Turbulent Coefficient Research Articles

Augmentation of Plate-Fin Heat Exchanger Performance with Support of Various Types of Fin Configurations

A plate fin heat exchanger PFHE is a form of compact heat exchanger CHE containing of a block of alternating layers of fins and flat separators known as parting sheets. In this paper, 3-dimensional incompressible laminar flow and heat transfer in a (PFHE) has been investigated numerically. The influences using different fin configurations and the effect of the offset of these fins, on thermal and hydro-dynamic fields are presented. The cases of study for the PFHE are established, by using the fins with different configurations (plain rectangular (PR) and it's offset (OR), plain triangular (PT) and it's offset (OT) which is a novel shape, and a novel combination of a two fin shapes, between rectangular and triangular (ORT)). The upper and lower plates are exposed to a constant heat flux and the working fluid is air where chosen under a laminar range of (Re) number (600 to 1400). The laminar flow and heat transfer is governed by continuity, momentum and energy equations. ANSYS FLUENT (2021 R1) is used to get the numerical results, based on finite volume method. One of the most utilized fins for a PFHE is the offset fin arrangement due to its higher heat change amount, adjustable structure, and enhances flow turbulence and heat transfer coefficient by interrupting the thermal boundary layer. The obtained results of using of the offset configuration increases the Nusselt number by 20.32% and 17.82% for OSF rectangular and OSF triangular, respectively as compared with the with plain configurations, as a result, a significant heat transfer enhancement is observed. And significant increase in the friction-factor is found to be 79.8% and 48.7% for OT and ORT, as compared with the PT. It can be observed that use of the OSF configuration leads to greater f-factor for triangular configuration values. In addition, the temperature fields for the primary and secondary flows were showed in a contour diagram.

Numerical Simulations of Dome-Collapse Pyroclastic Density Currents Using faSavageHutterFOAM: Application to the 3 June 1991 Eruption of Unzen Volcano, Japan

Pyroclastic density currents (PDCs) are one of the most dangerous but least understood phenomena of volcanic eruptions. An open-source numerical depth-averaged model of dense granular currents controlled by physical processes such as energy dissipation, basal deposition, and erosion (faSavageHutterFOAM) was applied to investigate the basal concentrated region of a dome-collapse PDC generated on June 3, 1991 at Unzen volcano (Japan) to assess the effects of the physical processes (and their interplay) on the flow dynamics and run-out area of the PDC. Numerical simulations show that energy dissipation process decreases the flow velocity and increases the basal deposition rate, which reduces the run-out distance. The simulations also reveal that erosion process during flow propagation decreases the flow velocity and increases the run-out distance. The numerical results are sensitive to the parameters of energy dissipation (dry friction coefficient μ and collisional or turbulent friction coefficient χ) and erosion (specific erosion energy eb). The results are fitted to field data for run-out distance and flow velocity when μ is between 0.01 and 0.1 with χ∼103 m-1 s-2 (or when χ is between 104 and 105 m-1 s-2 with μ∼0.2) and eb∼102 m2 s-2. The estimated value of eb suggests that re-entrainment of deposit mass played an important role in controlling the flow dynamics and run-out area of the PDC. The estimated values of μ and χ are correlated, but the estimation of these parameters might be improved by further constraints from field data. The presented results serve as a basis to make further quantitative estimations of the model parameters (μ, χ, and eb) for applying the faSavageHutterFOAM model to hazard assessments of PDCs.

