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This research paper presents a comprehensive study on the intricate interplay of rotational, magnetic field and heat transfer effects in squeezing fluid flow, utilizing the foundational framework of Navier–Stokes equations. Fluid flow in confined geometries has significant applications in various industrial processes, including lubrication systems, microfluidics, and heat exchangers. The integration of rotational motion, magnetic fields, and heat transfer phenomena into this context holds immense potential for optimizing performance and efficiency. The study commences with the derivation and analysis of the coupled Navier–Stokes equations, incorporating the Coriolis force due to rotational motion, the Lorentz force arising from magnetic fields, and the energy equation for heat transfer. This comprehensive model accounts for the complex interactions between these physical phenomena, offering a holistic perspective on squeezing fluid flow dynamics. Numerical analysis are conducted to investigate the behavior of fluids under the influence of rotational, magnetic field, and heat transfer effects. The results reveal intricate flow patterns, including vortex formation and heat transfer enhancement. Furthermore, the impact of key parameters such as rotational speed, magnetic field strength, and temperature gradients on flow characteristics is systematically analyzed. The Dufour effect pertains to the transfer of energy resulting from a gradient in mass concentration, occurring as a correlated consequence of irreversible processes. It functions as the inverse of the Soret effect. The temperature changes due to the concentration gradient, amplifying as the Dufour number increases. The most significant temperature rise is observed at the midpoint of the fluid domain. Conversely, the Soret number behaves in a similar but opposite manner. Tables 4–10 has been created to offer a comprehensive analysis of the optimal alignment between Homotopy Analysis Method (HAM) and BVP4c. Specifically, it demonstrates a continuous decrease in skin friction for ξ S o , ξ R d , and ξ R 2 , while showing an increase for ξ S c , ξ D o , and ξ R e m . Meanwhile, the skin friction remains constant for ξ P r . The research centers on analyzing heat and mass transfer properties within an incompressible fluid confined between two rotating and stretching disks amidst an unpredictable flow pattern. The study employs a blend of analytical and numerical approaches to solve the governing equations, delving into the intricate fluid dynamics and the intricate processes of heat and mass transfer within this intricate system. [ABSTRACT FROM AUTHOR]

This paper explores the combined influence of an axial electric field and a perpendicular magnetic field imposed on rotating micro-parallel plates immersed in an electrolyte solution. A specialized computer program was developed to solve the velocity as well as the EDL potential fields using the finite difference method, employing the Debye-Hückel (DH) approximation to linearization the EDL potential. The study examines the influence of various non-dimensional parameters, including rotational speed (ω), Hartmann number (Ha), Debye-Hückel parameter (κ), and the non-dimensional parameter ' S', on axial, and transverse velocities, wall shear stress, and net flow rate. Results demonstrate that, both velocity components decrease with increased rotational speed and Hartmann number, while the net flow rate increases with the Debye-Hückel parameter for both rotating and non-rotating systems. The impact of these parameters on shear stress was also analyzed. Analysis of Ekmann spirals in the velocity plane revealed closed spirals at a higher rotational speed and open spirals at lower speeds, with spiral size reducing as rotational speed increases. [ABSTRACT FROM AUTHOR]

Inelastic interactions between a small, intense dipole and a weak, neutral monopole in two-dimensional flows are analysed. The neutral vortex has vanishing exterior potential flow and the interactions involve the rotational flow of the vortices. It is shown that dipoles of small-size but large-amplitude, relative to the neutral vortex, may cross the vortex and scatter while leave the vortex stable. [ABSTRACT FROM AUTHOR]

Rotational moulding is a versatile polymer shaping process used to create enclosed parts from powdered precursors using heat and multi-axis rotation. Controlling the heating process and mould motion is critical to producing high-quality parts, and failures due to incorrect mould coverage or variable wall thickness are common. To date, limited simulation tools exist to predict the motion of the powder within the mould, and operators rely on unreliable prior experience to avoid defects. This paper presents an SPH simulation framework to predict particle flow patterns and powder contact time within a rotating mould. The powder-to-wall contact time was derived from the transient rigid body force (RBF) of different sensors on the mould. The method was compared with the results of DEM simulation and validated by the particle flow pattern of two experimental results. Results showed that the SPH method was capable of simulating particle flow macroscopic properties. The great computing efficiency of SPH compared to DEM simulation was also demonstrated. • Couple the SPH framework with a soil material model to simulate the polymer flow motion during rotational moulding process. • Modelling framework validated by two experimental benchmarks. • Present a significant benefit compared to the DEM method when simulating particle flow with millions of particles. [ABSTRACT FROM AUTHOR]

Pumps as turbines play an important role in micro pumped hydro energy storage (PHES) systems, which are widely applied in remote areas, and their operational safety can be significantly affected by the transient power-off process. The aim is to analyze the unsteady internal flow characteristics and time–frequency characteristics of the pressure fluctuations of the pump as turbine (PAT) after power-off process by using finite volume method (ANSYS CFX) and bidirectional test rig. During the transient process of power failure, internal flow instabilities were revealed by analyzing the flow field and turbulence kinetic energy. The results indicated that the flow field between the blades was extremely unstable during the brake mode. Additionally, the absolute values of the rotational velocity and flow rate were 1.21 and 0.93 times higher than the initial values, respectively, during the runaway mode. The pressure fluctuations were analyzed in the time-frequency domains using the continuous wavelet transform. The main frequency of pressure pulsation at the volute was related to the rotating speed owing to the rotor-stator interaction. This study revealed the transient flow features during the process of mixed-flow pump as turbine failure, which provides a fundamental theory for the safe transient operations of pump as turbine. [ABSTRACT FROM AUTHOR]

A comparative experimental study of a physical model of a stirred ladle for a rotor-injector aluminum degassing system in the turbulent regime has been carried out. A quantitative analysis of the gaseous oxygen mass transfer to the water in a physical model is performed by evaluating the power consumption and mass transfer capacity employing the typical methods used in mechanically stirred tanks. Three rotor injector devices were compared, including two conventional designs and one new rotor design. The rotors were evaluated as a function of the rotational speed and gas flow rates. The conventional rotors exhibited similar performance, while the new design consumed more power when operating at high gassing flow rates and rotational speeds resulting in a higher breakup rate of bubbles and promoting a better formation of tiny bubbles, which are better distributed over the entire ladle. This behavior avoids bubbles rising freely to the free surface; so that the gas hold-up increases leading to an improved mass transfer capacity when using this rotor-injector. The results reported in this work agreed with previously reported works in the literature. • Rotor-injectors for degassing aluminum have been evaluated in terms of power drawn and mass transfer. • A typical approach as used in stirred vessels allowed evaluating the devices. • A novel rotor has been analyzed and compared against two commercial designs used in industrial operations. • The novel rotor draws more power, but it exhibits better mass transfer capacity. [ABSTRACT FROM AUTHOR]

A characteristic feature of most magnetic materials is that they have a hysteresis cycle. When the magnetic field goes through the hysteresis cycle multiple times, the energy of the alternating magnetic field is supplied to magnetic nanoparticles located in the area of cancer cells. This energy supplied to the magnetic nanoparticles is converted into heat in the environment. As a result of heating to a certain temperature, diseased cells die, while healthy cells remain undamaged. This is the usual mechanism for heating a cancer tumor in hyperthermia. This work examines the possibility of heating a part of the body under the resonant influence of a radio frequency field. The resonant frequency is formed from the rotational flow of mean square fluctuations of magnetic nanoparticles. It has been shown that by selecting the parameters of the resonant field, it is possible to achieve an increase in tumor temperature by 6° (sufficient to destroy malignant cells) in about 60 s. [ABSTRACT FROM AUTHOR]

