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Liquid metal buoyant flow around two differentially heated horizontal cylinders in the presence of a uniform vertical magnetic field is investigated experimentally. While magneto-convection in pipes or ducts has been studied theoretically and experimentally in recent years, data for heat transfer at immersed obstacles are rare and, to our knowledge, detailed experimental investigations on this fundamental magnetohydrodynamic problem do not exist. In the present work, two horizontal cylinders inserted into an adiabatic rectangular cavity filled with gallium–indium–tin are kept at constant temperatures to establish a driving temperature gradient in the surrounding liquid metal. The buoyancy-driven flow, quantified by the Grashof number $Gr$ , is varied in the range ${10^{6} \leq Gr \leq ~5\times 10^{7}}$. With increasing magnetic field, expressed via the Hartmann number $Ha$ , different flow regimes are identified from measurements for $0 \leq Ha \leq ~3000$. The effect of the electromagnetic force primarily consists in suppressing turbulence and damping the convective flow. The heat transfer is quantified in terms of the non-dimensional Nusselt number $Nu$ , and its dependence on $Gr/{Ha}^{2}$ , which is identified as the important group governing the flow, is discussed. [ABSTRACT FROM AUTHOR]

This study delves into the convective heat transfer phenomena within a square cavity that houses a porous medium, analyzing the effects of Darcy (Da) and Rayleigh (Ra) numbers on the thermal and fluid dynamic behavior within the system. Utilizing a combination of computational fluid dynamics (CFD) and the finite element method (FEM), the research focuses on steady-state, laminar flow conditions in two dimensions. The cavity, which is impermeable at its boundaries, contains a centrally located square region filled with a porous, isotropic material. The thermal environment is controlled with insulated horizontal walls and vertically positioned walls that experience sinusoidal temperature variations. The study examines how variations in the permeability of the porous medium (Da numbers ranging from 10−1 to 10−4) and the buoyancy-driven flow strength (Ra numbers spanning from 102 to 105) influence the velocity fields and heat transfer rates, with results expressed through Nusselt number (Nu) distributions. The findings reveal that higher Ra numbers, particularly at 105, significantly intensify convection within the cavity, thereby boosting local rates of heat transfer, especially in the central vertical section. The research identifies that optimal flow resistance in the porous medium occurs within the Da number range of 10−3 to 10−4. These insights are critical for advancing thermal management techniques, particularly in the natural cooling of electronic devices and improving insulation methods. [ABSTRACT FROM AUTHOR]

A new turbulence model has been developed for a Reynolds-averaged Navier–Stokes (RANS) simulations of buoyancy-driven flows. This study proposes a modification to the buoyancy-related term in the conventional k–ε RANS model's ε equation. Typical two-equation RANS models provide accurate predictions in homogeneous shear flow, decaying turbulence, and log-law regions, but have uncertain effectiveness for buoyancy-driven flows, particularly concerning the buoyancy-related term in the ε equation. They have produced significant errors in natural convection scenarios where the buoyancy-related term dominantly affects the modeling results, such as in the Rayleigh–Bénard (RB) convection. Conventional models are known to inaccurately predict RB convection when treated as a steady-state problem with zero mean velocity, considering only the gravity-directed coordinate as the independent variable. The analysis reveals that the conventional RANS model, along with modeling terms for buoyancy effects, provides not only inaccurate but also divergent turbulent heat fluxes in RB convection at high Rayleigh numbers. The proposed model establishes mathematical conditions that enable steady-state RANS simulations to converge to consistent scaling relations for the Nusselt number across a wide range of Rayleigh and Prandtl numbers in RB convection. This approach algebraically modifies a single term in the ε equation, so that the term vanishes in the absence of buoyancy, so the modification integrates seamlessly with the conventional k–ε RANS model. [ABSTRACT FROM AUTHOR]

Buoyancy-driven flow and heat transfer characteristics of the solid/hollow cylinders with concave shapes were numerically analyzed in a turbulent regime. The effects of Ra , L / D , and D th / D on heat dissipation have been studied in the range of 1010 to 1012, 2 to 10, and 0.2 to 0.9, respectively. It has been found that the Nu ¯ increases with Ra for solid/hollow cylinders. For a hollow cylinder, Nu ¯ in is always higher than Nu ¯ out except at D th / D = 0.2. The Nu ¯ in of a hollow cylinder increases up to D th / D = 0.6, irrespective of the Ra , and L / D ratios thereafter reduced drastically has been observed. Whereas, at a low D th / D , and high Ra (i.e., Ra ≥ 1011), Nu ¯ out of a hollow cylinder significantly decreases with D th / D . However, it shows a marginal decrement at a high length-to-diameter ratio. For solid and hollow cylinders, the thermo-fluid dynamics have been delineated through the temperature contours, streamline patterns, and vortex generation at the inner as well as outer wall of the hollow cylinder. This numerical study also proposes a correlation for the Nu ¯ of the solid/hollow cylinders to have an accuracy ± 6 % of relevant parameters. [ABSTRACT FROM AUTHOR]

The turbulence mixing initiated by the Rayleigh–Taylor instability has been reported in a two-dimensional (2D) strongly coupled dusty plasma system using classical molecular dynamics simulation. The entire evolution cycle, including the initial equilibrium, the instability, turbulent mixing, and, finally, a new equilibrium through the thermalization process, has been demonstrated via the respective energy spectra. The fully developed spectrum follows the Bolgiano-Obukho k − 11 / 5 scaling at smaller wavenumbers, a characteristic 2D buoyancy-driven turbulent flow feature. At higher wavenumbers, the energy spectrum E (k) ∝ k represents the thermalization of the system and is a characteristic feature of 2D Euler turbulence. At longer timescales, the system reflects the Kolmogorov scale of k − 3 . Moreover, strong coupling slows the turbulent mixing process, though the final state is a complete thermalized system. Our results also help us to understand the thermalization process in Yukawa fluids, other strongly coupled plasma families, and turbulent mixing in low Reynolds number fluids. [ABSTRACT FROM AUTHOR]

The existence of temperature gradients within eukaryotic cells has been postulated as a source of natural convection in the cytoplasm, i.e. bulk fluid motion as a result of temperature-difference-induced density gradients. Recent computations have predicted that a temperature differential of ΔT ≈ 1 K between the cell nucleus and the cell membrane could be strong enough to drive significant intracellular material transport. We use numerical computations and theoretical calculations to revisit this problem in order to further understand the impact of temperature gradients on flow generation and advective transport within cells. Surprisingly, our computations yield flows that are an order of magnitude weaker than those obtained previously for the same relative size and position of the nucleus with respect to the cell membrane. To understand this discrepancy, we develop a semi-analytical solution of the convective flow inside a model cell using a bi-spherical coordinate framework, for the case of an axisymmetric cell geometry (i.e. when the displacement of the nucleus from the cell centre is aligned with gravity). We also calculate exact solutions for the flow when the nucleus is located concentrically inside the cell. The results from both theoretical analyses agree with our numerical results, thus providing a robust estimate of the strength of cytoplasmic natural convection and demonstrating that these are much weaker than previously predicted. Finally, we investigate the ability of the aforementioned flows to redistribute solute within a cell. Our calculations reveal that, in all but unrealistic cases, cytoplasmic convection has a negligible contribution toward enhancing the diffusion-dominated mass transfer of cellular material. [ABSTRACT FROM AUTHOR]