Waves on the surface of a thin liquid film entrained by a turbulent gas flow in a narrow channel

The paper considers the problem of a joint flow in a narrow vertical channel of a turbulent gas flow and a wave film of liquid flowing down its walls. The calculation of tangential stresses on the interface is performed. The components of the Reynolds stress tensor were determined within the framework of the Boussinesq hypothesis. The turbulent viscosity coefficient was taken into account both when calculating the average velocity profile and when considering disturbances caused by wavy interface. The main difference this case and the semi-infinite channel case is observed in the longwave region. Nonlinear waves on a liquid film flowing down under the action of gravity are studied in a known stress field at the interface. For the case of low Reynolds numbers of the liquid (Re ∼1), the problem is reduced to a nonlinear integro-differential equation for the deviation of the layer thickness from the unperturbed level. For this equation, the character of branching from the unperturbed solution of weakly nonlinear steady-state traveling solutions, whose wave numbers lie in the neighborhood of neutral points, is studied. A numerical study of the evolution of periodic perturbations, whose wave numbers noticeably differ from neutral wave numbers, has been carried out. Several characteristic scenarios for the development of such disturbances are presented.

A multiobjective surrogate-assisted optimisation and exploration of low-boom supersonic transport planforms

Optimal non-planar wing planform geometries for a Mach 2.2 45-seat supersonic transport are generated using Kriging-based Bayesian optimisation techniques on a 22-variable, 3-objective problem for two wing-loading conditions. Sonic boom loudness, drag, and root bending moment are simultaneously minimised at a fixed lift. A Python-based framework is developed for rapid evaluation of designs in a parallel computation environment, automating conceptual geometry generation, optimised mesh griding, Euler CFD evaluation, and thermoviscous atmospheric boom propagation. An empirical turbulent skin friction coefficient is used to correct the Euler drag and an estimate of wave drag is performed. Self-organising maps and polynomial chaos expansion Shapley effects are used to explore the design variables and their associated sensitivities with respect to the design objectives. A geometric centroid-based proxy for trim is used to filter the results; feasible extreme designs and a compromise design are compared and discussed. The results indicate a trade-off between each of the three objectives due to competing design requirements, however an improvement in two of the objective functions is possible by sacrificing the remaining objective. One possible compromise solution reduces the root bending moment coefficient by 25% and the sonic boom loudness by 24% at the cost of a 5% increase in drag.

Dynamic Coefficients of Tilting Pad Bearing by Perturbing the Turbulence Model

Tilting pad bearings are appropriate for the trend of high efficiency and reliability design of rotating machinery due to their high stability. The laminar and turbulent flow states exist in the lubricating oil film of high-speed and heavy-load tilting pad bearings simultaneously. By perturbing the multiple flow state lubrication model with a partial derivative method, together with the pad-pivot structural perturbations, the frequency-dependent stiffness and damping coefficients of tilting pad bearings, embracing the effect of dynamical variations of both turbulence and pressure-viscous, were numerically solved in this research. The importance of each perturbed variable was studied, and the results indicate that the perturbed film thickness included in turbulence coefficients perturbations is significant enough to be taken into account otherwise the equivalent stiffness coefficients will be obviously overestimated. Unlike the perturbed film thickness, the consideration of the perturbed viscosity is optional, because it makes the stiffness and damping coefficients larger at both laminar and turbulent flow states. For a simplified simulation and conservative prediction results, the perturbed viscosity can be neglected.

Modeling of Lateral Flow in CFD for Subchannel Analysis

This paper is aimed at the application of computational fluid dynamics (CFD) calculations for lateral flow modeling in rod bundles of Russian-type pressurized water reactors with hexagonal fuel rod lattice by subchannel analysis under a constant temperature. The subchannel code SUBCAL and CFD code ANSYS Fluent with the Reynolds stress turbulence model, which is capable of solving the anisotropic flow present in rod bundles, are used. Both methods are compared in terms of calculations in rod bundles. The literature review of available experiments of rod bundles suitable for CFD calculation validation follows. This paper describes the created CFD models on a triangular lattice, which are subsequently validated on selected experimental data in a wide range of Reynolds numbers and geometry (pitch-to–rod diameter ratio) together with mesh sensitivity analysis. The main part of this work is to develop a new equation for the lateral flow resistance coefficient for the subchannel code based on CFD calculations. Within these calculations, the turbulent mixing coefficient β for hydraulically smooth rod bundles, which is related to the geometry, and the momentum-energy transfer analogy correction factor ε are also evaluated and for which the equation is subsequently proposed.

