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The transport properties of solids are better compared to liquids or base fluids. Thus, when solid nanoparticles are added to a base fluid, the resultant nanofluid is more efficient for cooling or heating phenomena compared to the base fluid. The study will help thermal engineers in predicting the transmission of thermal energy. In this aspect, Cattaneo-Christov heat flux is used to compute the rate of transferring heat in a material. Cattaneo-Christov heat flux, also known as heat paradox, is used in the flow for heat transfer. Ag-silver is taken as the nanoparticles with the ethylene glycol C $ _{2} $ 2 H $ _{6} $ 6 O $ _{2} $ 2 the base fluid. Heat transfer is analyzed for the two-phase flow when the heated rod is placed vertical as well as horizontal in the cavity. The simulation is made in Open-source Field Operation And Manipulation. The projection method and the finite volume method (FVM) are used for the computation of the model developed for the flow of nanofluid. A comparison between the projection method and the FVM is made. The transmission of thermal energy via the FVM in OpenFOAM better suits compared to the results obtained via the projection method shown in the figures. [ABSTRACT FROM AUTHOR]

This experimental study examines the exergy efficiency and entropy generation of shot-blasted heat exchangers using two types of nanofluids: solar glycol-activated carbon and solar glycol-multi-walled carbon nanotubes. The copper inner tube's external surface was roughened using pressurized mechanical shot-blasting machinery. Also, the activated carbon was prepared from biowaste using a pyrolysis process with a higher temperature sintering method. The thermal conductivity of the solar glycol-multi-walled carbon nanotubes (SG-MWCNTs)- and solar glycol-activated carbon (SG-AC)-based nanofluids increased by 22.22 and 12.73% at a nanomaterial dispersion of 0.6% and a temperature of 50 °C, compared with the base fluid respectively. The thermal exergy destruction value of SG-MWCNTs and SG-ACs rises by nearly 38.01 and 29.84% at the nanomaterial dispersion of 0.6% and MFR nanofluid of 80 g s−1 compared with SG. For an SG-MWCNTs-based nanofluid volume fraction of 0.6%, the exergy efficiency was enhanced by approximately 29.15% associated with SG-AC nanofluids at an MFR nanofluid of 55 g s−1. The thermal evaluation parameter of SG-MWCNTs nanofluids enhanced nearby 28.81, 24.07, and 18.15% at particle dispersion of 0.2, 0.4, and 0.6%, respectively, compared to AC-SG nanofluids at MFR of 80 g s−1. This study evaluates the effects of different nanofluids on convection in shot-blasted heat exchangers by considering the Grashof, Rayleigh, and Richardson numbers. These dimensionless numbers, which are influenced by the Reynolds number, provide a comprehensive understanding of the interplay between buoyancy and inertial forces, thermal diffusivity, and the relative importance of natural and forced convection. [ABSTRACT FROM AUTHOR]

This article investigates the simultaneously developing pure turbulent mixed convective regime and compares the hydrodynamic and thermal features of both buoyancy-assisted and opposed flows in a vertical tube. Two-dimensional (2D) axisymmetric steady-state simulations were carried out for Reynolds number, 5,000–20,000; Grashof number, 1.25 × 106 to 108; and Richardson number, 0.05–0.25 for a length-to-diameter ratio of 150 with uniform heat flux boundary condition and water as the working fluid. Three Reynolds-averaged-Navier–Stokes turbulence models were compared and then the most suitable model was used for the simulations. At a given Richardson number, the friction factor and Nusselt number are lower in the case of buoyancy-assisting flow compared to buoyancy-opposing flows. Similar friction factors and heat transfer trends were obtained at a given Grashof number. At varying Grashof numbers and Richardson numbers keeping the Reynolds number constant, no discernible variations were observed for both flows. The entry length was also examined, and it has been found that the hydrodynamic and thermal entry lengths are restricted to a length-to-diameter ratio of 25 and 20 for assisting and opposing flows, respectively. Correlations were developed for both flows to quantify the friction factor, Colburn factor, and Nusselt number in terms of the Reynolds number. [ABSTRACT FROM AUTHOR]

The Northwest Pacific is a source of strong typhoons accompanied by significantly changing ocean heat content (OHC). Based on the GDCSM_Argo dataset, all typhoons within twenty years are considered to explore the regulation of OHC between 0 and 2000 m with typhoons in this study. The results show a weak correlation between OHC and typhoons but a strong correlation between ocean heat content uptake anomaly (OHUA) and typhoons by wavelet, lag/lead, and EOF analyses. The energy reserve effect by the OHUA on typhoon generation is most significant at a 3-month lag. The OHUA above 300 m primarily influences typhoons' temporal and spatial characteristics. On the other hand, typhoons enhance vertical transmission of OHC through entrainment. A modified version of the Richardson number (Rohc) is used for the characterization of the hydrostatic stability between ocean layers. The entrainment is particularly strong in the Northwest Pacific north of 20° N, where Rohc is between −0.2 and 0. The OHC below the mixed layer also responds to typhoon disturbances but transports less heat vertically than the near-surface layers. Our results suggest that GDCSM_Argo provides reliable data support for the study of the relationship between OHC and typhoons. [ABSTRACT FROM AUTHOR]

In contemporary power engineering and microelectronics, the efficiency of cooling systems is of crucial importance. To meet this requirement, specialized approaches and the use of nanofluids are employed to improve the heat dissipation of heat-generating components. This study presents a methodology based on a numerical simulation investigation and statistical analysis using the Response Surface Methodology (RSM) to estimate the average Nusselt number (Nuavg) associated with mixed convection in a ventilated cavity. The study considered pure water and mixtures of nanoparticles (Cu, Ag, and TiO2) as heat transfer fluids, exploring various values of the Richardson number (0.1 to 100) and volume fractions (0 to 8%). Analysis of Variance (ANOVA) and the quadratic mathematical model developed by RSM effectively predicted the results of the numerical simulation with a coefficient of determination R2 close to 1. The results obtained from the 3D curves of the RSM show that the average Nusselt number (Nuavg) increases significantly with the Richardson number. Conversely, an increase in the volumetric fraction leads to a slight decrease in Nuavg. Furthermore, it is observed that the agent (Ag) generates higher Nuavg values compared to other materials such as copper (Cu) and TiO2. Combining the RSM method with the desirability function (DF) allows for achieving the optimal average Nusselt number (Nuavg). Validation of the values proposed by the DF and those obtained by simulation shows a very small relative error, less than 0.13%. [ABSTRACT FROM AUTHOR]

The ocean surface mixed layer plays a crucial role as an entry or exit point for heat, salt, momentum, and nutrients from the surface to the deep ocean. In this study, we introduce a framework to assess the evolution of the mixed layer depth (MLD) for realistic forcings and preconditioning conditions. Our approach involves a physically‐based parameter space defined by three dimensionless numbers: λs representing the relative contribution of the buoyancy flux and the wind stress at the air‐sea interface, Rh the Richardson number which characterizes the stability of the water column relative to the wind shear, and f/Nh which characterizes the importance of the Earth's rotation (ratio of the Coriolis frequency f and the pycnocline stratification Nh). Four MLD evolution regimes ("restratification," "stable," "deepening," and "strong deepening") are defined based on the values of the normalized temporal evolution of the MLD. We evaluate the 3D parameter space in the context of 1D simulations and we find that considering only the two dimensions (λs, Rh) is the best choice of 2D projection of this 3D parameter space. We then demonstrate the utility of this two‐dimensional λs − Rh parameter space to compare 3D realistic ocean simulations: we discuss the impact of the horizontal resolution (1°, 1/12°, or 1/60°) and the Gent‐McWilliams parameterization on MLD evolution regimes. Finally, a proof of concept of using observational data as a truth indicates how the parameter space could be used for model calibration. Plain Language Summary: Vertical mixing of water near the ocean surface occurs when cold air temperatures create dense cold water at the surface that tends to sink in the ocean or when a strong wind induces turbulence at the ocean surface. These processes mix heat and salt and create a layer at the top of the ocean that has a uniform temperature and salinity and that is called the "mixed layer." This mixed layer plays a fundamental role in the Earth climate system, and the representation of its evolution in ocean models hence needs to be assessed. For this purpose, we propose to map the mixed layer evolution in a three‐dimensional space where the first axis is related to the wind and the surface heat flux, the second axis to the stability of the water column, and the third axis to the Earth's rotation. We show that this tool performs statistically well and we present how to use it in the context of realistic ocean models. Key Points: A parameter space is proposed to assess the evolution of the mixed layer depth for realistic forcings and preconditioning conditionsAn evaluation of a collection of 1D simulations shows a statistically good performance of the parameter spaceTwo applications demonstrate the utility of the parameter space for assessing and comparing realistic 3D simulations [ABSTRACT FROM AUTHOR]

