Viscous Effects Research Articles

Finding wave equations for sediment acoustic theories

The two main theories for wave propagation in sediments, the Extended Biot theory and the Viscous Grain Shearing (VGS) theory, have been formulated in terms of dispersion equations only. Some have considered the lack of a wave equation to be a weakness that may indicate lack of a physical basis for these theories. In the Biot theory, it is the frequency-dependent viscodynamic operator which models viscous boundary effects in pores that poses the problem. It can be formulated as a ratio of Bessel functions for circular pores and as a ratio of tanh-functions for a 2D parallel plane duct. There is no simple equivalent time domain operator for use in the wave equation. In both geometries, the factor may, however, be approximated well with (1 + icω)1/2, where c is a constant. This factor also appears in the Cole-Davidson dielectric theory for complex media. The equivalent time domain operator, the fractional pseudo-differential operator, enables the formulation of wave equations for all three wave modes. The same operator turns out to be central for transforming the dispersion relations of the VGS theory to time-space wave equations. These wave equations enable a closer study of properties of the medium models than that obtained from dispersion relations alone.

Research on pressure fluctuation induced by tip leakage vortex of axial flow circulating pump under unpowered driven conditions

Axial flow circulating pumps (AFCPs) are large marine steam turbine units for large-sized ships. One peculiar operation condition for AFCPs is when a ship cruises beyond a certain speed, the energy of pump inflow can completely overcome the frictional resisting moment of the pump itself, thereby driving the impeller to rotate. Such a condition is also known as the unpowered driven condition (UDC). At this time, the fluid is in the artesian flow state. In this paper, pressure fluctuation and inner flow of the AFCP under UDCs and different inflow conditions are analyzed using delayed detached-eddy simulation turbulence model. It is found that the intensity of the tip leakage vortex (TLV) decreases from the leading edge to the trailing edge of the blade, and the amplitude of pressure pulsation caused by TLV also decreases. Due to the jet wake structure at the blade trailing edge, the amplitude of pressure fluctuation at the trailing edge of the blade increases by 7.8% under the optimal UDC. In addition, the compression–expansion term determines the strength of the core of TLV, thus affecting the amplitude of pressure fluctuation. The viscous dissipation effect of TLV can cause high-frequency components of pressure fluctuation.

Viscous dissipation effect on unsteady magneto-convective heat-mass transport passing in a vertical porous plate with thermal radiation

The effects of radiative and viscous dissipation on the transfer of unsteady magnetic-conductive heat-mass across a vertically porous sheet is studied in this article. The non-dimensional ODEs are solved by applying the Finite Difference Method (FDM) through the MATLAB software numerically. The fluid temperature and velocity enhance for uplifting values of the Eckert number. Enhancing values of the transpiration parameter the velocity, concentration, and temperature distributions reduce. The local skin friction enhances about 9%, and 18% due to increase the Eckert number (0.5–3.0) and Dufour number (0.5–4.0), respectively and reduces 17%, 38%, and 31% due to increase Prandtl number (0.71–7.0), magnetic force parameter (0.5–3.0), and suction parameter (0.5–3.0), respectively. Enhancing values of the Eckert number (0.5–3.0) reduces the heat transfer rate by 40%. The increasing value of the Prandtl number (0.71–7.0) and the suction parameter (0.5–3.0) increases the heat transfer rate by 27% and 92%, respectively. With an increase in the values of the Schmidt number (0.22–0.67), the mass transfer rate increased by approximately 94%. At last, the numerical results of this paper has compared with the previously published paper. We noticed that the comparison has an excellent acceptance.

