Mean Temperature Gradient Research Articles

Single-Mode Solutions for Convection and Double-Diffusive Convection in Porous Media

This work employs single-mode equations to study convection and double-diffusive convection in a porous medium where the Darcy law provides large-scale damping. We first consider thermal convection with salinity as a passive scalar. The single-mode solutions resembling steady convection rolls reproduce the qualitative behavior of root-mean-square and mean temperature profiles of time-dependent states at high Rayleigh numbers from direct numerical simulations (DNS). We also show that the single-mode solutions are consistent with the heat-exchanger model that describes well the mean temperature gradient in the interior. The Nusselt number predicted from the single-mode solutions exhibits a scaling law with Rayleigh number close to that followed by exact 2D steady convection rolls, although large aspect ratio DNS results indicate a faster increase. However, the single-mode solutions at a high wavenumber predict Nusselt numbers close to the DNS results in narrow domains. We also employ the single-mode equations to analyze the influence of active salinity, introducing a salinity contribution to the buoyancy, but with a smaller diffusivity than the temperature. The single-mode solutions are able to capture the stabilizing effect of an imposed salinity gradient and describe the standing and traveling wave behaviors observed in DNS. The Sherwood numbers obtained from single-mode solutions show a scaling law with the Lewis number that is close to the DNS computations with passive or active salinity. This work demonstrates that single-mode solutions can be successfully applied to this system whenever periodic or no-flux boundary conditions apply in the horizontal.

Analytical solutions for the acoustic field in thin annular combustion chambers with linear gradients of cross-sectional area and mean temperature

Predictions of thermoacoustic instabilities in annular combustors are essential but difficult. Axial variations of flow and thermal parameters increase the cost of numerical simulations and restrict the application of analytical solutions. This work aims to find approximate analytical solutions for the acoustic field in annular ducts with linear gradients of axially non-uniform cross-sectional area and mean temperature. These solutions can be applied in low-order acoustic network models and enhance the ability of analytical methods to solve thermoacoustic instability problems in real annular chambers. A modified WKB method is used to solve the wave equation for the acoustic field, and an analytical solution with a wide range of applications is derived. The derivation of the equations requires assumptions such as low Mach number, high frequency and small non-uniformity. Cases with arbitrary distributions of cross-sectional surface area and mean temperature can be solved by the piecewise method as long as the assumptions are satisfied along the entire chamber.

Novel Wentzel–Kramers–Brillouin Solutions to the Nonisentropic Helmholtz Equation in a Nonuniform Duct With Mean Temperature Gradient and Mean Flow

Abstract We derive the generalized Helmholtz equation (GHE) governing nonisentropic acoustic fluctuations in a quasi 1D duct with nonuniform cross section, mean temperature gradient, and nonuniform mean flow. Nonisentropic effects are included via heat conduction terms in the mean and fluctuating energy equations. To derive the Helmholtz equation exclusively in terms of the fluctuating pressure field, a relationship between density and pressure fluctuations is needed, which is shown to be a second-order differential equation for nonisentropic motions. Novel analytical solutions that are accurate for both low/high frequencies and small/large mean gradients are presented for the GHE based on the Wentzel–Kramers–Brillouin (WKB) method. WKB solutions are developed using the ansatz that the pressure fluctuation field has a travelling wave form, p^(x)=exp[∫0x(a+ib)dx], where x is the axial coordinate. Substituting this form into the Helmholtz equation yields coupled, nonlinear ordinary differential equations (ODEs) for a and b. Analytical solutions to the ODEs are obtained using the approximations of high frequency and slowly varying mean properties. This simplification allows us to obtain the lower order solutions b0 and a0. We then enhance solution accuracy by using a0 to solve for b1 without any approximations. Finally, b1 is employed to get a1, giving us the higher order solution. The p^ calculated from (a1, b1) is in good to excellent agreement with numerical solution of the GHE for both low and high frequencies and for a range of mean Mach numbers, including M¯≳1.