Intertidal groundwater springs provide thermally stable, nutrient‐rich freshwater that causes fine‐scale variability in water temperature and salinity and promotes biodiversity in coastal estuaries and lagoons. In this study, we combined three thermal sensing techniques to elucidate summer water temperature patterns at the mouths of intertidal groundwater springs and the ambient coastal lagoon in Prince Edward Island, Canada. Thermal infrared imagery captured the spatiotemporal variability in relative temperatures of the lagoon channel and cold‐water plumes from the springs. Thermal anomalies due to the springs were detected at the surface throughout a tidal cycle, suggesting that the thermal plumes were buoyant. Fiber‐optic distributed temperature sensing paired with temperature loggers near the spring outlets recorded groundwater temperatures at low tide (~ 7°C) but ambient lagoon temperatures (up to 26°C) at high tide due to the vertical thermal gradient in the stratified water column. Calculated estuarine Richardson numbers throughout the study confirm intertidal spring buoyancy due to salinity differences. The fiber‐optic distributed temperature sensing results revealed pronounced variations in temperature as evidenced by spatial (3.7°C) and temporal (5.5°C) standard deviations over the cable length during the study and lower mean lagoon bed water temperatures at high tide (22.5°C) than low tide (24.3°C) due to heat advection from tidal pumping. Lagoon temperatures fluctuate at diurnal (solar) and semi‐diurnal (tidal) frequencies. The findings emphasize the efficacy of a multi‐technology approach to reveal fine‐scale and dynamic thermal processes that drive temperature patterns and habitat distribution in coastal lagoon ecosystems and highlight the thermal influence of intertidal springs. [ABSTRACT FROM AUTHOR]

The impact of thermal and velocity slips on mixed convection magnetohydrodynamic flow of ceramic nanofluids past a thin needle with variable physical properties has been investigated in the present study. Numeric computation of nonlinear differential expressions has been executed by Runge–Kutta Fehlberg-quadrature method for varying physical parameters. The study is more important in contributing to medicine and engineering. Fluid velocity and temperature exhibit opposite behavior in relation to amplifying Hartmann number. The rise in slip parameters causes the shrinkage of thermal boundary layer which in turn yields significantly greater heat transfer rate. Flow velocity is an increasing function of Richardson number. Higher surface viscous drag is attained for $ CuO $ CuO suspension while least of that is obtained for $ Ti{O_2} $ Ti O 2 suspension. [ABSTRACT FROM AUTHOR]

This paper is motivated by an interest in understanding the characteristics of buoyant fluids discharged from the bottom wall of channels, such as encountered during tunnel fires or in river effluent discharge. Direct numerical simulation is used to model the upward release of a planar buoyant jet or plume from the bottom wall of a channel into an incoming turbulent crossflow. The well-studied jet-in-crossflow with only a momentum source is simulated first, and subsequently, fixing the incoming Reynolds number, buoyancy source as heat flux is added alongside varying momentum source, with two cases where only a buoyancy source is present. Appropriate five non-dimensional parameters relevant for this flow are defined, of which three are fixed and two—source to channel momentum ratio and Richardson number—are varied. The changes in turbulence characteristics as the buoyant jet or plume evolves downstream are presented. In all cases with buoyancy, except for the pure jet case, the plume is initially confined to the lower half of the channel before it suddenly lifts to the top half, an effect that occurs at an increasingly smaller downstream distance with increasing buoyancy, and dividing the flow into a near and far field. The distributions of mean and Reynolds stresses in the near and far field of the source are reported, and it is found that the channel flow becomes more turbulent downstream of the source, and further, the turbulent vertical temperature flux switches sign from near to far field owing the a change in the mean temperature gradient sign. From the input parameters and using the integrated temperature equation a reasonable estimate of the far field mean channel temperature can be obtained by a reference temperature based on the heat conservation that includes the convective and diffusive source heat flux. A monotonic behaviour of the back-layering distance is also observed a function of this reference temperature, which was difficult to obtain with the two specified non-dimensional parameters. [ABSTRACT FROM AUTHOR]

In high-altitude tunnels, due to the ambient pressure and density of air being different from those under normal pressure, the convection and heat radiation in tunnels are also different when fires occur. As a result, the smoke exhaust capacity varies under different pressures. This work aimed to numerically explore the impact of ambient pressure on the smoke exhaust efficiency at high-altitude shallow tunnels with natural ventilation by shaft. The numerical results demonstrated that the smoke exhaust capacity is enhanced with increasing ambient pressure. This is because of the increase in the air entrainment coefficient and air density, and it causes plug-holing more easily to occur under higher ambient pressures. Once the plug-holing has taken place, the fresh air can be directly exhausted through the shaft, which results in a poor smoke exhaust capacity. By accounting for the factors of the smoke layer thickness, ambient pressure, the exhausted smoke temperature and heat release rate, the Richardson number was introduced as the criterion for determining whether plug-holing occurs. As ambient pressure was increased, the critical Richardson number for plug-holing was observed to decrease, a finding supported by existing research. [ABSTRACT FROM AUTHOR]

The current study presents mixed convective flow inside a square chamber holding a centrally placed and thermally conductive oscillating porous circular cylinder. The left boundary's temperature is kept larger than that of the right edge, and the horizontal edges are preserved at adiabatic settings. The circumferential speed of the cylinder is sinusoidal and oscillating in nature. The fluid region within the chamber is modeled employing 2D Navier-Stokes and heat energy equations. Furthermore, the fluid circulation and heat transmission within the porous cylinder are modeled using the Darcy-Brinkman-Forchheimer formulation. The leading equations are discretized utilizing the Galerkin finite element technique. The parametric study is undertaken considering three distinct diameters of the porous cylinder and three distinct oscillation frequencies. The instant Nusselt number is evaluated along the heated wall, which varies in an oscillatory pattern owing to the repeated contraction and enlargement of the thermal boundary layer. The Nusselt number is averaged over time once the value becomes statistically stationary. The study is conducted within a mixed convection region with Reynolds (Re = 100), Richardson (0.1 ≤ Ri ≤ 10), and Grashof (103 ≤ Gr ≤ 105) numbers. Upon thorough examination, it becomes clear that the system's thermal performance shows promising improvement with the largest cylinder diameter and the lowest oscillation frequency. Specifically, the average Nusselt number shows a maximum improvement of 21.50 % at the largest cylinder diameter.