A Highly Settled Disk around Oph163131

High dust density in the midplane of protoplanetary disks is favorable for efficient grain growth and can allow fast formation of planetesimals and planets, before disks dissipate. Vertical settling and dust trapping in pressure maxima are two mechanisms allowing dust to concentrate in geometrically thin and high-density regions. In this work, we aim to study these mechanisms in the highly inclined protoplanetary disk SSTC2D J163131.2-242627 (Oph 163131, i ∼ 84°). We present new high-angular-resolution continuum and 12CO ALMA observations of Oph 163131. The gas emission appears significantly more extended in the vertical and radial direction compared to the dust emission, consistent with vertical settling and possibly radial drift. In addition, the new continuum observations reveal two clear rings. The outer ring, located at ∼100 au, is well-resolved in the observations, allowing us to put stringent constraints on the vertical extent of millimeter dust particles. We model the disk using radiative transfer and find that the scale height of millimeter-sized grains is 0.5 au or less at 100 au from the central star. This value is about one order of magnitude smaller than the scale height of smaller micron-sized dust grains constrained by previous modeling, which implies that efficient settling of the large grains is occurring in the disk. When adopting a parametric dust settling prescription, we find that the observations are consistent with a turbulent viscosity coefficient of about α ≲ 10−5 at 100 au. Finally, we find that the thin dust scale height measured in Oph 163131 is favorable for planetary growth by pebble accretion: a 10 M E planet may grow within less than 10 Myr, even in orbits exceeding 50 au.

Numerical assessment of the impact of transverse roughness ribs on the turbulent natural convection in a BIPV air channel

The effect of varying rib geometry on the turbulent natural convective heat transfer coefficient in a BIPV air channel was assessed numerically. The CFD model was validated with experimental data from the literature to within reasonable accuracy. The study investigated parameters such as the rib shape, dimensionless rib height (e/D), dimensionless rib pitch (p/e), and channel inclination angle (θ). In each case, the heat flux is varied from 100 W/m2 – 1000 W/m2. The natural convection heat transfer coefficient on the heated wall is maximized for a vertical channel with triangular rib of e/D = 0.16 and p/e = 8.84. The enhancement in heat transfer afforded by the transverse ribs translates to a reduction of the summer heat gain of up to 35.5%. The natural convection heat transfer coefficient correlates with Ras*(S/H), e/D, p/e and θ to within 15% error.

Numerical analysis of influence of cavitation characteristics in nozzle holes of curved diesel engines

By targeting at the high-pressure common rail nozzle of diesel engines, we put forward a curved nozzle structure, established six groups of nozzle models with different curvatures. By using the CFD software STAR-CCM+, based on the incompressible fluid volume function (VOF) multiphase flow model, applying the K-Epsilon two-layer turbulence model, combined with the Schnerr-Sauer cavitation model, we investigated the degree of influence of the curved nozzle on the cavitation characteristics in the nozzle hole. Cavitation at the inlet, middle and outlet of nozzles was observed under injection pressure of 50, 100 or 150 MPa. The effects of curvature on cavitation were analyzed in detail according to cavitation volume fraction, cavitation volume content, mass flow, turbulent kinetic energy and velocity coefficient. It was found the curved nozzle can significantly reduce the cavitation degree in the nozzle holes, and the larger nozzle bending led to a smaller cavitation degree in the holes. Meanwhile, the average turbulent kinetic energy increased obviously and the average velocity decreased in both the holes and outlet, but the mass flow did not change much.

