Fluid Rotation Research Articles

Air core vortexing in liquid draining tanks: Influence of surface roughness

This paper study the influence of roughness of the tank base in the formation of air core vortex when liquid inside the cylindrical tank is rotated and subsequently drained. The vortex air core formation in drain tanks can lead to the blockage of drain port and can result in reduced discharge of draining liquid as an immediate consequence. The formation of such a vortex in propellant tanks of spacecraft and rockets will lead to underutilization of propellants and can adversely affect the performance of rocket engines. Ingestion of air core vortex in metal casting process can affect the mechanical properties of casted metal. Hence, suppression of air core vortex is inevitable in the fields of aerospace, metal casting and other hydraulic engineering systems. Current study makes use of roughness of the tank base to suppress vortexing which is the first of its kind and therefore, novel. Experimental investigations have been carried out at several values of roughness height and initial fluid rotation to study the characteristics of air core vortex. It is found that at the highest value of initial rotation provided to the liquid, air core vortexing can be subdued up to 25% by making use of base roughness. Current study also recommends drain tank manufacturers not to smoothen the tank base surface spending time at extra cost. In addition, applying roughness on the tank base will further weaken the formation of air core vortex, in the light of this study.

The outcome of Newtonian heating on Couette flow of viscoelastic dusty fluid along with the heat transfer in a rotating frame: second law analysis

The outcome of Newtonian heating on the viscoelastic fluid plays a vital role in daily life applications such as conjugate heat transfer around fins, heat exchanger, solar radiation, petroleum industry, etc. Also, rotation of viscoelastic fluid has various importance in product-making industries and engineering. Viscoelastic dusty fluids and Newtonian heating are applicable in nuclear reactors, gas cooling systems, control temperature of the system and centrifugal separators, etc. Therefore, based on this motivation, the present study presents the Newtonian heating effect on the dusty viscoelastic fluid. Additionally, a free convective heat transfer is taken for Couette flow in a rotating frame along with a uniform applied magnetic field. The dust particles possess complex velocities due to rotation and therefore it is the combination of the primary and secondary velocities. For the specified flow, the entropy generation and Bejan number are also computed. Poincare-Light Hill technique has been used for the solution of the system of partial differential equations. The velocity profile for dust particles and fluid are discussed in this article. The influence of different parameters on the Nusselt number, temperature profile, velocity of fluid and dust particle is discussed thoroughly.

Chaotic convection in a magnetic fluid in rotation subjected to a pseudo-vector type force

This paper reports the chaos control on the convection in a magnetic fluid in rotation subjected to a pseudo-vector type force. We performed a truncated Galerkin expansion which allowed to describe the system by a Lorenz-type model. We characterized the dynamical system by plotting bifurcation diagrams, Lyapunov exponents and phase spaces. It is found that the system exhibits rich behaviors depending on the variation of the system parameters. Finally, we noticed that the chaotic domain is considerably reduced with the increase of the helical force whereas the Taylor number enlarges it.

Free convective couette flow analysis of viscoelastic dusty fluid along with Newtonian heating in a rotating frame

Applications in daily life heavily rely on the viscoelastic fluid's response to Newtonian heating. The importance of viscoelastic fluid rotation in engineering and the production of goods is also varied. Nuclear reactors, gas cooling systems, system temperature control, centrifugal separators, and other systems can all benefit from viscoelastic dusty fluids and Newtonian heating. In light of this inspiration, the current study describes the Newtonian heating effect on a viscoelastic fluid that contains dust particles. In addition, a uniformly applied magnetic field and a free convective heat transfer are taken into account for Couette flow in a rotating frame. Because the dust particles have complex velocities due to rotation, the primary and secondary velocities are combined. Poincare-Light Hill technique has been used for the solution of the system of partial differential equations. The velocity and temperature profile for dust particles and fluid are discussed in this article. The influence of different parameters on the Nusselt number is also discussed thoroughly.