This study proposes a new mechanism that can lead to layering or convection from the finite amplitude perturbation acting on the double diffusive convection with uniform background shear. We focus on the double diffusive convection in the diffusive regime with the cold fresh water laying above the warm salty water. We demonstrate that, although the unperturbed system is linearly stable, the finite amplitude perturbation can trigger the initial flow motions which subsequently obtain energy from the gravitational potential energy and from the uniform background shear, and evolve to layering or convection. By using the linear stability analysis for the initial growth stage and the energy analysis for the following transitional stage, the critical Richardson number can be predicted theoretically. Here the Richardson number measures the relative strength of stratification to the background shear. The dominant wavenumbers and the growth rates of the corresponding modes given by linear theory agree well with the two-dimensional direct numerical simulations, and so does the critical Richardson number predicted by the theoretical model. The layering state is dominated by the double diffusion process, while the convection state at smaller Richardson number exhibits stronger influences from shear and generates smaller heat and salinity fluxes. The theoretical model is further applied to the parameter range which is relevant to the real oceanic environments and reveals that for the typical density ratio observed in the staircase regions in the Arctic Ocean, the current mechanism can lead to layering for relatively weak shear. [ABSTRACT FROM AUTHOR]

Turbulent plumes are fascinating to study in large part due to the ability to see the eddies and structures that comprise the exterior structure as they develop in space and time. We perform a laboratory study in which positively buoyant turbulent plumes are generated in a quiescent water tank. Buoyancy is varied by modifying the relative percentages of isopropyl alcohol to water in a mixture placed in a head tank. Photographs captured at steady frame rates record the evolution of the plume as it develops in time and space. A custom algorithm tracks the visible exterior outline of the plume, from which eddies and structures can be identified along the interface between the plume fluid and ambient fluid. Statistical analyses are performed to characterize differences in the distributions of external structures to study their dependence on relative buoyancy between the fluids. Spectral analysis of the edge signal of the plume reveals a - 2.2 slope, indicative of the range of eddy lengths that comprise turbulent plumes. We explore the relationship between buoyancy with both the plume front velocity and plume spread angle. We find the front velocities to be functions of both the buoyancy and source Reynolds number. However, the spread angles were found to vary only with buoyancy of the plumes, thus proportional to their Richardson numbers. [ABSTRACT FROM AUTHOR]

In this study, numerical experimentation was performed to explore the impact of electro-thermo-convection on unsteady combined convection flow within a square chamber driven by dual ventilation channels with opposing flow. An electrical emitter was placed on the left wall to influence the hot wall, with a collector electrode on the other wall, while the remaining walls were thermally and electrically insulated. The equations which govern the system were solved using the finite difference method with an alternate direction implicit scheme and an iterative successive under-relaxation (SUR) technique. Key physical parameters, including Reynolds number (50 ≤ R e ≤ 500), Richardson number (0.1 ≤ R i ≤ 20), and a range of electrical Rayleigh numbers (0 ≤ R a e ≤ 1200), were examined for their effects on charge density distribution, streamlines, isotherms, and the mean Nusselt number. The study reveals that electrical effects significantly boost heat transfer, with an 88% increase in the mean Nusselt number under low forced convection and buoyancy (R i = 0.1 , R e = 50). However, as buoyancy (R i = 20) and forced ventilation (R e = 500) intensify, this enhancement decreases to 25% and 33%, indicating that these forces moderate the influence of electrical effects. Additionally, Richardson and Reynolds numbers strongly affect heat transfer, with rates increasing by 52% and 126%, respectively, under pure thermal convection. The numerical model results align well with previous research, suggesting the potential application of advanced cooling techniques to enhance the heat transfer efficiency in an electronic devices and similar systems. [ABSTRACT FROM AUTHOR]

The jet stream is a primary factor contributing to turbulence, especially for upper-level aircraft. This study utilized pilot reports and ERA5 data from 2023 to investigate the relationship between upper-level turbulence and the East Asian westerly jet (EAJ). The results indicate that approximately 45.9% of upper-level aircraft turbulence occurs within the jet stream, with the lowest proportion in August and the highest in January. Additionally, the strongest vertical wind shear (VMS) is found concentrated in the lower part of the jet stream core, particularly in the South–Down part of the jet stream, where upper-level aircraft turbulence occurs most frequently (27.1%). The most turbulent area is located between 30–40° N and 110–120° E, with the main air routes experiencing turbulence being the Henan sections of G212 and B208. From a seasonal perspective, there is less frequent occurrence of upper-level aircraft turbulence in summer and autumn but more in winter and spring. The EAJ volume increases with the strengthening of the jet core wind speed, with the jet core regions being most distinct at altitudes of 200~300 hPa. Meanwhile, the jet stream intensity index peaks at 70.6 m/s in January and reaches its lowest value of 7.1 m/s in August. The jet stream axis shifts southward in winter and northward in summer, reaching the southernmost position in December at 32.2° N and the northernmost position in August at 43.5° N. Furthermore, the VMS at turbulence points within the jet stream is higher than that at the turbulence points outside the jet stream, and the Richardson number (RI) is lower. Moreover, the temporal distribution of upper-level aircraft turbulence is primarily determined by the location and intensity of the jet stream, of which the jet stream intensity index provides guidance and thus serves as a reliable indicator. [ABSTRACT FROM AUTHOR]

This study investigates the use of a balloon-launched uncrewed aircraft system (UAS) for the measurement of turbulence in the troposphere and lower stratosphere. The UAS was a glider which could conduct an automated descent following a designated flight trajectory and was equipped with in situ sensors for measuring thermodynamic and kinematic atmospheric properties. In addition, this aircraft was equipped with an infrasonic microphone to assess its suitability for the remote detection of clear-air turbulence. The capabilities of the UAS and sensing systems were tested during three flights conducted in New Mexico, USA, in 2021. It was found that the profiles of temperature, humidity, and horizontal winds measured during descent were in broad agreement with those made by radiosonde data published by the US National Weather Service, separated by up to 380 km spatially and by 3 to 5 h temporally. Winds measured during controlled flight descent were consistent with the winds measured by global-positioning-system-derived velocity during balloon ascent. During controlled descent with this particular payload, a nominal vertical resolution on the order of 1 m was achieved for temperature, relative humidity, and pressure with a nominal vertical resolution of the wind velocity vector on the order of 0.1 m ; the aircraft had a glide slope angle from 1 to 4° during this time. Analysis approaches were developed that provided turbulent kinetic energy and dissipation rate, but it was found that the corresponding Richardson number was sensitive to the methodology used to determine the vertical gradients from a single flight. The low-frequency content of the infrasonic microphone signal was observed to qualitatively align with long-wavelength wind velocity fluctuations detected at high altitude. Moreover, the microphone measured more broadband frequency content when the aircraft approached turbulence produced by the boundary layer. [ABSTRACT FROM AUTHOR]

This article deals with the effects of thermophoresis on thermosolutal mixed convection in a vertical wavy porous cavity. Three distinct flow features are chosen by changing the directions of the moving horizontal borders. A nonuniform temperature, as well as concentration distributions, are introduced to the bottom wall while keeping cold temperature and low concentration for the other walls. The governing equations are modeled to describe thermosolutal phenomena. These equations are solved by reconstructing a recently developed compact scheme. Furthermore, the significance of well-defined parameters influencing the fluid rotation and thermosolutal transfer, namely Richardson number ( 0.01 ≤ Ri ≤ 100 ), Buoyancy ratio (N = 1), number of undulations ( 0 ≤ d ≤ 2 ) of the wavy walls, Lewis number ( 1 ≤ Le ≤ 10 ), thermophoretic coefficient ( 0.0 ≤ K T ≤ 1.0 ), Darcy number ( 0.001 ≤ Da ≤ 0.1 ), and porosity of the porous medium ( 0.1 ≤ ε ≤ 1.0 ) are performed generously. Results are displayed in terms of streamlines, isotherms, iso-concentrations, Nusselt, and Sherwood numbers to evoke the thermosolutal phenomena for various physical parameters. It is observed that thermophoresis is effective in certain circumstances. In addition, heat and mass transfer enhancement is noted with decreasing Richardson number while heat and mass transfer reduction is noted with increasing undulation number of the wavy walls. We have noticed that for the change in Le from 1 to 10, heat transfer is diminished up to 2.91% in Case-1, 3.03% in Case-2, and 2.20% in Case-3 while mass transfer is enhanced by 162.85% in Case-1, 164.05% in Case-2, and 87.03% in Case-3. [ABSTRACT FROM AUTHOR]