Experimental determination of the convection heat transfer coefficient in an eccentric annular duct

The use of bayonet tube heat exchangers and heaters is widespread in many industrial applications and an improvement in the heat transfer coefficient may provide benefits over other technologies. This work presents novel experimental results about the turbulent convection heat transfer coefficient of air in the annular section of a bayonet tube for two different configurations: concentric and eccentric tubes. For both configurations, the convection heat transfer coefficient was obtained at different air flow rates, therefore, at different Reynolds numbers. In the case of the eccentric configuration, the angular position of the inner tube was varied to determine the circumferential distribution of the local convective heat transfer coefficient. An increase of the convection coefficient was observed for both configurations at higher Reynolds numbers. Concerning the angular position with regard the inner tube, the largest local convective heat transfer coefficient was obtained at the angular position where the distance between the inner and outer tubes was maximum, yielding a value 22.3% higher than in the case of a concentric annular section. All these experimental results were used to propose a new correlation for the local convective heat transfer coefficient as a function of the Prandtl and Reynolds numbers, the eccentricity, and the angular position of the inner tube, with a maximum discrepancy between correlation and experimental data below 10%.

Implications of inertial subrange scaling for stably stratified mixing

We investigate the effects of the turbulent dynamic range on active scalar mixing in stably stratified turbulence by adapting the theoretical passive scalar modelling arguments of Beguier, Dekeyser & Launder (1978) (Phys. Fluids, vol. 21 (3), pp. 307–310) and demonstrating their usefulness through consideration of the results of direct numerical simulations of statistically stationary homogeneous stratified and sheared turbulence. By analysis of inertial and inertial–convective subrange scalings, we show that the relationship between the active scalar and turbulence time scales is predicted by the ratio of the Kolmogorov and Obukhov–Corrsin constants, provided mean flow parameters permit the two subrange scalings to be appropriate approximations. We use the resulting relationship between time scales to parameterise an appropriate turbulent mixing coefficient $\varGamma \equiv \chi /\epsilon$ , defined here as the ratio of available potential energy ( $E_p$ ) and turbulent kinetic energy ( $E_k$ ) dissipation rates. With the analysis presented here, we show that $\varGamma$ can be estimated by $E_p,E_k$ and a universal constant provided an appropriate Reynolds number is sufficiently high. This large Reynolds number regime appears here to occur at $ {{Re_b}} \equiv \epsilon / \nu N^{2} \gtrapprox 300$ where $\nu$ is the kinematic viscosity and $N$ is the characteristic buoyancy frequency. We propose a model framework for irreversible diapycnal mixing with robust theoretical parametrisation and asymptotic behaviour in this high- $ {{Re_b}}$ limit.

7 February Chamoli (Uttarakhand, India) Rock-Ice Avalanche Disaster: Model-Simulated Prevailing Meteorological Conditions

The present study aims to analyze the high-resolution model-simulated meteorological conditions during the Chamoli rock-ice avalanche event, which occurred on 7 February 2021 in the Chamoli district of Uttarakhand, India (30.37° N, 79.73° E). The Weather Research and Forecasting (WRF) model is used to simulate the spatiotemporal distribution of meteorological variables pre- and post-event. The numerical simulations are carried out over two fine resolution nested model domains covering the Uttarakhand region over a period of 2 weeks (2 February to 13 February 2021). The model-simulated meteorological variables, e.g., air temperature, surface temperature, turbulent heat flux, radiative fluxes, heat and momentum transfer coefficients, specific humidity and upper wind patterns, were found to show significant departures from their usual patterns starting from 72 h until a few hours before the rock-ice avalanche event. The average 2 m air and surface temperatures near the avalanche site during the 48 h before the event were found to be much lower than the average temperatures post-event. In-situ observations and the ERA5-Land dataset also confirm these findings. The total turbulent heat flux mostly remained downward (negative) in the 72 h before the event and was found to have an exceptionally large negative value a few hours before the rock-ice avalanche event. The model-simulated rainfall and Global Precipitation Measurement (GPM, IMERG)-derived rainfall suggest that the part of the Himalayan region falling in the simulation domain received a significant amount of rainfall on 4 February, around 48 h prior to the event, while the rest of the days pre- and post-event were mostly dry. The results presented here might be helpful in further studies to identify the possible trigger factors of this event.