Three-Dimensional Analytical Solutions for Acoustic Transverse Modes in a Cylindrical Duct with Axial Temperature Gradient and Non-Zero Mach Number

Cylindrical ducts with axial mean temperature gradient and mean flows are typical elements in rocket engines, can combustors, and afterburners. Accurate analytical solutions for the acoustic waves of the longitudinal and transverse modes within these ducts can significantly improve the performance of low order acoustic network models for analyses of acoustic behaviours and combustion instabilities in these kinds of ducts. Here, we derive an acoustic wave equation as a function of pressure perturbation based on the linearised Euler equations (LEEs), and the modified WKB approximation method is applied to derive analytical solutions based on very few assumptions. The eigenvalue system is built based on the proposed solutions and applied to predict the resonant frequencies and growth rate for transverse modes. Validations of the proposed solutions are performed by comparing them to the numerical results directly calculated from the LEEs. Good agreements are found between analytical reconstruction and numerical results of three-dimensional transverse modes. The system with both mean temperature profile and mean flow presents a larger absolute value of the growth rate than the condition of either uniform mean temperature or no mean flow.

On the seasonal prediction and predictability of winter surface Temperature Swing Index over North America

The rapid day-to-day temperature swings associated with extratropical storm tracks can cause cascading infrastructure failure and impact human outdoor activities, thus research on seasonal prediction and predictability of extreme temperature swings is of huge societal importance. To measure the extreme surface air temperature (SAT) variations associated with the winter extratropical storm tracks, a Temperature Swing Index (TSI) is formulated as the standard deviation of 24-h-difference-filtered data of the 6-hourly SAT. The dominant term governing the TSI variability is shown to be proportional to the product of eddy heat flux and mean temperature gradient. The seasonal prediction skill of the winter TSI over North America was assessed using Geophysical Fluid Dynamics Laboratory's new seasonal prediction system. The locations with skillful TSI prediction show a geographic pattern that is distinct from the pattern of skillful seasonal mean SAT prediction. The prediction of TSI provides additional predictable climate information beyond the traditional seasonal mean temperature prediction. The source of the seasonal TSI prediction can be attributed to year-to-year variations of the El Niño-Southern Oscillation (ENSO), North Pacific Oscillation (NPO), and Pacific/North American (PNA) teleconnection. Over the central United States, the correlation skill of TSI prediction reaches 0.75 with strong links to observed ENSO, NPO, and PNA, while the skill of seasonal SAT prediction is relatively low with a correlation of 0.36. As a first attempt of diagnosing the combined predictability of the first-order (the seasonal mean) and second-order (TSI) statistics for SAT, this study highlights the importance of the eddy-mean flow interaction perspective for understanding the seasonal climate predictability in the extra tropics. These results point toward providing skillful prediction of higher-order statistical information related to winter temperature extremes, thus enriching the seasonal forecast products for the research community and decision makers.

Net heat current at zero mean temperature gradient

The existence of a net heat current of conductive thermal waves is demonstrated even in the absence of a mean temperature gradient. This effect, which we called heat shuttling, is generated by the temperature-dependent thermal conductivity of materials excited with a thermal excitation periodically modulated in time. We show that this modulation gives rise to a heat current superimposed on the one generated by the mean temperature gradient, which enhances the heat transport when the thermal conductivity increases with temperature. By contrast, if the thermal conductivity decreases as temperature increases, the thermal-wave heat current inverts its direction and reduces the total heat flux. The reported shutting effect is sensitive to the amplitude of the periodic thermal excitation, which can facilitate its observation and application to harvest energy from the temperature variations of the environment.

