Fluid Rotation Research Articles

Light Diffraction in Magnetic Emulsions with High Interfacial Tension

Specific features of small-angle light scattering by aqueous magnetic emulsions under the action of a magnetic field and a hydrodynamic field of a rotating fluid have been investigated. It has been shown that the experimentally observed diffraction lines that have no pronounced maxima and minima are due to diffraction on an irregular system of droplet chains arising in the magnetic field. Under the combined action of the magnetic and hydrodynamic fields, a rotation of a diffraction line is observed. This phenomenon has been interpreted using the known models of orientation of extended particles having complex shapes. It has been shown that the experimental nonlinear dependence of the rotation angle of a droplet chain on the angular rate of fluid rotation may be explained by S-shaped deformations of a chain.

Hall and ion‐slip effects on MHD free convection flow of rotating Jeffrey fluid over an infinite vertical porous surface

AbstractAn attempt has been made to explore Hall and ion‐slip effects on an unsteady magnetohydrodynamic rotating flow of an electrically conducting, viscous, incompressible, and optically thick radiating Jeffrey fluid past an impulsively vertical moving porous plate. Analytical solutions of the governing equations are obtained by Laplace transform technique. The analytical expressions for skin friction, Nusselt number, and Sherwood number are also evaluated. The velocity, temperature, and concentration distributions are displayed graphically in detail. From engineering point of view, the changes in skin friction, Nusselt number, and Sherwood number are observed with the computational results presented in a tabular manner. It is observed that the effects of rotation and Hall current tend to accelerate secondary velocity and decelerate primary velocity throughout the boundary layer region. Thermal and concentration buoyancy forces tend to accelerate both velocity components. Thermal radiation and thermal diffusion tend to enhance fluid temperature throughout the boundary layer region. Rotation and Jeffrey fluid parameters tend to enhance both stress components.

How baroclinic vortices intensify resulting from erosion of their cores and/or changing environment

The structure of circular baroclinic vortices in rotating stratified fluids is examined in order to rationalize the observed amplification of fluid rotation inside long-lived geophysical vortices during their evolution. New relations between basic vortex parameters at horizontal mid-depth are derived in order to compare vortices with the same potential vorticity extremum at the vortex center. The fluid rotation is shown to be larger for smaller vortices, which can be interpreted as a capability of vortex amplification due to radial redistribution of the angular momentum resulting from erosion of their cores and/or changing environment with the cyclo-geostrophic adjustment. The results are consistent with observational, numerical, and laboratory examples. This mechanism of vortex intensification has important implications for understanding the longevity of coherent geophysical vortices.

Push/Pull Inequality Based High-Speed On-Chip Mixer Enhanced by Wettability.

In this paper, a high-speed on-chip mixer using two effects is proposed, i.e., push/pull inequality and wettability. Push/pull inequality and wettability are effective for generating a rotational fluid motion in the chamber and for enhancing the rotational speed by reducing the viscous loss between the liquid and channel wall, respectively. An on-chip mixer is composed of three components, a microfluidic channel for making the main fluid flow, a circular chamber connected to the channel for generating a rotational flow, and an actuator connected at the end of the channel allowing a push/pull motion to be applied to the liquid in the main channel. The flow patterns in the chamber under push/pull motions are nonreversible for each motion and, as a result, produce one-directional torque to the fluid in the circular chamber. This nonreversible motion is called push/pull inequality and eventually creates a swirling flow in the chamber. Using hydrophilic treatments, we executed the experiment with a straight channel and a circular chamber to clarify the mixing characteristics at different flow speeds. According to the results, it is confirmed that the swirling velocity under appropriately tuned wettability is 100 times faster than that without tuning.

Temporal shaping and time-varying orbital angular momentum of displaced vortices

The fundamental mode of rotation in quantum fluids is given by a vortex whose quantized value yields the orbital angular momentum (OAM) per particle. If the vortex is displaced (off-centered) from the reference point for rotation, the angular momentum is reduced and becomes fractional. Such displaced vortices can further exhibit a peculiar dynamics in the presence of confining potentials or couplings to other fields. We study analytically a number of 2D systems where displaced vortices exhibit a noteworthy dynamics, including time-varying self-sustained oscillation of the OAM, complex reshaping of their morphology with possible creation of vortex–antivortex pairs, and peculiar trajectories for the vortex core with sequences of strong accelerations and decelerations that can even send the core to infinity and bring it back. Interestingly, these do not have to occur conjointly, with complex time dynamics of the vortex core and/or their wavepacket morphology possibly taking place without affecting the total OAM. Our results generalize to simple and fundamental systems a phenomenology recently reported with Rabi-coupled bosonic fields, showing their wider relevance and opening prospects for new types of control and structuring of the angular momentum of light and/or quantum fluids.