Observation on Liutex similarity in the dissipation subrange of turbulent boundary layer

The motion of the small vortices in the dissipation region (large wave number) is not fully understood due to the influence of the kinematic viscosity and energy dissipation rate. Studying the motion law of small vortices is of great significance to understand the physical mechanism of turbulence. It is well known that the motion of small vortices is statistically isotropic in the dissipation region. Liutex is a new physical quantity recently found to define the rigid rotation of fluids in turbulent flow. In this study, the turbulent flow of boundary layer on a flat plate at freestream Mach number of 0.5 was studied based on a high-order direct numerical simulation (DNS). Using our DNS of flat plate and one DNS of plane turbulent channels of Fluid Dynamics Group UPM, the spectrum of Liutex is analyzed, and the similarity law of Liutex in the dissipation region is obtained. The study results show that the wavenumber spectrum of Liutex exactly follows the -5/3 law, i.e. EL(κ)∼Cκ−5/3, where κ=1/l is the wavenumber and EL is the amplitude of the Liutex spectrum. The scaling of Liutex with the frequency shows a same law of -5/3, since turbulent vortices propagate downstream with almost equal speeds. This paper reports the Liutex similarity for the dissipation subrange of different areas in fully developed turbulent boundary layers at low Reynolds number. Meanwhile, the vorticity and Q-criteria are found having no such similarity in boundary layers due to the shear contamination.

Significance of nanoparticles aggregation and Coriolis force on the dynamics of Prandtl nanofluid: The case of rotating flow

A comparative study is provided by this article with rotational Prandtl host fluid flux of aggregated nano particles and non aggregated nano particles on linear stretching surface. Along with the chemical species diffusion, Arrhenius activation energy is examined. The nano particles thats are playing vital role in modern technology like heat exchange, electronics and material sciences are incorporated because of enhancing heat transmission. The current analysis has significant applications in rolling and manufacturing of polymer sheet, lubrication processes, crystal growing, polymer industry, biomedical and polymer industry. By applying similarity transformation to mathematical formulation based upon conservation laws yielded a related set of differential equations. For obtaining the numerical solution of non linear problem, Runge Kutta technique is employed and listed in platform of MATLAB. The goal of this study is to illustrate the comprehensive analysis of repercussions of parameters on heat, velocity and nanoparticles concentration via graphical and numerical outcomes is computed. Both velocities (f1′ and f2) reduced against amplified value of β, λ and Fr but, have increasing behavior for α1 and α2. Heat distribution is rise with growing values of Fr and λ but, reduce in case of α1 (Prandtl fluid parameter) and α2 (elastic parameter) and concentration of nano particles is higher for λ and E but, lessen for δ. It is observed that the increment and decrement in values of f1′, f2, θ, ϕ by impact of variation in values of parameters is slightly fast in non aggregated phase as compared to aggregated phase. On linearly extending surface, Nu and friction factor variational patterns are numerically calculated.

Dynamical stability analysis for a micro shell subjected to swirling annular flow including the coupling effect of small size and fluid rotation

This paper is concerned with stability analysis for an outer thin-walled shell conveying a swirling flowing fluid in the annular space between the inner shell and outer shell with micro-dimensions. It describes the development of theoretical model in the framework of the modified coupled stress theory along with the Donnell shell theory. The theoretical model uses the Hamilton’s principle to derive the governing motion equations of the shell. The fluid is assumed to be incompressible and irrotational and the hydrodynamic pressure is considered with the version of the potential flow theory. The zero-level contour method is utilized to display the complex dynamical behaviors of micro shell subjected to swirling annular flow. The effects of the material intrinsic parameter, the fluid rotation on stabilities of the fluid microscale shell system are discussed fully. The results elucidate that the coupling effect of the fluid rotation and the material intrinsic parameter on such system.

Study on cavern evolution and performance of three mixers in agitation of yield-pseudoplastic fluids

The hydrodynamic performance of three mixers (single shaft central mixer (SSC), single shaft off-centred mixer (SSO), dual shaft off-centred mixer (DSO), was investigated in the mixing of yield-pseudoplastic fluids (xanthan gum solutions) in the laminar regime. To explore and determine the efficiency of three mixers, both numerical and experimental approaches were adopted. The fluid rheology was described by the Herschel–Bulkley rheological model. Computational fluid dynamics was employed to simulate the apparent viscosity distribution, mixing time, and the flow pattern inside the stirred tank. The developed model was validated through experimentally measured torque. The influence mechanism of the rotational speed and fluid rheology on the cavern evolution was explored deeply. The performances of three mixers in this work were compared at the constant power input and fluid rheology with respect to the flow pattern, mixing time, and mixing efficiency. The results verify that the faster the rotating speed, the greater influence of the fluid rheology on the cavern evolution, and the more uniform apparent viscosity distribution. Moreover, the mixing time decreases continuously as the increasing power consumption per unit volume, and the dimensionless mixing time of DSO mixer was nearly 42.8% and 6.1% shorter than that of SSC and SCO mixer at the same Reynolds number, respectively. According to the mixing efficiency criteria, these data also revealed that DSO was more efficient than SSC and SSO.

