulence models. However, the k−ε turbulence model easily overestimates the turbulence viscosity in the wake, which results in fast recovery of wake velocity and failure in wake forecasting. In addition, ADM with the oversimplified geometrical structure ignores the effects of nacelle and tower on the wind turbine wake, which further lowers the accuracy of wake simulation. Therefore, the numerical simulation of wind turbine wake based on the extended k−ε turbulence model of EI Kasmi coupling with ADM considering nacelle and tower is proposed. Comparing the results of Marchwood Engineering Laboratories (MEL) ABL wind tunnel measurements and TNO wind tunnel experiments, it has been found that the proposed model improves the simulation effect for the near wake and has a certain contribution to the wake prediction accuracy overall. [ABSTRACT FROM AUTHOR]

Aviation has wide aspects to challenge and discover, the ability to land and take off at slow speed, sudden increase in drag for short runway landings. This paper puts forth the solution by the use of adjustable multi slots configuration of an airfoil. In this case, the slots extend from the wing leading edge to trailing edge. This causes change in the chord, thereby changing the camber of unsymmetrical airfoil. An investigation was made to determine and compare the aerodynamic characteristics of multi slotted adjustable airfoil with un-morphed unsymmetrical airfoil at varied speeds and Angle of Attack (AoA). There are three slots distanced equally along the airfoil. The extension of these slots increases the chord length by 10% of total chord. The slotted and un-slotted airfoil profile are then studied using computational fluid dynamics of external flow over a body. The flow simulation is done at 10m/s, 20m/s, 30m/s, 40m/s and 50 m/s flow velocity and at 0, 3, 6, 9,12, 15 AoA. The results were obtained for each case and the values for base and slotted model were compared. It was found that lift of slotted model is slightly higher than base model at low flow velocity. It was also seen that the use of slots at high speed causes a large amount of drag. This increased drag factor can be used in UAV's as spoilers during landing or for landing at shorter runways at lower speed, allowing a sudden decrease in aircraft speed and also to glide at a steeper angle over obstruction. [ABSTRACT FROM AUTHOR]

The excess hydraulic pressure in water supply network pipes is one of the major problems in design and implementation stages of these projects. To reduce the excess pressure and maintain network safety, a variety of pressure reducing valves are used, which waste all the excess pressure. However, having used the appropriate water microturbines, while reducing the pressure loss to an optimum value, the system could recover the wasted energy. In this study, numerical simulation and experimental investigation of microturbine in a water supply system have been performed to evaluate the electrical power generation capacity of an over‐pressured network. The numerical simulation of the microturbine was conducted using Ansys‐Fluent software. The microturbine has been experimentally investigated with different inlet flow rates, the effect of different post‐microturbine heads and also the effect of different opening angles of guide plate on its performance, three different scenarios were defined. Based on numerical simulation and laboratory results, the best performance of the microturbine was obtained when the inlet flow rate was 0.01184 m3 /s and also opening angle 20° for the guide plate, in which the microturbine output was equal to 59.01 W. The generated power by the microturbine can meet the electrical needs of sensors and other network monitoring equipment. [ABSTRACT FROM AUTHOR]

By exploring the effects of energy and velocity under different inlet speeds and abrasive concentrations, different inlet boundary conditions were selected for numerical analysis, and the intrinsic properties of the solid–liquid two-phase abrasive flow research and development calibre pipes were explored. The influence of law and process characteristics of solid–liquid two-phase abrasive flow is discussed. The fourth-order variable diameter pipe is taken as the research object. It is concluded that the inlet velocity is increased, the total energy and kinetic energy of the abrasive grains are also increased, and the total energy and kinetic energy are increased. The more intensely the abrasive grains collide with the workpiece wall, the more favourable is the effect of the abrasive flow on the wall surface finishing, and the increase of the abrasive concentration. The number of collisions of the disordered abrasive grains on the wall surface is increased, which is more conducive to the wall surface. The finishing process provides theoretical reference and technical support for the engineering application of solid–liquid two-phase abrasive flow. [ABSTRACT FROM AUTHOR]