Detachment fold duplexes within gravity-driven fold and thrust systems

Fold duplexes transfer displacement from a lower to an upper bounding detachment system via trains of folds with broadly parallel geometries. While they have been previously recognised in orogenic systems where they are considered to be kinematically equivalent to imbricating thrust ramps, we here describe the first example from a gravity-driven fold and thrust system (FATS) developed within late-Pleistocene mass transport deposits (MTDs) that formed around the Dead Sea Basin. The recognition in this study of basal and upper detachments that bound the FATS, together with later thrust ramps that imbricate the previously folded sequence, indicates that a fold duplex model is applicable in this case. Truncation of synclinal hinges, together with trapping of duplex roof stratigraphy in synclinal fold cores indicates that initiation of buckling precedes detachments, which then propagated along the upper and lower boundaries of the FATS to create a fold duplex. Downslope-verging folds, which are bound by the detachments, are subsequently cut by thrust ramps with greatest displacement recorded where ramps branch from the basal detachment. As thrust displacement increases then ramp angles generally reduce, which allows thrusts to continue to move and accrue larger displacements. Sequential flattening of lower thrusts in overstep sequences may create apparent ‘back-steepening’ up the slope in what superficially resembles ‘pseudo-piggyback’ sequences. Flattening of thrusts is achieved through tightening, rotation and expulsion of wet sediment and fluid from the cores of footwall synclines and is a consequence of loading from overlying thrust sheets. We speculate that expelled fluids may pond directly beneath overlying detrital-rich units that act as baffles and locally increase fluid pressures thereby facilitating further movement along the upper detachment. We establish a new model, whereby the vergence of structures formed above the upper detachment depends on the relative rates of roof and FATS translation, with slower downslope translation of the roof generating upslope verging folds in a ‘sub-active’ roof, while more rapid movement of a ‘super-active’ roof creates downslope verging folds. The observation that such patterns of minor fold vergence in the roof still largely correspond with the position of folds and thrusts in the underlying FATS indicates that only limited relative translation subsequently occurred between the roof and the FATS. This suggests that displacement must have transferred upwards to new upper detachments shortly after the folds in the roof were created, thereby ‘fixing’ the spatial correlation. As older detachments are folded and ‘lock up’, displacement migrates to new upper detachments that develop along pristine ‘easy-slip’ laminations at higher stratigraphic levels, thereby thickening the deforming FATS towards the sediment free surface. The creation of these new upper detachments at higher stratigraphic levels, together with the development of local overstep imbricate sequences are the principal differences between fold duplexes observed in orogenic settings and those in surficial gravity-driven FATS.

Unsteady magneto-hydrodynamic transport of rotating Maxwell nanofluid flow on a stretching sheet with Cattaneo–Christov double diffusion and activation energy

A description of magnetohydrodynamic effects on the transient rotational flow of Maxwell nanofluids is considered. The temperature and concentration distributions are associated with Cattaneo- Christove double diffusion, Brownian motion and thermophoresis. The diffusion of chemically reactive specie is investigated with Arrhenius activation energy. 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, the 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 recently 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.

Experimental study on dynamic mechanism of vortex evolution in a turbulent boundary layer of low Reynolds number

The dynamic mechanism of the vortex generation and evolution process in a fully developed turbulent boundary layer with Reθ =97–194 is experimentally investigated. In this study, a moving single-frame and long-exposure (MSFLE) imaging method and a moving particle image velocimetry/particle tracing velocimetry (M-PIV/PTV) are designed and implemented for measuring the temporal and spatial evolution of vortex cores in both qualitative and quantitative ways, respectively. On the other hand, the Liutex vector, which is a new mathematical definition and identification of the vortex core proposed by Liu’s group, is first applied in the experiment for the structural visualization and quantitative analysis of the local fluid rotation. The results show that an intuitional process of vortex evolution can be clearly observed by tracking the vortex using MSFLE and verify that the roll-up of the shear layer induced by shear instability is the origin of vortex formation in turbulence. Furthermore, a quantitative investigation in terms of the critical vortex core boundary (size) and its accurate rotation strength is carried out based on the Liutex vector field analysis by M-PIV/PTV. According to statistics of the relation between vortex core size and the rotation strength during the whole process, the phy sical mechanism of vortex generation and evolution in a turbulent boundary layer of low Reynolds number can be summarized as a four-dominant-state course consisting of the “synchronous linear segment (SL)-absolute enhancement segment (AE)-absolute diffusion segment (AD)-skewing dissipation segment (SD)”.