Study of a lead-bismuth eutectic jet issued into a heated cavity using large eddy simulation

Low Prandtl number convection of an axisymmetric turbulent lead-bismuth eutectic (LBE) jet discharged into a heated confined geometry using large eddy simulation is investigated. The Reynolds number based on jet centerline velocity and jet diameter is Re = 44,706. The results demonstrate some features of liquid metal that deviate from those of ordinary fluids. Examples include the differences between fluctuations of temperature and velocity, the distributions of turbulent viscosity and turbulent diffusivity of heat, and the misalignment between the turbulent heat flux vector and the gradient of mean temperature, all of which imply that standard turbulence models may not be suitable for the simulation of such flows. The LBE jet at Pr = 0.03 is compared with a high-pressure water jet at Pr = 0.8 under the same Re and Fr. The centerline decay of the mean velocity for LBE demonstrates the same behavior as that of water, which is governed by a linear variation for the self-preservation region between 1.5D and 8.5D, where D is the diameter of the jet orifice. In contrast, the centerline mean temperature for LBE decreases slower compared with that of water. The difference in temperature results from the high intensity of molecular diffusion in heat transport in LBE, while the momentum transport is mainly by turbulent diffusion in both flows. Self-preserving characteristic of temperature r.m.s (Trms) is observed. The radial profiles of Trms are presented by an axisymmetric curve with a maximum at around 0.7b, where b is the half-value radius of Trms. Good agreement of mean temperature distribution between the simulation results and the experiments are obtained.

Investigation of turbulent entropy production rate with SWCNT/H2O nanofluid flowing in various inwardly corrugated pipes

AbstractThis paper presents turbulent heat transfer performance and entropy production rate in different inwardly corrugated pipes with single‐walled carbon nanotube (SWCNT)/H2O nanofluid as a working fluid using the finite volume method approach. The configurations considered were circular, triangular, and trapezoidal. The SWCNT/H2O nanofluid was modeled using a single‐phase approach and the model was used to simulate the turbulent flow. A parametric study was carried out on the effect of Reynolds number (5 × 103 ≤ Re ≤ 3 × 104) and nanoparticle volume ratio (0% ≤ φ ≤ 0.25%) on hydrodynamic, heat transfer performance, thermal entropy production rates (TEPRs; due to mean and turbulent temperature gradients), and viscous entropy production rates (VEPRs; due to mean and turbulent velocity gradients). The results showed that the mean temperature gradient contributes most to the TEPR, compared with the turbulent temperature gradient. However, the opposite was the case for the VEPR. Furthermore, the presence of corrugation decreases the TEPR but enhanced friction factor, Nusselt number, and VEPR. For example, at a Reynolds number of 2.5 × 104, the normalized friction factor, average Nusselt number, TEPR, and VEPR (referencing a smooth pipe) in circularly, triangularly, and trapezoidal corrugated pipes are {3.86, 1.39, 0.80, 3.88}, {3.80, 1.41, 0.72, 3.98}, and {4.34, 1.55, 0.69, 4.19}, respectively.

Analyzing Canopy Height Patterns and Environmental Landscape Drivers in Tropical Forests Using NASA’s GEDI Spaceborne LiDAR

Canopy height is a fundamental parameter for determining forest ecosystem functions such as biodiversity and above-ground biomass. Previous studies examining the underlying patterns of the complex relationship between canopy height and its environmental and climatic determinants suffered from the scarcity of accurate canopy height measurements at large scales. NASA’s mission, the Global Ecosystem Dynamic Investigation (GEDI), has provided sampled observations of the forest vertical structure at near global scale since late 2018. The availability of such unprecedented measurements allows for examining the vertical structure of vegetation spatially and temporally. Herein, we explore the most influential climatic and environmental drivers of the canopy height in tropical forests. We examined different resampling resolutions of GEDI-based canopy height to approximate maximum canopy height over tropical forests across all of Malaysia. Moreover, we attempted to interpret the dynamics underlining the bivariate and multivariate relationships between canopy height and its climatic and topographic predictors including world climate data and topographic data. The approaches to analyzing these interactions included machine learning algorithms, namely, generalized linear regression, random forest and extreme gradient boosting with tree and Dart implementations. Water availability, represented as the difference between precipitation and potential evapotranspiration, annual mean temperature and elevation gradients were found to be the most influential determinants of canopy height in Malaysia’s tropical forest landscape. The patterns observed are in line with the reported global patterns and support the hydraulic limitation hypothesis and the previously reported negative trend for excessive water supply. Nevertheless, different breaking points for excessive water supply and elevation were identified in this study, and the canopy height relationship with water availability observed to be less significant for the mountainous forest on altitudes higher than 1000 m. This study provides insights into the influential factors of tree height and helps with better comprehending the variation in canopy height in tropical forests based on GEDI measurements, thereby supporting the development and interpretation of ecosystem modeling, forest management practices and monitoring forest response to climatic changes in montane forests.