The objective of current study is to analyze the magnetohydrodynamic (MHD) natural convection flow of couple-stress fluid and entropy generation (second law analysis) inside the cavity with heated fin by using the Galerkin finite element method. The heated fin has been placed in middle of the heated bottom wall, the temperature T c is fixed on the vertical walls and an insulated situation is considered at the top wall. The irreversibility ratio and heat flux inside the enclosure are examined through entropy generation and Bejan heatlines, respectively. The obtained results show that the intensity of circulations of streamlines decrease from 3.9744 to 0.03148 and heatlines from 7 to 4.5 due to increasing couple-stress parameter (K) from 0 to 1.5. It is noted that the heatlines bowls appear due to enhanced buoyancy-driven flow against high Rayleigh number. The reverse relation is noted between the entropy generation and the Hartmann number. The overall heat transfer rate along with the bottom and vertical side walls increase 111.65 % and 75.8297 % , respectively, with increasing the fin height from 0 to 0.25. Obtained results could help to optimize heat transfer in engineering systems like heat exchangers, cooling processes of devices, chemical reactors, and solar collectors. [ABSTRACT FROM AUTHOR]

To provide computational fluid dynamics (CFD)–grade experimental data for studying stratification, measurements on the High-Resolution Jet (HiRJet) facility at the University of Michigan have been conducted with density differences of $1.5\% $ 1.5 % and $ - 1.5\% $ − 1.5 % , respectively. Fluid with a density different from the fluid initially present in the HiRJet tank was injected, and the propagation of the time-dependent density stratification was captured on a two-dimensional plane with the aid of the wire-mesh sensor technique for Reynolds numbers near 5000 and Richardson numbers near 0.29. Direct numerical simulations (DNSs) of the two cases have also been conducted to expand the multifidelity database. The novel experimental and DNS data were then used to assess the predictive capabilities of the Standard $k - \varepsilon $ k − ε (SKE) model and the Reynolds Stress Transport (RST) model. In particular, the propagation speed and thickness of the stratification fronts were assessed by comparing the CFD results against the experimental and DNS data. It was found that the general trends of the stratified density fronts were well predicted by the CFD simulations; however, slight overprediction of the thickness of the stratification layer was found with the SKE model while the RST model gave a larger overprediction of the mixing. Examination of the turbulent statistics showed that the turbulent viscosity was largely overpredicted by the RST model compared to the SKE model. [ABSTRACT FROM AUTHOR]

Code_Saturne, an open-source computational fluid dynamics (CFD) code, has been applied to a range of problems related to turbomachinery internal air systems. These include a closed rotor-stator disk cavity, a co-rotating disk cavity with radial outflow and a co-rotating disk cavity with axial throughflow. Unsteady Reynolds-averaged Navier-Stokes (RANS) simulations and large eddy simulations (LES) are compared with experimental data and previous direct numerical simulation and LES results. The results demonstrate Code_Saturne's capabilities for predicting flow and heat transfer inside rotating disk cavities. The Boussinesq approximation was implemented for modeling centrifugally buoyant flow and heat transfer in the rotating cavity with axial throughflow. This is validated using recent experimental data and CFD results. Good agreement is found between LES and RANS modeling in some cases, but for the axial throughflow cases, advantages of LES compared to URANS are significant for a high Reynolds number condition. The wall-modeled large eddy simulation (WMLES) method is recommended for balancing computational accuracy and cost in engineering applications. [ABSTRACT FROM AUTHOR]

Ground‐coupled heat exchangers (GCHE) have received significant attention over several decades as a result of increasing the world's energy demand and the need for reducing fossil fuels consumption. Prior studies have demonstrated the effectiveness of utilizing GCHE with refrigeration and heating systems. However, optimizing the performance of GCHE coupled with chillers for heat rejection, especially in extreme hot‐humid climates (where cooling towers are not very effective) is lacking in the literature. In this work, a ground borehole fitted with a coaxial‐tubes heat exchanger (BHE) is numerically simulated. Based on a wide range of data collected for the soil of Dubai, its real in situ thermophysical properties are characterized. The soil's upper layer thickness is relatively small and dry that operates in conduction mode, while the lower one is water‐saturated that works in coupled conduction‐advection mode. The study aims at optimizing the parameters advancing heat rejection into ground considering the actual properties of the soil of Dubai. The results indicate that the more feasible high‐density polyethylene pipes can perform as good as the steel ones. Also, a great finding based on the presented novel design is that insulating the inner pipe can increase the temperature duty by 55%. The proposed design of BHE is relatively inexpensive, more feasible and efficient, which is achieved for the first time based on a deep analysis of Dubai climate and soil. This makes the technology ready to be implemented for industrial applications in Dubai and other regions having a similar climate and soil nature. [ABSTRACT FROM AUTHOR]

This paper investigates a numerical code-coupling technique to tackle multiphysics and multiscale simulations using state-of-the-art software packages that typically address some specific modeling domain. The coupling considers the in-house FEM code FEMuS and the FVM code OpenFOAM by exploiting the MED library from the SALOME platform. The present approach is tested on a buoyancy-driven fluid flow within a square cavity, where the buoyancy force constitutes the coupling term. In uncoupled scenarios, momentum and temperature equations are solved in both FEM and FVM codes without data exchange. In the coupled setting, only the OpenFOAM velocity and the FEMuS temperature fields are solved separately and shared at each time step (or vice versa). The MED library handles the coupling with ad hoc data structures that perform the field transfer between codes. Different Rayleigh numbers are investigated, comparing the outcomes of coupled and uncoupled cases with the reference literature results. Additionally, a boundary data transfer application is presented to extend the capabilities of the coupling algorithm to coupled applications with separate domains. In this problem, the two domains share interfaces and boundary values on specific fields as fluxes are exchanged between the two numerical codes. [ABSTRACT FROM AUTHOR]

Through a combination of laboratory experiments and theoretical models, we investigate the interaction of a mean upwelling through a closed basin with a vertical buoyancy flux. The fluid is mixed by a horizontally oscillating rake, which either traverses the whole basin or which oscillates just near one vertical boundary. We first review the steady state and demonstrate that, in both mixing regimes, the vertical density profile across the basin is controlled by the steady-state balance between the upward advective and diffusive fluxes of salinity as described by the classical model introduced by Munk (Deep-Sea Res. , vol. 13, issue 4, 1966, pp. 707–730). However, with boundary mixing, we show that both the upwelling and the buoyancy transport are localised to the mixing zone near the boundary, and the interior fluid is stagnant. We then develop a model to describe the transient evolution of the system if there is either a discrete increase or gradual decrease to the buoyancy flux. In the boundary mixing case, the change in the buoyancy flux at the lower boundary leads to a change in the buoyancy of the fluid in the boundary mixing region, and this induces a transient, buoyancy-driven flow in the boundary region in addition to the steady upwelling. In turn, an equal and opposite vertical flow develops in the interior, and this leads to a change in the density stratification of the interior fluid as the system adjusts to a new equilibrium. However, in our experiments, there is no vertical mixing in the interior and interior fluid may upwell or downwell dependent on the change to the buoyancy forcing. We discuss the implications of our results for the transport and mixing in the deep ocean, and the associated interpretation of field experiments. [ABSTRACT FROM AUTHOR]

Motivated by buoyancy-driven flows within geological formations, we study the evolution of a (dense) gravity current in a porous medium bisected by a thin interbed layer. The gravity current experiences distributed drainage along this low-permeability boundary. Our theoretical description of this flow takes into account dispersive mass exchange with the surrounding ambient fluid by considering the evolution of the bulk and dispersed phases of the gravity current. In turn, we model basal draining by considering two bookend limits, i.e. no mixing versus perfect mixing in the lower layer. Our formulations are assessed by comparing model predictions against the output of complementary numerical simulations run using COMSOL. Numerical output is essential both for determining the value of the entrainment coefficient used within our theory and for assessing the reasonableness of key modelling assumptions. Our results suggest that the degree of dispersion depends on the dip angle and the depth and permeability of the interbed layer. We further find that the nose position predictions made by our theoretical models are reasonably accurate up to the point where the no mixing model predicts a retraction of the gravity current front. Thereafter, the no mixing model significantly under-predicts, and the perfect mixing model moderately over-predicts, numerical data. Reasons for the failure of the no mixing model are provided, highlighting the importance of convective instabilities in the lower layer. A regime diagram is presented that defines the parametric region where our theoretical models do versus do not yield predictions in good agreement with numerical simulations. [ABSTRACT FROM AUTHOR]