Smoothed particle hydrodynamics (SPH) is a meshfree, Lagrangian, particle method, which combines the advantages of Euler and Lagrangian method and has special advantages in simulating violent non-linear fluid–structure interaction problems. In this study, an improved SPH method is used to simulate four fluid–structure interaction cases. Firstly, the violent flow in the mould filling process is simulated to validate that the SPH model can obtain accurate flow patterns with any complex solid boundaries. Secondly, the dam-break flow against a vertical wall is simulated, and the pressure curves are compared with the experiment. Then liquid sloshing problems under different external excitations are simulated, and the complex coupling characteristics can be captured. Finally, the interactions between fluid and floating bodies are researched. The obtained numerical results show good agreement with the results from other sources, and clearly demonstrate the effectiveness of the presented SPH method in modelling fluid–structure interaction problems. [ABSTRACT FROM AUTHOR]

To enhance the power grid's stability and safety, pumped‐storage power stations (PSPSs) have to keep themselves stable and safe strictly. However, instabilities happen frequently in some PSPSs due to the S‐shaped characteristics of pump‐turbines. When the operating point goes through the S‐shaped region, intensive radial forces on the runner could cause shaft swing of the turbine‐generator unit. In this study, the runaway transient scenarios of a pump‐turbine in a model PSPS were simulated by using a one‐dimensional and three‐dimensional coupled computational fluid dynamics model, and the influence of the unit rotational inertia on the runner radial forces was investigated. The results show that when the pump‐turbine runs in the S‐shaped region, large rotational inertia is easier than a small one to induce abrupt increases in runner radial forces. The reason is that large rotational inertia gives slower changes in rotational speed and discharge, providing enough time to generate unstable and uneven flow patterns in the pump‐turbine. This indicates that apart from the running away region in the characteristics plane, the running away duration is also essential for the transient instability of a pump‐turbine. The finding is different from the traditional understandings and should be considered when selects the rotational inertia of a pump‐turbine unit. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of separated exhaust expansion chamber parameters on pressure oscillations in spark-ignited internal combustion (IC) gasoline engines. It is known that exhaust expansion chambers are becoming increasingly more popular among both - original equipment (OE) and aftermarket equipment (AE) exhaust system manufacturers for performance-oriented motorcycles equipped with mainly single cylinder engines, but the companies are reluctant to reveal any detailed principles of operation of the mentioned expansion chambers. The subject of this research is the type of expansion chamber (separate) as used on performance-oriented motorcycles, particularly its' effect on exhaust pressure pulsations as different chamber volumes, locations and passage sizes are tested. Time-dependent computational fluid dynamics (CFD) analysis was carried out in Solidworks Flow Simulation environment on a simplified exhaust header pipe model imitating engine operation at full load and steady speed. Honda CRF450R motorcycle engine was used as the example and fully defined using a 1D engine performance calculator software to determine the combustion chamber pressure and exhaust valve lift at any given crankshaft position. Volume flow rate of exhaust gasses at the header pipe inlet was calculated based on engine parameters and operating speed. The average pressure values with respect to physical time were measured and graphed across the header pipe inlet cross-section. Eight different header pipe and exhaust expansion chamber combinations were modelled, tested, and results compared at low, medium and high engine speeds. It was found that the presence of exhaust expansion chamber tends to dampen the amplitude and decrease the frequency of pressure oscillations generated at the opening of the exhaust valve(s). Observations show that the addition of an expansion chamber as per design of performanceoriented motorcycles helps to decrease the negative effect of engine tuning while also dampening the positive effect. [ABSTRACT FROM AUTHOR]

In order to improve the working performance of the ceramic catalyst filter, a model of nozzle blowback was designed to change the nozzle diameter. The blowback tube blowback model with variable diameter and the blowback blowback model with equal diameter were used for backflush simulation analysis. Also the influence of the sum of the injection tube inlet velocity, nozzle length, and nozzle cross-sectional area on the uniformity of backflush was studied. Through simulation analysis, it can be obtained that the outlet flow of nozzles with equal diameters and blowback models increases gradually from front to back; the variable-diameter blowback model can make the nozzle outlet flow uniform, but the nozzles at both ends still deviate from the average flow; continuing to change the nozzle diameter. The nozzle outlet flow can continue to be uniform; different boundary conditions and sizes can affect the uniformity of the backflush: the smaller the inlet velocity of the injection tube, the larger the nozzle length, the smaller the sum of the nozzle areas, and the more uniform the nozzle outlet flow.