Investigation of the entropy production rate of ferrosoferric oxide/water nanofluid in outward corrugated pipes using a two-phase mixture model

This study investigates the turbulent entropy production rate of ferrosoferric oxide/water (Fe3O4/H2O) nanofluid flowing through outward corrugated pipes of different profiles (circular, triangular, and trapezoidal). Both the multi-phase mixture model and the k−ω turbulent model were adopted for simulating the turbulent ferrofluid flow. The effects of Reynolds number (between 5.0 × 103 and 3.0 × 104) and nanoparticle concentration (0.0–3.0%) on viscous entropy production rates (due to mean and turbulent velocity gradients) and thermal entropy production rates (due to mean and turbulent temperature gradient) were examined parametrically. The results show that trapezoidally corrugated pipes tend to have the best heat transfer performance, but also the worst hydraulic performance, where they increase the pressure drop and the average Nusselt number by 2.92 and 1.66 folds, respectively, for a 2.0% nanoparticles’ concentration at Reynolds number of 3.0 × 104. Increasing the concentration of nanoparticles from 0.0 to 3.0% has the same effect, where the two quantities increase by 1.31 and 1.07, respectively, for a triangularly corrugated pipe at a Reynolds number of 1.5×104. The mean temperature gradient contributes most to the thermal entropy production rate, compared to the turbulent temperature gradient. However, the opposite is the case for the viscous entropy production rate. Furthermore, the presence of corrugation was found to increase the viscous entropy production rate but reduce the thermal entropy production rate. The normalized thermal and viscous entropy production rates (referencing a smooth pipe) in circularly, triangularly, and trapezoidally corrugated pipes are {0.81, 0.75}, {0.56,3.38}, and {3.29,3.45}, respectively. It is also noticed that the Bejan number decreases as the Reynolds number increases by 51.4, 81.4, 82.2, and 87.6% for smooth, circularly corrugated, triangularly corrugated, and trapezoidally corrugated pipes, respectively.

Thermal entrance problem for blood flow inside an axisymmetric tube: The classical Graetz problem extended for Quemada's bio-rheological fluid with axial conduction.

The heat-conducting nature of blood is critical in the human circulatory system and features also in important thermal regulation and blood processing systems in biomedicine. Motivated by these applications, in the present investigation, the classical Graetz problem in heat transfer is extended to the case of a bio-rheological fluid model. The Quemada bio-rheological fluid model is selected since it has been shown to be accurate in mimicking physiological flows (blood) at different shear rates and hematocrits. The steady two-dimensional energy equation without viscous dissipation in stationary regime is tackled via a separation of variables approach for the isothermal wall temperature case. Following the introduction of transformation variables, the ensuing dimensionless boundary value problem is solved numerically via MATLAB based algorithm known as bvp5c (a finite difference code that implements the four-stage Lobatto IIIa collocation formula). Numerical validation is also presented against two analytical approaches namely, series solutions and Kummer function techniques. Axial conduction in terms of Péclet number is also considered. Typical values of Reynolds number and Prandtl number are used to categorize the vascular regions. The graphical representation of mean temperature, temperature gradient, and Nusselt numbers along with detail discussions are presented for the effects of Quemada non-Newtonian parameters and Péclet number. The current analysis may also have potential applications for the development of microfluidic and biofluidic devices particularly which are used in the diagnosis of diseases in addition to blood oxygenation technologies.