We explore the transient evolution of thermo-fluid-dynamics of evaporating sessile droplets over curved substrates in the liquid and gaseous domains. A computational model using the Arbitrary Lagrangian-Eulerian framework is adopted. The governing equations in both liquid and gaseous domains are solved in a fully coupled manner, considering coupled effects of evaporative cooling and heat advection due to bulk fluid motion. This bulk motion in the liquid domain is caused by natural advection due to thermal actuations such as thermal Marangoni flow and buoyancy-driven convection. For the gaseous domain, the additional effects of solutal convection (due to vapour-concentration variation), Stefan flow and interfacial viscous stresses are also considered. To depict a generalized role of substrate curvature, both concave and convex surfaces with curvatures over a wide range are studied. The surface wettability effects are also explored by varying the true contact angle of the droplets. Computational predictions on evaporation rate and internal flow field are validated against experimental results from literature. The interplay of wetting state and substrate curvature is noted to substantially affect the evaporation process and its thermo-fluidics. The convex curvature significantly augments internal advection while the same is weakened over concave substrates due to altered mass loss rate. Consequently, the duration of multi-vortex Marangoni flows in the development stages of evaporation and the advection in the external gaseous domain is markedly different for different curvatures. Further, on superhydrophobic curved surfaces, the effects of re-distributed evaporative fluxes play a major role. In such cases, the reduced mass flux over a large interfacial area near the periphery expedites the stable state Marangoni and external flow features. [ABSTRACT FROM AUTHOR]

Enzymatic reactions in solution drive the convection of confined fluids throughout the enclosing chambers and thereby couple the processes of reaction and convection. In these systems, the energy released from the chemical reactions generates a force, which propels the fluids' spontaneous motion. Here, we use theoretical and computational modeling to determine how reaction-convection can be harnessed to tailor and control the dynamic behavior of soft matter immersed in solution. Our model system encompasses an array of surface-anchored, flexible posts in a millimeter-sized, fluid-filled chamber. Selected posts are coated with enzymes, which react with dissolved chemicals to produce buoyancy-driven fluid flows. We show that these chemically generated flows exert a force on both the coated (active) and passive posts and thus produce regular, self-organized patterns. Due to the specificity of enzymatic reactions, the posts display controllable kaleidoscopic behavior where one regular pattern is smoothly morphed into another with the addition of certain reactants. These spatiotemporal patterns also form "fingerprints" that distinctly characterize the system, reflecting the type of enzymes used, placement of the enzyme-coated posts, height of the chamber, and bending modulus of the elastic posts. The results reveal how reaction-convection provides concepts for designing soft matter that readily switches among multiple morphologies. This behavior enables microfluidic devices to be spontaneously reconfigured for specific applications without construction of new chambers and the fabrication of standalone sensors that operate without extraneous power sources. [ABSTRACT FROM AUTHOR]

Pulsing emanations of native hydrogen (H 2) have been observed at the surface of emitting structures, specifically "Fairy circles" in Minas Gerais State, Brazil. However, the underlying cause of these H 2 pulses remains unclear. Possible controlling factors include deep migration processes, interactions with the atmosphere and near-surface conditions. In this study, we examine the mechanisms that may trigger pulsating fluid migration and the resulting periodicity, with particular attention to the influence of deep geological processes. We employed a numerical model to simulate the migration of a constant deep fluid flow. To ensure the accuracy of the model in solving complex fluid flows, we conducted initial simulations to compare the morphology and amplitude of 2D thermal anomalies induced by buoyancy-driven water flow within a fault zone with another numerical model. Following the validation of our model in capturing complex fluid flows, we proceeded to model the H 2 gas flow along a 1-km draining fault, intersected by a low permeable rock layer acting as a "pressure relief valve" system. Our objective is to investigate the conditions that give rise to a pulsing regime. Our results indicate that sustained surface bursts in the model only occur if: (I) a permeability with an effective-stress dependency is considered, (II) a significant contrast in permeability exists between different zones, (III) an adequately high initial effective stress state is present at the base of the low-permeability layer, and (IV) the incoming and continuous fluid flow of H 2 at depth is sufficiently low to prevent instant "opening" of the low-permeability layer due to overpressure. The predicted periodicity for surface H 2 pulses regulated by the fault-valve mechanisms is expected to range from 100 to 300 days, representing a considerably longer duration compared to the measurements observed up to now in Brazilian Fairy circles. • Examined natural H 2 pulsing flow along a fault via numerical simulation. • H 2 pulse generation linked to stress-dependent deep permeability zones. • H 2 pulse intervals span months, longer than prior São Francisco basin data. [ABSTRACT FROM AUTHOR]

The occurrence of underground mine fires remains a significant and persistent safety challenge in the mining industry, posing imminent risks to both miners' lives and the operational integrity of mining facilities. Current underground mine fire studies lack scale accuracy due to lab experiments and fail to consider bifurcation effects on smoke gas temperature. This study performed full-scale experiments and built validated CFD models to explore the interactive impact of ventilation and fire size on temperature attenuation, gas behavior, and CO generation in underground mines. A new empirical correlation for temperature decay in the mine drift was developed and its accuracy was compared with established models in the literature. In addition, the influence of bifurcation on maximum smoke temperature was analyzed. This research combines full-scale experiments and validated CFD modeling to address major gaps in underground mine fire studies. Unlike previous methods, this study explores the interactive effects of ventilation, fire size, temperature attenuation, and toxic gas spread, offering unprecedented insights. This innovation enables the development of tailored fire safety standards for mines, ensuring safer designs, rapid fire suppression, and improved evacuation strategies. By bridging theory and practice, this work transforms fundamental knowledge, empowering the mining industry to enhance safety measures, protect lives, and mitigate the impact of underground mine fires. [ABSTRACT FROM AUTHOR]

Multi-wall carbon nanotubes (MWCNTs) characterize innovative nanoparticles that progress the thermal characteristics of base fluids, compelling them appropriate for utilizing in renewable energy, heat exchanger, and automotive engineering. In this analysis, the buoyancy-driven flow in a superposed spherical enclosure packed with amalgamated porous (Fe3O4-MWCNTs/H2O) hybrid nanofluid layers was explored by employing the procedure of Levenberg–Marquardt with backpropagated artificial neural networks (LMB-ANN) for two temperature models. The exterior wall of enclosure was kept at a constant frigid condition, while the inner surface received partial heating to create a heat flux. The flow situation within the porous cavity was modeled using the Darcy–Boussinesq model. To evaluate the model equations, the control volume-based finite element method (CVFEM) was adopted. The results obtained from numerical method explain the reference data of LMB-ANN for several situations of porous cavity by modifying model variables. By varying the model parameters within the scope of the present numerical approach, a set of proposed data LMB-ANN is generated for cases. The proposed model has equaled for perfection after the numerical findings of various instances have been evaluated using the LMB-ANN train, test, and validating strategy. Several error graphs and statistical visualizations focused on mean square errors, error histogram, and regression assessment are designed to support the proposed methodology (LMB-NN). The proposed approach (LMB-ANN) has been verified based on the correlation of the suggested and benchmark (numerical) outputs, with a validity level ranging from 10–02 to 10–09. Also, the principal findings revealed that elevating the Rayleigh and Darcy numbers improves energy transmission inside the enclosure. [ABSTRACT FROM AUTHOR]