Direct numerical simulations of optimal thermal convection in rotating plane layer dynamos

The heat transfer behaviour of convection-driven dynamos in a rotating plane layer between two parallel plates, heated from the bottom and cooled from the top, is investigated. At a fixed rotation rate (Ekman number, $E=10^{-6}$ ) and fluid properties (thermal and magnetic Prandtl numbers, $Pr=Pr_m=1$ ), both dynamo convection (DC) and non-magnetic rotating convection (RC) simulations are performed to demarcate the effect of magnetic field on heat transport at different thermal forcings (Rayleigh number, $Ra=3.83\times 10^{9}\unicode{x2013}3.83\times 10^{10}$ ). In this range, our turbulence resolving simulations demonstrate the existence of an optimum thermal forcing, at which heat transfer between the plates in DC exhibits maximum enhancement, as compared with the heat transport in the RC simulations. Unlike any global force balance reported in the literature, the present simulations reveal an increase in the Lorentz force in the thermal boundary layer, due to stretching of magnetic field lines by the vortices near the walls with a no-slip boundary condition. This increase in Lorentz force mitigates turbulence suppression due to the Coriolis force, resulting in enhanced turbulence and heat transfer.

On the physical nature of the turbulent/turbulent interface

The existence of a turbulent/turbulent interface (TTI) has recently been verified in the far wake of a circular cylinder exposed to free-stream turbulence (Kankanwadi & Buxton, J. Fluid Mech., vol. 905, 2020, p. A35). This study aims to understand the physics within the TTI. The wake boundary, approximately 40 diameters downstream of a circular cylinder subjected to grid-generated turbulence, was investigated through simultaneous cinematographic, stereoscopic particle image velocimetry and planar laser induced fluorescence experiments. With no grid placed upstream of the cylinder, the behaviour of the resultant interface, our closest approximation to a turbulent/non-turbulent interface, exactly matched what is observed in existing literature. When background turbulence is present, viscous action is no longer the only method by which enstrophy is transported to the background fluid, unlike for turbulent/non-turbulent interfaces. The presence of rotational fluid on both sides of the TTI allows the vorticity stretching term of the enstrophy budget equation to be the dominant actor in this process. The role of viscosity within a TTI is greatly diminished as the vorticity stretching term takes over responsibilities for enstrophy production. The turbulent strain rate normal to the TTI was found to be enhanced in the interfacial region. Decomposing the vorticity stretching term into components aligned with the three principal strain-rate directions, it was found that the term most aligned with the interface-normal direction contributed to the largest share of enstrophy production. This indicates that better ‘organised’ vorticity on the wake side of the interface yields the enstrophy amplification leading to the previously discovered enstrophy jump across the TTI by Kankanwadi & Buxton (J. Fluid Mech., vol. 905, 2020, p. A35).

Analysis of Unsteady Magnetohydrodynamic 3-D Rotating Flow and Transfer of Heat in Carbon Nanotube-Water Nanofluid: An Engineering Application

We have analysed unsteady Magnetohydrodynamic (MHD) 3-D rotating flow of Carbon Nanotube (CNT) water nanofluid past a stretching surface dealing with thermal radiation mechanism of heat transfer and heat source/sink. The mathematical model consists of a system of non-linear coupled Partial Differential Equations (PDEs). Numerical solution is obtained and discussed in detail. The influence of flow dominant parameters on the temperature profiles and flow-field are also discussed in detail using tables and graphs. Results are justified by previously published results in the limiting sense. Various crucial results are obtained, for example, unsteadiness parameter accelerates the fluid velocities in both directions near the sheet and reverse behaviour is noticed away from the sheet. However, fluid rotation causes reduction in primary velocity but it tends to accelerate secondary velocity near the sheet. Insertion of nanoparticle volume fraction intensifies fluid velocity and attenuates fluid temperature. We also found that multi-Walled Carbon Nanotubes (MWCNTs) offer more resistance for primary skin friction and less resistance for secondary skin friction when compared with Single-Walled Carbon Nanotubes (SWCNTs).