In order to improve the working performance of the ceramic catalyst filter, a model of nozzle blowback was designed to change the nozzle diameter. The blowback tube blowback model with variable diameter and the blowback blowback model with equal diameter were used for backflush simulation analysis. Also the influence of the sum of the injection tube inlet velocity, nozzle length, and nozzle cross-sectional area on the uniformity of backflush was studied. Through simulation analysis, it can be obtained that the outlet flow of nozzles with equal diameters and blowback models increases gradually from front to back; the variable-diameter blowback model can make the nozzle outlet flow uniform, but the nozzles at both ends still deviate from the average flow; continuing to change the nozzle diameter. The nozzle outlet flow can continue to be uniform; different boundary conditions and sizes can affect the uniformity of the backflush: the smaller the inlet velocity of the injection tube, the larger the nozzle length, the smaller the sum of the nozzle areas, and the more uniform the nozzle outlet flow. [ABSTRACT FROM AUTHOR]

Copyright of Methods in Ecology & Evolution is the property of Wiley-Blackwell 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.)

In the present paper, the effect of blade cone angle on low-frequency noise of horizontal-axis wind turbines is studied to investigate the noise reduction, by adjusting the blade cone angle in different wind speeds. In wind turbines, a significant part of the noise is in infrasound range to which exposure could have adverse effects on human health. In this study, a small turbine is selected as a test case, and the sound field is simulated for different blade cone angles from 0° to 10° with a wind speed range between 5 and 25 m/s. The results of flow simulation show that the change in the output power is < 5% in comparison with the planar turbine. In addition, the calculated results for the low-frequency noise demonstrate that the blade cone angle significantly affects the noise value and the directivity pattern. The investigation of the directivity pattern shows that blade cone angle could have opposite effects on different observer positions, and therefore, the noise calculation at only one position is not enough to conclude about the effect of blade cone angle. The obtained directivity also shows that the turbines with blade cone angles of 2.5° and 5° are preferred in order to reduce the maximum noise, in comparison with the planar turbine. Overall, it is concluded that the adjustment of blade cone angle in different wind speeds can be an effective solution for reducing the low-frequency noise. [ABSTRACT FROM AUTHOR]

Abstract In this study an array of four commercial U-type evacuated tube collectors with mini-CPC reflectors was analyzed both experimentally and numerically. The operation of the array was examined in a range of 35–80 °C inlet temperature in Athens/Greece from 11:00 to 16:30 local hour at 2nd May using water as working medium. The data acquisition regarding the solar irradiation intensity, the inlet, the outlet and the ambient temperature was conducted every 10 min Α time-dependent computational fluid dynamic model was developed in Solidworks for validating the results while an analytical solution was, also, proposed. It was found that the simulation and the analytical results diverge 3.7% and 9.3% on average from the experimental regarding the thermal efficiency of the array while the mean divergence between them was 6.1%. The specific simulation gave us the opportunity to predict the receiver temperature as well as the thermal efficiency of each module something that the experimental process could not provide. The receiver temperature was also predicted through the analytical solution for further validation. The experiments were conducted in the National Technical University of Athens at the Applied Thermodynamics laboratory of Mechanical Engineering Department while the design of the simulated model was conducted in Solidworks. Highlights • The experimental results agree sufficiently with the CFD and the analytical one. • The CFD approach appears a good agreement with the analytical solution. • The outlet water temperature of each module was predicted. • The receiver temperature of each module was predicted. • The thermal efficiency of each module was predicted. [ABSTRACT FROM AUTHOR]

The effects of blockage ratio and boundary proximity on tidal turbine performance are quantified in this study using computational fluid dynamics (CFD). Reynold averaged Navier–Stokes (RANS) equations are solved using the commercial CFD code ANSYS CFX. Steady‐state analyses are performed using a rotating frame of reference technique, and a shear stress transport turbulence model is used. Results from the numerical model are validated with experimental data. RANS CFD simulations are performed over tip speed ratios (TSRs) from 1 to 9. The simulation‐based performance curve approximately match the experimental performance curve, with errors ranging from 4 to 9%. Blockage ratios from 0.02 to 0.19 are evaluated for a constant depth of two rotor diameters to study the effect of blockage on turbine performance. Results show that shaft power increased by 13 and 47% for TSRs of 5.11 and 9.05, respectively, when the blockage ratio increased from 0.02 to 0.19. Additionally, for these TSRs and blockage ratios the turbine thrust increased by 7 and 10%. The presence of a boundary layer resulted in a calculated thrust increases between 1.6 and 2.3% and power between 2.7 and 3.5% for the entire range of evaluated blockage ratios. [ABSTRACT FROM AUTHOR]