The current work presents a 3D numerical investigation of heat transfer characteristics of twin heaters exposed to cooling. The liquid nitrogen is considered as the fluid medium for heat rejection. Six distinct heater configurations are taken into account and the impact of heater configuration on flow and heat transfer pattern is demonstrated. The heaters provide heat at a steady rate (W/m3). The velocity and temperature contours, average Nusselt number ( Nu Avg ) , the maximum vertical velocity of fluid flow, and average velocity of fluid flow is plotted for all the six heater configurations for the comparative study. Moreover, another parametric study has been done to find the optimum spacing between two heaters for the best heat transfer rate. The reliance on average Nusselt number, average fluid flow velocity, entropy generation as a function of heat generation rate for various heater configurations are outlined graphically. The after-effects of this study show that heater configurations can impressively influence the heat transfer rate, fluid flow characteristics, and entropy generation under the same heat generation rate in the heater. The most noteworthy Nu Avg on the heater surface is acquired when heater configuration is circular. In each one of the heater configurations, the value of Bejan number is under 0.5. Henceforth, it may be expressed that irreversibility because of fluid friction prevails over irreversibility because of heat transfer. [ABSTRACT FROM AUTHOR]

Heat transport issues of wedge-shaped flow on hybrid nanofluids are of special significance by reason of their importance in manufacturing uses including heat exchangers solar panels, electronic equipment cooling, drying processes, and air heaters. Consequently, the current investigation investigates the behavior of dissipative Single-walled Carbone nanotubes (SWCNT) — Multi-walled Carbon nanotubes (MWCNT) hybrid nanofluid in the buoyant flow towards a radiative vertical permeable wedge subjected to variable wall temperature considering heat source/sink. By selecting appropriate similarity conversions, the resultant flow regulating nonlinear boundary layer PDEs are subsequently transformed into coupled nonlinear ODEs. After that, the boundary layer Boussinesq approximations are numerically resolved. The significant outcome of the current investigation is the heat transport which is higher for linear radiation, volume fraction, and uniform heat source parameters. The momentum is controlled with wedge angle and volume fraction of nanotube particles. The momentum boundary layer is upsurged with mixed convection parameters for an assisting flow. Changes to the Nusselt number and fluid flow rate are measured for flow-controlling parameters. Furthermore, the results are compared and effectively validated with previously reported literature results. [ABSTRACT FROM AUTHOR]

Turbofan compressor cooling circuits exhibit inherent unsteadiness within their cavities due to the interplay of forced and natural convection phenomena. This dynamic is fueled by axial cooling throughflow, centrifugal forces, and large temperature gradients. This paper introduces an extended compressible lattice-Boltzmann approach tailored for accurately modeling centrifugal buoyancy-driven flows in such cavities. The approach integrates a local rotating reference frame model into a hybrid thermal lattice Boltzmann method, facilitating the simulation of rotating flows of perfect gases. Moreover, a new mass-conserving boundary treatment, based on the reconstruction of distribution functions, enhances precision in predicting rotor disk heat transfer. Finally, an adapted direct-coupling mesh-refinement strategy, accounting for source terms at grid transitions, enables efficient high buoyancy flow simulations. The proposed approach effectively recovers flow and heat transfer mechanisms on sealed and open rotating compressor cavity rigs, spanning a large range of Rayleigh numbers (up to 109). Through an analysis of the compressibility effects, adjustments to the adiabatic exponent and Eckert number allow for a significant boost in computational speed without undermining the reliability of the flow and heat transfer dynamics, aligning well with established theoretical models and numerical studies. With computational efficiency that outperforms conventional compressible finite volume solvers, the proposed approach stands as a promising method for industrial-scale modeling of turbomachinery cooling circuits. [ABSTRACT FROM AUTHOR]

• SPH and FVM models have been compared for buoyant flow in a stomach geometry. • The curved shape of the stomach leads to rapid layer inversion due to the development of a swirling flow. • Rayleigh–Taylor instability (RTI) is well–captured in the SPH model. • The FVM leads to more complete final separation. • SPH kernels with smaller compact support behave better in separation processes. The primary functions of the stomach, including mixing, digestion, and emptying, are affected by the spatial distribution of content properties, and how this distribution changes in response to gravity and wall contraction forces. One aspect that is not well studied is the buoyancy effects that result from content with heterogenous density. A buoyancy–driven flow in a non–deforming stomach is simulated using the Smoothed Particle Hydrodynamics (SPH) and Finite Volume Method (FVM). An aqueous liquid layer is initially placed above a fatty layer of the same volume. The buoyancy effect driven by gravity and strongly influenced by the stomach shape, causes the fat to rise to the top layer and the aqueous liquid to sink to the bottom. Rayleigh–Taylor Instability (RTI) is well–captured in the SPH model in the initial interface flow development. Some detailed flow behaviours are slightly different between the two models once the bulk turnover flow is established, but both models show that the separation process happens rapidly (within 6 s) in the curved geometry of the stomach. The final phase separation is more complete in the FVM compared with the SPH. Sensitivity analysis is conducted in both models to examine the solution accuracy. This work suggests that buoyancy driven flow effects, which have not been investigated previously, occur on a much shorter timescale (6 s) than peristaltic (20 – 60 s) and digestion timescales (hours). This result may help basic understanding of digestive processes and be used to guide food and drug design. [ABSTRACT FROM AUTHOR]

The occurrence of buoyancy-driven flow and reactive solute transport in a fluid-saturated porous medium can be induced by either natural processes or human activities. Typical examples include the groundwater salinization in carbonate-rock aquifers and the acid treatment of oil wells in petroleum drilling industry. In this paper, the classical Elder problem of buoyancy-driven convection in two-dimensional porous media is extended to include the local chemical interactions between the solute in the pore liquid (e.g. salt such as NaCl or acids such as HCl and HCl/HF mixtures) and the solid space of the porous medium (e.g. minerals such as calcite and dolomite). Effects of the geochemical processes on the flow and mass transport are investigated. For the reactive, strongly solute-driven case in the regime dominated by the diffusive mass transport, a decrease in the net solute concentration is found as compared to the non-reactive case. This decrease is pronounced at higher values of the Damköhler number when the solute reaction rate becomes larger than the solute diffusion rate. Furthermore, the flow structure is affected by products generated by the chemical reaction when the Rayleigh number for the products is sufficiently high. In that case, numerical simulations show the formation of diluted fluid tongues exhibiting damped periodic oscillations about a nonzero mean. The results are obtained using the pseudospectral numerical method, verified against the analytical solution for the non-reactive, purely diffusive case. [ABSTRACT FROM AUTHOR]

Many geological layers include cross bedding, which leads to different values for permeability along and across the bedding planes. We explore how such cross bedding impacts buoyancy-driven flow through an inclined aquifer. For each bedding angle and ratio of the permeability along and across the bedding, a free buoyancy-driven plume rises at a particular angle to the horizontal. If the angle of inclination of the aquifer to the horizontal is smaller than this angle, then the plume rises along the upper boundary, otherwise, somewhat surprisingly, the buoyant plume rises along the lower boundary of the aquifer. We present new laboratory experiments to support these predictions. We also test a model for the effective permeabilities which control the speed and the rate of spread of the plume along one or other boundary of the aquifer. We consider the impact of our results for modelling geological storage of CO2 or aquifer thermal energy storage. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of buoyancy‐driven double‐diffusive convection within an elliptical annulus enclosure filled with a saturated porous medium. An in‐house built FORTRAN code has been developed, and computations are carried out in a range of values of Darcy–Rayleigh number Ram (10 ≤ Ram ≤ 500), Lewis number Le (0.1 ≤ Le ≤ 10), and the ratio of buoyancy forces N (−5 ≤ N ≤ 5). In addition, three methods are used, namely the multi‐variable polynomial regression, the group method of data handling (GMDH), and the artificial neural network (ANN) for the predictions of heat and mass transfer rates. First, results are successfully validated with existing numerical and experimental data. Then, the results indicated that temperature and concentration distributions are sensitive to the Lewis number and thermal and mass plumes are developing in proportion to the Lewis number. Two particular values of Lewis number Le = 2.735 and Le = 2.75 captured the flow's transition toward an asymmetric structure with a bifurcation of convective cells. The average Nusselt number tends to have an almost asymptotic value for Le » 5. For the case of aiding buoyancies N > 1, the average Nusselt Number Nu¯ $\bar{{Nu}}$ decreased by 33% when the Lewis number increased to its maximum value. Then, it increased by 10% when the Lewis number increased to Le = 1 for the case of opposing buoyancies N < 1 and then decreased by 33% when the Lewis number increased to its maximum value., contrary to the behavior of the average Sherwood number Sh¯ $\bar{{Sh}}$ that increased by 700% for both cases N > 1 and N < 1. New correlations of Nu¯ $\bar{{Nu}}$, and Sh¯ $\bar{{Sh}}$ as a function of Ram, Le, and N are derived and compared with GMDH and ANN methods, and the ANN method showed higher performance for the prediction of Nu¯ $\bar{{Nu}}$ and Sh¯ $\bar{{Sh}}$ with R2 exceeding 0.99. [ABSTRACT FROM AUTHOR]