Removing cuttings from inclined and horizontal wells: Numerical analysis of the required drilling fluid rheology and flow rate

Inclined and horizontal wells are prone to the accumulation of drilling cuttings. Determination of the optimal drilling parameters that facilitate cuttings removal is a key problem. Existing experimental, theoretical and field-based empirical analyses of the hole cleaning problem have failed to fully reveal the processes of cuttings transport, settlement, and accumulation concerning drilling string rotation in large annuli with high-density non-Newtonian drilling fluids. In this study, a coupled computational fluid dynamics-discrete element method (CFD-DEM) simulation model of the interaction between cuttings and drilling fluid was established. This allows the influences of well inclination, drill pipe rotational rate, flow rate, fluid density, and rheological properties on hole cleaning efficiency to be analyzed. A multi-parameter correlation equation between wellbore cleaning efficiency and wellbore size, inclination angle, drill string eccentricity, drill string rotational speed, rate of penetration, cuttings size, flow rate, and fluid density was obtained using dimensional analysis and multivariate nonlinear regression of simulation data. Finally, with consideration of wellbore cleaning characteristics, formation pressure bearing capacity, and pump condition constraints, the proposed multi-parameter correlation model was used to provide optimal wellbore cleaning parameters. The cleaning efficiency of horizontal wells is lowest in the inclined section. Hole cleaning efficiency increases significantly with drill pipe rotational rate, flow rate, and 6 RPM Fann dial reading. The proposed model can correlate hole cleaning efficiency with the 6 RPM Fann dial reading of drilling fluid and flow rate. At a given hole cleaning efficiency, the required minimum flow rate decreases with increases in the 6 RPM Fann dial reading. Similarly, the required minimum 6 RPM Fann dial reading decreases with increases in flow rate. The models and design layout proposed in this paper provide a new approach to solving hole cleaning parameter design problems in highly inclined and horizontal wells.

Investigation of cutting transport in horizontal/deviated annulus using visualization and pressure drop techniques for two-phase slurry flow

Inadequate hole-cleaning in an annulus leads to several problems such as mechanical pipe sticking, premature bit wear, formation fracturing, and/or slow drilling. However, the literature suggests a lack of experimental analysis of the impact of various parameters on cutting transport. Therefore, the present study investigates the impact of various hydrodynamic and operational parameters on the cuttings transport for two-phase Newtonian and non-Newtonian slurry flow using pressure drop and visualization techniques. Several annular flow experiments were performed in 6.16 m (20.2 ft) long horizontal pipe with 2.5" (6.4 cm) inner and 4.5" (11.4 cm) outer diameter with varying pipe eccentricity (0–30%), drill pipe rotational speeds (0–120 RPM), fluid rheology (Newtonian and non-Newtonian fluids), and pipe inclination (0-5° from Horizontal) for different mass flow rates (170–350 kg/min). Furthermore, novel correlations were developed using the original experimental data and were validated with two independent data sets from literature. Results revealed that mass flow rate and drill pipe rotation positively impact cuttings transport, whereas eccentricity and higher non-Newtonian concentration have a negative impact. Solid in-situ bed height significantly impacts pressure drop and determines its trend. The developed empirical correlations are simpler and quicker tools as compared to the existing models, with a MAPE of 8.18% for the power-law model that can be effectively used during real-time drilling operations. Moreover, the presented experimental and modeling results can tremendously augment the current understanding of the impact of various parameters on cutting transport.