The time-dependent acceleration of fluid particles in an arbitrary superposition of multipolar spherical and cylindrical vortices in presence of a background rotational rigid flow is the gradient of the difference between their kinetic energy and the product of their total axial angular momentum times the angular velocity of the background flow. If the potential energy is defined as the time-dependent field whose minus gradient equals the acceleration of the flow, then the total energy, defined as the sum of kinetic and potential energies, equals the total axial angular momentum times the angular velocity of the background flow. The total energy of a fluid particle has therefore a linear relationship with the azimuthal velocity field. The role of the axial angular momentum in these oscillating flows is explained also in the classical Lagrangian and Hamiltonian descriptions of motion. The linear relation between total energy and angular momentum makes possible that the free parameters of these flows may be obtained, in a way similar to that developed in the quantum mechanics description of motion, as the eigenvalues of linear operators acting on some components of the spherical modes. Beltrami flow solutions in prolate spheroidal geometry for axisymmetric flows are also discussed. • The total energy of fluid particles has a linear relationship with the azimuthal velocity. • The axial angular momentum in oscillating flows is explained in the Lagrangian and Hamiltonian theories. • The free parameters of the oscillating flow may be obtained using linear operators. • There is an analogy to the quantum mechanics description of motion. [ABSTRACT FROM AUTHOR]

Machine learning method was applied for rapid and precise prediction of flow and heat transfer characteristics within co-rotating disk cavity with a finned vortex reducer. A new data preprocessing scheme was developed to reduce modeling cost. By using this scheme, classical radial basis function neural network (RBFNN) shows better prediction performance compared with deconvolutional neural network. Furthermore, RBFNN has a simpler topological structure and fewer hyperparameters. By testing, the relative root mean square error for total pressure, total temperature, and swirl ratio is 0.51 %, 0.32 %, and 1.99 %, and corresponding coefficient of determination reaches 99.68 %, 96.55 %, and 99.16 %. The effects of input parameters on the outputs of RBFNN were analyzed, and a sensitivity analysis was conducted. Within the investigated parameter range, the total pressure loss increases as dimensionless mass flow rate, rotational Reynolds number, and radial position of the fin increases. The total temperature drop increases with the increase of dimensionless mass flow rate and rotational Reynolds number, but the decrease of radial position of the fin. Additionally, an increase in dimensionless mass flow rate or a decrease in rotational Reynolds number causes the increase of swirl ratio. This research provides an efficient modeling method for components in secondary air system in gas turbines. [ABSTRACT FROM AUTHOR]

The single-channel jet control strategy, with a suction slot on the upper surface and an injection slot near the trailing edge on the lower surface, has the dual benefit of both obviating the additional air requirement and effectively suppressing the reversed flow. Nevertheless, most studies focused on the control device application to airfoils leading to the three-dimensional rotation effect being ignored. In light of this, the objective of this study is to investigate the impacts of the single-channel jet control strategy with suction-injection combination on the rotational blade flow field. Numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) method accompanied by the k-ω shear stress transport turbulence (SST) model and the multi-reference frame (MRF) method are performed. It is confirmed that the control device can improve the net power output across a wide range of inflow wind speeds, particularly at low tip speed ratios. For instance, when the control strategy is applied to the span from 0.25 R to the blade tip, the net output power can be increased by 45.68 % at a wind speed of 10 m/s for the NREL Phase VI rotor, and simultaneously the axial thrust is only increased by 23.98 %. • Suction-injection combination reshapes the boundary layer of the rotation blade. • Torque of the blade across a wide range of inflow wind speeds is improved. • Tip segment control has greater positive effects than the root and mid-segment. • Net output power can be improved by 45.68 % at 10 m/s for the NREL Phase VI rotor. [ABSTRACT FROM AUTHOR]

The spatial evolution of three-dimensional wake field at the stern of a KCS ship model is experimentally studied using two-dimensional multi-plane automatic PIV measurement technique. It is found that when the curvature of the bilge reaches a certain degree, it forms an adverse pressure gradient. The original low-speed flow near the wall of the bilge, which is inclined upward to stern side, cannot overcome the adverse pressure gradient, and changes to a downward trajectory towards the propeller shaft. Meanwhile, the high-speed flow from the bottom of the ship to the bilge, which is far from the wall, still maintains an upward inclination. The surface of the bilge near the propeller shaft maintains a relatively cylindrical surface, giving the above two components of flow a sufficient rotational component. Combined with downstream convective velocity, a spiral bilge vortex ultimately forms. The bilge vortex spirals downwards near the ship's centerline plane, drawing the wake at the stern side into the propeller shaft vicinity, and spirals upwards on the outer side of the propeller shaft, mixing the wake at the propeller shaft with the wake at the stern side. Thus, the bilge vortex establishes a connection between the wake near the propeller shaft and the stern side. The analysis of the distribution of streamwise vorticity and the in-plane velocity in streamwise planes indicates that the bilge vortex has a good full field transmission characteristic. The strong shear between the low-speed flow at the lower edge of the bilge vortex and the mainstream causes a Kelvin-Helmholtz instability, which further induces the formation of complex vortex structures surrounding the bilge vortex. • Bilge vortex arises from opposite flow direction near and far from bilge wall, cylinderical shape and convective velocity. • The full field transmission bilge vortex has a strong full field transmission characteristic and establishes connection between wake near propeller shaft and stern side. • Strong shear at lower boundary of bilge vortex causes a K-H instability, inducing formation of secondary vortices. [ABSTRACT FROM AUTHOR]

We introduce a new computational framework that utilises Pulse Wave Velocity (PWV) extracted directly from 4D flow MRI (4DMRI) to inform patient-specific compliant computational fluid dynamics (CFD) simulations of a Type-B aortic dissection (TBAD), post-thoracic endovascular aortic repair (TEVAR). The thoracic aortic geometry, a 3D inlet velocity profile (IVP) and dynamic outlet boundary conditions are derived from 4DMRI and brachial pressure patient data. A moving boundary method (MBM) is applied to simulate aortic wall displacement. The aortic wall stiffness is estimated through two methods: one relying on area-based distensibility and the other utilising regional pulse wave velocity (RPWV) distensibility, further fine-tuned to align with in vivo values. Predicted pressures and outlet flow rates were within 2.3 % of target values. RPWV-based simulations were more accurate in replicating in vivo hemodynamics than the area-based ones. RPWVs were closely predicted in most regions, except the endograft. Systolic flow reversal ratios (SFRR) were accurately captured, while differences above 60 % in in-plane rotational flow (IRF) between the simulations were observed. Significant disparities in predicted wall shear stress (WSS)-based indices were observed between the two approaches, especially the endothelial cell activation potential (ECAP). At the isthmus, the RPWV-driven simulation indicated a mean ECAP>1.4 Pa - 1 (critical threshold), indicating areas potentially prone to thrombosis, not captured by the area-based simulation. RPWV-driven simulation results agree well with 4DMRI measurements, validating the proposed pipeline and facilitating a comprehensive assessment of surgical decision-making scenarios and potential complications, such as thrombosis and aortic growth. [ABSTRACT FROM AUTHOR]