This study investigates the effects of magnetic induction, ion slip and Hall current on the flow of linear viscous fluids in a rectangular buoyant channel. In a hydro-magnetic flow scenario with permeable and conducting walls, one wall has a temperature variation that changes over time, while the other wall keeps a constant temperature; the research focuses on this situation. Asymmetric wall heating and suction/injection effects are also examined in the study. Using the Laplace transform, analytical solutions in the Laplace domain for temperature, velocity and induced magnetic field have been determined. The Stehfest approach has been used to find numerical solutions in the real domain by reversing Laplace transforms. The generalized thermal process makes use of an original fractional constitutive equation, in which the thermal flux is influenced by the history of temperature gradients, which has an impact on both the thermal process and the fluid's hydro-magnetic behavior. The influence of thermal memory on heat transfer, fluid movement and magnetic induction was highlighted by comparing the solutions of the fractional model with the classic one based on Fourier's law. [ABSTRACT FROM AUTHOR]

Accurate evaluation of thermo-fluid dynamic characteristics in tanks is critically important for designing liquid hydrogen tanks for small-scale hydrogen liquefiers to minimize heat leakage into the liquid and ullage. Due to the high costs, most future liquid hydrogen storage tank designs will have to rely on predictive computational models for minimizing pressurization and heat leakage. Therefore, in this study, to improve the storage efficiency of a small-scale hydrogen liquefier, a three-dimensional CFD model that can predict the boil-off rate and the thermo-fluid characteristics due to heat penetration has been developed. The prediction performance and accuracy of the CFD model was validated based on comparisons between its results and previous experimental data, and a good agreement was obtained. To evaluate the insulation performance of polyurethane foam with three different insulation thicknesses, the pressure changes and thermo-fluid characteristics in a partially liquid hydrogen tank, subject to fixed ambient temperature and wind velocity, were investigated numerically. It was confirmed that the numerical simulation results well describe not only the temporal variations in the thermal gradient due to coupling between the buoyance and convection, but also the buoyancy-driven turbulent flow characteristics inside liquid hydrogen storage tanks with different insulation thicknesses. In the future, the numerical model developed in this study will be used for optimizing the insulation systems of storage tanks for small-scale hydrogen liquefiers, which is a cost-effective and highly efficient approach. [ABSTRACT FROM AUTHOR]

The understanding of the impact of buoyancy-driven flow on the migration of respiratory droplets remains limited. To investigate this phenomenon, the Lagrangian–Eulerian approach (k-ε turbulent model and discrete phase model) was employed to analyze the interaction between buoyancy-driven flow and coughing activity. The simulation approach was validated by simulating a jet problem in water. Although this problem describes the jet penetration in water, the governing equations for this problem are the same as those for coughing activity in the air. The results demonstrated that an umbrella-shaped airflow was generated above a person and a temperature stratification existed in the room. The buoyancy-driven flow significantly altered the dispersion pattern of the droplets. Notably, for large droplets with an initial diameter of 100 μm, the flow in the boundary layer led to an increased deposition time by about five times. Conversely, for small droplets with an initial diameter of 20 μm, the umbrella-shaped airflow resulted in a more rapid dispersion of droplets and subsequently facilitated their quicker removal by the room walls. After a duration of 300 s, the suspended droplet number of the case with buoyancy-driven flow was 33.4% smaller than that of the case without buoyancy-driven flow. Two or three persons being in the room resulted in a faster droplet removal. [ABSTRACT FROM AUTHOR]

Stochastic versions of a classical model for natural ventilation are proposed and investigated to demonstrate the effect of random fluctuations on stability and predictability. In a stochastic context, the well-known deterministic result that ventilation driven by the competing effects of buoyancy and wind admits multiple steady states can be misleading. With fluctuations in the buoyancy exchanged with an external environment modelled as a Wiener process, such systems tend to reside in the vicinity of global minima of their potential, rather than states associated with metastable equilibria. For a heated space with a leeward low-level and windward high-level opening, sustained buoyancy-driven flow opposing the wind direction is unlikely for wind strengths exceeding a statistically critical value, which is slightly larger than the critical value of the wind strength at which bifurcation in the deterministic system occurs. When fluctuations in the applied wind strength are modelled as an Ornstein–Uhlenbeck process, the topology of the system's potential is effectively modified due to the nonlinear role that wind strength has in the equation for buoyancy conservation. Consequently, large fluctuations in the wind of sufficient duration rule out the possibility of sustained ventilation opposing the wind direction at large base wind strengths. [ABSTRACT FROM AUTHOR]

Large-eddy simulation (LES) resolves large-scale turbulence directly and parametrizes small-scale turbulence. Resolving micro-scale turbulence, e.g., in wind turbine wakes, requires both a sufficiently small grid spacing and a domain large enough to develop turbulent flow. Refining a grid locally via a nesting interface effectively decreases the required computational time compared to the global grid refinement. However, interpolating the flow between nested grid boundaries introduces another source of uncertainty. Previous studies reviewed nesting effects for a buoyancy-driven flow and observed a secondary circulation in the two-way nested area. Using a nesting interface with a shear-driven flow in LES, therefore, requires additional verification. We use PALM model system 21.10 to simulate a boundary layer in a cascading self-nested domain under neutral, convective, and stable conditions and verify the results based on the wind speed measurements taken at the FINO1 platform in the North Sea. We show that the feedback between parent and child domains in a two-way nested simulation of a non-neutral boundary layer alters the circulation in the nested area, despite spectral characteristics following the reference measurements. Unlike the pure buoyancy-driven flow, a non-neutral shear-driven flow slows down in a two-way nested area and accelerates after exiting the child domain. We also briefly review the nesting effect on the velocity profiles and turbulence anisotropy. [ABSTRACT FROM AUTHOR]

This paper provides an assessment of fluid transport and mixing processes inside the primary circuit of the test facility ROCOM through the numerical simulation of Test 2.1 with the system code ATHLET. The experiment represents an asymmetric injection of cold and non-borated water into the reactor coolant system (RCS) of a pressurized water reactor (PWR) to restore core cooling, an emergency procedure which may subsequently trigger a core re-criticality. The injection takes place at low velocity under single-phase subcooled conditions and presents a major challenge for the simulation in lumped parameter codes, due to multidimensional effects in horizontal piping and vessel arising from density gradients and gravity forces. Aiming at further validating ATHLET 3-D capabilities against horizontal geometries, the experiment conditions are applied to a ROCOM model, which includes a newly developed horizontal pipe object to enhance code prediction inside coolant loops. The obtained results show code strong simulation capabilities to represent multidimensional flows. Enhanced prediction is observed at the vessel inlet compared to traditional 1-D approach, whereas mixing overprediction from the descending denser plume is observed at the upper-half downcomer region, which leads to eventual deviations at the core inlet.