Finite Element Study of Magnetohydrodynamics (MHD) and Activation Energy in Darcy–Forchheimer Rotating Flow of Casson Carreau Nanofluid

Here, a study for MHD (magnetohydrodynamic) impacts on the rotating flow of Casson Carreau nanofluids is considered. The temperature distribution is associated with thermophoresis, Brownian motion, and heat source. The diffusion of chemically reactive specie is investigated with Arrhenius activation energy. The governing equations in the 3D form are changed 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 variation patterns of Sherwood number, Nusselt number, skin friction coefficients, velocities, concentration, and temperature functions are computed to reveal the physical nature of this examination. It is seen that higher contributions of the magnetic force, Casson fluid, and rotational fluid parameters cause a raise in the temperature like thermophoresis and Brownian motion does but also causes a slowing down in the primary as well as secondary velocities. The FEM solutions show an excellent correlation with published results. The current study has significant applications in the biomedical, modern technologies of aerospace systems, and relevance to energy systems.

Finite element investigation of Dufour and Soret impacts on MHD rotating flow of Oldroyd-B nanofluid over a stretching sheet with double diffusion Cattaneo Christov heat flux model

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.

Finite Element Study of MHD Impacts on the Rotating Flow of Casson Nanofluid with the Double Diffusion Cattaneo—Christov Heat Flux Model

A study for MHD (magnetohydrodynamic) impacts on the rotating flow of Casson nanofluids is considered. The concentration and temperature distributions are related along with the double diffusion Cattaneo–Christov model, thermophoresis, and Brownian motion. The governing equations in the 3D form are changed 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 nonlinear partial differential problem. The variation patterns of Sherwood number, Nusselt number, skin friction coefficients, velocities, concentration, and temperature functions are computed to reveal the physical nature of this examination. It is seen that higher contributions of the magnetic force, Casson fluid, and rotational fluid parameters cause to raise the temperature like thermophoresis and Brownian motion does but causes slowing the primary as well as secondary velocities. The FEM solutions showing an excellent correlation with published results. The current study has significant applications in the biomedical, modern technologies of aerospace systems, and relevance to energy systems.

PF-LBM Modelling of Dendritic Growth and Motion in an Undercooled Melt of Fe-C Binary Alloy

In the present study, a two-dimensional phase field model coupled with Lattice Boltzmann method (PF-LBM) is proposed to predict the dendritic growth and motion in the melt of Fe-C binary alloy, where the phase field method (PF) is used to calculate the dendritic growth, including the phase field and the concentration field, and the lattice Boltzmann method (LBM) is used to calculate the flow field. The dendrite motion is determined by Newton’s Second Law and tracked by Lagrangian point in a Cartesian coordinate system. Later, the model validations were performed with the benchmark of a solid particle settlement in a stagnant fluid and particle motion in a shear flow, and the results show that the present model is capable of predicting the solid particle motion in the fluid flow. Finally, the model is adopted to investigate the dendritic growth and motion in a forced fluid flow (laminar flow or rotational flow), and the dendrite settlement in a terrestrial environment. The results show that when the forced fluid flow is a laminar flow, the free dendrite would be driven to translate, and the relative velocity between the dendrite and flow fluid decreases, resulting in weak influence of fluid flow on the dendritic growth. When the forced fluid flow is a rotational fluid flow, the dendrite would centrifugally rotate on the domain center with a counterclockwise self-spinning, and the rotation radius becomes larger and larger. For the case of dendrite settlement in a terrestrial environment, the relative movement between the dendrite and melt promotes the downward branch growth, but inhibits the upward branch growth, and two vortices form at the wake region of dendrite. Therefore, the settling dendrite shows a significant asymmetrical morphology.

Computational modeling of media flow through perfusion-based bioreactors for bone tissue engineering.