Macroscopic model for porous media in oscillating flow for CFD applications

In this paper a macroscopic model for porous media in oscillating flow is derived for CFD applications. In non -linear modelling of thermoacoustic devices, their cores, useful for the energy conversion, cannot be, in general, modelled like a traditional porous media through friction factor and Nusselt number correlations, recovered from steady state. In this work the analytical solutions in the frequency domain of the linearized Navier-Stokes equations are spatially averaged for an oscillating flow between parallel plates case to build a macroscopic model of an equivalent porous media through a complex permeability and Nusselt number. The results, obtained by assuming a zero mean temperature gradient, show that there is a good agreement between macroscopic solution of a porous box (representing a parallel plates stack) and the average of the solutions of oscillating flow between parallel plates, both in terms of temperature and velocity fields.

Difference between brain temperature and core temperature in severe traumatic brain injury: a systematic review.

Intensive care management for traumatic brain injury (TBI) patients aims to prevent secondary cerebral damage. Targeted temperature management is one option to prevent cerebral damage, as hypothermia may have protective effects. By conducting a systematic literature review we evaluated: 1) the presence of a temperature difference (gradient) between brain temperature (Tb) and core temperature (Tc) in TBI patients; and 2) clinical factors associated with reported differences. The PubMed database was systematically searched using Mesh terms and key words, and Web of Sciences was assessed for additional article citations. We included studies that continuously and simultaneously measured Tb and Tc in severe TBI patients. The National Institutes of Health (NIH) quality assessment tool for observational cohort and cross-sectional studies was modified to fit the purpose of our study. Statistical data were extracted for further meta-analyses. We included 16 studies, with a total of 480 patients. Clinical heterogeneity consisted of Tb/Tc measurement site, measurement device, physiological changes, local protocols, and medical or surgical interventions. The studies have a high statistical heterogeneity (I2). The pooled mean temperature gradient between Tb and Tc was +0.14 °C (95% confidence interval: 0.03 to 0.24) and ranged from -1.29 to +1.1 °C. Patients who underwent a decompressive (hemi)craniectomy showed lower Tb values compared to Tc found in three studies. Studies on Tb and Tc are heterogeneous and show that, on average, Tb and Tc are not clinically significant different in TBI patients (<0.2 °C). Interpretations and interventions of the brain and central temperatures will benefit from standardization of temperature measurements.

On cataloguing the possible waveforms for impulse propagation along ground to ground thermospheric paths

Infrasound propagation in the thermosphere is characterized by very low mean density, a very steep mean temperature gradient, and tidal winds. The steep temperature gradient means that there is always a thermospheric duct and this always provides ground to ground propagation paths that pass through the thermosphere. These paths are modulated by the atmospheric tides, while the very low density in the thermosphere causes severe attenuation and non-linear distortion. For an impulsive signal initially in the form of an N-like wave, such as the signal produced by a large explosion, non-linear propagation effects cause the positive pressure phases to propagate more rapidly than the negative pressure phases, in turn causing the duration of the impulse to increase. This effect can be quite significant in the thermosphere and continues until a caustic is encountered transforming the N-wave into a U-wave. The severe attenuation causes the high frequency components of the signal to attenuate resulting in a long period and fairly clean waveform that propagates back to the ground. The combination of steep temperature gradient and atmospheric tides produce a canonical thermospheric propagation environment with a diurnal cycle. In this presentation, it is shown that non-linear ray theory (weak shock theory) can be used to catalogue the waveform shapes of ground returns from explosive signals traveling along thermospheric paths. Qualitative comparisons to observed thermospheric returns are made.