This research work deals with the design of a tunable muzzle brake [10] for a rifle chambered in 5.56 × 45 NATO ammunition. It proposes to solve the problem of handling differences from shooter to shooter by incorporating the feature of tunability. Beside this, it also solves the problem of requirement of optimum recoil in short recoil weapons. This innovation gives this design an edge over its already existing counterparts in the market. The product is designed using the internal ballistics calculations and the investigations been performed using solidworks flow simulation tool and ANSYS static structural to check the parameters like velocity distribution, pressure growth, and muzzle brake force along the series of ports and comparison of the so found results with those devised by the authors of the documents mentioned in references. This assures the market adaptability of the product for satisfactory performance, when brought among its already existing counterpart, though with a slight edge over them due to tunability. The results so found shall be concluded satisfactory regarding the performance of muzzle brake. [ABSTRACT FROM AUTHOR]

A special kind of flat plate collectors was examined in detail through CFD analysis. The distinctiveness of the current model has to do with the piping system was applied which is a serpentine flow conduit. The operation of the collector was examined at four different inclination angles (0°, 15°, 30°, and 45°) and several values of the inlet water temperature (10-80 °C per 10 °C) by providing the same heat perpendicular to the cover in each case. The thermal efficiency as well as the temperature fields of the collector was determined first. Furthermore, the overall heat losses were calculated and compared to these arisen from the Cooper-Dunkle assumption while the mean divergence between these two solutions was around 5%. Moreover, the natural convection inside the gap as well as the tube to water convection was examined and the heat transfer coefficients were validated from theoretical models in horizontal position. In particular, the simulation results found to diverge from the theoretical ones about 12.5% and 7% as regards the pipe flow and the air-gap, respectively. In addition, a remarkable flow phenomenon was observed at the bends of the pipe and the nature of it was explained in detail. Last but not least, the inclination angle seems that affects significantly the collector's performance since the higher the slope the lower the convection losses. Solidworks and its simulation program Flow Simulation were used to design and simulate the whole collector. [ABSTRACT FROM AUTHOR]

The motion mechanism of the single droplet during wing cleaning of aeroengine is studied, and the force acting on the droplet entering the fan at low speed is analysed, and the motion model of a single droplet in swirl field is established. The influence of the main parameters such as droplet diameter, incident velocity and incidence angle on the droplet trajectory is analysed. The mechanism of droplet movement in the fan is described qualitatively.

The aero-engine to be cleaned online can significantly improve compressor performance and increase maintenance intervals, but the cleaning online cannot achieve the anticipated effects due to the lack of cognisance of the internal multiphase flow field. In order to explore the characteristics of the compressor's internal flow field, a compressor and nozzle's flow channel model was established based on the data of the Rotor36 compressor blades published by NASA. The fluid simulation software was used to analyse the effects of circumferential vortex and axial vortex on the wall surface at different jet parameters and characteristics of the gas–liquid flow field formed by the compressor blades at different rotation speeds. It is concluded that the flow field formed at a jet pressure of 5 atm and a rotational speed of 2880 rpm is more favourable to the removal of fouling.

In order to investigate the internal flow field of an axial blood pump, two-dimensional (2D) particle image velocimetry (PIV) was applied to test the blood pump under three different conditions. Acquiring the images of inlet, front guide vane, impeller, back guide vane and outlet area, the distribution of internal flow field was then analysed. The rotation speed of the blood pump was set to 6000, 7000 and 8000 r/min, respectively. The results show that the flow field of blood pump is stable relatively at the inlet area. Some vortices and reflux existed due to the block of guide vane in the import and impeller area. With the increase of rotating speed, the overall disturbance degree of flow field increases. Under the condition of low rotation speed, the flow field acceleration is insufficient. Under the medium rotation speed condition, the flow field is stable and the velocity distribution is even. Under the condition of high rotating speed, the number of vortices in the flow field increased significantly, the flow separation phenomenon at the impeller was obvious and more unstable flow appeared at the back guide vanes and outlet area.