ВПЛИВ ФІЗИЧНИХ І ОКЕАНОГРАФІЧНИХ ФАКТОРІВ НА РОЗШИРЕННЯ ЗОНИ ЗАБРУДНЕННЯ КАСПІЙСЬКОГО МОРЯ (ПІВНІЧНО-СХІДНА ПРИБЕРЕЖНА ЗОНА АЗЕРБАЙДЖАНУ)

Aim. Our main goal is to study the spread of pollution caused by natural and anthropogenic factors in the water area of the Caspian Sea, the largest closed basin in the world, according to physical and oceanographic factors. The methodological basis of the article. The article uses methods of processing statistical indicators and selects the Brooks-Koch method to calculate the rise height (∆H0) of wastewater in a stratified environment. Results. In the water area of the Republic of Azerbaijan, the pollution of the Caspian Sea occurs mostly in the Absheron Peninsula. The main reason for this is that the area is rich in oil and gas reserves and there are many oil production enterprises. In addition to natural factors such as wind, temperature and currents, anthropogenic factors also influence the spread of oil-contaminated seawater. As a result of the analysis of the physical and oceanographic factors, we determined that the depth of sewage should be more than 70 meters when it is discharged into the sea. The main reason for this is that the sewage dumped in the depth is mixed with the cold, and with time, heavy bottom currents. As sewage mixed with clean seawater rises to the surface, it continues to mix in the intermediate layers because its weight is heavier than the layer above it. The main reason why this happens only in the Caspian Sea is that the temperature of the sea water increases instead of decreasing with depth. The fact that the turbulent mixing coefficient calculated for the area confirmed in the article is 104-106 shows that the concentration pulsation intensifies with the increase in the diameter of the sewage sludge. This situation creates conditions for the mixing of waste water with the surrounding water. Scientific novelty. The effect of physical and oceanographic factors on the change, expansion and deepening of the area of sewage in the Caspian Sea water area was studied. Also, the turbulent diffusion coefficient of pollution in coastal zones was calculated.

Mechanism analysis of magnetohydrodynamic control in hypersonic turbulent flow

Under the assumption of the low magnetic Reynolds number, the coupled model is established for the turbulent flow field and the externally applied magnetic field. The AUSMPW+ scheme and LUSGS method are used to solve turbulent magnetohydrodynamics (MHD) flow equations, in which the Spalart-Allmaras one-equation turbulence model is used. A series of numerical simulations over various geometry configurations, namely, a flat plate and a compression corner, is conducted by using an external electromagnetic field. Results show that the performance of MHD boundary layer flow control is determined mainly by the Lorentz force in the streamwise direction. With an external magnetic field used, the low velocity fluid in the boundary layer can decelerate and increase the static temperature locally. Moreover, the counter-flow Lorentz force always brings a negative effect on the turbulent skin friction coefficient, and the location for the MHD zone has a great influence on the control efficiency of the ramp-induced separation. A reasonable magnetic field layout scheme should be configured in practical engineering application.

Power generalization of the linear constitutive equations of heat and mass transfer and the variants of writing the equations of momentum transfer, heat and diffusion arising from them

Currently, when solving problems of heat and mass transfer, linear constitutive equations are used - in hydrodynamics, the viscous stress tensor is proportional to the strain rate tensor (Newton's rheological ratio), in heat transfer, the heat flux density is linearly related to the temperature gradient (Fourier's heat conduction law), in mass transfer, the diffusion flux density proportional to the concentration gradient (Fick's law). When writing these linear governing equations, proportionality coefficients are used, which are called the viscosity coefficient, thermal conductivity coefficient and diffusion coefficient, respectively. Such constitutive equations are widely used to describe the processes of heat and mass transfer in a laminar flow regime. For turbulent flows, these equations are unsuitable, it is necessary to introduce into consideration the empirical turbulent coefficients of viscosity μt, thermal conductivity λt and diffusion Dt. However, to describe turbulent flows, it is possible to go in another way - to modify the linear constitutive relations by giving them a nonlinear power-law form. Two-parameter power-law generalizations of Newton's, Fourier's and Fick's formulas for shear stress, heat flux density and diffusion, which, depending on the value of the exponents, can be used to describe the processes of heat and mass transfer both in laminar and turbulent fluid flow. Also, this generalization can be used to describe the behavior of power-law fluids and flows of polymer solutions exhibiting the Toms effect.