This research work highlights the relationship between heat transport in nanofluids and wall velocity ratios in the context of mixed convection heat transport in porous cavities. The research scrutinizes the inspiration of numerous flow variables such as Richardson number, porosity, Hartmann number, Darcy number, wall velocity ratio, nanomaterials volume fraction and Eckert number on fluid flow and heat transport performance. The governing flow expressions are tackled using the SIMPLE algorithm, and the outcomes are authenticated against prior research. The findings designate that heat transfer rates upsurge with higher values of Richardson number, Darcy number, nanomaterials volume fraction, and absolute value of wall velocity ratio, while decreasing with increasing porosity and Hartmann number. [ABSTRACT FROM AUTHOR]

Two-layer flow of a density-stratified fluid with mass transfer between the layers is considered. In the Boussinesq approximation, the equations of motion are reduced to a homogeneous quasilinear system of partial differential equations of mixed type. The flow parameters in the intermediate mixed layer are determined from the equilibrium conditions in a more general model of three-layer flow of a miscible fluid. In particular, the equilibrium conditions imply the constancy of the interlayer Richardson number in velocity-shift flows. A self-similar solution to the problem of breakdown of an arbitrary discontinuity (the lock-exchange problem) in the domain of hyperbolicity of the system under consideration is constructed. The transcritical flow regimes over a local obstacle are studied and the conditions under which the obstacle determines the upstream flow are determined. A comparison of steady-state and time-dependent solutions with the solutions obtained for the original three-layer models of miscible fluid flow is carried out. [ABSTRACT FROM AUTHOR]

This study is intended to determine the thermal management capability of different closed-loop controllers inside a cylindrical three-dimensional cooling system with multiple O-Ring type heat sources. The motivation for this research stems from the need for efficient thermal regulation in advanced cooling systems, which is critical for applications ranging from electronics cooling to industrial processes. The uniqueness of this study lies in its comprehensive evaluation of different controllers such as proportional (P), proportional–integral (PI), and proportional–integral–derivative within a geometrically complex cooling environment using a novel trial-and-error approach for tuning controller parameters. The observational domain is a hollow cylinder, and the four discrete heat sources are placed at regular intervals along the cylinder's longitudinal axis, with all the remaining walls insulated. At the center of the system is a temperature probe that measures and provides feedback to the control module to continuously compare it to a pre-specified setpoint temperature. The flowing fluid, air, enters through the semi-circular inlet at one end, whose velocity is controlled by a controller response, and is discharged through the semi-circular outlet at the other end at atmospheric conditions. This study uses the Galerkin finite element method, using proper initial and boundary conditions to solve the governing equations, namely, the Navier–Stokes and heat energy equations. We analyze the time-dependent behaviors of the cooling system by measuring controller responses such as overshoot, rise time, oscillation, steady-state error, and settling time. Additionally, the impacts of the Reynolds number (Re), Richardson number (Ri), and Grashof number (Gr) on the overall mean Nusselt number over time are observed to understand the influence of flow regulation due to the controllers' actions. This comprehensive analysis provides insights into the controllers' inlet flow control based on the set temperature at the probe's center location. A unique trial-and-error approach for selecting Kp and Ki values, which is crucial for controller analysis, is also presented. Based on the results, it can be inferred that increasing the Kp value from 0.003 to 0.010 ms−1 K−1 reduces the steady-state error from 40.8% to 13.97%. For a Ki value of 0.006 ms−2 K−1, the PI controller achieves a zero steady-state error with faster settling at 3.29 s, along with an overshoot of approximately 80.51%. Conversely, a lower Kd value of about 0.0001 mK−1 results in a reduction in the settling time and overshoot compared to the PI controller, while a higher Kd value ensures optimum stability with a higher settling time and a stable Nusselt number of 1.93. This trial-and-error approach to parameter tuning provides valuable insights into the design of controlled environments and the effective management of thermal conditions in various thermo-fluidic applications. [ABSTRACT FROM AUTHOR]

A weakly nonlinear theoretical model is established for the two-dimensional incompressible Rayleigh–Taylor–Kelvin–Helmholtz instability (RT–KHI). The evolution of the perturbation interface is analytically studied by the third-order solution of the planar RT–KHI induced by a single-mode surface perturbation. The difference between the weakly nonlinear growth for Rayleigh–Taylor instability (RTI), Kelvin–Helmholtz instability (KHI), and RT–KHI in plane geometry is discussed. The trend of bubble and spike amplitudes with the Atwood number and the Richardson number is discussed in detail. The bubble and spike amplitudes of RT–KHI change from the KHI case to the RTI case as the Richardson number increases. The deflecting distance of bubble and spike vertices becomes smaller compared to the KHI case as the Richardson number increases. The dependence of the nonlinear saturation amplitude of RT–KHI on the Atwood number, the Richardson number, and the initial perturbation is obtained. The Richardson number is as vital to the nonlinear saturation amplitude as the Atwood number. It is found that the variation of the nonlinear saturation amplitude with the Atwood number at different Richardson numbers is divided into three parts, namely, "RTI-like part," "transition part," and "KHI-like part." In the transition part, the trend of the nonlinear saturation amplitude increasing with the Atwood number is completely opposite to the RTI and KHI cases. Finally, the theory is compared to the numerical simulation under identical initial conditions and displays good correspondence in the linear and weakly nonlinear stages. [ABSTRACT FROM AUTHOR]

Upper layer thickness (mixing depth) is an essential parameter for estimating the dissolved inorganic carbon and carbon flux at the water surface based on their association with the vertical flux of dissolved inorganic carbon. Previous studies quantified the mixing depth without SAV meadow or penetration depth in the SAV meadow without stratification and wind stress. However, mixing depth related to interaction with submerged aquatic vegetations (SAVs), stratification, and wind stress has yet to be quantified in the previous studies. Our study is the first to quantify the theoretical mixing depth with SAVs according to wind stress, SAV height, and drag coefficient. Theoretical mixing depth was quantified from modeled vertical temperature profile, vertical profile of horizontal velocity, and gradient Richardson number (Rig,veg). We found that mixing depth at a Rig,veg of 100 demonstrated good agreement with numerical results on average, with the mixing depth estimated in this study (hU,this study) showing high applicability to observations at Komuke Lagoon. Moreover, hU,this study increased with the increasing wind stress and decreasing drag coefficient and SAV height. Further, we found that SAV meadows with stratification and wind stress could be divided into four hydrodynamic regimes: non‐vegetated layers, upper vegetated layers, thermoclines, and benthic boundary layers. Our findings help us estimate mixing depth or vertical flux without complicated numerical simulation and understand flow interaction with SAV, wind stress, and stratification. Plain Language Summary: Upper layer thickness (mixing depth) and flow fields are important to estimate the carbon flux (e.g., "blue carbon") and the transportation of dissolved materials (e.g., dissolved oxygen, dissolved inorganic carbon, dissolved inorganic nitrogen, etc) in submerged aquatic vegetation (SAV) meadows. However, it may not be easy to estimate mixing depth without complex numerical simulations. Additionally, we have not understood the interaction of SAV meadows with stratification, currents, or waves. Our study is the first to quantify the mixing depth analytically and to show the hydrodynamic regimes in SAV meadows with stratification. Our finding helps us to estimate carbon flux and the transportation rate of dissolved materials easily without complicated numerical simulation. Key Points: Mixing depth with submerged aquatic vegetation (SAV) meadows was estimated using an average gradient Richardson number 100SAV meadows with stratification and wind stress were divided into four hydrodynamic regimesWind stress, SAV, and stratification effects were used to accurately estimate the mixing depth [ABSTRACT FROM AUTHOR]