Aiming at the complicated internal flow state of hydraulic cone valve and the effect of fluid force on the performance, radial offset was seldom considered in the research of cone valve, so the inner flow field model of cone valve was established by UG software, and the mesh model was divided by ICEM CFD software. Then, the simulation calculation was carried out by FLUENT. The distribution of steady-state flow force, pressure field, and velocity field under the different opening of the cone valve was obtained. In order to verify the correctness of radial offset, the hydraulic simulation under the same working condition was carried out by AMESim software. Finally, the radial force on both sides of valve core was calculated on the basis of the pressure field on both sides of the valve core. The results show that the radial force difference on both sides of the spool is small when the valve port is small. With the increase of the valve port opening, the radial force difference between the two sides of the valve core changes larger, and finally fluctuating within a certain range. Then, the radial offset value can be calculated by the radial force formula. According to the obtained offset, the simulation and experimental study on the cavitation of the cone valve are carried out. The simulation results of radial offset are verified according to the distribution position of the cavitation, which lay the foundation for the design and performance research of the hydraulic poppet valve

Based on the theories of heat transfer and the method of computational fluid dynamics, a liquid–solid mathematical model of heat transfer of an axial piston hydraulic motor pump is constructed in this study. Through the finite volume method, the model with different cooling runners has been solved. Meanwhile, the oil flow regularity of runner and temperature distribution of the motor pump and oil duct has been obtained. On the basis of the model of long-strip runner, the influence of ambient temperature on the motor pump's temperature rise has been analysed. The result shows that the cooling channels on the housing of the hydraulic motor pump effectively reduce the temperature rise, and a long-strip channel is for optimum cooling. The average temperature rise of the motor pump increases linearly with the increase of ambient temperature.

The influence of inclined angle on the flow characteristics of angle seat valve is investigated by the numerical and experimental study. The accuracy of numerical modelling and calculation is verified by comparing the flow coefficients obtained from numerical simulation and experiments under the different pressure difference at the inclined angle of 45° and 60°. The experiment results showed that the highest flow velocity, the maximum flow coefficient, and the minimum flow resistance exist as the inclined angle is 45°. The flow coefficient increases as the increase of inclined angle when it ranges from 45° to 60°, and the flow resistance decreases correspondingly. The observed result is discussed and explained by the computational fluid dynamics (CFD) method. The calculation results indicated that the flow coefficient mainly depends on the maximum flow velocity in the angle seat valve. Moreover, the flow capacity is also affected by the flow direction near the sealing surface, and the number, locations and intensities of flow vortex.

Centrifugal fan in series is the core facility for pneumatic transportation. Its operation is required to be adjusted real time as the flow rate of transported materials changes. For optimisation performance, internal flow of a type 700 three-stage fan at rated rotation speed is analysed with FLUENT6.3 for various total pressure. Multiple reference frame (MRF) model is used for the impellers rotation in simulation, and Re-Normalisation group (RNG) κ-ɛ turbulence model and Roe-FDS flux type with first-order upwind difference scheme are used for calculation of compressible flow under various total pressure. Flow characteristics are obtained and differences of total pressure and velocity distribution in every impeller are analysed in different conditions, and velocity distribution on meridian plane as well as section of wind guide plates and volute are compared. Results show that there are many vortexes and backflows in fan with higher total pressure, and the lower pressure, the more smoothly flows, besides flow at inlet and outlet of impellers and in guide plates is seriously influenced by total pressure. Curves of P-Q and P-η at 4600 r/min are predicted based on simulation, which is helpful reducing the impact caused by off-design operation and improving efficiency.

In order to improve the pressure distribution, the aerostatic circular thrust bearing with single supply hole was studied. In the computational fluid dynamics (CFD) simulation, the laminar model, the turbulent model, the mixture model of laminar and turbulent were used simultaneously. The micro-characteristics of the gas flows were analysed based on the simulation results. One test rig was built for measuring the pressure distribution with the single test hole, and the calculated and experimental results were compared. The results showed that when the gas film clearance is small and the gas flow is subsonic completely, the whole gas flow is laminar flow, which should be calculated based on the laminar model and when the gas film thickness is large and there is supersonic flow in some region, which should be calculated according to the mixture model; at the same time, there is no surface of discontinuity for Mach number and pressure distribution, and no shock, and the pressure is recovered due to the boundary layer separation, the change of the flow state and the change of viscosity. The method for testing the pressure distributions with a single test hole is effective.