Free-convection heat transfer from vertical surfaces is widely encountered in engineering applications, yet the role played by surface alterations in the heat transfer process and their practical effectiveness are still points of confusion. In this work, buoyancy-driven flows over periodically ribbed vertical plates of different surface micro-textures are investigated, mainly based on an asymptotic homogenization model through which the expensive resolution of the velocity and thermal fields within the inter-rib regions is bypassed, by imposing equivalent effective boundary conditions at a virtual plane surface. Efficiency of the homogenized simulations in detecting macroscopic behavior of the Nusselt number is first assessed, compared with full feature-resolving simulations in which the effects of complex flow patterns, near and within wall corrugations, on the local Nusselt number are captured. Second, the validated model is used to construct a database of numerical results describing deviations of the average Nusselt number over different ribbed surfaces, relative to a corresponding smooth surface. Under the conditions investigated, it is found that surface roughening generally deteriorates heat transfer from vertical surfaces, with slight enhancement for geometries characterized by low thermal slip, for example, rectangular ribs of narrow inter-rib spaces. Finally, a multiple-regression analysis is conducted to formulate a correlation describing effects of the thermal-slip coefficient, the number of ribs, and the Grashof number on the surface-averaged Nusselt number; accuracy of the proposed correlation is attested via further validation. This paper aims to call attention of the heat transfer society to the ability of the homogenization approach to considerably alleviate the computational requirements for relevant simulations and, thus, to significantly accelerate parametric optimization studies. [ABSTRACT FROM AUTHOR]

In this research article, the behavior of 2D non-Newtonian Sutterby nanofluid flow over the parabolic surface is discussed. In boundary region of surface buoyancy-driven flow occurred due to considerable temperature differences produced by the reaction happen between Sutterby nanofluid and catalyst at the surface. Free convection which is sighted easily on the parabolic surface is initiated by reaction on the catalyst surface modeled the 1st order activation energy. Applications of parabolic surfaces are upper cover of bullet, car bonnet, and air crafts. Under discussion flow is modelled mathematically by implementing law of conservation of microorganism's concentration, momentum, mass and heat. The governing equations of the system is of the form of non-linear PDE's. By the use of similarity transform, the governing PDE's transformed as non-dimensional ODE's. The resultant system of non-dimensional ODE's are numerically solved by built-in function MATLAB package named as 'bvp4c'. Graphical representation shows the influence of different parameters in the concentration, velocity, microorganisms and temperature profiles of the system. In temperature profile, we examined the impact of thermophoresis coefficient Nt (0.1, 0.5, 1.0), Prandtl number Pr (2.0, 3.0, 4.0), and Brownian motion variable Nb (0.1, 0.3, 0.5). Velocity profile depends on the non-dimensional parameters i.e. (Deborah number De & Hartmann number Ha) and found that these numbers (De, Ha) cause downfall in profile. Furthermore, mass transfer, skin friction, and heat transfer rates are numerically computed. The purpose of the study is to enumerate the significance of parabolic surfaces for the transport of heat and mass through the flow of bio-convective Sutterby nanofluid. [ABSTRACT FROM AUTHOR]

The core goal of the current theoretical exertion is to explore the impacts of step and sinusoidal bottom heating patterns on the buoyancy-driven flow and their heat flow aspects that are triggered by the temperature gradient inside the cavity which is commonly essential for many engineering applications like solar cells, food processing unit, materials processing unit, nuclear reactor core, etc. The domain of study is an air-filled cavity with an aspect ratio of 1, while the bottom wall is subjected to these two types of boundary conditions. The vertical walls are retained at reasonably lower temperatures whereas the top wall is kept insulated. The thermal and flow properties have been perceived with the aid of pertinent parameters like entropy generation, Nusselt number, non-dimensional temperature profiles and stream functions. The Ra is varied in the range of 103 ≤ Ra ≤ 106. The SIMPLE algorithm is applied to solve the governing differential equations by using a commercial software Ansys Fluent 2019. A significant observation found from the work is that the heat transfer rate is greater in the case of the step temperature profile. The average Nusselt number enhances 1.7 times from Ra = 105 to Ra = 105 for both the heating cases. Additionally, the heat transfer irreversibility is more near the wall as related to far from the wall due to high temperature gradients. The total entropy generation is 1.4 times more for step temperature profile as related to sinusoidal heating. [ABSTRACT FROM AUTHOR]

This investigation was inspired by the work of Dorbolo et al. (Phys Rev E 93(3):15, 2016), which was the first to study, at a laboratory scale, the phenomenon observed in the natural world of floating disks of ice rotating. They conclude that, in controlled conditions, ice disks are able to induce their own rotation. Whilst their work successfully exposes multiple aspects of the kinematics of such disks, and the buoyancy-driven flow generated beneath them as they melt, the mechanism by which rotation is triggered remains unsubstantiated. We therefore return in this work to the study of floating ice disks, focusing specifically on the importance of experimental technique in obtaining reliable measurements of disk behaviour. Our investigation reveals that the motion of ice disks placed on a nominally quiescent body of fresh water is unpredictable, with some disks remaining motionless, and others rotating clockwise or anticlockwise. For those in motion, the average rate of rotation observed was less than half of that recorded by Dorbolo et al., a discrepancy possibly explained by residual background motions in the nominally quiescent surrounding body of water. However, given our observation that non-melting disks of high-density polyethylene (HDPE) cooled to the same temperature as the ice (comparable HDPE and ice disks differing by only ∼ 4 % in mass) consistently rotated at rates less than those made of ice, it is hypothesised that, within the confines of the freshwater environment, the motion of the turbulent meltwater plume that forms beneath an ice disk amplifies the effect of residual background motions. From our observations, it is concluded that residual motions are an underlying physical trigger for disk rotation. Article Highlights: The trigger for the rotation of freely floating ice disks on a nominally quiescent body of freshwater is investigated. The requisite 'settling' time for residual background motions to decay, such that the initial experimental conditions can be considered as quiescent, is measured. No systematic trends in the rate and sense of ice disk rotation with disk radius were observed. Our data supports the notion that the negatively buoyant meltwater plume that forms beneath an ice disk may amplify rotation, once this has been triggered by residual background motions. [ABSTRACT FROM AUTHOR]

The finite element method is implemented to determine solutions for buoyancy-driven flow in a square cavity. We consider cases with no extended surface, only one extended surface, and an extended surface on walls opposite and adjacent to the cold wall. An investigation of the Péclet number provides an estimate for the amount of artificial diffusion to be added to the Boussinesq and heat transfer equations for stable numerical solutions to be obtained. The importance of the characteristic length on the flow in the square cavity is investigated in detail. We show grid convergence by computing the grid convergence index (GCI). The impact of the boundary conditions and extended surfaces on the isotherms, velocity streamlines and flux are plotted and discussed. We find that the case with insulated boundary conditions on the sidewalls gives a 31 and 33 percent decrease in the flux when we have two and three extended surfaces, respectively.

Small-scale (mm-dm scale) heterogeneity has been shown to significantly impact CO2 migration and trapping. To investigate how and why different aspects of small-scale heterogeneity affect the amount of capillary trapping during buoyancy-driven upward migration of CO2, we conducted modified invasion percolation simulations on heterogeneous domains. Realistic simulation domains are constructed by varying two important aspects of small-scale geologic heterogeneity: sedimentary bedform architecture and grain size contrast between the matrix and the laminae facies. Buoyancy-driven flow simulation runs cover 59 bedform architecture and 40 grain size contrast cases. Simulation results show that the domain effective CO2 saturation is strongly affected by both grain size and bedform architecture. At high grain size contrasts, bedforms with continuous ripple lamination at the cm scale tend to retain higher CO2 saturation than bedforms with discontinuous or cross lamination. In addition, the "extremely well sorted" grain sorting cases tend to have lower CO2 saturation than expected for cross-laminated domains. Finally, both a denser CO2 phase and greater interfacial tension increase CO2 saturation. Again, variation in fluid properties seems to have a greater effect on CO2 saturation for cross-laminated domains. This result suggests that differences in bedform architecture can impact how CO2 saturation values respond to other variables such as grain sorting and fluid properties. [ABSTRACT FROM AUTHOR]