Bioreactor system has been used in bone tissue engineering in order to simulate dynamic nature of bone tissue environments. Perfusion bioreactors have been reported as the most efficient types of shear-loading bioreactor. Also, combination of forces, such as rotation plus perfusion, has been reported to enhance cell growth and osteogenic differentiation. Mathematical modeling using sophisticated infrastructure processes could be helpful and streamline the development of functional grafts by estimating and defining an effective range of bioreactor settings for better augmentation of tissue engineering. This study is aimed to conduct computational modeling for newly designed bioreactors in order to alleviate the time and material consuming for evaluating bioreactor parameters and effect of fluid flow hydrodynamics (various amounts of shear stress) on osteogenesis. Also, biological assessments were performed in order to validate similar parameters under implementing the perfusion or rotating and perfusion fluid motions in bioreactors' prototype. Finite element method was used to investigate the effect of hydrodynamic of fluid flow inside the bioreactors. The equations used in the simulation to calculate the velocity values and consequently the shear stress values include Navier-Stokes and Brinkman equations. It has been shown that rotational fluid motion in rotating and perfusion bioreactor produces more velocity and shear stress compared with perfusion bioreactor. Moreover, implementing the perfusion together with rotational force in rotating and perfusion bioreactors has been shown to have more cell proliferation and higher activity of alkaline phosphatase enzyme as well as formation of extra cellular matrix sheet, as an indicator of bone-like tissue formation.

Thermodynamics Analysis of an MHD Casson Fluid Flow Through a Rotating Permeable Channel with Slip and Hall Effects

In this paper, the inherent irreversibility in a Casson fluid flow through a rotating permeable microchannel with wall slip and Hall current is investigated. It is assumed that the lower wall is subjected to the velocity slip and fluid injection while the fluid suction occurs at the upper wall. The nonlinear governing equations of momentum and energy balance are obtained, analyzed and solved numerically using the shooting technique together with the Runge-Kutta-Fehlberg integration method. Pertinent results depicting the effects of various embedded thermophysical parameters on the fluid velocity, temperature, skin friction, the Nusselt number, entropy generation rate and the Bejan number are presented graphically and discussed. It is found that the entropy generation rate is enhanced by fluid rotation and velocity slip but lessened with a rise magnetic field intensity. Our results will undoubtedly augment the design and efficient operation of micro-cooling devices, micro-heat exchangers, micropumps and micro-mixing technologies.

Noise Reduction of UAV Using Biomimetic Propellers with Varied Morphologies Leading-edge Serration

The Leading-Edge (LE) serrations on owls’ wings are known to be responsible for silent flight. However, this design has rarely been applied to reduce the noise of rotational rotor propellers and the morphologies of the existing serration designs are diverse. Here, we present a comparative study of LE serrations with different morphologies in terms of the effectiveness in suppressing noise and promoting thrust forces. The performances of biomimetic propellers are investigated by Computational Fluid Dynamics (CFD) simulations and rotation experiments. The simulation results reveal that LE serrations could reduce velocity fluctuations and change the lamina-turbulent transition and turbulence distribution on the suction surface of propeller, but the morphology of the serrations influences its effectiveness. Rotation testing results indicate that the sawtooth propeller has the best performance on noise reduction (on average 2.43 dB and in maximum 4.18 dB) and simultaneously enhancing the thrust forces (3.53%). The largest practical noise reductions (4.73 dB and 3.79 dB) using the sawtooth propeller are observed when the quad-rotor Unmanned-Aerial Vehicle (UAV) is hovering at heights of 5 m and 8 m, respectively. Our results indicate the robustness and usefulness of owl-inspired biomimetic serration devices for aero-acoustic control and aerodynamic performance promotion on propeller designs. This finding is expected to contribute to suppressing the sound of propeller and the rotor-based aircraft.