Evaluation of experimental thermal performance of a single pass solar air dryer is compared with a transient CFD studies is performed. Vertical hollow plates are placed below the absorber plate and compared against the flat solar absorber plate for its performance improvement. Effect of mass-flow rate, the outlet temperature of air is computationally analyzed in comparison with the experimental work, transient boundary conditions for CFD like ambient temperature, solar insolation are taken from the experimental work, and computational results are in good agreement of with experimental results with maximum error percentage of 10%. Thermal efficiency was increased with increase in mass-flow area for without fin configuration, for a specific mass-flow rate thermal efficiency had a good improvement with fin configuration than the without fin configuration. [ABSTRACT FROM AUTHOR]

Currently there are no available methods for prediction of thrombotic complications in Coronary Artery disease. Additionally, blood coagulation tests are mainly performed in a steady system while coagulation in vivo occurs under flow conditions. In this work, a phenomenological model for coagulation up-to thrombin generation is proposed; the model is mainly based on the results of thrombin generation assays and therefore it can account for the variation of the coagulability that is observed in different individuals. The model is applied on 3 cases of left anterior descending arteries (LAD) with 50% maximum stenosis placed at a different location and have been statistically assessed as of different complication risk. The simulations showed that parameters of thrombin generation assays obtain different values when they refer to thrombin generation under realistic coronary flow conditions. The flow conditions prevailing locally because of the geometric differences among the arterial trees can lead to different initiation times and thrombin production rates and it also alters the spatial distribution of the coagulation products. Similarly, small changes of the coagulation characteristics of blood under identical flow conditions can allow or prevent the initiation of coagulation. The results indicate that combined consideration of geometry and coagulation characteristics of blood can lead to entirely different conclusions compared to independent assessment of each factor. [ABSTRACT FROM AUTHOR]

Blood flow imaging is a novel technology in cardiovascular medicine and surgery. Today, two types of blood flow imaging tools are available: measurement-based flow visualization including 4D flow MRI (or 3D cine phase-contrast magnetic resonance imaging), or echocardiography flow visualization software, and computer flow simulation modeling based on computational fluid dynamics (CFD). MRI and echocardiography flow visualization provide measured blood flow but have limitations in temporal and spatial resolution, whereas CFD flow calculates the flow according to assumptions instead of flow measurement, and it has sufficiently fine resolution up to the computer memory limit, and it enables even virtual surgery when combined with computer graphics. Blood flow imaging provides profound insight into the pathophysiology of cardiovascular diseases, because it quantifies and visualizes mechanical stress on the vessel walls or heart ventricle. Wall shear stress (WSS) is a stress on the endothelial wall caused by the near wall blood flow, and it is thought to be a predictor of atherosclerosis progression in coronary or aortic diseases. Flow energy loss (EL) is the loss of blood flow energy caused by viscous friction of turbulent diseased flow, and it is expected to be a predictor of ventricular workload on various heart diseases including heart valve disease, cardiomyopathy, and congenital heart diseases. Blood flow imaging can provide useful information for developing predictive medicine in cardiovascular diseases, and may lead to breakthroughs in cardiovascular surgery, especially in the decision-making process. [ABSTRACT FROM AUTHOR]

Polluted insulators frequently face flashover accident and it threatens the safety and stability of power system. In order to help to reduce the occurrence of flashover, it is necessary to study the contamination characteristics of insulators and its influence factors. In this study, the contamination of insulator is simulated by the Eulerian multiphase model in computational fluid dynamics. The flow field around insulators is calculated and the volume fraction of the particle phase is used to characterise the pollution degree on insulator surface. Results show that the pollution is mainly distributed on windward side and leeward side of insulator. The crosswind side of insulator is slightly contaminated. The four influence factors, wind velocity, particle concentration, particle diameter and flow angle have different effects on insulator contamination. Among these factors the particle concentration contributes most to the whole contamination degree of insulators. A wind tunnel contamination test on insulator is carried out to verify the feasibility of the numerical simulation. It can be found that simulated contamination distribution and variation of contamination degree with wind velocity well coincide with the results of wind tunnel test. The numerical simulation in this study is practical in studying the insulator contamination. [ABSTRACT FROM AUTHOR]