The key objective of the current examination is to examine a symmetrically peristaltic movement of microorganisms in a Rabinowitsch fluid (RF). The Boussinesq approximation, buoyancy-driven flow, where the density with gravity force term is taken as a linear function of heat and concentrations, is kept in mind. The flow moves with thermophoretic particle deposition in a horizontal tube with peristalsis. The heat distribution and volume concentration are revealed by temperature radiation and chemical reaction characteristics. The originality of the existing study arises from the importance of realizing the benefits or the threats that nanoparticles, microbes, and bacteria cause in the flow inside peristaltic tubes. The results are an attempt to understand what factors perform additional advantages and or reduce damages. The controlling nonlinear partial differential equations (PDEs) are made simpler by employing the long wavelength (LWL) and low-Reynolds numeral (LRN) approximations. These equations are subjected to a set of non-dimensional transformations that result in a collection of nonlinear ordinary differential equations (ODEs). By employing the Homotopy perturbation method (HPM), the configuration of equational analytical solutions is examined. Analytical and graphical descriptions are provided for the distributions of axial speed, heat, microbes, and nanoparticles under the influence of these physical characteristics. The important findings of the current work may help to comprehend the properties of several variations in numerous biological situations. It is found that the microorganisms condensation decays with the rise of all the operational parameters. This means that the development of all these factors benefits in shrinking the existence of harmful microbes, viruses, and bacteria in the human body's peristaltic tubes, especially in the digestive system, and large and small intestines. [ABSTRACT FROM AUTHOR]

We investigate theoretically the impact of adding convective dissolution to the sharp interface problem of gravity current propagation along a sloping permeability jump. Three different dissolution modes are explored: constant dissolution, dissolution with simultaneous shutdown and dissolution with sequential shutdown. The last two modes are bookend opposites that make different assumptions about ambient mixing. For simultaneous (sequential) shutdown, different portions of the gravity current interface experience dissolution identically (differently). To gage the effectiveness of dissolution for trapping e.g., supercritical CO 2 , we consider the evolution of storage efficiencies and examine the impact of changing the dissolution strength, the time, t 1 , for the onset of shutdown and, for t 1 < ∞ , the e-folding decay time, t 2 , characterizing dissolution decay. We also highlight the phenomenon of intermediate run-out, a state where there is a balance between the fluid supplied to the gravity current vs. that lost by dissolution and basal draining. The state in question is transient because, for time t > t 1 , shutdown decreases the rate of dissolution. The ensuing readjustment causes a remobilization of the previously-arrested gravity currents and their subsequent (though not indefinite) elongation. Our analysis concludes by studying unsteady sources, which provides keen insights into similarities and differences between simultaneous vs. sequential shutdown. [ABSTRACT FROM AUTHOR]

We report mean flow and turbulence characteristics of a buoyant jet evolving in a linearly stratified ambient with stratification strength N = 0.4 s − 1 . The velocity and density fields are captured experimentally using simultaneous particle image velocimetry and planar laser-induced fluorescence technique. We report our findings by strategically choosing four axial locations such that it covers different flow regimes; namely, momentum-dominated region, buoyancy-dominated region, neutral buoyant layer, and plume cap region. The results at these axial locations are presented as a function of the radial co-ordinate to provide a whole field picture of the flow dynamics. From the mean axial velocity and density fields, it is seen that the velocity and the scalar (density) widths are of the same magnitude in the momentum-dominated region but show significant difference in the buoyancy-dominated region and beyond. It is also seen that the axial velocity for the buoyant jet is consistently higher than pure jet at different axial locations due to buoyancy-aided momentum. With the help of turbulent kinetic energy (TKE) budget analysis, it is seen that the shear production (P) and TKE dissipation (ϵ) for a buoyant jet are higher compared to the case of pure jet at different axial locations, cementing the role of buoyancy and stratification on the flow dynamics. Further, it is observed that the buoyancy flux (B) aids and destroys TKE intermittently in the radial direction, and it is at least O (10 2) smaller than P, ϵ , and the mean flow buoyancy flux (F). Finally, the relative strength of the turbulent transport of momentum to that of scalar in the radial direction is quantified using the turbulent Prandtl number, P r t . It is seen that P r t ≈ 1 upto the neutral buoyant layer and ≈ 0.6 in the plume cap region. The current set of results obtained from experiments are first of its kind and elucidates various aspects of the flow which hitherto remained unknown and will also prove to be useful in testing numerical simulations for buoyancy-driven flows. [ABSTRACT FROM AUTHOR]

Hydromagnetic natural convection heat transfer in an improved designing has sustainable importance in high performance thermal equipment and geothermal energy systems. This investigation explores the fluid flow and temperature behaviours along with entropy generation for buoyancy driven flow of hybrid nanofluid in a partially heated cavity saturated by porous medium having heat conductive cylinder in presence of external magnetic field. Effective thermal conductivity model is formulated based on Brownian motion of Cu and Al 2 O 3 nanoparticles. The developed governing equations are solved implementing Galerkin finite element method. Results-based discussion is presented through streamlines, temperature contours, heat transfer rate and entropy generation tools, respectively. The results endorse that fluid flow and temperature and also local entropy generation are phenomenally influenced with higher buoyancy parameter but these impacts are correlated with magnetic field strength, amount of hybrid nanoparticles and also cavity permeability. The heat transfer rate and average entropy generation components are increased with the increase in Rayleigh number and these trends are expedited with the increase in cavity porosity and volume fraction but reverse trend is found for magnetic field effect except magnetic-irreversibility. In addition, Bejan number is declined for increasing Rayleigh and Darcy numbers but increased for higher Hartmann number and amount of hybrid nanoparticles. [ABSTRACT FROM AUTHOR]

Multi-component fluid mixing by buoyancy-driven circulation is a common engineering process. Buoyancy-driven flows have been studied extensively using mesh-based Eulerian methods, but challenges remain especially near the fluid component interface. Smoothed particle hydrodynamics (SPH) is a meshless Lagrangian method able to deal with large deformations and a changing interface between the fluid components. Herein, an SPH formulation is proposed by employing the Boussinesq approximation to model buoyancy-driven flows where the temperature evolves by a governing equation, as well as multiple components with variable viscosities. In addition, a new implementation of an adiabatic boundary condition in SPH is included by adapting the recently developed modified dynamic boundary condition. The SPH results are compared against reference solutions for 2-D and 3-D, single and multi-component cases such as a differentially heated cavity and a cylindrical tank. Agreement is found with reference solutions for differentially heated cavity cases, provided the ratio of smoothing length to particle size is sufficiently large. Furthermore, the combined volume fraction - finite time Lyapunov exponent mixing measure gives insight into the relative movement of components at both a local and global level. • New adiabatic SPH boundary condition simulates buoyancy-driven circulation. • New SPH formulation models multiple components with variable viscosities. • Validated against a range of 2-D & 3-D multi-component test cases. • Agreement is found with reference solutions for differentially-heated cavity cases. • New mixing measures quantify local composition and movement within mixture. [ABSTRACT FROM AUTHOR]