Heat transfer modulation in Rayleigh–Bénard convection by an oscillatory bottom plate

In this paper, we consider a heat transfer modulation in Rayleigh–Bénard convection by imposing a periodic sinusoidal oscillation to the bottom hot plate parallel to itself. Two-dimensional numerical simulations are carried out under lateral periodic conditions, over a Rayleigh number range of 106≤Ra≤109 and for a fixed Prandtl number of Pr = 7.1. For a given Rayleigh number, it is found that the Nusselt number, characterizing the global heat transfer efficiency of the system, shows a counter-intuitive initial drop and subsequent rise behavior, as the characteristic oscillatory velocity Vosc increases. Accordingly, taking the classical Rayleigh–Bénard convection as a reference, a heat transfer reduction regime for low Vosc and a heat transfer enhancement regime for high Vosc are recognized. The reduction regime is resulted from the thickening of the thermal boundary layer due to the amplified viscous effect by the oscillation, which increases the thermal resistance of the system. In addition to thickening the thermal boundary layer, a stronger oscillation could also trigger a thermal boundary layer instability, inducing massive emission of the thermal plumes and eventually giving rise to a significant global heat transfer enhancement. Moreover, the combined effect of thickening and destabilizing of the thermal boundary layer leads to a temporal periodic evolution of the Nusselt number at the bottom plate in the enhancement regime. A critical oscillatory velocity Vc is selected at the crossover between two regimes, and it is found decreasing with an increasing Ra as Vc∼Ra−0.2. Through dimensional analysis, we provide a physical explanation for this dependence.

Aerodynamic interference of three flapping wings in tandem configuration

Collective movements are common in nature, such as the swimming of fish schools and the flight of birds in formation. The aero/hydrodynamic performance of such movements is a research hotspot at present. As a continuation of the previous research [X. G. Meng et al., “Aerodynamic performance and flow mechanism of multi-flapping wings with different spatial arrangements,” Phys. Fluids 34, 021907 (2022)], this study examined the aerodynamic interference effect of three tandem flapping wings at different morphological and kinematic parameters. Computational fluid dynamics was used with the aspect ratio (AR) of the wing ranging from 2.75 to 4.75, stroke amplitude (Φ) from 60° to 120°, advance ratio (J) from 0.25 to 0.6, and Reynolds number (Re) from 200 to 2000. The aerodynamic interference for the tandem flapping wings includes three effects, namely, the narrow channel effect, the downwash effect, and the wake capture effect. The AR, Φ, and J can significantly influence the evolution of the vortex structures of the three-flapping-wing system, especially the velocity of wake vortices developing downstream. As a result, the downwash effect in the downstroke and the wake capture effect in the upstroke change obviously with these parameters. Due to the decreasing viscous effect with the increase in Re, the wake capture effect, which can improve the thrust of the wings, is more obvious at higher Re. This study further deepens our insight into the flow physics of the multi-flapping wings and provides a theoretical basis for improving the aerodynamic performance of multi-flapping-wing vehicles in the future.

Multiphysics simulation of an anisothermal reactive spontaneous capillary rise between electric rotor wires

Introduction: The rotor is the mobile component of an electric motor. A wound rotor is composed primarily of a steel core with insulated copper wires wound around it, after which the winding is immersed into a liquid acrylate-based thermosetting resin bath whose role is to ensure the performance and durability of the motor. This impregnation with resin between the wires occurs under controlled temperature settings to facilitate resin flow and polymerization. This process does not involve any pressurization to further facilitate resin flow between the wires; this suggests that, in addition to viscous effects, capillary and gravity forces play a significant role in the impregnation process.Methods: Our ultimate objective is to evaluate the quality of this impregnation. Doing so requires the characterization and simulation of a multi-material and multiphysics process in which heat transfer, polymerization kinetics, and resin flow are strongly coupled. This paper presents a fully coupled macroscopic multiphysics simulation of a unidirectional thermo-regulated capillary rise set-up.Discussion: The modeling choices made produced a good level of agreement with experimental data and enable explanation of a sudden change of regime observed at 120°C, which can be attributed to the polymerization and thermal gradients and their impact on fluid dynamics.