Friction stir lap welding (FSLW) technology was utilized to join 2 mm-thick 2A12-T42 aluminum alloy plates in the current study. Experimental findings demonstrated successful plate joining without welding defects across rotational speeds ranging from 400 to 600 rpm. Higher rotational speeds facilitated ample material flow, resulting in joints that are free of hole defects. The presence of a step can be attributed to a non-synergistic material flow caused by the shoulder and pin. The fracture behavior of the joint is primarily influenced by joint formation factors, such as the distribution of the aluminum cladding (alclad) layer and effective lap width (ELW), as well as the microstructure. The continuous distribution of the alclad layer promotes crack propagation into the nugget zone (NZ). In cases where the ELW is inadequate (at 400 rpm), shear fracture occurs due to crack propagation along the NZ. With an increase in ELW (at 600 rpm), crack propagation is hindered by grain refinement in the NZ, causing the crack to propagate along the weaker thermomechanically affected zone (TMAZ) leading to tensile fracture. [ABSTRACT FROM AUTHOR]

Semi-solid extrusion (SSE), an additive manufacturing technique, is gaining significant attention for the printing of thermosensitive drugs. Hydrogels, one of the materials used in SSE, have emerged as a focus in pharmaceutical applications due to their ability to control the release of therapeutic agents spatially and temporally. Understanding the non-Newtonian flow and evaluating the mechanical properties of hydrogel-based materials during extrusion is, however, essential for successful 3D printing. Thus, users often find themselves conducting both rheological and texture profile analyses to characterize the hydrogel. While texturometers are primarily used to evaluate mechanical or sensory properties, viscosity measurements are typically performed using rotational rheometers or viscometers. In this study, we demonstrated how comparable rheological information can be obtained using a texturometer as a capillary rheometer. By preparing similar formulations to a previous study, we compared the rheological data obtained from a rotational rheometer to the data obtained from the texturometer. The means of the parameters obtained by fitting the data from both techniques to the power law model showed insignificant differences. In addition, three clusters were formed based on the flow behaviour and printability of the samples using principal component analysis. Furthermore, the printability was predicted using the samples' consistency and flow indexes, and the regression coefficient was 96.62 and 60.03% for capillary and rotational flow parameters, respectively. This approach thus holds the potential to streamline the time, expertise and equipment required for the rheological characterization of hydrogels for applications in semi-solid extrusion. [Display omitted] [ABSTRACT FROM AUTHOR]

Rotational modulation and the third diffusive component are investigated in relation to transports in the Rayleigh Bènard convection in the x − direction of an infinitely extended fluid layer or fluid-saturated porous layer using a weakly non-linear theory. The direction of travel for the z -axis is upward. The z -axis is interpreted as pointing upward. Temperature and concentration of both the solutes at lower plate are higher than the upper plate. The time dependent rotational speed of fluid is assumed to be modulated by small parameter ϵ 2 with amplitude (δ). A linear differential matrix approach is used to examine the system's behaviour. Ginzburg–Landau's equation, a non-autonomous differential equation, has been derived using the Fredholm-solvability condition. The impact of dimensionless parameters on stationary convection is also discussed. The expression of the critical Rayleigh number is obtained for three different cases: clear fluid layer, Darcy porous layer, and sparsely packed porous layer (Darcy–Brinkman model). The Nusselt number (N u) and Sherwood numbers (S h 1 , S h 2 ) for each solute are used to quantify the convective transports. The impact of modulation and other dimensionless parameters on these convective transports has been discussed using graphical representation Furthermore, among the three models under consideration, it is discovered that the heat and mass transports are highest in the fluid layer and minimum in the densely packed porous layer. • The rate of transports under modulated rotation flow are analysed. • Two different solute concentrations are mixed from opposite boundaries. • Asymptotic expansion method is used to determine the solution of system. • The heat and mass transports are highest in the fluid layer. • The parameters δ , R C 1 , M and D a enhance the rate transports. [ABSTRACT FROM AUTHOR]

The CFD simulations for external flow problems can request high computational costs. To reduce these costs, viscous/inviscid interaction methodology based in the domains decomposition and the Helmholtz velocity decomposition has been developed. The calculation of viscous flow by the Navier–Stokes equations is made on a computational reduced domain. In this work, an interactive methodology is presented, which consists of: calculate the potential flow outside the rotational region, impose the potential flow velocity field as a boundary condition in the reduced domain boundary, calculate the transpiration velocity to correct the potential flow, recalculate the potential flow velocity field outside the rotational region, and update the boundary conditions on the reduced domain. To formulate the transpiration velocity, the velocity decomposition approach was used, but to calculate the transpiration, it is necessary determine the boundary of the rotational region, called rotational boundary, where the vorticity is negligible. For this, negligible vorticity criteria were developed to find that boundary; however, determining it can be a complex task, as is the case of flow around multiple bodies. Some techniques, which may include the use of an auxiliary surface, have been developed to facilitate the determination of the rotational boundary. Thus, two proposals were made in this work, first: the use of an auxiliary surface to determine the rotational boundary to multiple bodies cases; and second: a new negligible vorticity criterion based on the total pressure field. Calculations were performed in the viscous reduced domain for two-dimensional incompressible flow, around a single body and multiple bodies. The use of the present methodology allowed reducing the computational costs. The aerodynamic coefficients and viscous flow fields obtained in the reduced domain were satisfactory for such engineering problems. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) Khanun in 2017 was simulated in this study by the Weather Research and Forecasting (WRF) model. The observation-validated simulation data were used to examine how asymmetric rotational and environmental flows played the roles in determining the contraction of the radius of maximum kinetic energy of symmetric rotational flow (K ψs). The radius of maximum K ψs was contracted rapidly before rapid intensification (RI) and moved inward slowly, then barely moved, and moved inward slowly again during RI. The conversion from kinetic energy of asymmetric rotational flow (K ψa) to K ψs was induced by advection of asymmetric rotational tangential wind by asymmetric divergent radial wind. The conversion and convergence of inward flux of K ψs led to the rapid contraction before RI. During RI, in additional to horizontal and vertical flux convergence of K ψs , the conversion from environmental kinetic energy (K e) to K ψs through the interaction between K ψs and symmetric radial environmental flow was important for the second slow contraction. • Symmetric rotational kinetic energy (K ψs) budget was used to examine radius contraction processes of maximum K ψs of Khanun. • The conversion from asymmetric rotational kinetic energy to K ψs and K ψs flux convergence were crucial for rapid contraction. • The conversion from environmental kinetic energy to K ψs and K ψs flux convergence were important for slow contraction. [ABSTRACT FROM AUTHOR]

• Three novel tube-tube premixers were designed and their macromixing were simulated. • Micromixing efficiency in RPBs with tube-tube premixers were experimentally studied. • Coupling mechanism of tube-tube premixers and RPBs was revealed. • Micromixing times of RPBs with tube-tube premixers ranged from 2 to 10 ms. Rotating packed beds (RPBs), as the typical chemical intensification devices, have been widely applied in liquid-phase fast reactions and precipitation processes. In this study, three novel tube-tube premixers were designed, and three-dimensional CFD models of the flow and mixing processes for non-Newtonian fluids in tube-tube premixers were established. Meanwhile, the micromixing efficiency in RPBs with different tube-tube premixers was experimentally investigated. The results show that TG-2 premixer exhibits the best premixing performance. The segregation index decreases as the rotational speed or flow rate increases, indicating the increase in micromixing efficiency. With the increase of CMC mass fraction, the segregation index initially decreases and then increases. Moreover, the micromixing efficiency of TG-0-RPB is the highest in aqueous solution, the micromixing efficiency of TG-4-RPB is the highest in 0.2 wt.% CMC system, and the micromixing efficiency of TG-2-RPB is the highest when the CMC concentrations is equal to or greater than 0.4 wt.%. The micromixing times of non-Newtonian fluid in RPBs range from 2 to 10 ms. [ABSTRACT FROM AUTHOR]