• We show the patterns of deformation, mixing, and decoupling of chemical heterogeneities marked by Nd-Hf isotope ratios in the residue at mid-ocean ridges. • The observed melt fraction (∼1%) beneath fast-spreading ridge would produce strong vertical dispersion of chemical heterogeneity. • If the melt fraction is less than 0.2%, probably in the case of ultraslow-spreading ridge, heterogeneities larger than 2 km in diameter would experience negligible dispersion. • A previous melting event could produce the residual peridotite with extremely depleted Hf isotope ratio that eventually gets recycled into the asthenosphere. The common assumption that residual peridotites retain the Nd-Hf isotope ratios in the mantle source is debated because melt and solid of different isotopic compositions could undergo chemical exchange during melt migration, altering the isotopic signature of the source. By modeling the transport of chemical heterogeneities in the melting region beneath a mid-ocean ridge, we show that the shape of a chemical heterogeneity marked by Nd or Hf isotope ratio changes systematically through subvertical dispersion, stretching, compression, and shearing. The isotope ratios inside the chemical heterogeneity decay toward the values of background mantle. The amount of decay depends on the strength of dispersion, which itself is strongly dependent on the melt fraction in the melting region. When the maximum melt fraction is greater than 1%, buoyancy-driven melt flow relative to the solid causes subvertical dispersion of isotopic signals in the solid. Differential flows of the melt and solid also produce chromatography fractionation of Nd with respect to Hf, causing their isotope ratios to decouple. Compositions of the residue in Nd-Hf isotope ratio diagram do not record the endmembers in the source, instead they represent an area that covers part of the binary mixing line between the background mantle and the original heterogeneity. In the case of small melt fraction (<0.2%), the low permeability results in sluggish melt flow, weak dispersion, and negligible chromatography fractionation. Consequently, Nd and Hf isotope ratios in the residue remain coupled, representing the endmember isotope ratios in the source. The ridge model with larger melt fraction may correspond to the fast-spreading ridge, while the model with smaller melt fraction may correspond to the ultraslow-spreading ridge. The present study underscores the importance of melt migration processes beneath mid-ocean ridges on the deformation, mixing and decoupling of Nd-Hf isotope ratios in residual peridotites. [ABSTRACT FROM AUTHOR]

A comprehensive comprehension of the intricate heat transfer mechanisms pertaining to supercritical fluids within U-bend tubes holds paramount significance in the optimization design of submerged combustion vaporizers and other water-bath heating heat exchangers. This paper employs a combined approach of experimental analysis and numerical simulation to explore the complicated heat transfer processes of supercritical liquefied natural gas in the U-bend tube. For a careful consideration of similarity and safety, the N 2 –Ar mixture is used as the alternative experimental media. Upon validating the model's accuracy using experimental data, this study unveils the mechanism of the coupling effect between centrifugal force and buoyancy on heat transfer based on simulation results. The results show that the internal circulation flow field structure caused by centrifugal force weakens the heat transfer on the inner side within an angle range of approximately 60°. Along the entrance region of downstream straight tubing, secondary flow continues to be predominantly governed by centrifugal forces due to inertia-driven effects. Subsequently, buoyancy-driven secondary flow impels compression upon centrifugally-induced secondary flow towards the inner side, thereby instigating significant augmentation in fluidic heat transfer resistance in both the viscous sub-layer and buffer layer of the inner side. Overall, the downstream straight tube section exhibits a special heat transfer variation pattern characterized by an initial strengthening, followed by deterioration, and ultimately recovery due to the influence of centrifugal force, with a maximum influence distance extending to 175.5 d. • Heat transfer performance of supercritical LNG in U-bend tubes is investigated. • Coupling mechanism of buoyancy and centrifugal force on heat transfer is analyzed. • Secondary flow intensity generated by centrifugal force is much higher than buoyancy. • Bend section significant influence heat transfer of downstream straight tube section. • Heat transfer initially improved, then deteriorated and eventually recovered in downstream straight tube section. [ABSTRACT FROM AUTHOR]

This research studies the ventilation flow patterns and density stratification in two parallel-connected chambers which respectively have a mechanical extractor and a localized buoyancy source. Two parallel-connected chambers are denoted as the forced and extracted chambers. The forced chamber having a continuous localized buoyancy source is located upstream, and the extracted chamber having a mechanical extractor is located downstream. Two chambers are interconnected by an internal connection opening and are connected to the exterior in a parallel manner through their own connection openings. The effects of the adjoining chamber having a mechanical extractor on the ventilation flow patterns and density stratification in the space are investigated in this study. The flow driving forces include the buoyant and inertial forces in this ventilated space. The buoyant force results from the buoyancy source, and the inertial force is due to the mechanical extractor. This research uses the theoretical analysis approach and the laboratory reduced-scale model to investigate this problem. This paper focuses on the ventilation flow patterns in the steady state and discusses different flow regimes due to the adjoining extracted chamber effect. The internal connection opening level and orientation between two chambers are discussed in this study. Three flow regimes, the small (or reduced), transition, and large (or enhanced) flow regimes, are found in two parallel-connected chambers and there is a range of critical flow rates to determine the flow regime when the internal connection opening is located in a partition wall as investigated in this research. If the internal connection opening is located in a horizontal ceiling, a clear-cut critical flow rate is expected and only two flow regimes exist. This study discusses the characteristics of different flow regimes in the space of two parallel-connected chambers. The paper presents three derived theoretical models and analogous salt-bath experimental results for three flow regimes, and comparisons between them show reasonable agreement. • This research studies the distribution of buoyant fluid or related pollutants in an indoor space with partitioned rooms. • The paper presents three derived theoretical models and analogous salt-bath experimental results for three flow regimes. • There is a transition flow regime if the internal connection opening is located in a vertical divider. • If the internal connection opening is located in a horizontal ceiling, only two flow regimes exist. • This study shows different flow patterns inside the interior space of two parallel-connected chambers. [ABSTRACT FROM AUTHOR]

• Mixed convection magnetized flow of Powell-Eyring fluid is modeled. • Formulation is based on Buongiorno nanofluid model. • Thermal and solutal transport expressions are modeled by considering thermal radiation, Joule heating, heat generation and chemical reaction effect. • Numerical solutions are obtained through the novel Levenberg-Marquardt artificial neural networks(ALM-ANNs). Magnetic nanoliquids are pondered cutting-edge heat transference liquids, representing a modern generation because of their aptitude to function as smart liquids. The deployed magnetism externally exerts a readily manageable impact, escalating their adaptableness and practicality in various applications. In this analysis, electro magnetized Powell-Eyring rheological nanoliquid is modeled considering stretching cylinder based buoyancy-driven flow. Transport expressions include thermal radiation, Brownian diffusion, chemical reaction, thermophoresis, and thermal source effect. Prandtl theory of boundary-layer (BL) assists to develop the governing problems. Appropriate transformations are deployed to obtain the dimensionless problems which are then computed numerically through the novel Levenberg-Marquardt artificial neural networks(ALM-ANNs). It is worth to mention that the close agreement between the error analysis of the reference dataset and the proposed datasets roughly from E−10 to E−03, further justifies the approaches utilized in this study. Besides the excellent measures of performance in terms of MSE are achieved at level 5.77E−11, 4.41E−11, 2.09E−12, 2.16E−11, 1.03E−11, 1.65E−11, 2.00E−11, and 1.91E−11against 272, 416, 266, 391, 142, 366, 425, and 508 epochs for first instance of all eight various scenarios. The acquired outcomes are compared with alternate analytical (homotopy) scheme and good agreement is witnessed. Furthermore it is noticed that as the values of Pr , R and S 1 increase in size, so does the EPFM temperature profile θ, and the evaluation of AE is between E-04 to E-10. [ABSTRACT FROM AUTHOR]

The present problem aims to examine the impact of quadratic buoyancy-driven flow nanofluid flow on two specific geometries such as cone and wedge in the presence of binary chemical reactions with activation energy, using liquid hydrogen species. This analysis is relevant for various industrial applications and are widely used in thermal energy storage devices for cooling or heating processes. The fluid flow model's governing equations are numerically solved using a fifth-order boundary value approach in matrix laboratory (MATLAB). In order to obtain the numerical solution, we initially transformed the coupled equations of the flow model and the partial differential equations into ordinary differential equations using similarity variables. The graphs and tables illustrate the importance of different physical factors that impact fluid flow and heat transfer. The quadratic combined convection parameter leads to an augmentation in fluid velocity while also inducing an elevation in frictional forces between the object's surface and the fluid. The increased in values of Schmidt number cause a decrease in mass diffusivity, which in turn leads to lower concentration profiles and improved mass transport efficiency. The activation energy is directly proportional to the decreased amplitude of the concentration profiles of liquid hydrogen species. [ABSTRACT FROM AUTHOR]