Acoustic absorption and generation in ducts of smoothly varying area sustaining a mean flow and a mean temperature gradient

In ducts with varying cross-sectional area and sustaining a subsonic non-isentropic mean flow, the axially varying flow conditions affect the acoustic energy balance of the system. This is significant in understanding and controlling thermo-acoustic phenomena, particularly in combustors. This work aims at quantifying the acoustic energy change in such configurations, using the acoustic absorption coefficient, Δ. The acoustic response of the duct to acoustic forcing is determined using an analytical model, neglecting the effect of entropy fluctuations on the acoustic field, and subsequently, Δ is estimated. The model predictions of Δ are validated using a linearised Euler equations (LEEs) solver. The model was found to be accurate for Mach numbers below 0.25, provided the lower frequency limit set by the analytical solution is satisfied. For conically varying area ducts with linear mean temperature gradient, it was observed that Δ showed very little dependence on frequency, and that the absolute value of Δ tended to be maximised when the upstream boundary was anechoic rather than non-anechoic. More importantly, Δ was also observed to show stronger dependence on the mean temperature gradient than area gradient variation for such configurations. Further parametric and optimisation studies for Δ revealed a crucial finding that a positive mean temperature gradient, representing a heated duct caused acoustic energy absorption. Similarly, a negative mean temperature gradient, representing a cooled duct caused acoustic energy generation – a key result of this analysis. This behaviour was shown to be consistent with a simplified analysis of the acoustic energy balance. Based on this finding, a linearly proportional reduction in acoustic energy generation was achieved by changing the mean temperature gradient.

Iterative two-layer thermal design strategy for step sandwich antenna of space solar power satellite using modified constrained multi-objective optimization

To utilize space solar energy efficiently, a concentrating-type space solar power satellite (SSPS) that can collect solar energy in space and transmit it to Earth through energy conversion and transmission is proposed. Given that the thermal subsystem is affected by high temperatures, which directly restricts its development, an iterative two-layer thermal design is proposed herein to optimize the step sandwich antenna (SSA) in the SSPS using a novel modified multi-objective optimization algorithm. To improve the feasibility of the SSPS, the thermal control coating requirements and structural configurations of the SSA are examined. The optimization of the SSA entails thermal analyses involving the conduction and radiation modes using thermophysical and structural parameters. The iterative two-layer thermal design of the SSA includes top-layer conceptual and bottom-layer precise designs. The coating requirement and structural configuration of the top-layer and the precise configuration and temperature uniformity of the bottom layer are improved iteratively to ensure global optimal solutions. Thus, the theoretical critical values of the optical properties of coatings are revealed using the proposed thermal design strategy. Furthermore, the solution set at the Pareto front is appraised, and the constrained multi-objective optimization algorithm is modified to obtain a more dispersed solution set. Finally, an actual SSA with the optimal design variables of the coatings and configurations is constructed using the two-layer strategy to achieve better heat dissipation with a mean temperature gradient of 7.22 °C/m and mass of approximately 2729 t; the effectiveness and feasibility of the design were also verified.

Associations between peripheral perfusion disorders, mean arterial pressure and dose of norepinephrine administrated in the early phase of septic shock.

The aim of the study was to explore the correlations between peripheral perfusion, mean arterial pressure and the dose-rate of norepinephrine (NE) infused for the treatment of septic shock. The study is retrospective analysis of data acquired prospectively on 57 patients during the first 24hours after the occurrence of the shock. Clinical and haemodynamic characteristics, skin perfusion parameters (capillary refill time [CRT], mottling score and temperature gradients) and the dose rate of NE infusion were collected. Negative correlations between mean arterial pressure (MAP) and temperature gradients (core-to-toe: P=.03, core-to-index: P=.04) were found and abnormal CRT was associated with lower MAP (P=.02). The dose rate of NE was negatively correlated with temperature gradients (core-to-toe: P=.02, core-to-index: P=.01, forearm-to-index: P=.008) in the overall population. In patients receiving NE for at least 12hours, the NE dose rate positively was correlated with the mottling score (P=.006), temperature gradients (core-to-toe: P=.04, forearm-to-index: P=.02, core-to-index: P=.005) and CRT (P=.001). The dose of NE administrated was associated with 14-days mortality (odds ration [OR]=1.21 [1.06-1.38], P=.006) and with 28-days mortality (OR=1.17 [1.01-1.36], P=0.04). In conclusion, the study described the presence of correlations between peripheral perfusion and MAP and between peripheral perfusion and the dose rate of NE infusion.