The present work, which has been carried out in the framework of EEA project BLUE-GREENWAY, is a contribution to the study of the evolution of hypoxia/ anoxia in Aitoliko lagoon, Greece. The study area suffers from anoxia which is a very important environmental problem lately mainly due to anthropogenic activities. Unpublished data from two measurement campaigns (2013–2014, 2023) have been used, and a 3D ocean model (SINMOD) has been configured for the region, that couples hydrodynamics, biochemistry and ecology. The analysis of model results includes monthly, annual and interannual variability of fields of dissolved oxygen, temperature, salinity, density, currents and wind as well as Brunt-Väisala frequency and Richardson number. Main results concerning oxygen are: a) the lagoon shows anoxic behavior at 5–7 m depth with a seasonal dependence, b) the seasonal variability in the upper water column with deeper ventilation during winter when the surface stratification is weaker than that during summer, c) anoxic water is reaching the surface of the lagoon for a short period of time. [ABSTRACT FROM AUTHOR]

AbstractThis research reports an analytical and numerical study of thermo-solutal convection in pulsating flows between two coaxial cylinders under a pressure gradient and subject to Dirichlet-type boundary conditions for temperature and concentration along the vertical walls of the annulus. The numerical procedure used in this work is mainly based on the solution of the momentum equations and coupled with the energy and concentration equations. The finite difference method is adopted to solve governing equations using the implicit Crank-Nicolson time marching scheme in the fluid domain and the alternating direction implicit method inside the inner cylinder. The effect of the various parameters such as the fluid-solid conductivity ratio, thermal diffusivity ratio, buoyancy ratio, Lewis number, Richardson number, aspect ratio, and radius ratio on the heat and mass transfer characteristics and the flow structure is presented and discussed. The governing equations are solved analytically after separating into a steady case and an oscillatory case, where an analytical solution for velocity profile, temperature, and concentration distributions is obtained in terms of Bessel’s functions, while the analytical solutions of temperature and concentration profiles are keeping symmetry with the increase of the radius ratio. The results show that the analytical profile can reproduce the three fields obtained numerically and thus for the whole range of parameters. [ABSTRACT FROM AUTHOR]

This article explores the phenomenon of natural convection in the rotatory flow of Cu-water nanofluid under the influence of non-uniform heat source. In order to design more effective and efficient cooling systems, this work attempts to increase our understanding of how nanofluids behave in the presence of non-uniform heat sources, convection, and rotatory force. The higher order partial differential equations governing the flow are remodelled into ordinary differential equations using similarity transformations. The remodelled equations were solved using shooting methodology and the Lobatto-III A algorithm. The impacts of various parameters such as the Richardson number (1 < Ri < 4), the Schmidt number (0.5 < Sc < 2), nanoparticle's volume fraction (0.02 < φ < 0.08), etc. on velocity, concentration and temperature was analysed. One of the main findings of this analysis was study of the impact of the space dependent heat source (0.2 ≤ A ≤ 1) and the temperature dependent internal heat source (0 ≤ B ≤ 0.5) on the heat regulation. Furthermore, increasing the quantity of the nano-additives and improving the fluid's thermophysical properties intensified the acceleration of the fluid elements in the flow region. The presence of spatial and temperature-sensitive parameters facilitated quantification of the effects of a standard and variable heat source in combination of Coriolis force in the case of a Cu-water flow. The findings of the investigation will be helpful in the process of medical, architectural planning systems, oil recovery systems and so on. [ABSTRACT FROM AUTHOR]

Flow circulation and heat removal through shield and reflector assemblies can have major impacts on safety in long transients for sodium fast reactors (SFRs). These transients are typically categorized by reduced flow rates and large-scale organized flow patterns, including potential intra-assembly circulation. Such low-flow cases can provide challenges for experiments because of complications in measuring the flow rates and temperatures with high accuracy in different areas. This consequently also raises the uncertainty of many modeling approaches for these phenomena. In an effort to address some of these issues, high-fidelity large eddy simulations are performed using the highly parallel solver NekRS. A 19-pin configuration of a tight-lattice wire-wrapped hexagonal bundle (pitch-to-diameter ratio = 1.07), representing a prototypical internal configuration of a shield assembly, was investigated. The sodium flow was set at a bundle Reynolds number of 2000, with simulations being performed for modified Richardson numbers of 0.0 (i.e., no buoyancy), 0.01, and 0.04, where mixed-convection effects are anticipated. The flow and temperature fields for these cases are discussed in detail. The high-fidelity data should prove useful as reference data for expanding and improving on various reduced-resolution approaches. A basic framework for combining subchannel and computational fluid dynamics methodologies in SFRs is also presented, with preliminary results from simulations of light water reactor bundles and a discussion of changes that need to be made for potential application to SFRs. [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]

This study aims to analyze the thunderstorm (TS) events in the megacity Istanbul by using thermodynamic indices and atmospheric stability parameters for the period of 2001–2022. It was determined that TS events did not show any trend on an annual basis, mostly (%69) occurred in the warm season (May–September), and mostly (%93) lasted for a few hours (0–3 h). The thermodynamic indices and atmospheric stability parameters used in the study are Showalter Index (SI), Lifted Index (LI), Severe Weather Threat Index (SWEAT), K-Index (KI), Totals Totals Index (TTI), Convective Available Potential Energy (CAPE), Convective Inhibition (CIN), and Bulk Richardson Number (BRN). Annual and seasonal analyzes of all indices and parameters were performed for TS and non-TS events. Significant differences were found in both average, maximum, and minimum values. The Probability of Detection (POD), False Alarm Ratio (FAR), Miss Rate (MR), Critical Success Index (CIS), Hiedke Skill Score (HSS), and True Skill Score (TSS) were used to analyze the success of the threshold values presented in the literature in detecting TS events. Then, the seasonal successes of these threshold values were tested. It was observed that the performance of the selected indices varied across seasons. The highest predictive skill was generally observed during the summer season, with the POD value ranging between 0.58 and 0.97 and the TSS value varying between 0.32 and 0.57. Conversely, the lowest predictive skill was typically observed during the winter season, where the POD value ranged from 0.00 to 0.75 and the TSS value varied between 0.00 and 0.40. The ideal threshold values were determined for indices and parameters by increasing or decreasing the existing threshold values at certain rates. Success increases of up to 15% in skill scores for the proposed threshold values. [ABSTRACT FROM AUTHOR]

The goal of this paper is to represent a numerical study of magnetohydrodynamic mixed convection heat transfer in a lid-driven vertical wavy enclosure with a fin attached to the bottom wall. We use a finite element method based on Galerkin weighted residual (GWR) techniques to set up the appropriate governing equations for the present flow model. We have conducted a parametric investigation to examine the impact of Hartmann and Richardson numbers on the flow pattern and heat transmission features inside a wavy cavity. We graphically represent the numerical results, such as isotherms, streamlines, velocity profiles, local and mean Nusselt numbers, and average surface temperature. Comparisons between the results of this work and previously published work in a literature review have been produced to examine the reliability and consistency of the data. The different sizes of the fin surface significantly impact flow creation and temperature fields. Additionally, the long fin size is necessary to enhance the heat transfer rate on the right surface at large Richardson numbers and low Hartmann numbers. Fin surfaces can significantly increase the mixing of fluid inside the enclosure, which can mean reductions in reaction times and operating costs, along with increases in heat transfer and efficiency. [ABSTRACT FROM AUTHOR]