Purpose: Blood flow in intracranial aneurysms has, until recently, been considered to be disturbed but still laminar. Recent high resolution computational studies have demonstrated, in some situations, however, that the flow may exhibit high frequency fluctuations that resemble weakly turbulent or transitional flow. Due to numerous assumptions required for simplification in computational fluid dynamics (CFD) studies, the occurrence of these events, in vivo, remains unsettled. The detection of these fluctuations in aneurysmal blood flow, i.e., hemodynamics by CFD, poses additional challenges as such phenomena cannot be captured in clinical data acquisition with magnetic resonance (MR) due to inadequate temporal and spatial resolutions. The authors' purpose was to address this issue by comparing results from highly resolved simulations, conventional resolution laminar simulations, and MR measurements, identify the differences, and identify their causes. Methods: Two aneurysms in the basilar artery, one with disturbed yet laminar flow and the other with transitional flow, were chosen. One set of highly resolved direct numerical simulations using the lattice Boltzmann method (LBM) and another with adequate resolutions under laminar flow assumption were conducted using a commercially available ANSYS Fluent solver. The velocity fields obtained from simulation results were qualitatively and statistically compared against each other and with MR acquisition. Results: Results from LBM, ANSYS Fluent, and MR agree well qualitatively and quantitatively for one of the aneurysms with laminar flow in which fluctuations were <80 Hz. The comparisons for the second aneurysm with high fluctuations of >~600 Hz showed vivid differences between LBM, ANSYS Fluent, and magnetic resonance imaging. After ensemble averaging and down-sampling to coarser space and time scales, these differences became minimal. Conclusions: A combination of MR derived data and CFD can be helpful in estimating the hemodynamic environment of intracranial aneurysms. Adequately resolved CFD would suffice gross assessment of hemodynamics, potentially in a clinical setting, and highly resolved CFD could be helpful in a detailed and retrospective understanding of the physiological mechanisms. [ABSTRACT FROM AUTHOR]

Valves are devices of great importance in the operation of hydro systems, in particular, when is necessary to control the flow. The objective of this paper is to determine, through SolidWorks Flow Simulation module, the minor loss through a globe valve at different partially open settings. The Flow simulation allows an analysis of current lines and the hydrodynamic parameters of flow. Therefore we can determine the hydraulic energy losses and can appreciate the value of the main flow parameters. [ABSTRACT FROM AUTHOR]

Digital microfluidics has recently emerged as an effective technology in providing inexpensive but reliable solutions to various biomedical and healthcare applications. On‐chip dilution of a fluid sample to achieve a desired concentration is an important problem in the context of droplet‐based microfluidic systems. Existing dilution algorithms deploy a sequence of balanced mix‐split steps, where two unit‐volume droplets of different concentrations are mixed, followed by a balanced‐split operation to obtain two equal‐sized droplets. In this study, the authors study the problem of generating dilutions using a combination of (1 : 1) and (1:2) mix/split operations, called weighted dilution (WD), and present a layout architecture to implement such WD‐steps. The authors also describe a simulation based method to find the optimal mix‐split steps for generating a dilution under various criteria such as minimisation of waste, sample, or buffer droplets. The sequences can be stored in a look‐up table a priori, and used later in real time for fast generation of actuation sequences. Compared with the balanced (1:1) model, the proposed WD scheme reduces the number of mix‐split steps by around 22%, and the number of waste droplets, by 18%. [ABSTRACT FROM AUTHOR]

Ultrasonic flowmeters have potential for wide application in natural gas and hydrogen flow measurements in China. Accurate measurement is essential; thus, data fusion of acoustic paths is of importance. A data integration method for multi‐path flowmeter measurement is introduced and investigated in this study. The novel data integration method is based on the Levenberg–Marquardt algorithm. Computational fluid dynamics has been used to simulate the flows, and a laboratory scale system was established to obtain experimental measurements. The results of the simulations and experiments reveal that the method is able to reduce measurement error compared with four traditional integration methods in flow‐rate measuring in a long straight pipe. Furthermore, both the simulation and experiment results validate the integration method for non‐ideal flow conditions, such as flow downstream a single elbow or a 180° bend. The relative errors are within 1%, instead of more than 2%, which is typical for traditional methods. [ABSTRACT FROM AUTHOR]