Species-environment relationships of fish and map-based variables in small boreal streams: Linkages with climate change and bioassessment.

Species–environment relationships were studied between the occurrence of 13 fish and lamprey species and 9 mainly map‐based environmental variables of Finnish boreal small streams. A self‐organizing map (SOM) analysis showed strong relationships between the fish species and environmental variables in a single model (explained variance 55.9%). Besides basic environmental variables such as altitude, catchment size, and mean temperature, land cover variables were also explored. A logistic regression analysis indicated that the occurrence probability of brown trout, Salmo trutta L., decreased with an increasing percentage of peatland ditch drainage in the upper catchment. Ninespine stickleback, Pungitius pungitius (L.), and three‐spined stickleback, Gasterosteus aculeatus L., seemed to benefit from urban areas in the upper catchment. Discovered relationships between fish species occurrence and land‐use attributes are encouraging for the development of fish‐based bioassessment for small streams. The presented ordination of the fish species in the mean temperature gradient will help in predicting fish community responses to climate change.

Hybrid RANS–LES Simulation of Turbulent Heat Transfer in a Channel Flow With Imposed Streamwise or Spanwise Mean Temperature Gradient

Abstract Computational fluid dynamics (CFD) results are presented for turbulent flow and heat transfer in a plane channel. This study investigates an idealized fully developed planar channel flow case for which the mean velocity gradient is nonzero only in the wall-normal direction, and the mean temperature gradient is imposed to be uniform and nonzero in the streamwise or spanwise direction. The objective is to evaluate the accuracy of turbulent heat flux predictions using hybrid Reynolds-averaged Navier–Stokes (RANS)–large eddy simulation (LES) models in wall-bounded flows. Results are obtained at Prandtl number of 0.71 and Reynolds number of 180 based on wall friction velocity and channel half-height and are compared to available direct numerical simulation (DNS) data and to a well-validated RANS model (k–ω shear-stress transport (SST)). The specific hybrid RANS–LES (HRL) models investigated include delayed detached eddy simulation (DDES), improved delayed detached eddy simulation (IDDES), and dynamic hybrid RANS–LES (DHRL). The DHRL model includes both the standard formulation that has been previously documented in the literature as well as a modified version specifically developed to improve predictive capability for flows in which the mean velocity and mean temperature gradients are not closely aligned. The modification consists of using separate RANS-to-LES blending parameters in the momentum and energy equations. Results are interrogated to evaluate the performance of the three different model types and specifically to evaluate the performance of the new modified DHRL variant compared with the baseline version.

Characteristics of 3‐Dimensional Structure and Heat Budget of Mesoscale Eddies in the South Atlantic Ocean

AbstractMesoscale eddies redistribute heat, salt, and nutrients in oceans. The South Atlantic Ocean (SA) is a basin that has active mesoscale eddies for which characteristics of the three‐dimensional structure and its leading mechanism are complex but have yet been studied sufficiently. Here based on ocean reanalysis datasets we use a composite analysis approach to analyze the mixed layer anomalous heat budget and find distinct two types of spatial patterns: dipole and monopole – mainly present in the northern and southern regions of the SA, respectively. The dipole can be attributed to ocean horizontal advection, especially to the combined effect of eddy anomalous meridional current and meridional gradient of mean temperature. The monopole, on the other hand, is associated with complex contributions, for which zonal and meridional advections play opposite roles as cooling or heating around the eddies. At the eddy center, the vertical advection is non‐negligible, especially the mean upwelling and vertical temperature gradient playing a vital role in the formation of a monopole. The analysis of eddy meridional heat transport shows that the stirring component is dominant, and poleward in most areas, especially at high latitudes. Such analysis on the leading mechanism of eddy‐induced temperature anomaly could help improve our understanding on meso‐ and small‐scale air‐sea interactions and eddy‐induced heat transport in the SA.