Investigation of fine viscous flow fields in ship planar motion mechanism tests by DDES and RANS methods

The fine large separated flow is a focus in the naval architecture and ocean engineering. In the present study, the CFD solver, naoe-FOAM-SJTU, coupled with delayed detached-eddy simulation (DDES) and Reynolds Averaged Navier-Stokes (RANS) is adopted to simulate the fine viscous flow field in the ship planar motion mechanism (PMM) tests for the benchmark model Yupeng Ship. This paper compares the time histories of forces/moment acting on the hull and their oscillation frequency obtained by Fast Fourier Transform. The predicted results are in good agreement with the experimental data. By comparing the turbulent kinetic energy (TKE) and eddy viscosity coefficient calculated by both numerical methods, the results show that the TKE and eddy viscosity coefficient obtained by DDES method are much less than that achieved by RANS approach. The capacity of four vortex identification methods to capture vortex structures is analyzed in this paper, indicating that the third generation of vortex identification methods (ΩR and Liutex methods) are more suitable for analyzing the flow mechanism in the viscous large separated flow field. The axial Liutex and streamlines on the cutting planes are used to depict the flow around the hull.

Aerodynamic Characteristics Over Fine-Grained Gravel Surfaces in a Wind Tunnel

Gravels can protect soil from wind erosion, however, there is little known about the effects of fine-grained gravel on aerodynamic characteristics of the near-surface airflow. Drag coefficient, wind-speed gradient, and turbulent transfer coefficient over different coverages of gravel surfaces were investigated in a compact boundary-layer wind tunnel. The drag coefficient of the fine-grained gravel surface reached the maximum value at 15% coverage and then tended to stabilize at gravel coverage 20% and greater. At a height of 4 cm, near-surface airflow on gravel surfaces can be divided clearly into upper and lower sublayers, defined as the inertial and roughness sublayers, respectively. The coefficient of variation of wind speed over gravel surfaces in the roughness sublayer was 8.6 times that in the inertial sublayer, indicating a greater effect of gravel coverage on wind-speed fluctuations in the lower layer. At a height of 4 cm, wind-speed fluctuations under the observed wind speeds were independent of changes in gravel coverage. In addition, an energy-exchange region, where sand particles can absorb more energy from the surrounding airflow, was found between the roughness and inertial sublayers, enhancing the erosional state of wind-blown sand. This finding can be applied to evaluate the aerodynamic stability of the gravel surface in the Gobi Desert and provide a theoretical basis for elucidation of the vertical distributions of wind-blown sand flux.

Parameterization of Sea Surface Drag Coefficient for All Wind Regimes Using 11 Aircraft Eddy-Covariance Measurement Databases

The drag coefficient is essential for calculating the aerodynamic friction between air and sea. In this study, we regress a set of relationships between the drag coefficient and the wind speed for different wind ranges using an observational dataset that consists of 5941 estimates of the mean flow and fluxes from 11 aircraft turbulent measurements over the sea surface. Results show that: (1) the drag coefficient is a power function of wind speed over smooth sea surface when it is no greater than 4.5 ms−1, and the drag coefficient decreases with the increase of wind speed; and (2) for rough sea surface, when the wind speed is greater than 4.5 ms−1 and less than or equal to 10.5 ms−1, the drag coefficient increases linearly with the increase of horizontal wind speed; when the wind speed is greater than 10.5 ms−1 and less than or equal to 33.5 ms−1, the drag coefficient changes parabolically with the increase of wind speed; when the wind speed is greater than 33.5 ms−1, the drag coefficient is constant. Additionally, regressed from drag coefficient, the saturated wind speed threshold is 23 ms−1. Parameterizations of turbulent heat transfer coefficient (Ch) and water vapor transfer coefficient (Ce) are also investigated.