Thermal Radiation and Mass Transfer Analysis in an Inclined Channel Flow of a Clear Viscous Fluid and H2O/EG-Based Nanofluids through a Porous Medium

Nanofluid flow has acquired various interesting dimensions with the advent of several novel approaches to studying thermophysical properties. The present work focuses on a comparative study of clear viscous and nanofluid (EG−Al2O3, EG−Zr, H2O−Al2O3, H2O−Zr) flow in a two-phase inclined channel saturated with a porous medium in the presence of thermal radiation, species diffusion, and viscous and Darcy dissipation effects. The controlling equations of the flow model were solved analytically using the regular perturbation technique. The graphical solutions are used to examine the impacts of physical parameters on the most significant flow features. Surface graphs with distinct entrenched parameters represent heat transfer rates and shear stresses on plates. The resulting heat transfer was enhanced by raising the thermal and solute buoyancy strengths, while thermal radiation had the opposite outcome. This enhancement of temperature was maximum for water–zirconium and minimum for ethylene glycol–aluminum oxide nanofluid. The concentration of the entire fluid medium is reduced by decreased mass diffusivity. The enhancement of temperature and velocity is found to be maximum in the nanofluid region and clear fluid region, respectively. This study is validated with previously published works to demonstrate its effectiveness.

Numerical treatment of hybrid water based nanofluid flow with effect of dissipation and Joule heating over a shrinking surface: Stability analysis

In the current work, the steady flow of magnetohydrodynamic of Cu-Al2O3/water hybrid nanofluid was investigated along with Joule heating and viscous dissipation effect across a porous shrinking sheet. Using an appropriate similarity transformation, the governing partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs). The system of ODEs is solved using the bvp4c function in MATLAB. The present findings are numerically and visually compared to the available literature, and excellent agreements are discovered. The impacts of several new physical governing factors on velocity and temperature profiles, while the variation of heat transfer and skin friction, are visually shown and explicated hypothetically. In addition, the findings demonstrate the presence of duality within a limited range of suction parameters. Increasing the solid volume fraction ϕCu increases the values of f′′(0) for an initial solution and reduces them for an unstable solution. The investigation of the temporal stability of the solutions concludes that the first solution is stable only. The values of smallest eigenvalues values (γ>0) are positive for first solution indicated the stability of solution while the values of smallest eigenvalues values (γ<0) are negative for second solution indicates the instability of solution. The quantitative outcomes are in Table 4. The concentration of Al2O3 and Cu is almost 20% (0.01≤ϕAl2O3≤0.2 and 0.01≤ϕCu≤0.2).

A viscosity equivalent reduced-order method and its application to ship roll prediction

The prediction of ship roll response in waves is still a major issue. The widely used potential flow theory can provide the results in a short time. However, its accuracy is highly dependent on the correction of fluid-viscosity. Viscous-flow theory can simulate the fluid viscosity directly, but it is accompanied by high computational costs. This study proposes a viscosity equivalent reduced-order method (VEROM) for predicting ship roll motion to achieve a balance between computational efficiency and prediction accuracy. To shorten the simulation time, the method neglects the fluid viscosity, solves the Euler equation, and uses large-size compatible meshes. To improve the prediction accuracy, the viscous effect is corrected in the time domain based on the principle of viscosity equivalence. A new type of forced roll motion with gradually increasing roll amplitude was introduced to obtain the nonlinear roll damping property for different KC numbers. The effectiveness of the VEROM model was examined by comparing the predicted roll responses with the experimental measurements. It was found that the maximum prediction error was less than 11%. Concerning the simulation time, the VEROM model is 20 times faster than the traditional viscous-flow model. The reduce-order method is effective for the seakeeping performance assessment.