The icing problem in aeroengine is prominent, posing a serious threat to flight safety. There are some limitations in current icing research for aeroengine, which limits the understanding of icing mechanism and potential impact. In this study, a 3D numerical method for air-water two phase flow in rotational situation is developed, and the icing thermodynamic model under the aeroengine environment is established. The study focuses on the icing characteristic of stage 35 compressor under different conditions, as well as the effect of icing shapes on aerodynamic performance. The results indicate that the icing distribution of stage 35 rotor shows obvious 3D characteristic, and the ice amount has an increasing trend with the rise of blade span. Due to the nonuniform distribution of temperature on rotor surface, the rime ice begins to transform into glaze ice from the top of blade when the temperature increases. The quantitative result also finds that the icing has a serious impact on compressor performance, in terms of mass flow, pressure ratio and isentropic efficiency. The flow obstruction caused by the blunt structure at the leading edge is the main reason affecting performance. The research indicates that the icing phenomenon in aeroengine is more complex than that on airfoil, and its threat to performance cannot be ignored in engineering. [ABSTRACT FROM AUTHOR]

The demand of energy saving and loss mitigation in modern industry gives rise to drag reduction techniques such as micro groove/riblet ever since the last century. Plenty of studies are conducted under straight flow condition showing relevance between drag reduction and flow features. However, the same issue has not been studied adequately for rotational flows, which is typical in turbopumps. In this paper, two-dimensional numerical simulations of rotating disks are performed together with verification experiments to investigate drag reduction effect of micro riblet under rotational flow condition. The numerical results show that riblets with certain dimensions can lessen the resistant torque by a maximum of 8.46% and the drag reduction efficiency depends on rotational Reynolds number and riblet dimensions. Meanwhile, the distributions of static pressure and swirl velocity on surfaces are changed and near-wall turbulence intensity is tranquilized by riblets which are considered as the main reasons to the diminish of drag. Finally, the relevance of vortexes inside riblets to swirl wall shear stress and torque is demonstrated revealing that the configuration of riblets plays an important role in cutting resistance. The results of this paper can be a supplement for the investigation of micro groove/riblet drag reduction mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3D CFD simulations were conducted to study the flow through SMX+ mixers in series. • Flow characteristics become repetitive from the second element onwards. • High dispersive mixing takes place in the entrance region of each element. • The successive rotation of mixers gives rise to a rotational flow downstream. • Downstream, the core spirals on its axis and outer part spins orthogonal to motion. A numerical investigation of the flow through an SMX+ mixer was undertaken in this study. Three elements were placed in series to assess various hydrodynamic parameters. Single-phase flows of different viscosities flowing at a hydraulic Reynolds number between 220 and 660 were considered to ensure turbulent conditions inside the mixer. The data was validated against pressure drop measurements collected under a wide range of hydrodynamic conditions. The results show that a three-dimensional velocity field dominate the flow within the mixer where the distribution of the strain rate and vorticity magnitudes undergo large fluctuations. The extensional efficiency was found to increase substantially in the first part of each mixer, indicating good dispersive behavior; however, its value decreased to values below 0.5 downstream of the last element. This was due to the presence of a significant rotational core as the fluid flowed farther from the last mixer. The core region of the flow spiraled on its axis as it moved downstream while the near-wall area whirled orthogonal to the flow direction. This also explained the persistence of a flatter velocity profile downstream of the mixing section. The energy dissipation rate and kinetic energy were also analyzed. [ABSTRACT FROM AUTHOR]

Different types of rotating disk boundary layers were previously shown to be absolutely unstable. The present study checks if this is also true for the flow between narrowly spaced co-rotating disks with merged boundary layers and imposed throughflow. The described method is able to reproduce the absolute instability of the von Kármán boundary layer and of radially outward flow between co-rotating disks with separated boundary layers. Nevertheless, no absolute instability is found for the case of narrow disk spacing with merged boundary layers for both radially inward and outward flow. The data does however show convective instability. Stability maps are provided for the analyzed parameter space. • No absolute, only convective instability found in the analyzed parameter space. • Absolute instability for von Kármán flow and large disk spacing was reproduced. • Different types of convective instability depend on mass flow and rotational speed. • Solution of quadratic eigenvalue problem, discretized by spectral method (Chebyshev). [ABSTRACT FROM AUTHOR]

The plasma rotating electrode process (PREP) is rapidly becoming an important powder fabrication method in additive manufacturing. However, the low production rate of fine PREP powder limits the development of PREP. Herein, we investigated different factors affecting powder formation during PREP by combining experimental methods and numerical simulations. The limitation of increasing the rotation electrode speed in decreasing powder size is attributed to the increased probability of adjacent droplets recombining and the decreased tendency of granulation. The effects of additional Ar/He gas flowing on the rotational electrode on powder formation is determined through the cooling effect, the disturbance effect, and the inclined effect of the residual electrode end face simultaneously. A smaller-sized powder was obtained in the He atmosphere owing to the larger inclined angle of the residual electrode end face compared to the Ar atmosphere. Our research highlights the route for the fabrication of smaller-sized powders using PREP. [Display omitted] • The limitation of increasing the rotational speed in decreasing powder size was clarified. • Cooling and disturbance effects varied with the gas flowing rate. • Inclined angle of the residual electrode end face affected powder formation. • Additional cooling gas flowing could be applied to control powder size. [ABSTRACT FROM AUTHOR]

The paper deals with the cavitation at tongue of a pump-turbine in pump mode, including the typical patterns, unsteady behaviors, and the influence on pump performance and fluid-borne noise. Visualization experiments were conducted under different flow rates and rotational speeds for variation cavity regimes. The results show the patterns can be divided into three regimes with cavitation development: bubble cavitation, cloud cavitation, and lock cavitation for the gas-lock phenomenon and performance plummet. The rotor-stator interaction and jet-wake flow could affect the cavitation generation. The blade passing effect is the leading cause of bubble clusters periodic collapsing or shedding at the early stages of cavitation, while playing a small role as cavities become thick and evaporation rate rises. The combined action of the attached vortex (re-entrant jet) and the depression by pressure gradient outside cavity surface account for the shedding at the developed cloud cavitation stage. Based on the noise measurement by hydrophone at the outlet, the broadband sound in the range of 1000 HZ-2000 Hz can be used for cavitation detection since it can be rarely influenced by operating conditions under non-cavitation. [ABSTRACT FROM AUTHOR]