The dissipation rates of the basic second-order moments are the key parameters playing a vital role in turbulence modelling and controlling turbulence energetics and spectra and turbulent fluxes of momentum and heat. In this paper, we use the results of direct numerical simulations (DNSs) to evaluate dissipation rates of the basic second-order moments and revise the energy and flux budget (EFB) turbulence closure theory for stably stratified turbulence. We delve into the theoretical implications of this approach and substantiate our closure hypotheses through DNS data. We also show why the concept of down-gradient turbulent transport becomes incomplete when applied to the vertical turbulent flux of potential temperature under stable stratification. We reveal essential feedback between the turbulent kinetic energy (TKE), the vertical turbulent flux of buoyancy, and the turbulent potential energy (TPE), which is responsible for maintaining shear-produced stably stratified turbulence for any Richardson number. [ABSTRACT FROM AUTHOR]

Diffusive‐convection (DC) staircases, characterized by interleaving well‐mixed layers and high‐gradient interfaces of thermohaline properties, are commonly observed in the Canada Basin, Arctic. Previous studies suggested a quasi‐steady state of the thermohaline structures of these staircases. In this work, we employ mooring and Ice‐Tethered Profiler (ITP) data to show emergent merger events of staircases mediated by subsurface eddies with warm cores located at 300–500 m depths in 2005, 2007 and 2009. Two types of merger events, the B‐merger (resulting from strengthening of stronger interfaces at the expense of weaker ones) and the H‐merger (produced by vertical drift and collision of staircase interfaces), are documented during the passage of subsurface eddies. The merging staircases are located at 320–450 m depths, with layers of up to 70 m thick and high‐gradient interfaces thinner than 5 m. Mooring measurements reveal the emergence of staircase mergers associated with a background Richardson number dropping from a typical magnitude of O(100) $\mathcal{O}(100)$–O(10) $\mathcal{O}(10)$ to O(0.1) $\mathcal{O}(0.1)$, indicating the persistence of DC staircases in the presence of strong shears. In parallel, ITP data suggest the formation of B‐mergers (H‐mergers) to be favored within the eddy core (flank). The vertical heat fluxes associated with the B‐merger (H‐merger) staircases are estimated to be ∼3 W/m2 (∼1.5 W/m2), which substantially exceed the typical staircase‐driven heat fluxes of O(0.1) $\mathcal{O}(0.1)$ W/m2. These observations imply the significance of subsurface eddies in shaping the halocline structures and thus the vertical heat fluxes in the Arctic Ocean, particularly in a warming climate. Plain Language Summary: In the Arctic Ocean, warm waters derived from the Atlantic Ocean lie beneath surface cold waters, and store sufficient heat capable of melting the Arctic ice cover. Residing between the surface cold and subsurface warm waters are stacked layers, commonly referred to as staircases. These staircases regulate the rate at which heat from underneath may reach the surface and melt the sea ice. This study employs field measurements in the Arctic Ocean to show that staircases can be substantially re‐structured to enhance the upward heat transfer if turbulent spinning bodies of waters named eddies are present at 300–500 m depths. Further calculations show that the existence of up to three such eddies may elevate the overall heat transfer of the western Arctic by up to ∼10%. In‐depth analyses on these processes are thus warranted, particularly in a warming climate that can increasingly "heat up" the subsurface Arctic Ocean. Key Points: Diffusive‐convection staircases are observed to persist and merge under strong vertical shearsBoth B‐mergers and H‐mergers are observed in individual subsurface eddiesVertical heat fluxes across merged staircases in subsurface eddies grow by one order of magnitude [ABSTRACT FROM AUTHOR]

Coastal reservoirs (CRs) are important water resources worldwide, but environmental problems can arise due to limited material mixing caused by the blocked propagation of tidal waves. The Saemangeum Reservoir is a large brackish reservoir in South Korea; owing to its complex fluctuation characteristics, accurate reproduction of its three-dimensional (3D) circulation and material distribution characteristics remains a challenge. Here, we aimed to improve the reproducibility of the Delft3D model through long-term precision monitoring and analyze problems occurring in CRs. The model reproduced the hydraulic flow and stratification phenomena in CRs. The Richardson number ([Formula: see text]) was higher than 100, and the Stratification Index ([Formula: see text]) was higher than 1 due to the density difference between the surface and bottom layers. The stratification strength of the Saemangeum Reservoir was, therefore, considered high. Moreover, a two-layer circulation occurred due to the strength of the eddy and the horizontal gradient of salinity. When the sluice gate was expanded, the area and number of days where hypoxia occurred decreased. It would also mitigate the retention of materials caused by the eddy and improve circulation. The findings of this study can be used as foundational data for solving and managing hydraulic problems within CRs.

Plume chimney is a plume that has chimney characteristics due to stack effects of plumes. In this study, Computational Fluid Dynamic (CFD) simulation was carried out for three different heights of chimney and three different diameters of chimney at various heat loads to cover a range of source Richardson number from 0.034 to 0.33, and plume function from 1.01 to 7.16. Reynold’s average Navier-Stokes’s conservation equations were solved in modelling the plume. A zero-gravity forced convection plume model was applied to obtain the overall total pressure drop. Effective Plume-Chimney Height (EPCH) was correlated with several parameters to obtain an empirical correlation. It was found that EPCH was related to the square root diameter of the chimney, as predicted by dimensional analysis in a pioneering plume rise study and concurred with all existing prediction methods. Through this finding, a scaling formula for plume characteristic height is proposed. The power indices of volumetric coefficient of expansion, temperature differences, mean density of plume source density difference of air between ambient and plume source were 0.45, 0,80, 1.09 and -0.97 respectively; and correlation with the air velocity was negligible. The EPCH predicted by the correlation derived using the current method was found to be very close to previous correlations at the same Richardson number and plume function. For improved applicability, the range of parameters should be sufficiently broad and evenly distributed in future analysis. The theory of effective plume-chimney height is strongly supported by this CFD analysis, in addition to experimental data from industrial tests. Implications of the phenomenon of effective plume-chimney height, where a lazy plume has invisible walls causing a stack effect, generates a sizeable up thrust that is recommended to be investigated as it may be one of several factors contributing to mesoscale Clear Air Turbulence phenomenon experienced by aircrafts.

Mountain gravity wave characteristics are important for analyzing the nighttime heavy rainfall events occurring in Sichuan. Based on the GPM satellite precipitation data, FY-4A satellite cloud data, and ERA5 reanalysis data, we analyze the mesoscale characteristics of a nighttime rainstorm with a gravity wave that occurred on 10-11 July 2018 in the northeastern Sichuan Basin mountains. The results are as follows. (1) The oscillatory feature of cloud water content and the wavelike variation of the potential temperature field reflect, to some extent, the influence of the fluctuations on the mesoscale system. (2) The fluctuation trends of wind vertical shear index, thermal helicity, and moisture helicity appear during the development of waves, indicating the characteristics of gravity waves. (3) The areas with large values of wind vertical shear index, the extreme center of thermal helicity, and moisture helicity are consistent well with the heavy precipitation regions. (4) The gravity wave may be formed by the interaction of topographic disturbances, shear instability, and non-geostrophic equilibrium, which enhance the rainstorm. The regions with a small value of the Richardson number and a nonzero value of the nonlinear equilibrium equation can indicate the location and movement direction of the rainbands. Diagnosis of Richardson number shows that the vertical shear instability is formed before the mesoscale wave is excited, but it decreases with increasing fluctuations, which indicates that part of the energy of the waves comes from the unstable flow.