Hydrothermal characteristics of fluid flow in a circular tube fitted with free rotating axial-turbine-type swirl generators: Design, swirl strength, and performance analyses

The effect of inserting free rotating axial-turbine-types swirl generators (ATTSGs) in a circular tube is numerically investigated for convective heat transfer enhancement. Different types of ATTSGs with different blade designs are placed inside the tube, which are rotating freely around their axis depending on the velocity of the fluid flowing in the tube. The moving reference frame (MRF) method is used to model the fluid rotation in the zones containing the ATTSGs and the source terms arising from the transformation of stationary to rotating reference frame. Free rotational speed of the ATTSGs is estimated at different Reynolds numbers by systematically analysing the net torque applied on the ATTSGs in terms of their angular velocity. The local and average convective heat transfer and pressure drop are investigated for the cases with ATTSGs and the case of a plain tube. Considerable enhancement in the convective heat transfer is observed for all the ATTSGs, with the maximum of around 75%. To investigate the efficiency of the ATTSGs in terms of heat transfer enhancement, the intensity of the vortex structures generated by the ATTSGs is represented by the Q-criterion iso-surfaces. The ATTSGs which generate stronger swirling effect at the vicinity of the heated wall cause greater heat transfer enhancement. Inserting the ATTSGs leads to an increase in the pressure drop. Performance evaluation criterion (PEC) is introduced and evaluated for different ATTSGs to identify configurations that enhance the convective heat transfer at the lowest pumping power. The highest PEC of 1.4 is reported for the ATTSG with trapezoid twisted blade design.

Influence of swirl and viscosity of annular flow on instability mechanisms of an FGMs micro shell

The influences of the swirl (the fluid rotation) and the steady viscous forces of an annular flow on instability mechanisms of an outer functionally graded materials (FGMs) cylindrical micro shell are investigated. The annular flow passes the annulus between the inner micro shell and outer micro shell. The inviscid fluid-elastic forces related to the shell vibration are modeled in the frame of potential flow theory. The steady viscous forces induced by the fluid viscosity are obtained by using the time-averaged Navier-Stokes equations and then are coupled into the shell model in the form of initial loadings. The pre-loaded shell model is developed by means of the Hamilton's principle in conjunction with the modified couple stress theory. The pre-loaded shell motion equations are described based on the Flügge's thin shell theory. Afterwards, the zero-level contour method and the Galekin's method are employed to solve the problem. A parameter study and numerical comparisons are performed to evaluate the influences of all terms of inviscid fluid-elastic forces on the instability character of micro shell. Especially, the swirl effects are discussed fully. The results display different instability mechanisms of the fluid-micro shell system controlled by the swirl or/and the axial flow velocity. Eventually the fluid viscosity effects are given.

Synergistic Effects in Coaxial Mixers: The Controlling Strategy of the Flow and Shear

AbstractSynergistic effects implying that strong flow and high shear can be obtained simultaneously were found in coaxial mixers. The flow field, axial pumping rate Qzave, and shear strain rate were studied to characterize the synergistic effect quantitatively. The indicator of synergy S was proposed to judge the goodness of synergy. The influences of the fluid viscosity, speed ratio, and rotation mode were studied. The S value becomes larger and smaller with increasing fluid viscosity for helical ribbon and pitched blade turbine impellers, respectively. The variation trend is opposite to the increase of the speed ratio. The co‐rotation mode has better mixing performance than that of the counter‐rotation mode at constant specific power.

Experimental study of the flows in a non-axisymmetric ellipsoid under precession

Precession driven flows are of great interest for both, industrial and geophysical applications. While cylindrical, spherical and spheroidal geometries have been investigated in great detail, the numerically and theoretically more challenging case of a non-axisymmetric cavity has received less attention. We report experimental results on the flows in a precessing triaxial ellipsoid, with a focus on the base flow of uniform vorticity, which we show to be in good agreement with existing theoretical models. As predicted, the uniform vorticity component exhibits two branches of solutions leading to a hysteresis cycle as a function of the Poincaré number. The first branch is observed at low forcing and characterized by large amplitude of the total fluid rotation and a moderate tilt angle of the fluid rotation axis. In contrast, the second branch displays only a moderate fluid rotation and a large tilt angle of the fluid rotation axis, which tends to align with the precession axis. In addition, we observe the occurrence of parametric instabilities early in the first branch, which saturate in the second branch, where we observe the same order of the kinetic energy in the base flow and instabilities.

