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The turbulent boundary layer in a viscous incompressible fluid developing longitudinally past the surface of a thin cone or cylinder at a finite distance from the laminar–turbulent transition zone is studied. The characteristic Reynolds number, determined from the external flow velocity and the length of the body, is assumed to be large, and the thickness of the boundary layer is small and comparable to the radius of the body. The asymptotic method of multiple scales is used to find solutions to the Navier–Stokes equations. Instead of the traditional decomposition of the solution into time-averaged values and their fluctuations, the velocities and pressure are expressed as an asymptotic series consisting of steady and perturbed terms. As a result, the viscous steady flow (‘secondary’) that arises in the boundary layer as a mandatory component of fast turbulent fluctuations was described. Analytical and numerical solutions for the radial steady velocity are presented, describing the self-induced suction of fluid from the external flow into the boundary layer. Further analytical solutions are obtained for the longitudinal and circumferential velocities, which differ markedly from the laminar regime. The solutions found are somewhat similar to the degenerate (one-dimensional) case of self-sustaining longitudinal thin structures in turbulent shear flows. A qualitative comparison with direct numerical simulations is presented. [ABSTRACT FROM AUTHOR]

This paper focuses on the numerical modelling of the autoignition process in an ethanol-air mixture within a turbulent droplet-laden temporally evolving mixing layer, utilising the Large Eddy Simulation (LES) method. We compare results obtained by implementing two notably distinct discretisation methods (second-order Total Variation Diminishing – TVD, and fifth-order Weighted Essentially Non-Oscillatory – WENO) in the species and energy transport equations. Additionally, we examine three widely recognised evaporation models (the ' $ D^2 $ D 2 ' model, the Abramzon–Sirignano model, and a non-equilibrium model based on the Langmuir-Knudsen law). For modelling the combustion process, we employ the Eulerian Stochastic Field method and a laminar chemistry model. The simulations encompass two droplet diameter distributions, one with low and the other with significant diameter non-uniformity. Furthermore, nine distinct initial conditions are considered. Our findings indicate that adjusting the discretisation scheme or the evaporation model can yield simulation outcomes differing to a substantial degree, similar to the impact of modifying the actual properties of the spray droplets or their initial distribution. This is particularly pronounced in the case of sprays featuring a narrowed droplet diameter distribution. We found that the Abramzon–Sirignano model results in the most rapid autoignition. The TVD scheme contributes to a more even spatial distribution of the evaporated fuel, consequently facilitating quicker evaporation and faster autoignition. Using the WENO scheme generates higher fuel vapor gradients near the droplets, leading to less intense evaporation and slower fuel transport in space. [ABSTRACT FROM AUTHOR]

A new high-flow, compact aerosol concentrator, using rapid, turbulent mixing to grow aerosol particles into droplets for dry spot sample collection, has been designed and tested. The "TCAC (Turbulent-mixing, Condensation Aerosol Concentrator)" is composed of a saturator for generating hot vapor, a mixing section where the hot vapor mixes with the cold aerosol flow, a growth tube where condensational droplet growth primarily occurs, and a converging nozzle that focuses the droplets into a beam. The prototype concentrator utilizes an aerosol sample flow rate of 4 L min−1. The TCAC was optimized by varying the operating conditions, such as relative humidity of the aerosol flow, mixing flow ratio, vapor temperature, and impaction characteristics. The results showed that particles with a diameter ≥ 25 nm can be grown to a droplet diameter > 1400 nm with near 100% efficiency. Complete activation and growth were observed at relative humidity ≥ 25% of the aerosol sample flow. A consistent spot sample with a diameter of D90 = 1.4 mm (the diameter of a circle containing 90% of the deposited particles) was obtained regardless of the aerosol particle diameter (dp = 20–1900 nm). For fiber counting applications using phase contrast microscopy, the TCAC can reduce the sampling time, or counting uncertainty, by two to three orders of magnitude, compared to the 25-mm-filter collection. The study shows that the proposed mixing-flow scheme enables a compact spot sample collector suitable for handheld or portable applications, while still allowing for high flow rates. [ABSTRACT FROM AUTHOR]