Goldilocks mixing in oceanic shear-induced turbulent overturns

We present a new, simple and physically motivated parameterization, based on the ratio of Thorpe and Ozmidov scales, for the irreversible turbulent flux coefficient $\varGamma _{\mathcal {M}}= {\mathcal {M}}/\epsilon$ , i.e. the ratio of the irreversible rate ${\mathcal {M}}$ at which the background potential energy increases in a stratified flow due to macroscopic motions to the dissipation rate of turbulent kinetic energy $\epsilon$ . Our parameterization covers all three key phases (crucially, in time) of a shear-induced stratified turbulence life cycle: the initial, ‘hot’ growing phase, the intermediate energetically forced phase and the final ‘cold’ fossilization decaying phase. Covering all three phases allows us to highlight the importance of the intermediate one, to which we refer as the ‘Goldilocks’ phase due to its apparently optimal (and so neither too hot nor too cold, but just right) balance, in which energy transfer from background shear to the turbulent mixing is most efficient. The value of $\varGamma _{\mathcal {M}}$ is close to 1/3 during this phase, which we demonstrate appears to be related to an adjustment towards a critical or marginal Richardson number for sustained turbulence ${\sim }0.2\text {--}0.25$ . Importantly, although buoyancy effects are still significant at leading order for the turbulent dynamics during this intermediate phase, the marginal balance in the flow ensures that the turbulent mixing of the (density) scalar is nevertheless effectively ‘locked’ to the turbulent mixing of momentum. We present supporting evidence for our parameterization through comparison with six oceanographic datasets that span various turbulence generation regimes and a wide range of geographical location and depth. Using these observations, we highlight the significance of parameterizing an inherently variable flux coefficient for capturing the turbulent flux associated with rare energetic, yet fundamentally shear-driven (and so not strongly stratified) overturns that make a disproportionate contribution to the total mixing. We also highlight the importance of representation of young turbulent patches in the parameterization for connecting the small scale physics to larger scale applications of mixing such as ocean circulation and tracer budgets. Shear-induced turbulence is therefore central to irreversible mixing in the world's oceans, apparently even close to the seafloor, and it is critically important to appreciate the inherent time dependence and evolution of mixing events: history matters to mixing.

Numerical Simulation of Turbulent Mixing of LBE between Sub-Channels of Wire-Wrapped Fuel Assembly

The lead-bismuth eutectic (LBE) is a candidate coolant for the fourth generation liquid metal reactors. In view of its special thermophysical properties, its flow and heat transfer process in the fuel assembly sub-channels need to be studied. For this purpose, the authors conduct numerical simulation and analysis of the turbulent flow of the LBE in the wire-wrapped fuel assembly, and compare the numerical simulation results of the wall temperature of fuel rods with the experimental data for response. The simulation results agree well with the experimental data, indicating that the mathematical model and numerical results are highly reliable and accurate. The authors also characterize the turbulent mixing of LBE between different sub-channels at different values of the ratio of spacing between fuel rods to the fuel rod diameter (S/D), using the turbulent mixing coefficient β. The characterization results show that the fluctuation of β between different sub-channels varies and that the β value is negatively correlated with the S/D. Based on different calculation results of the S/D and Renolyd number, the correlation formula for the β between different sub-channels is obtained by fit. It provides a turbulent mixing model for the development of a sub-channel analysis code of fuel assembly consisting of wire-wrapped fuel rods arranged in triangular form.