AbstractThe mixed convective transport in a vertically shear-driven square cavity with a rotating circular porous cylinder is investigated numerically in two dimensions. This study aims to enhance the understanding of heat distribution within a closed environment containing intricate electronic systems and heat exchangers by employing a porous media modeling approach. The vertical walls of the enclosure are kept isothermal, while both the horizontal walls are assumed to be adiabatic. Upward progress is being made by the left wall at a constant translational speed. The porous circular cylinder is inserted within the square cavity concentrically, which is then rotated both clockwise and counter-clockwise. While the Reynolds number based on the motion of the lid is maintained constant at Re = 100, the porosity of the cylinder fluctuates in accordance with the Darcy number range 10−6 ≤ Da ≤ 10−2 The streamline and the isotherm patterns for a range of controlling factors, including the Richardson number (0.5 ≤ Ri ≤ 10) and the dimensionless rotational speed (−5≤Ω≤5) are used to show how the flow and the thermal fields within the enclosure evolve. Additionally, the entropy generation is calculated and compared for the above mentioned parameters. The irreversibility generation as well as the flow and the heat transfer phenomena are observed to be significantly influenced by the rotation and the porosity of the cylinder. [ABSTRACT FROM AUTHOR]

Featured Application: The elbow-type thermal storage tank is an innovative solution for thermal energy storage, with a uniquely designed bent pipe inlet structure that significantly increases hot water output and optimizes thermal stratification. This tank has demonstrated exceptional performance in reducing hot/cold water mixing and improving hot water availability. With its simple manufacturing process and easy installation, it not only meets users' demands for an efficient hot water energy-saving application but is also in line with modern environmental and energy-saving concepts. The elbow-type storage tank has a wide range of applications in areas such as energy-efficient air conditioning and residential buildings, offering a new approach to energy use. Thermal storage tanks are the most widely used devices for thermodynamic storage. Their stratification performance is a key factor in determining their effectiveness. In this study, a structure was proposed to improve the thermal stratification of an elbow-type thermal storage tank. An experimental study was conducted on its exothermic properties for applications in hot water storage tanks. An experimental analysis was performed to investigate the exothermic properties of the proposed structure, and the results were compared with those obtained from simulations using CFD (ANSYS 19.1) software. To investigate the effect of thermal stratification on the water inlet structure, the Richardson number, hot water output rate, and MIX number of the elbow inlet structure were compared with those of the water distributor inlet structure. The results show that the MIX numbers corresponding to the inlet structures of the two types of tanks, the elbow and water distributor types, are not very different. These values were almost identical to the Richardson numbers. Under the same working conditions, the hot water output rate was 84.90% for the elbow inlet structure and 76.39% for the water distributor inlet structure. In conclusion, elbow-type water inlet structures are easy to install, and the manufacturing process is simplified. [ABSTRACT FROM AUTHOR]

The objective of this investigation is to explore the various factors affecting the heat exchange characteristics of a heating block that is cooled using hybrid nano-fluids. The results from this investigation can be useful to enhance the thermal performance and heat transmission efficiency in the design of thermal engineering equipment. To achieve this, we conducted a (3-D) numerical investigation of mixed convection within an L-cavity filled with hybrid nanofluid. Within this cavity, a heating block is located either on the west wall (Case VB) or on the bottom wall (Case HB). In both cases, cold hybrid nanofluids were introduced at a constant temperature and flowed through a portion of the top wall, while the remaining walls were considered adiabatic. The finite volume method along with the Boussinesq approximation were used to solve the governing equations. The numerical results were presented in the form of iso-lines, global Nusselt numbers, and isotherms for several thermal parameters, including Reynolds numbers, Richardson numbers, and hybrid volume fraction. Our results indicated that for all Richardson numbers and in both configurations, VB and HB, the total Nusselt number increased with increasing Reynolds numbers and volume fraction of particles, except in the case of configuration HB when the volume fraction (φ = 0%) and the Re ≥ 840, and that when the heated block was repositioned from configuration, HB, to configuration, VB, heat transfer increased significantly by 51.16%. Furthermore, we uncovered intriguing results when comparing the two configurations, VB and HB. [ABSTRACT FROM AUTHOR]

In this paper, we discuss parameterizations of turbulent mixing processes in models of inland water bodies (lakes and reservoirs) that allow one to sustain turbulent fluctuations in the presence of small velocity shears even in the case of highly stable stratification. The proposed parameterization of the turbulent Prandtl number takes into account the nongradient correction for the mass flux and depends on two parameters: the anisotropy parameter, which describes the differences in the vertical and horizontal scales of the density field correlations, and the maximum flux Richardson number. It is shown that the value of the maximum flux Richardson number and, as a consequence, the asymptotical increase in the turbulent Prandtl number under strong stability are associated with differences in the integral time scales determined by the dissipation rate of the kinetic or potential energy and the fluctuation intensities of the corresponding fields. This is consistent with the direct numerical simulation of shear-driven stably stratified turbulence. The anisotropy parameter specifies the transitional regime from neutral stratification to strong stability. Using the proposed parameterization, numerical experiments are carried out to reproduce the thermal and biochemical regime of inland water bodies (Kuivajärvi Lake and Rybinsk Reservoir). The results show that the distribution of biochemical concentrations and gas transfer processes are more sensitive to specifying the value of the maximum flux Richardson number. [ABSTRACT FROM AUTHOR]

This work investigates the dynamics of heavy particles dispersed in turbulent channel flows under unstable thermal stratification conditions using point-particle direct numerical simulations (PP-DNS), to quantify the influence of large-scale coherent vortex rolls, arising from the combined effects of shear and buoyancy, on the spatial distribution and preferential sampling behavior of inertial particles. We examined three particle Stokes numbers ( St + = 0.6 , 60 , 120 ) and two friction Richardson numbers, Ri τ = 0.272 and Ri τ = 27.2 , which exemplify the regimes below and above the critical condition for vortex roll formation, respectively. The results indicate that the flow reorganization into large-scale longitudinal vortices significantly alters the topological features of small scales in the near-wall region impinged by the thermal plumes, resulting in a prevalence of vorticity-dominated topologies. The interplay between this phenomenon and the tendency of particles to preferentially sample strain-dominated topologies leads to a distinctive asymmetric particle distribution in the near-wall planes. Inertial particles markedly accumulate in the strain-dominated regions where the coherent thermal plumes emerge from the walls, while avoiding the vorticity-dominated impingement zones. This peculiar particle response to the vortex rolls is most pronounced when the particle response time matches the characteristic timescale of the large-scale coherent motions in the cross-stream planes. [ABSTRACT FROM AUTHOR]

Studies of Kelvin-Helmholtz (KH) instability have typically modelled the initial mean flow as an isolated stratified shear layer. However, geophysical flows frequently exhibit multiple layers. As a step towards understanding these flows, we examine the case of two adjacent stratified shear layers using both linear stability analysis and direct numerical simulations. With sufficiently large layer separation, the characteristics of instability and mixing converge towards the familiar KH turbulence, and similarly when the separation is near zero and the layers add to make a single layer, albeit with a reduced Richardson number. Here, our focus is on intermediate separations, which produce new and complex phenomena. As the separation distance D increases from zero to a critical value Dc, approximately half the thickness of the shear layer, the growth rate and wavenumber both decrease monotonically. The minimum Richardson number is relatively low, potentially inducing pairing, and shear-aligned convective instability (SCI) is the primary mechanism for transition. Consequently, mixing is relatively strong and efficient. When D ~ Dc, billow length is increased but growth is slowed. Despite the modest growth rate, mixing is strong and efficient, engendered primarily by secondary shear instability manifested on the braids, and by SCI occurring on the eyelids. Shear-aligned vortices are driven in part by buoyancy production; however, shear production and vortex stretching are equally important mechanisms. When D > Dc, neighbouring billow interactions suppress the growth of both KH instability and SCI. Strength and efficiency of mixing decrease abruptly as Dc is exceeded. As turbulence decays, layers of marginal instability may arise. [ABSTRACT FROM AUTHOR]