A relatively simple approximate single-phase model (SPM) was developed for flow simulation of viscous liquid motion generated by a chain of rising bubbles. The complete detailed information about the gas–liquid two-phase flow was obtained with help of the full multi-phase model (MPM) using the direct numerical simulation (DNS) approach of the volume of fluid method (VOF), as implemented in the Fluent software. The overall driving effect of the bubble chain was expressed with an approximate buoyancy force closure formula, obtained in form of correlations of the MPM numerical data. This formula was compared with other published closures and used as a source term in SPM. SPM was solved and the results compared with MPM. Good agreement was found. SPM worked well in a range of bubbling frequency, liquid viscosity, and with temperature gradients. The replacement of the highly demanding and complex MPM with SPM is a great simplification of the flow modelling. SPM can be readily used for simulating the flow structure in containers with pneumatic mixing and design of equipment, where several rows of bubbling nozzles are installed. In this work, our modelling was done for the case of glass melts in glass furnaces. [ABSTRACT FROM AUTHOR]

In this paper, in order to design a useful computational flow simulation for the governing equation of two phase incompressible (water and oil), a robust and efficient scheme is proposed. This hybrid method consisting of IMPES technique for the linearisation, control volume finite element method on hexagonal grids for spatial discretisation, backward Euler method for time discretisation and stable variant (adaptive-simpler-GMRES) of simpler generalised minimum residual technique with incomplete factorisation preconditioners is used to solve the corresponding linear system. Moreover, we proposed the general Courant Friedrich Levy condition for two phase immiscible flow with Von Neumann method. Numerical results for oil pressure, oil and water production rates and water saturation in the injection and production wells are illustrated. [ABSTRACT FROM AUTHOR]

This paper presents a systematic investigation of the influence of complex flow profiles on the performance of multipath ultrasonic gas flow meter by using computational fluid dynamics (CFDs) simulation. To guarantee the overall agreement between the CFD predictions and the measurements, the meshing approaches, generation of boundary layers, turbulence models, and wall treatment methods for CFD simulation are elaborated carefully. The performances of a multipath ultrasonic gas flow meter under complex flow profiles, regarding to an out-plane double-elbow with a half-moon block and an out-plane double-elbow with a half-moon block equipped with a Spearman conditioner, are investigated. The simulation results demonstrate that for complex flows with strong asymmetric and swirling velocity profiles inside an out-plane double-elbow pipeline with a half-moon block, a four-path ultrasonic flow meter located at 20-D right after the second elbow together with a Spearman conditioner installed 16-D upstream the meter is of providing a flow velocity estimation that the error is within ±0.5%, while the Reynolds number ranges from 3.25×103 to 3.25×105. The effect of sound path orientation on the performance of flow meter is also discussed. [ABSTRACT FROM PUBLISHER]

Comparing to pumps with moving parts water-jet pumps have a lower efficiency and surface roughness is an important factor for these types of pumps. The aim of this simulation study is to numerically determine how the scaling-up, downscaling and change in the absolute and relative roughness would impact on the energy efficiency of the pumps, using a commercial computational fluid dynamics (CFD) solver ANSYS FLUENT. In order to select the turbulence model that produces the predictions closest to the actual data from four turbulence models, a preliminary study was conducted on a full-scale jet pump. Using the transition SST model, which gives the best results among all the models, the effects of scale and roughness on the performance of the pumps were investigated in the scale range from 1/4 to 20/1. The optimum efficiencies for different area ratios over a wide range were determined according to the scale and size of roughness. It was seen that the efficiency increases significantly up to a given scale size at a constant absolute roughness, while it is generally independent of the scale size at constant relative roughness. The relative efficiency for the area ratio 5.92 reduces to 60% at the relative roughness value of 0.05. Moreover, CFD appears to be the most appropriate tool for model studies of jet pumps. [ABSTRACT FROM AUTHOR]