Turbulence is a fundamental process that drives mixing and energy redistribution across a wide range of astrophysical systems. For warm (T≈104 K) plasma, the material is partially ionized, consisting of both ionized and neutral species. The interactions between ionized and neutral species are thought to play a key role in heating (or cooling) of partially ionized plasmas. Here, mixing is studied in a two-fluid partially ionized plasma undergoing the shear-driven Kelvin–Helmholtz instability to evaluate the thermal processes within the mixing layer. Two-dimensional numerical simulations are performed using the open-source (PIP) code that solves for a two-fluid plasma consisting of a charge-neutral plasma and multiple excited states of neutral hydrogen. Both collisional and radiative ionization and recombination are included. In the mixing layer, a complex array of ionization and recombination processes occur as the cooler layer joins the hotter layer, and vice versa. In localized areas of the mixing layer, the temperature exceeds the initial temperatures of either layer with heating dominated by collisional recombinations over turbulent dissipation. The mixing layer is in approximate ionization-recombination equilibrium, however the obtained equilibrium is different to the Saha–Boltzmann local thermal equilibrium. The dynamic mixing processes may be important in determining the ionization states, and with that intensities of spectral lines, of observed mixing layers. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

Although the roll-streak (R-S) is fundamentally involved in the dynamics of wall turbulence, the physical mechanism responsible for its formation and maintenance remains controversial. In this work we investigate the dynamics maintaining the R-S in turbulent Poiseuille flow at R = 1650. Spanwise collocation is used to remove spanwise displacement of the streaks and associated flow components, which isolates the streamwise-mean flow R-S component and the second-order statistics of the streamwise-varying fluctuations that are collocated with the R-S. This partition of the dynamics into streamwise-mean and fluctuation components facilitates exploiting insights gained from the analytic characterization of turbulence in the second-order statistical state dynamics (SSD), referred to as S3T, and its closely associated restricted nonlinear dynamics (RNL) approximation. Symmetry of the statistics about the streak centreline permits separation of the fluctuations into sinuous and varicose components. The Reynolds stress forcing induced by the sinuous and varicose fluctuations acting on the R-S is shown to reinforce low- and high-speed streaks, respectively. This targeted reinforcement of streaks by the Reynolds stresses occurs continuously as the fluctuation field is strained by the streamwise-mean streak and not intermittently as would be associated with streak-breakdown events. The Reynolds stresses maintaining the streamwise-mean roll arise primarily from the dominant proper orthogonal decomposition (POD) modes of the fluctuations, which can be identified with the time average structure of optimal perturbations growing on the streak. These results are consistent with a universal process of R-S growth and maintenance in turbulent shear flow arising from roll forcing generated by straining turbulent fluctuations, which was identified using the S3T SSD. [ABSTRACT FROM AUTHOR]

Space plasma turbulence is inherently characterized by anisotropic fluctuations. The generalized k-th order correlation tensor of magnetic field increments allow us to separate the mixed isotropic and anisotropic structure functions from the purely anisotropic ones. In this work, we quantified the relative importance of anisotropic fluctuations in solar wind turbulence using two Alfvénic data samples gathered by the Solar Orbiter at 0.8 astronomical units. The results based on the joined statistics suggest that the anisotropic fluctuations are ubiquitous in solar wind turbulence and persist at kinetic scales. Using the R T N coordinate system, we show that their presence depends on the anisotropic sector under consideration, e.g., the R N and R T sectors exhibit enhanced anisotropy toward kinetic scales, in contrast with the T N . We then study magnetic field fluctuations parallel and perpendicular to the local mean magnetic field separately. We find that perpendicular fluctuations are representative of the global statistics, resembling the typical picture of magnetohydrodynamic turbulence, whereas parallel fluctuations exhibit a scaling law with slope ∼1 for all the joined isotropic and anisotropic components. These results are in agreement with predictions based on the critical balance phenomenology. This topic is potentially of interest for future space missions measuring kinetic and MHD scales simultaneously in a multi-spacecraft configuration. [ABSTRACT FROM AUTHOR]

In this paper, we investigate two-dimensional direct numerical simulations of a transcritical shear layer. Three configurations are chosen, which are distinguished by the level of presence of two-phase phenomena. The thermodynamic model is based on a cubic equation of state. It was extended for multicomponent mixtures, and it is able to account for vapor–liquid equilibrium. The thermodynamic modeling with phase-transition is validated using experimental data from the literature. Special focus is put on the effect of the density gradient and the density changes caused by phase-transition on the development of the turbulent shear layer and the associated mixing. In addition to this, the vorticity distribution and the components of its transport equation are analyzed and compared for the different configurations. [ABSTRACT FROM AUTHOR]