Influence of Deformation and Fluids on Ti Exchange in Natural Quartz

AbstractUsing a combination of microstructural, spectroscopic, and geochemical analyses, we investigate how subgrain rotation recrystallization and fluid migration affect Ti concentration [Ti] in naturally deformed quartz veins from the Prijakt Nappe (Austroalpine Unit, Eastern Alps). These coarse‐grained quartz veins, that formed at amphibolite facies conditions, were overprinted by lower greenschist facies deformation to different degrees. During the overprint, subgrain rotation recrystallization was dominant during progressive deformation to ultramylonitic stages. The initial [Ti] (3.0–4.7 ppm) and cathodoluminescence (CL) signature of the vein crystals decrease during deformation mainly depending on the availability of fluids across the microstructure. The amount of strain played a subordinate role in resetting to lower [Ti] and corresponding darker CL shades. Using a microstructurally controlled analysis we find that the most complete re‐equilibration in recrystallized aggregates ([Ti] of 0.2–0.6 p.m.) occurred (a) in strain shadows around quartz porphyroclasts, acting as fluid sinks, and (b) in localized microshear zones that channelized fluid percolation. [Ti] resetting is mainly observed along wetted high angle boundaries (misorientation angle >10–15°), with partial [Ti] resetting observed along dry low angle boundaries (<10–15°). This study shows for the first time that pure subgrain rotation recrystallization in combination with dissolution‐precipitation under retrograde condition provide microstructural domains suitable for the application of titanium‐in‐quartz geothermobarometry at deformation temperatures down to 300–350°C.

On the shape of air–liquid interfaces with surface tension that bound rigidly rotating liquids in partially filled containers

Abstract The interface shape of a fluid in rigid body rotation about its axis and partially filling the container is often the subject of a homework problem in the first graduate fluids class. In that problem, surface tension is neglected, the interface shape is parabolic and the contact angle boundary condition is not satisfied in general. When surface tension is accounted for, the shapes exhibit much richer dependencies as a function of rotation velocity. We analyze steady interface shapes in rotating right-circular cylindrical containers under rigid body rotation in zero gravity. We pay special attention to shapes near criticality, in which the interface, or part thereof, becomes straight and parallel to the axis of rotation at certain specific rotational speeds. We examine geometries where the container is axially infinite and derive properties of their solutions. We then examine in detail two special cases of menisci in a cylindrical container: a meniscus spanning the cross-section and a meniscus forming a bubble. In each case, we develop exact solutions for the respective axial lengths as infinite series in powers of appropriate rotation parameters, and we find the respective asymptotic behaviors as the shapes approach their critical configuration. Finally, we apply the method of asymptotic approximants to yield analytical expressions for the axial lengths of the menisci over the whole range of rotation speeds. In this application, the analytical solution is employed to examine errors introduced by the assumption that the interface is a right circular cylinder; this assumption is key to the spinning bubble method used to measure surface tension.

Significance of non-Fourier heat flux and radiation on PEG – Water based hybrid Nanofluid flow among revolving disks with chemical reaction and entropy generation optimization

Investigation of entropy generation assures significantly the trustworthiness of mechanical and electronic components. Entropy generation is useful in many applications including heat exchangers, capacitors, circuit boards and resistors. In this article, we discussed the optimization of entropy generation on a radiative MHD fluid flow combined with CCHF model in two instances i.e., hybrid nanofluid(PEG − Water + ZrO2 + MgO)and mono- nanofluid(PEG − Water + ZrO2)amidst (two) revolving disks with chemical reaction. Mathematical model describing the fluid flow is resolved by using a shooting procedure together with R-K 4th order method after converting as a system of ODEs. Outcomes are displayed via plots and impacts of the pertinent parameters on physical quantities such as heat transfer rate are elucidated using a statistical tool, correlation coefficient in two cases. Primary conclusions of this study are larger stretching parameter of the lower disk ameliorates axial velocity, volumetric nanoparticle parameter alleviates radial velocity, higher thermal relaxation parameter belittles the fluid temperature, radiation and rotation parameters improve the entropy generation in the fluid flow and concentration diminishes with larger chemical reaction parameter. Further, we observed that elongating parameters of both disks are having significant positive association with surface drag force near the disks in both occasions. However, there is a significant negative association between the heat transfer rates. Rotation parameters improves the entropy generation in the fluid flow. Validation of the current study is done by comparing the present findings with the available outcomes in the literature and found an adequate agreement.