Thermoacoustic instability typically presents in the operation of various engines and is harmful. It is thus necessary to investigate the influence mechanisms on it. When the effect of natural convection caused by buoyancy is equivalent to that of forced convection, the buoyancy effect will have a significant effect on the thermoacoustic instability. In order to study these effects, an electrically heated Rijke tube with adjustable pitch angle was designed. By adjusting the pitch angle under different operating conditions, the instability map as the functions of flow rates and heating powers was obtained. As the temperature field within the Rijke tube varies greatly at different pitch angles, its effect was also investigated associated with the numerical simulation. The results showed that the growth rates of the thermoacoustic instability exhibited a sinusoidal-like dependence on the pitch angle under certain operating conditions. This variation relationship only occurs when the Richardson number is sufficiently large. [ABSTRACT FROM AUTHOR]

The purpose of this study is numerical investigation, the laminar flow hydrodynamic and mixed convection of water-copper nanofluid in a microtube by applying the two-phase mixture method. This 3D simulation is run at Re = 10, Ri = 0.1 - 10 ) and volume fraction of nanoparticles φ = 0–6% through Finite Volume Method. The nanofluid flow is assumed Newtonian, assessed in a horizontal microtube of 90 ∘ curvature angle. The objective is to assess the impact of the buoyancy and centrifugal forces on the flow in a bent geometry. In this research, the interpretation and investigation of Nusselt Number (Nu), coefficient of friction and temperature distribution in three-dimensional macrotube with changes in volume fraction and Richardson number will be discussed. The results reveal that the nanofluids' hydrodynamic properties and behavior next to their heat transfer in bent geometries vary from those of other geometries and flat surfaces while being more trajectory dependent. The average Nusselt number and the average friction factor in the inner, outer, top, and bottom regions of the microtube strongly depend on the Ri number and φ. The increase in φ promotes the micron heat transfer mechanisms in the microtube, thus, an enhancement in the heat transfer rate. The variations in velocity components and the buoyancy and centrifugal forces are among the most influential factors on hydrodynamic and heat transfer parameters like the friction factor and Nu number. The value of the local Nu number has an ascending trend when the φ increases in the initial stage of the flow from the inlet section to the middle of the path. This is while the local Nu number decreases as the φ increases after the 45 ∘ curvature upward. The increase in the friction factor level from the entrance up to 45 ∘ angle is due to the more substantial effects of buoyancy and centrifugal forces. [ABSTRACT FROM AUTHOR]

The linkage between the salt wedge, tidal patterns, and the Magdalena River discharge is established by assessing the ensuing parameters: stratification (ϵ), buoyancy frequency (β), potential energy anomaly (φ), Richardson number by layers (RL), and bottom turbulent energy production (P). The salinity, temperature, density, and water velocity data utilized were derived from MOHID 3D, a previously tailored and validated model for the Magdalena River estuary. To grasp the dynamics of the river, a flow regime analysis was conducted during both the wet and dry climatic seasons of the Colombian Caribbean. The utilization of this model aimed to delineate the estuary's spatial reach, considering flow rates spanning from 2000 to 6500 m3/s across two tidal cycles. This approach facilitates the prediction of the position, stability, and stratification degree of the salt front. Among the conclusions drawn, it is highlighted that: 1. The river flow serves as the principal conditioning agent for the system, inducing a strong estuary response to weather stations; 2. The extent of wedge intrusion and the river discharge exhibit a non-linear, inversely correlation; 3. Tidal waves cause differences of up to 1000 m in the horizontal extent of the wedge; 4. Widespread channel erosion occurs during the rainy season when the salt intrusion does not exceed 2 km; 5. Flocculation processes intensify during the transition between the dry and wet seasons; 6. The stability of the salt layering and the consolidation of the FSI–TMZ are contingent upon the geometric attributes of the channel. [ABSTRACT FROM AUTHOR]

This paper investigates the transport of drugs delivered by direct injection into the cerebrospinal fluid (CSF) that fills the intrathecal space surrounding the spinal cord. Because of the small drug diffusivity, the dispersion of neutrally buoyant drugs has been shown in previous work to rely mainly on the mean Lagrangian flow associated with the CSF oscillatory motion. Attention is given here to effects of buoyancy, arising when the drug density differs from the CSF density. For the typical density differences found in applications, the associated Richardson number is shown to be of order unity, so that the Lagrangian drift includes a buoyancy-induced component that depends on the spatial distribution of the drug, resulting in a slowly evolving cycle-averaged flow problem that can be analysed with two-time scale methods. The asymptotic analysis leads to a nonlinear integro-differential equation for the spatiotemporal solute evolution that describes accurately drug dispersion at a fraction of the cost involved in direct numerical simulations of the oscillatory flow. The model equation is used to predict drug dispersion of positively and negatively buoyant drugs in an anatomically correct spinal canal, with separate attention given to drug delivery via bolus injection and constant infusion. [ABSTRACT FROM AUTHOR]

Fully resolved direct numerical simulations are used to quantify the effect of evolving heat, due to idealized smoldering processes, on the aerodynamic forces of a spherical particle, representing an idealized fixed-shape firebrand particle. Firebrand particles are small glowing particles that are generated in fires and can be transferred long distances by the wind and create new spot fires. Understanding the transport of firebrands is of great importance in fire science. The simulations are performed at a Reynolds number of 500, relevant for a wide range of firebrand size and wind velocity combinations. The spatiotemporal variation of temperature over the surface of the particle is obtained using a detailed surface energy balance analysis. The firebrand particle is assumed to have the thermal and material properties of pine needles and has a Biot number larger than unity, which means that the particle undergoes notable internal temperature gradients. The results indicate that the buoyancy-induced flow around the particle significantly modifies the trailing vortices and produces two non-interacting tunnel-shaped plumes in the wake of the sphere as the particle's Richardson number increases. As a result, the particle's drag and lift coefficients show large deviations from those of a non-heated particle and an isothermal particle. The increased surface temperatures result in an increase in the drag force while inducing a negative lift. The significant variations seen in the aerodynamic forces as a function of the particle's instantaneous temperature indicate that the influence of the transient thermal conditions of firebrands should be considered in the prediction of the particles' trajectory and landing spots. [ABSTRACT FROM AUTHOR]

The present study deals with the conjugate mixed convection of a non-Newtonian nanofluid in an enclosure with a left thick side wall. We adopt Buongiorno's non-homogeneous model to incorporate the effects due to Brownian motion and thermophoretic diffusion of the nanoparticles. The non-Newtonian behavior of the nanofluid is captured through the widely accepted power-law model. We employ the radial basis function (RBF)-based meshless numerical scheme for the simulation. In order to check the accuracy of the present numerical scheme, the simulated results are compared with the available numerical as well as experimental data. The excellent agreement of our results with the available ones ensures the capability of the newly adopted numerical tools to study the conjugate heat transfer problems. The results are presented by varying the pertaining parameters governing the undertaken conjugate mixed convection problem. Richardson number and Reynolds number are varied up to a moderate range with different permissible choices of the nanoparticle volume fractions, diameter of the nanoparticles, power-law index, and solid-to-fluid conductivity ratio, etc. The entropy generation and Bejan number are further evaluated to analyze the heat transfer characteristics. Results show that the degree of inhomogeneity of the nanoparticles depends strongly on the fluid behavior index. Rheological behavior of the nanofluid has substantial impact on the heat transfer rate and entropy generation, which can further be controlled through the value of the solid-to-fluid conductivity ratio. The pattern in Bejan number shows the predominance of the heat transfer irreversibility over the fluid friction irreversibility for all the cases considered in the study. [ABSTRACT FROM AUTHOR]

The theory of stratified turbulent flow developed earlier by the authors is applied to data from different areas of the ocean. It is shown that turbulence can be amplified and supported even at large gradient Richardson numbers. The cause of that is the exchange between kinetic and potential energies of turbulence. Using the profiles of Brunt–Väisälä frequency and vertical current shear given in , the profiles of the kinetic energy dissipation rate are calculated. The results are in reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]