A comprehensive experimental investigation of water cold plate with different flow configurations for electronic cooling was conducted. Serpentine, parallel and wavy channels cold plate were designed to study the hydrothermal performance of water cold plate for electronic servers cooling. Thermal resistance, pressure drop, Nusselt number, servers' temperatures and performance evaluation criterion were measured, evaluated and compared to evaluate the hydrothermal performance of the different configurations. The results showed that the serpentine channels cold plate has a better thermal performance than both parallel and wavy channels cold plate. The serpentine channels cold plate yields a lower thermal resistance by (6.02–10.5%), (2.4–8.7%) and a higher average Nusselt number by (7.9–13.9%), (6.3–13.7%) compared to parallel and wavy channels cold plate, respectively. Also, the results indicated that the serpentine channels cold plate has a higher pressure drop and pumping power compared to parallel and wavy channels cold plates. Similarly, the results showed that the wavy channel has better thermal performance than parallel channels due to the larger flow path and the rotational flow occurred. The I-Type inlet and outlet configuration used in the wavy channel cold plate provide a lower pressure drop compared to parallel channels however the large flow path. The performance evaluation criterion showed that the wavy channels cold plate has a higher performance evaluation criterion than serpentine channels due to its lower pressure drop. [ABSTRACT FROM AUTHOR]

There is a huge demand for the development of a coarse-grained model of a discrete element method (DEM) to perform a numerical simulation of a high-shear mixer with large-scale production. Recently, we developed a coarse-grained method for granular shear flow (CGSF) for coarse-graining dense granular shear flow. Using the CGSF, we here perform a coarse-grained DEM simulation of a vertical high-shear mixer at different coarse-graining ratios and different rotational speeds of the impeller. The simulation results with the CGSF are quite similar to those in the original case in terms of the particle velocity distribution, geometry of the moving powder bed, and particle mixing behavior. The CGSF is effective at various rotational speeds of the impeller. In particular, the CGSF exhibits high accuracy under a fully developed granular shear flow at a high rotational speed. We demonstrate the effectiveness of CGSF for coarse-grained DEM simulation of a high-shear mixer. [Display omitted] • Coarse-grained method for a granular shear flow was applied to high-shear mixer. • Successful coarse-grained DEM in terms of the particle flow and particle mixing. • Applicability of the coarse-grained method to high-shear mixer was demonstrated. [ABSTRACT FROM AUTHOR]

The blade unit of the tridimensional rotational flow sieve tray (TRST) makes the fluid form a rotational–perforated flow. The analysis of the flow properties of the unit is helpful to understand the hydrodynamic characteristics of TRST. The gas–liquid concurrent flow field was studied using the multi-fluid VOF method. The rotational and perforated flows at each section were analyzed based on the section rotational flow ratios. The section rotational flow ratio for the gas phase was between 0.6 and 0.85, and the transition section of the rotational and perforated flows of the liquid phase was z = 30 mm. The relationships between TRST and blade unit were clarified. The simulation performed for analyzing the mass transfer and structural optimization of the blade unit and TRST. • The rotational and perforated flows are separated by the simulation. • The variation for rotational–perforated flow at each section for gas–liquid phase is studied. • The simulation clarified the transition point of rotational-perforated flow on the blade unit. • The relationships between the blade unit and TRST are analyzed. [ABSTRACT FROM AUTHOR]

• Unsteady rotating flow of nanofluid persuaded by Cattaneo–Christov diffusion is modeled. • Buongiorno model for nanoparticles is taken into account for modeling. • Variational finite element technique is implemented to solve the non-linear systems of partial differential equations. • Chemical reaction with novel aspect of activation energy is accounted. • Skin friction attains higher values for variable viscosity flow than that for constant viscosity flow. This article addressees the dynamics of fluid conveying tinny particles and Coriolis force effects on transient rotational flow toward a continuously stretching sheet. Tiny particles are considered due to their unusual characteristics like extraordinary thermal conductivity, which are significant in advanced nanotechnology, heat exchangers, material sciences, and electronics. The main objective of this comprehensive study is the enhancement of heat transportation. The governing equations in three dimensional form are transmuted in to dimensionless two-dimensional form with implementation of suitable scaling transformations. The variational finite element procedure is harnessed and coded in Matlab script to obtain numerical solution of the coupled non-linear partial differential problem. It is observed that higher inputs of the parameters for magnetic force and rotational fluid cause to slow the primary as well as secondary velocities, but the thermophoresis and Brownian motion raise the temperature. However, thermal relaxation parameter reduces the nanofluid temperature. The velocities for viscosity constant case are faster than that for the variable viscosity, but temperature and species concentration depict opposite behavior. [ABSTRACT FROM AUTHOR]

In this study, we propose an efficient turbine retrofit based on the use of bio-inspired winglets to increase the power production of a wind turbine. To assess the capability of the modified wingtips, we perform the steady-state Reynolds Averaged Navier–Stokes simulations of a DTU 10 MW wind turbine using ANSYS Fluent. The addition of this novel retrofit, inspired by the world's heaviest soaring bird, the Andean condor, aims to increase the power output of a wind turbine while requiring only a modest capital investment. The results indicate that the addition of this retrofit leads to an increase of 9.69% in power production (average of four cases of 8, 9, 10, and 11 m/s). In addition to examining power production, the study also investigates the load distribution on the blade and the flow structures at the blade tip. The results illustrate that the winglets significantly affect the wingtip's vortical structures, leading to an overall increase of 8.5 % in the axial loading along the span. We also show that the presence of the winglet affects the velocity recovery at the wake, leading to a more compact velocity recovery in the wake. • Retrofitting wind turbines with bio-inspired winglets can enhance the power output, with an average increase in energy production by 10%. • The boost in the power production is attributed to the aerodynamic changes introduced by the winglets, not just an increase in the rotor's swept area. • The presence of winglets modifies the vortex structures at the blade tips, reducing the rotational tendencies of the flow near the tip. • The winglets improve wake recovery and have a positive effect on the recovery of velocity deficit. [ABSTRACT FROM AUTHOR]

Micro vortex generators (micro-VGs) could affect cavitation, but the control mechanism is not yet fully understood. Simulating and analyzing the effect of micro vortex generators (micro-VGs) on cloud cavitation is crucial as it can help in suppressing the collapse of cavitation clouds, which is beneficial for marine machinery. In this work, micro-VGs were installed parallel to the initiation of the attached cavity on a NACA0015 hydrofoil. A compressible simulation method was used to obtain the cavitating flows around both the smooth hydrofoil and the one with micro-VGs. Subsequently, the generation of micro vortex flows and the effect of micro-VGs on transient evolution of cloud cavitation were analyzed. The results indicate that the installation of triangular micro vortex generators alters the flow vectors around them, inducing micro vortex flows with opposite rotational directions behind adjacent vortex generators. These vortex generators potentially affect cavitation on the hydrofoil by modifying pressure distribution, vortex structures, and turbulent kinetic energy. Under the specified cloud cavitation operating condition, the shedding and collapse of clouds on the smooth hydrofoil are replaced by the partial separation and collapse of sheet cavitation on the hydrofoil with micro-VGs. Despite a minor loss in time-averaged lift, the lift-to-drag ratio is improved, and the stability of the flow field is enhanced. After installing micro-VGs, the pressure fluctuation is primarily caused by the partial collapse and separation of sheet cavitation. Installing micro VGs at the hydrofoil's leading edge suppresses pressure pulsation. • The installation of triangular micro vortex generators alters the flow vectors around them, inducing micro vortex flows with opposite rotational directions behind adjacent vortex generators. • Under the specified cloud cavitation operating condition, the micro vortex generators could enhance the stability of flow field, improving the lift and drag ratio. • Under the specified cloud cavitation operating condition, installing micro VGs at the hydrofoil's leading edge suppresses pressure pulsation. [ABSTRACT FROM AUTHOR]