We apply the scale-relativity theory of turbulence to the turbulent boundary layer problem. On the basis of Kolmogorov's scaling, the time derivative of the Navier–Stokes equations can be integrated under the form of a macroscopic Schrödinger equation acting in velocity-space. In this equation, the potential coming from pressure gradients takes the form of a quantum harmonic oscillator (QHO) in a universal way. From the properties of QHOs, we can then derive the possible values of the ratio of turbulent intensities in the shear flow, R = σ u / σ v = 1.35 ± 0.05. We show that the Karman constant is theoretically predicted to be κ = 1 / R 3 , in good agreement with its typical value κ ≈ 0.4 and its observed possible variations. Then, we find a generic solution of our equations for the normal Reynolds stress pure profile, which closely fits the data from laboratory and numerical experiments. Its amplitude, μB, is the solution of an implicit equation that we solve numerically and analytically through power series, yielding to lowest order μ B − 1.35 ≈ − 2 (R − 1.35) , plus smaller contributions from other parameters. Consequently, the correlation coefficient of velocities is given by ρ ≈ 1 / R μ B 2 ≈ 1 / R 3 ≈ 0.4 and is therefore equal to the Karman constant to lowest order, in agreement with its universally measured value ≈ 0.4 for all shear flows. We also find a general similarity between turbulent round jets and boundary layers in their outer region. These results therefore apply to a wide set of turbulent flows, including jets, plane boundary layers, and, to some extent, channels and pipes. [ABSTRACT FROM AUTHOR]

The reciprocal energy and enstrophy transfers between normal fluid and superfluid components dictate the overall dynamics of superfluid 4He including the generation, evolution and coupling of coherent structures, the distribution of energy among lengthscales, and the decay of turbulence. To better understand the essential ingredients of this interaction, we employ a numerical two-way model which self-consistently accounts for the back-reaction of the superfluid vortex lines onto the normal fluid. Here we focus on a prototypical laminar (non-turbulent) vortex configuration which is simple enough to clearly relate the geometry of the vortex line to energy injection and dissipation to/from the normal fluid: a Kelvin wave excitation on two vortex anti-vortex pairs evolving in (a) an initially quiescent normal fluid, and (b) an imposed counterflow. In (a), the superfluid injects energy and vorticity in the normal fluid. In (b), the superfluid gains energy from the normal fluid via the Donnelly–Glaberson instability. [ABSTRACT FROM AUTHOR]

While yearly budgets of CO2 flux (Fc) and evapotranspiration (ET) above vegetation can be readily obtained from eddy‐covariance measurements, the separate quantification of their soil (respiration and evaporation) and canopy (photosynthesis and transpiration) components remains an elusive yet critical research objective. In this work, we investigate four methods to partition observed total fluxes into soil and plant sources: two new and two existing approaches that are based solely on analysis of conventional high frequency eddy‐covariance (EC) data. The physical validity of the assumptions of all four methods, as well as their performance under different scenarios, are tested with the aid of large‐eddy simulations, which are used to replicate eddy‐covariance field experiments. Our results indicate that canopies with large, exposed soil patches increase the mixing and correlation of scalars; this negatively impacts the performance of the partitioning methods, all of which require some degree of uncorrelatedness between CO2 and water vapor. In addition, best performances for all partitioning methods were found when all four flux components are non‐negligible, and measurements are collected close to the canopy top. Methods relying on the water‐use efficiency (W) perform better when W is known a priori, but are shown to be very sensitive to uncertainties in this input variable especially when canopy fluxes dominate. We conclude by showing how the correlation coefficient between CO2 and water vapor can be used to infer the reliability of different W parameterizations. Plain Language Summary: Forests and vegetated ecosystems play a crucial role in the water and carbon cycles. During the day, plants absorb CO2 through photosynthesis (P), releasing water vapor via transpiration (T). On the other hand, the soil underneath contributes to CO2 through respiration (R), and moist soil leads to water evaporation (E). While meteorological towers currently measure total CO2 (Fc = P + R) and water vapor (ET = E + T) exchanges, distinguishing the contributions from soil respiration and evaporation versus tree photosynthesis and transpiration remains a challenge. This study addresses this gap by investigating methods to separate Fc and ET into their individual components. Using a simulated forest environment with a virtual meteorological tower, the study tests four methods to estimate respiration, photosynthesis, evaporation, and transpiration. Results reveal that more reliable estimates are obtained when measurements are collected close to the forest top, especially in the absence of significant vegetation gaps that lead to strong mixing. Additionally, the study highlights the expected errors in two approaches when faced with real‐world uncertainties. By elucidating optimal conditions for method application, this research contributes to advancing our understanding of ecosystem‐atmosphere interactions and informs the accurate measurement of vital components in the carbon and water cycles. Key Points: The performance of four partitioning methods are explored with aid of large‐eddy simulationsThe methods' performance is shown to depend on flux ratios, canopy sparseness, and measurement heightThe correlation coefficient between CO2 and water vapor is shown to help inform the choice of water‐use efficiency models [ABSTRACT FROM AUTHOR]