Variable fluid properties analysis for thermally laminated 3-dimensional magnetohydrodynamic non-Newtonian nanofluid over a stretching sheet

This article is mainly focused on the viscous flow of cu-water/Methanol suspended nanofluids towards a three-dimensional stretching sheet reformed by magnetohydrodynamic phenomenon. The viscous effect is considered as temperature dependent with water treated as a base fluid. Similarity conversions are employed to set forth the non-linear equations of this physical problem. An innovative model for 3D analysis for cu-water/Methanol nanofluid with an irregular viscosity is presented in the present study. Reynold’s model of viscosity is considered in the present study. Moreover, shooting technique is employed to elaborate the non-linear coupled governing equations with the relevant boundary conditions. The physical interpretation of these numerical calculations is presented through a graphical specimen of velocity, Nusselt number, temperature, and skin friction etc. The results of present model are showing quality harmony with the results of existing model. This model is being used for manipulating and designing the surfaces such as stretching/shrinking wrapping and panting devices in nanotechnology. The results also show the significant changes in flow characteristics with changing the value of stretching parameter. It is observed that with an increasing in nanoparticles volume fraction boundary layer thickness decreases. Further, it is also observed that with an increase in viscosity parameter, temperature increases because here we are considering temperature dependent viscosity.

Enhanced singular jet formation in oil-coated bubble bursting

Bubble-bursting aerosols have a key role in mass and momentum transfer across interfaces. Previous studies report that the bursting of a millimetre-sized bare bubble at an aqueous surface produces jet drops with a typical size on the order of 100 μm. Here we show that jet drops can be as small as a few micrometres when the bursting bubble is coated by a thin oil layer. The faster and smaller jet drops result from the singular dynamics of the oil-coated cavity collapse. The air–oil–water compound interface offers a distinct damping mechanism to smooth out the precursor capillary waves during cavity collapse, leading to a more efficient focusing of the dominant wave and thus allowing singular jets over a much wider parameter space than that of a bare bubble. We develop a theoretical explanation for the parameter limits of the singular jet regime by considering the interplay between inertia, surface tension and viscous effects. Contaminated bubbles are widely observed, therefore previously unrecognized fast and small contaminant-laden jet drops may contribute to the aerosolization and airborne transmission of bulk substances.

Normal Operating Performance Study of 15 MW Floating Wind Turbine System Using Semisubmersible Taida Floating Platform in Hsinchu Offshore Area

This study predicted the motion response and power performance of a floating wind turbine system equipped with a semisubmersible Taida platform, an IEA 15 MW wind turbine, and a 3 × 2 mooring design in the Hsinchu offshore area in the Taiwan Strait. The hydrodynamic properties were calculated using ANSYS-AQWA and STAR-CCM+. The motion equations were solved by OrcaFlex to obtain the motion response and generator power, as well as the dynamics of the mooring system and aerodynamics of the wind turbine. The waves were assumed to share the same direction as the wind. This study compared the mean values and standard deviations of the motion response, generator power, and mooring line tension between the potential- and viscous-flow approaches by considering the combination of seven wind directions and four current directions under two wave conditions in the Hsinchu offshore area. The numerical prediction shows that the viscous effect has a larger impact on the hydrodynamic properties in the heave, roll, and pitch motions. The angle between the leading mooring line of the system and dominant wind direction in the Taiwan Strait, which comes from the northeast, should be from 120° to 180° in order to deliver a relatively favorable performance of the system.

Numerical simulation of the 2D lid-driven cavity flow of chiral liquid crystals

ABSTRACT In this study, the two-dimensional (2D), lid-driven cavity flow of chiral liquid crystals (LCs) was modelled using the Landau de-Gennes (LdG) theory. Parametric studies investigating the effect of Er (Ericksen number) and Θ (chiral strength) on the microstructure of chiral LCs were performed. In this study, we observed that an increase in Θ caused the chiral texture to have more striations and shorter pitch lengths as causes for an increased number of defects. When Θ was held constant, an increase in Er disrupted the chiral structure and even broke it at very high Er. Interestingly, a transition from low Er (10) to moderate Er (1,000) increased the number of defects; however, further increases in Er reduced the number of defects since much of the chiral structure was destroyed by the high viscous flow effects. In particular, even at very high Er, the chiral structure and defects were still present as a vortex was always present with lower velocities, where the viscous flow effect was smaller. We also found that a hexagonal structure with penta-hepta defects formed at high chiral strengths.