Reduced-order modelling of thick inertial flows around rotating cylinders

A new model for the behaviour of a thick, two-dimensional layer of fluid on the surface of a rotating cylinder is presented, incorporating the effects of inertia, rotation, viscosity, gravity and capillarity. Comparisons against direct numerical simulations (DNS) show good accuracy for fluid layers of thickness of the same order as the cylinder radius, even for Reynolds numbers up to . A rich and complex parameter space is revealed, and is elucidated via a variety of analytical and numerical techniques. At moderate rotation rates and fluid masses, the system exhibits either periodic behaviour or converges to a steady state, with the latter generally being favoured by greater masses and lower rotation rates. These behaviours, and the bifurcation structure of the transitions between them, are examined using a combination of both the low-order model and DNS. Specific attention is dedicated to newly accessible regions of parameter space, including the multiple steady state solutions observed for the same parameter values by Lopes et al. (J. Fluid Mech., vol. 835, 2018, pp. 540–574), where the corresponding triple limit point bifurcation structure is recovered by the new low-order model. We also inspect states in which the interface becomes multivalued – and thus outside the reach of the reduced-order model – via DNS. This leads to highly nonlinear multivalued periodic structures appearing at moderate thicknesses and relatively large rotation rates. Even much thicker films may eventually reach steady states (following complex early evolution), provided these are maintained by a combination of forces sufficiently large to counteract gravity.

Giant spin hydrodynamic generation in laminar flow

Hydrodynamic motion can generate a flux of electron-spin’s angular momentum via the coupling between fluid rotation and electron spins. Such hydrodynamic generation, called spin hydrodynamic generation (SHDG), has recently attracted attention in a wide range of fields, especially in spintronics. Spintronics deals with spin-mediated interconversion taking place on a micro or nano scale because of the spin-diffusion length scale. To be fully incorporated into the interconversion, SHDG physics should also be established in such a minute scale, where most fluids exhibit a laminar flow. Here, we report electric voltage generation due to the SHDG in a laminar flow of a liquid-metal mercury. The experimental results show a scaling rule unique to the laminar-flow SHDG. Furthermore, its energy conversion efficiency turns out to be about 105 greater than of the turbulent one. Our findings reveal that the laminar-flow SHDG is suitable to downsizing and to extend the coverage of fluid spintronics.

Effects of temperature and fluid velocity on beer pasteurization in open and closed loop heating systems: numerical modeling and simulation

Abstract A two-dimensional symmetric heat transfer model and a fluid rotation model were established to study beer pasteurization process through the COMSOL Multiphysics software. Two heating modes, including closed-loop heating (CLH) and open-loop heating (OLH), were considered. There was a significant natural convection phenomenon in both heating systems. However, the natural convection became weaker with a gradual increase in the heating temperature of the beer. The maximum fluid velocity (FV) in CLH and OLH modes was 69.34 and 43.74 mm/s, respectively. After heating at 333.13 K for 20 min, the minimum and maximum pasteurization unit (PU) values in CLH were 55 and 59, respectively, while the corresponding values for OLH were 30 and 55, respectively. The pasteurization effect under the CLH mode was better than the OLH one. The heat transfer was also affected by fluid flow (laminar and turbulence) patterns. The PU value was nonlinearly related to the FV. The optimal FV can be obtained at ∼50 mm/s.

On the instability of finite-amplitude inertia-gravity waves

The hydrodynamic instability of monochromatic inertia-gravity waves (IGWs) of finite amplitude, propagating at small angles either to the vertical or horizontal, is studied. In both cases, the corresponding angle serves as a small parameter in the problem, and instability is investigated using the Galerkin method. For IGWs that propagate at a small angle to the vertical, it is shown that stable density stratification is a stabilizing factor, and fluid rotation is destabilizing. The opposite is true for IGWs that propagate at a small angle to the horizontal. Previous analysis of the short wave instability of the monochromatic internal gravity waves of finite amplitude that propagate at small angles to the vertical is generalised to the case of the IGW. As an auxiliary but methodologically useful problem, the stability of a monochromatic inertial wave of finite amplitude in a fluid of uniform density is investigated in the same mathematical formulation.

Principal coordinates and principal velocity gradient tensor decomposition

Helmholtz velocity decomposition and Cauchy-Stokes tensor decomposition have been widely accepted as the foundation of fluid kinematics for a long time. However, there are some problems with these decompositions which cannot be ignored. Firstly, Cauchy-Stokes decomposition itself is not Galilean invariant which means under different coordinates, the stretching (compression) and deformation are quite different. Another problem is that the anti-symmetric part of the velocity gradient tensor is not the proper quantity to represent fluid rotation. To show these two drawbacks, two counterexamples are given in this paper. Then “principal coordinate” and “principal decomposition” are introduced to solve the problems of Helmholtz decomposition. An easy way is given to find the Principal decomposition which has the property of Galilean invariance.