A set of time-dependent fully nonlinear mild slope equations is established in terms of velocity vector at still water level and free surface elevation, which is derived from the Euler equations without approximation in nonlinearity and only with the potential flow assumption adopted for bottom slope terms. Apart from the fully nonlinear property, the model is also different from previous nonlinear mild slope equations by adopting the velocity expression accurate to the first-order in bottom slope, which allows the new expressions of higher-order bottom slope terms to be established and the fully nonlinear terms related to bottom slope to be included in the equations. The model can be reduced to the classical mild slope equation for linear waves and the fully nonlinear Boussinesq equations for nonlinear waves. The advantages of the present model are validated against the related laboratory experimental results and demonstrated by comparison with the numerical results of other relevant models. • A set of fully nonlinear mild slope equations is established with the following advantages. • The model possesses the fully nonlinear property and the fully dispersive property. • The model has higher-order bottom slope terms to consider the bottom rapid variation. • The model incorporates the nonlinear terms containing the bottom slope. • The model can take the rotational flow into account in surf zone. [ABSTRACT FROM AUTHOR]

• Construction of flowable interior mesh faces on a blade in tridimensional rotational flow sieve tray (TRST). • The effects of centrifugal force, projected area of the sieve holes, and rotational fluid accumulation were clarified. • The formulas were established to calculate the proportions along the flow direction. The distribution law of the rotational and perforated fluid in tridimensional rotational flow sieve trays (TRST) is the key point for revealing its working mechanism and engineering application. Due to complex issues such as overlapping blades, rotational fluid accumulation, and centrifugal force within TRST, it is very difficult to accurately calculate the flow ratio. In this paper, the flowable interior mesh faces were constructed at all sieve holes on a blade, and the velocity distribution on the interior faces was simulated as the fluid perforated through the different sieves, thus calculating the volume flow rate and ratio of the flow through perforations. And the three-blade unit experiment was designed to calculate the perforated ratio of the entire blade. Compared with the simulated values, the relative differences of the gas and liquid phases were within 25% and 10%, respectively, which were in good agreement. [ABSTRACT FROM AUTHOR]

• Long-term experiments on polymer degradation in turbulent pipe flow. • Comparison of DR in rotational and pipe flow. • Relation of molecular weight distribution and drag reduction. • M w sets minimum drag reduction. • High molecular weight tail drives overshoot. The effect of molecular weight distribution of polyacrylamide (PAAm) on drag reduction was studied in two flow geometries. Commercial PAAm with different weight averaged molecular weights (M w = 5 × 105 to 1.8 × 107 g/mol) were investigated in turbulent pipe and rotational flows. Comparison of PAAm with different molecular weight distributions showed that drag reduction is not only a function of the averaged molecular weight. Broader polymer molecular weight distributions provided increased drag reduction over polymers of same average molecular weight but with a more narrow distribution. The role of distribution widths is of significance as polymer degradation in turbulent flows causes narrowing of the molecular weight distributions. Multiple linear regression was employed to connect weight fractions of polyacrylamide with drag reduction. Multiple linear regression was successfully applied to describe drag reduction in turbulent pipe and rotational flows indicating that drag reduction can be quantitatively derived from the molecular weight distribution of PAAm. [Display omitted] [ABSTRACT FROM AUTHOR]

In common parabolic trough solar collectors (PTC), solar irradiation is concentrated at the bottom of the absorber tube, causing high surface temperatures, thermal stresses, and deflections with subsequent damages and costs. Also, the performance improvement of PTCs is always of significant importance. The new idea of rotating the absorber tube is proposed, and its effects on the PTC performance are studied experimentally. The effects of the working fluid flow rate (Re number) and the rotational velocity of the absorber tube (Ta number) on the energy characteristics of the PTC are analyzed. Results indicate that the optimal selection of the rotational speed makes it possible to reduce and control the temperature of the absorber by about 60% reduction in the fluid-tube temperature difference, and 15% reduction in the maximum surface temperature. Furthermore, about 17% enhancement in the efficiency of the PTC is attained. The share of the natural and both the rotational and mass flow forced convection forces in the total heat transfer is analyzed through Gr, Re, Ta, and a convection evaluation parameter (CEP). Ta/Re ratio and CEP provide valuable information such that, CEP<0.5 and T a / R e ≈ 0.5 led to the highest efficiency (average and maximum efficiencies of 30% and 87% respectively). A novel active method, rotating absorber tube, is used to improve PTC performance. Experimental analysis performed for various Gr , Re and Ta numbers. Rotating absorber tube could improve collector efficiency about 17.5%. Rotating absorber tube could reduce the maximum tube temperature about 15%. Ta to Ra ratio of about 0.5 could result in the highest collector efficiency. [ABSTRACT FROM AUTHOR]

Compared with other ways to produce hydrogen, water electrolysis is the best way to obtain ultra-pure hydrogen, but its low energy efficiency greatly limits its wide application. It was proved that external magnetic field can reduce energy consumption, thereby increase electrolysis efficiency. Most of the researchers are focused on the impact of uniform magnetic field but few on a non-uniform one. To address the industrial operation reality, in our work, water electrolysis was operated using alkaline solution and plate electrodes in a non-uniform Magnetic field. The results show that a rotational flow on the vertical plane was formed by Lorentz force within the entire cell range. Although the entrainment effect of rotating flow made the cell full of microbubbles, the cell voltage was still reduced. By measuring the voltage difference of cathode side and anode side, we think that the bubble layer in the vicinity of the electrode surface matters the most among the sources of electric resistance. And the velocity distribution near the electrode was measured by PIV, it reveals that MHD flow is the dominant effect on the flow field of the cell. The results show that non-uniform magnetic field has potential merit in industrial electrolysis process. • Water electrolysis experiments are performed in a non-uniform magnetic field. • A rotational magnetohydrodynamic convection is induced by magnetic field. • The velocity distribution in the cell has been obtained by PIV method. • The bubble layer near electrodes may be the main source of resistance. [ABSTRACT FROM AUTHOR]

Viscous/inviscid interaction methods employing velocity decomposition have been explored for reducing computational costs in external flow problems. For this, viscous simulations are made in reduced computational domains encompassing the rotational flow region. The coupling of potential and viscous solutions is made on a boundary of negligible vorticity, assessed by means of sampling lines normal to the body wall and the wake. For bluff bodies, sampling lines at the rear tend to be submerged in rotational regions, making it difficult to build the coupling boundary. For overcoming this difficulty, it is proposed in this work to use a transpiration auxiliary surface to represent the influence of the body and the wake. The null vorticity criterion for finding the coupling boundary is also proposed. The proposals are tested for laminar flows around a square, a circular cylinder and a semi-ellipse. The obtained results are compared with those for extended domains. The velocity decomposition with an auxiliary surface is able to reproduce with satisfactory accuracy the flow fields in the reduced domain as well as the drag coefficient on the bodies. [ABSTRACT FROM AUTHOR]