Influence of chemical reaction and variable mass diffusivity on non-Newtonian fluid flow due to a rough stretching sheet with magnetic field and Cattaneo-Christov fluxes

A non-Newtonian Williamson fluid flow due to a stretching sheet with radiation, magnetic field, and viscous dissipation effects is described using variable conductivity and variable diffusivity. The Cattaneo-Christov model is used to correctly compute the physical properties of a heat and mass flux model. Both the chemical reaction phenomenon and the slip velocity have an impact on the heat and mass mechanism. The physical problem is represented mathematically as a nonlinear coupled differential system. After that, the shooting method is used to solve the mathematical model numerically. To gain a better understanding of the behavior of governing emergent factors on dimensionless velocity, concentration, and temperature profiles, physical interpretations are created and discussed utilizing graphical and tabular representations. The results show that the Sherwood number and the Nusselt number are both decreased by the magnetic, viscosity, and slip velocity parameters. Also, according to the findings it has been observed that the concentration outlines enhances for the magnetic number, the viscosity parameter, and the slip velocity parameter, but they dwindle for expanding reaction rate values. Finally, after confirmation of our numerical results, the theoretical results show good agreement with previously published work.

Kinematic, dynamic and energy characteristics of swirling sloshing waves

The numerical study was made to investigate the evolution of swirling waves during the transient period, including the dynamic, kinematic and energy characteristics of the waves. A rigorous benchmark was made with the experimental measurement to validate the developed numerical model. The viscous effect (Reynolds number effect) of fluid during resonant sloshing was studied and discussed. The beating phenomenon of sloshing waves is described by the relationship between the wave energy and the energy flux transferred from the tank walls. The energy transfer characteristics of swirling waves represent the intensity of sloshing, which can cause significant instability for moving vehicles. The strength of the swirling waves is varied with the excitation angle, excitation frequency and water depth of the tank. The most dangerous excitation angle of a tank during the first beating period is 30°. The beating phenomena of the swirling waves under different water depths exhibit dissimilar behaviours. In the finite depth (d0/L > 0.3), the energy of sloshing waves is still stored inside the tank between the second and third beatings, which will have a serious influence on the stability of the storage containers. The evolutions of swirling waves are very sensitive to physical conditions, including liquid depth, excitation angles, excitation amplitudes and frequencies of external forcing.

Electro-osmotically generalized bio-rheological fluid flowing through a ciliated passage

In this article, we have investigated a non-Newtonian Jeffrey fluid model, which shows the role of cilia generated metachronal waves in a vertical tube. Electroosmosis effects, a viscous dissipation term is also adopted in this current analysis. The partial differential equations that govern the flow are transformed into a non-dimensional form by considering a low wavelength and small Reynolds number approximations. The obtained set of coupled ordinary differential equations is further solved by using Mathematica solver to get the required flow properties. The current model's output has important heat transfer rate applications in the ciliated channel due to the enhanced viscous dissipation effects, which can be used for the analysis of various areas of biological transport processes such as to design artificial cilia and for the operation of some mechanical devices.

One-dimensional nonlinear rheological consolidation analysis of soft ground under continuous drainage boundary conditions

This work presents an upgraded one-dimensional (1D) nonlinear rheological system of soft ground consolidation. In the system, the boundaries are characterized by the time-dependent drainage boundary conditions at the surface and bottom of the layer. Meanwhile, the modified UH relationship and non-Newtonian index flow model are used to simulate the viscous effect of clay and the flow of excess pore-water during consolidation, respectively. Then, two numerical discretization formats of the system, namely the finite volume method (FDM) and finite difference method (FVM), are given, and corresponding calculation programs are compiled. The model solutions have been validated by degraded analytical solutions, FDM and FVM comparison solutions, and available laboratory data. Further, the consolidation behaviour under different model parameters is illustrated. The calculated results indicate that the change of interface parameters and flow mode does not influence the final foundation settlement, but both significantly affect the overall dissipation process of EPWP of soils. At last, an efficient method for determining CDB parameters is proposed and verified by available test data.