A description for magnetohydrodynamic effects on the transient rotational flow of Oldroyd-B nanofluids is considered. The temperature and concentration distributions are associated with Cattaneo-Christove double diffusion, Brownian motion, thermophoresis, Soret, and Dufour. The governing equations in the three-dimensional form are transmuted into dimensionless two-dimensional form with the implementation of suitable scaling transformations. The variational finite element procedure is harnessed and coded in Matlab script to obtain the numerical solution of the coupled non-linear partial differential problem. The varying patterns of velocities, skin friction coefficients, Nusselt number, Sherwood number, fluid temperature, and concentration functions are computed to reveal the physical nature of this study. It is observed that higher inputs of the parameters for magnetic force, Deborah number, rotational fluid, and cause to slow the primary as well as secondary velocities but they raise the temperature like thermophoresis and Brownian motion does. However, thermal relaxation parameter reduces the nanofluid temperature. The local heat transfer rate reduces against Nt, rotational, and Nb parameters, and it is higher for Prandtl number. The current FEM (finite element method) solutions have been approved widely with the recent published results, showing an excellent correlation. The examination has significant applications in the food industry and relevance to energy systems, biomedical, and modern technologies of aerospace systems. Unlabelled Image • Unsteady rotating flow of Oldroyd-B nanofluid persuaded by double diffusion Cattaneo Christov is modeled. • Buongiorno model for nanoparticles is taken into account for modeling. • Finite element technique is implemented to solve the non-linear systems of partial differential equations. • Higher inputs of the parameters for rotational fluid cause to slow the primary as well as secondary velocities. [ABSTRACT FROM AUTHOR]

• Exergy drop within a tube enhanced by tapes has been investigated. • Al 2 O 3 was dispersed into water to reduce thermal irreversibility. • At TT n = 2, temperature of absorber declines about 4.26% with increase of Re. • Utilize of turbulator led to the greatest second law efficiency factor up to 0.78. • If Re augments, η II augments about 92.86% when TT n = 4. Current article deals with investigation of exergy drop within a tube enhanced by tapes. Hydrothermal treatment and exergy behavior of carrier fluid were scrutinized to find the best design regarding to greater available energy. Second law efficiency (η II ) and exergy loss (X d) are main goal functions and simulations were reported for various number of tapes (TT n) and Reynolds number (Re). As tapes installed in the pipe, cross section area decreases and significant increment occurs in swirl flow. Intensification of rotational flow with rise of TT n makes higher disruption of flow and resistance enhances. The greatest impacts of Re and TT n on exergy ratio are reduction about 24.45% and 45.45%, respectively. Second law efficiency (η II ) for TT n = 3 is 2.04 times greater than that of TT n = 1 when Re = 4000. If Re augments, η II augments about 92.86% when TT n = 4. Utilize of turbulator led to the greatest second law efficiency factor up to 0.78 when TT n = 4 when Re = 20000. Exergy drop becomes 2.22 times smaller if Re augments when TT n = 1. Value of exergy drop for Re = 4000 is 2.75 times higher than that of Re = 20,000 when TT n = 4. When Re = 20,000, growth of number of tapes to 3 makes X d to reduce about 34.54%. In view of energy saving, it is better to install the tapes at low Re while it possess higher exergy drop. Influence of Re on temperature of absorber is higher than that of nanomaterial flow. At TT n = 2, temperature of absorber declines about 4.26% with increase of Re while nanomaterial temperature reduces about 0.43%. [ABSTRACT FROM AUTHOR]

Reasonable structural design for a inlet pipe is an important way of improving the hydrocyclone's separation performance. The inlet can not only guide and accelerate particles but also achieve pre-separation of particles. However, there still lacks of clear governing equation of ideal inlet pipe. In order to gain in-depth understanding of the effects of different structures of the inlet pipes on the inner flow field and separation performance of the hydrocyclone, this study employed numerical simulation to compare the performances of the inlet pipe with different structures (linear, arc-type, spiral-line inlet pipe, denoted as Type A, Type B and Type C). Moreover, a novel hydrocyclone (Type D) mainly consisted of spiral-line inlet pipe, arc-type overflow pipe and parabolic cone was developed in this study. The simulation results fit well with classical experimental data, thereby validating the accuracy of the simulation results. Based on the simulation results, using Type B and Type C inlet pipe, both pressure drop and tangential velocity increased, which facilitated the movement of coarse particles towards the wall as well as finer particles towards the center. The pressure drop and the tangential velocity were greatest in Type C but lowest in Type D. The axial velocity of the internal rotational flow in a curved inlet pipe (especially Type D) was low, which can prolong the retention time of fine particles and contribute to more thorough separation. Using Type D inlet pipe, both the short-circuit flow rate and the turbulent viscosity were effectively lowered, which reduced the occurrence probability of eddy and enhanced the smoothness of particle movement. In addition, using spiral-line inlet pipe can promote the movement of coarse particles towards the wall, which significantly enhanced the recovery rate of coarse particles. Conclusively, Type D inlet pipe exhibited the highest separation precision and the lowest cut size, accompanied with better product quality. Unlabelled Image • The effect of hydrocyclone inlet pipe on separation performance was studied. • The accuracy of the model used in the numerical simulation was verified. • The developed novel hydrocyclone had lower turbulent viscosity. • The developed novel hydrocyclone possessed better product quality. [ABSTRACT FROM AUTHOR]

To explore the load impact and instantaneous flow characteristics of a tubular pump under unconventional operating conditions, the runaway condition caused by the unit power failure are investigated. Unsteady three-dimensional (3D) numerical simulation and model test were executed on whole flow system of the pump, where a 3D VOF method was specifically adopted to simulate water surfaces of the upstream and downstream reservoirs. The results of numerical simulation in terms of system performance parameters and runaway speed presented a quite good agreement with the experimental data. During the transient process, both the rotational speed and flow rate of the pump unit were found to rapidly decrease with time until maximum runaway speed (1.51 n 0) was reached, where however, a time lag of 0.7s between the rotational speed and flow rate has been noticed. The explored increase of pressure pulsations is generally believed to have taken source from incurred water shock waves, where the main pulsation frequencies throughout the whole flow passage were the blade passing frequency (BPF) and its harmonics. Large flow vortical structures immerged within the rear guide vanes when the flow rate decreased to zero, while the same flow vortices appeared within the front guide vanes when the impeller rotational speed gradually fell to zero. This study's results provide a meaningful reference about pump transient operations, leading to the prevention of associated structural vibrations and possible blade cracks, for safe operations of the pumping stations. • Power-off process of a pump was studied by using numerical simulation and model test. • 3D VOF model was specifically adopted to simulate free surfaces of reservoirs. • Maximum runaway speed of 1.51 times the rated speed was observed during the process. • External characteristics and flow regime were analyzed for the transient process. [ABSTRACT FROM AUTHOR]

Over the years, the Discrete Element Method (DEM) has attracted significant attention for its capacity to simulate granular flows because it captures physical phenomena that cannot be observed using continuum methods. However, the simulation of granular systems with DEM is computationally demanding, especially in the case of systems in rotation. One solution is to perform simulations in a non-inertial rotating frame of reference, which requires the addition of fictitious velocity-dependent forces such as the Coriolis force. We assess the numerical feasibility and accuracy of such DEM simulations. We show that the velocity Verlet scheme in its classical form no longer defines a symplectic map and is no longer of second order when there are velocity dependent forces. Nevertheless, our study of a dense particle flow within a rotating hourglass shows that the relevant properties of such flow are accurately reproduced in a non-inertial frame and that computational performance is improved. Unlabelled Image • Modeling of granular flow in a rotational frame using DEM is investigated. • A velocity dependent force degrades the order of the velocity Verlet scheme. • The symplectic property of the velocity Verlet scheme is lost with the Coriolis force. • It is possible to perform DEM in a rotating frame if there are dissipative forces. [ABSTRACT FROM AUTHOR]

The multi-regime CFB riser equipped with a bottom diameter-enlarged section has been demonstrated to be efficient in increasing the overall solids holdup and enhancing the gas-solid contact previously. In this work, the swirling gas nozzles have been incorporated into the diameter-enlarged section to further improve the gas-solid mixing behavior, and the effect of the nozzle directions on the gas-solid flow patterns has been systematically studied. The results indicated that, with the sacrifice of small amount of solids circulation rate, the solids concentration in the diameter-enlarged section using swirling gas nozzles was further increased, and the height of the dense phase was elevated, providing more available catalyst for gas-solid contact reactions. In addition, the gas phase injected through the swirling nozzles exhibited a rotational rising flow behavior and effectively penetrated into the solid phase near the wall region, consequently intensifying the gas-solid fluctuation and contact. Unlabelled Image • The swirling gas nozzles were incorporated into the multi-regime riser. • The effects of directions of swirling gas nozzles on flow structure were studied. • Solids holdup was increased with negligible sacrifice in solids circulation rate. • Gas-solid contact and mixing behaviors were improved by the swirling gas flow. [ABSTRACT FROM AUTHOR]

• Optic flow arising from self-motion provides a rich source of information. • Optic flow detection and related behaviors have been studied extensively in insects. • Translational flow affords spatial vision and estimation of travel speed. • Rotational flow mediates estimation and compensation of involuntary course changes. • All optic flow-based behaviors likely depend on the same local motion detectors. Vision is an important sensory modality for navigation in roaming animals. In contrast to most vertebrates, insects usually must cope with low resolution retinal images and the inability to infer spatial features using accommodation or stereovision. However, during locomotion, the retinal input is dominated by characteristic panoramic image shifts, termed optic flow, that depend on self-motion parameters and environmental features. Therefore, optic flow provides a rich source of information guiding locomotion speed as well as the position and orientation of animals over time relative to their surroundings. Here, focusing on flight behavior, we describe the strategies and putative underlying neuronal mechanisms by which insects control their course through processing of visual motion cues. [ABSTRACT FROM AUTHOR]

• Thermal performance of supercritical n-decane in self-rotational circular/rectangular tubes was comprehensively investigated. • The relaminarization and centrifugal force determine the uneven temperature and velocity, respectively, in circular tubes. • The velocity near the wall is not close to zero in rectangular tubes. Concerning the rotation flight of a hypersonic vehicle centered on its geometric axis, the rotational flow and heat transfer characteristics of supercritical n-decane in horizontal circular and rectangular tubes were comprehensively analyzed based on numerical simulation. The computational domain was established and the corresponding governing equations of mass conservation, momentum conservation, and energy conservation were mathematically formulated as well were the thermophysical properties and boundary conditions. A procedure for setting up the numerical simulation was finally implemented. A mesh independence study in the case of a rotating speed of 300 rpm and a turbulence model study based on a stationary/swinging tube were comprehensively conducted and the RANS model was well validated. For the circular tube, the wall temperature distribution trend along the flow direction is similar but the magnitude is not uniform. Also, the fluid temperature near the upper wall is larger than that in the vicinity of the lower wall, i.e., the relaminarization plays an essential role in this phenomenon. The velocity difference near the wall can be weakened by the centrifugal force. For the rectangular tube, the velocity magnitude and temperature distribution are found to be greatly affected by the rotation (i.e., centrifugal force). The relative temperature magnitude near the upper and lower walls will be reversed at a rotation speed of n = 100–500 rpm. Subsequently, a symmetrical temperature distribution can be observed once the speed increases to a certain value (e.g., n = 700–900 rpm). In summary, the centrifugal force plays a more important role in a rectangular tube than in a circular tube. [ABSTRACT FROM AUTHOR]

Incorporation of the free-surface dynamics plays an important role in the numerical modelling of non-hydrostatic flows. In the present work a novel semi-Lagrangian splitting (SLS) scheme for the free-surface Euler system is proposed. Using the operator splitting technique, the three main components emerge: the multilayer Shallow Water Equations (mSWE) (enforcing the free-surface kinematics), the Vertical Remeshing Operator (VRO) (that blends the Eulerian and Lagrangian techniques) and the Pressure Correction Operator (PCO) (that is a classic elliptic equation used in projection-type pressure coupling schemes). The first two are solved by two separate Finite Volume schemes, while the latter is resolved in a Finite Difference manner. In order to assess the SLS's performance, numerical simulations of periodic waves and solitons propagating over variable bathymetry are performed. The last case concerns the propagation of waves on top of a shear current, showcasing the use of the SLS on rotational flows. The results are compared with experiments and analytic relations and the method is proven to be robust and efficient. • A novel semi-Lagrangian splitting (SLS) scheme for the free-surface Euler system is proposed. • Consistent derivation from the free-surface Euler system through operator splitting. • Simple incorporation of free-surface dynamics by introduction of the layer indicators. • Highly modular algorithm treating sequentially the 3 simple components multilayer SWE, VRO, PCO. • Simulations of periodic waves and solitons over variable bathymetry in the presence of currents. [ABSTRACT FROM AUTHOR]

This paper is concerned with the radiated wave and the rotational flow fields generated by the forced oscillations of the water columns within surface-piercing hollow cylinders. The present study utilised Open Foam as the viscous flow solver to numerically model the forced oscillations. An investigation of the radiated waves in the fields near the water columns confirms two distinct nonlinear characteristics. These are progressively reduced amplitude and progressively reduced phase difference. An evaluation of the rotational flow fields around the mouths of the water columns helps explain their origins. This study confirms that the nonlinear characteristics in the near-field are physically caused by the formation and motion of vortex ring at the bottom edge of the cylinder. Interestingly, the progressively reduced amplitude is not evident in the far-field. All these new findings support the confirmation regarding the appropriateness of linear radiation theory and the implication of the vortex motion on the effective draft of a fixed cylindrical Oscillating Water Column (OWC). • Wave radiations generated by forced oscillations of water columns are studied. • Near-field radiated waves have progressive reductions in amplitude and phase difference. • Vortex formation and motion cause nonlinear characteristics in near field. • Far-field radiated waves exhibit insignificant progressive amplitude reductions. • Location of vortex closest to the mouth affects the effective draft of water column. [ABSTRACT FROM AUTHOR]

The normal impingement of the rotational stagnation-point flow on a surface executing bi-axial stretching is studied. This problem is governed by two parameters, α the dimensionless stretching along the x -axis, and β the dimensionless stretching along the y -axis. Consideration is given to both stretching and shrinking surfaces. At fixed β turning points are found at α = α c for which no solutions exist for α < α c and dual solutions exist for all α > α c . Shear stress results are presented in graphical form as are sample similarity velocity profiles. The boundary for the existence of solutions is presented over a range of the governing parameters. Shrinking in both directions occurs only over the relatively small region − 1. 212 ≤ α < 0 and − 1. 212 ≤ β < 0. An investigation of the zero stress values of F ′ ′ (0) reveals a bifurcation in solutions for β = − 0. 075 at α = − 0. 07675 that leads to triple solutions for α ≥ 0. 21. This bifurcation is responsible for a discontinuity that appears in the lower branch of the F ′ ′ (0) = 0 curve at this value of β. [ABSTRACT FROM AUTHOR]