Numerical investigation on hydrodynamic performance of a pre-swirl stator pump-jet propulsor with special emphasis on energy loss mechanism

The objective of this paper is to evaluate the hydrodynamic performance of the newly developed pre-swirl stator pump-jet propulsor (PJP) and to investigate its underlying flow characteristics and energy loss mechanisms. Numerical simulations are carried out for the scaling model of the PJP, the experimental tests are also performed to verify the numerical simulation results. The energy balance equation is loaded to investigate the energy loss combining with vortex structures. The numerical results show a reasonable agreement with the available experiments. The stator performs well for generating pre-swirl flow with tangential velocity, which could be effectively absorbed by the rotating rotor to varying levels under different operating conditions. The stator-rotor interaction flow is complicated and causes obvious non-uniformity for the flow field due to the generation of trailing vortices. The energy losses within the PJP are well quantified and visualized by different loss terms in energy balance equation. The production of turbulent kinetic energy and then dissipates due to viscous effects is the leading cause for energy loss, which originates from vortex evolutions and impact loss without considering the friction loss. The generation of tip leakage vortex dominates the energy loss in the rotor domain and wake field of PJP.

A discrete model for the geometrically nonlinear mechanics of hard-magnetic slender structures

Hard-magnetic soft (HMS) materials and structures, which can undergo rapid configurational transformation under non-contact magnetic stimuli, have attracted extensive attentions in a wide range of engineering applications, such as soft robotics, biomedical devices and stretchable electronics, etc. In order to realize the full potentials of HMS structures, it is crucial to be able to predict their mechanical (both static and dynamic) responses. In this work, we propose a discrete magneto-elastic rod model with the aim to analyse the mechanical behaviours of slender structures made of HMS materials under magnetic loading. The configuration of a slender object is described by multiply connected nodes and edges, from which the force vector and the associated Hessian matrix are derived by taking the variation of Kirchhoff-like magneto-elastic potentials. The nonlinear dynamical equations of motion are next evaluated through Newton-type optimization, and the static analysis can be obtained using dynamical relaxation method. For verification, we quantitatively compare our numerical results with either analytical solutions or experimental data for several representative cases. Good agreements in all these cases indicate the correctness and accuracy of our discrete model. We further extend the model to take the dipole–dipole interaction and viscous effect into consideration. Finally, as a demonstration, we perform simulations to reproduce the locomotion of a magnetic crawling robot. The developed discrete magneto-elastic model significantly improves the computational efficiency, enabling the practicability of simulating the mechanical, especially dynamic, behaviours of the hard-magnetic slender structures.

Estimating Three-Dimensional Permeability Distribution for Modeling Multirate Coreflooding Experiments

Characterizing subsurface reservoirs such as aquifers or oil and gas fields is an important aspect of various environmental engineering technologies. Coreflooding experiments, conducted routinely for characterization, are at the forefront of reservoir modeling. In this work, we present a method to estimate the three-dimensional permeability distribution and characteristic (intrinsic) relative permeability of a core sample in order to construct an accurate model of the coreflooding experiment. The new method improves previous ones by allowing to model experiments with mm-scale accuracy at various injection rates, accounting for variations in capillary–viscous effects associated with changing flow rates. We apply the method to drainage coreflooding experiments of nitrogen and water in two heterogeneous limestone core samples and estimate the subcore scale permeability and relative permeability. We show that the models are able to estimate the saturation distribution and core pressure drop with what is believed to be sufficient accuracy.