Direct numerical simulation (DNS) of turbulent wall-bounded flows requires long streamwise computational domains to establish the correct spatial evolution of large-scale structures with high fidelity. In contrast, experimental measurements can relatively easily capture large-scale structures but struggle to resolve the dissipative flow scales with high fidelity. One methodology to overcome the shortcomings of each approach is by incorporating experimental velocity field measurements into DNS as an inflow boundary condition. This hybrid approach combines the strengths of DNS and experimental measurements, allowing for a reduction in the streamwise computational domain and accelerated development of large-scale structures in turbulent wall-bounded flows. To this end, this paper reports the results of an investigation to establish the impact of limited spatial resolution and limited near-wall experimental inflow data on the DNS of a wall-bounded turbulent shear flow. Specifically, this study investigates the spatial extent required for the DNS of a turbulent channel flow to recover the turbulent velocity fluctuations and energy when experimental inflow data is typically unable to capture fluctuations down to the viscous sub-layer or the smallest viscous scales (i.e. the Kolmogorov scale or their surrogate viscous scale in wall-bounded turbulent shear slows) is used as the inflow to a DNS. A time-resolved numerically generated experimental field is constructed from a periodic channel flow DNS (PCH-DNS) at R e τ = 550 and 2300, which is subsequently used as the inflow velocity field for an inflow–outflow boundary conditions DNS. The time-resolved experimental inflow field is generated by appropriately filtering the small scales from the PCH-DNS velocity by integrating over a spatial domain that is representative of a particle image velocimetry interrogation window. This study shows that the recovery of small scales requires a longer domain as the spatial resolution at the inflow decreases with all flow scales recovered and their correct scale-dependent energy is re-established once the flow has developed for 3 channel heights. [ABSTRACT FROM AUTHOR]

This study reports the development and characterization of a multiple-supersonic-jet wind tunnel designed to investigate the decay of nearly homogeneous and isotropic turbulence whose generation process is strongly influenced by fluid compressibility. The interaction of 36 supersonic jets generates turbulence that decays in the streamwise direction. The velocity field is measured with particle image velocimetry by seeding tracer particles with ethanol condensation. Various velocity statistics are evaluated to diagnose decaying turbulence generated by the supersonic jet interaction. The flow is initially inhomogeneous and anisotropic and possesses intermittent large-scale velocity fluctuations. The flow evolves into a statistically homogeneous and isotropic state as the mean velocity profile becomes uniform. In the nearly homogeneous and isotropic region, the ratio of root-mean-squared velocity fluctuations in the streamwise and vertical directions is about 1.08, the longitudinal integral scales are also similar in these directions, and the large-scale intermittency becomes insignificant. The turbulent kinetic energy per unit mass decays according to a power law with an exponent of about 2, larger than those reported for incompressible grid turbulence. The energy spectra in the inertial subrange agree well with other turbulent flows when normalized by the turbulent kinetic energy dissipation rate and kinematic viscosity. The non-dimensional dissipation rate C ε is within a range of 0.56–0.87, which is also consistent with incompressible grid turbulence. The dependence of C ε on the turbulent Reynolds number aligns with the scaling of non-equilibrium turbulence, leading to the large decay exponent. [ABSTRACT FROM AUTHOR]

Experiment and numerical simulation are combined to reveal the influence of the obstacle position on the combustion and explosion characteristics of methane–hydrogen–air mixture in a closed 90° bend pipe. The result shown that the synergistic effect of the obstacle and the hydrogen addition significantly enhances the explosion intensity of the mixed gas. Affected by the turbulent vortex near the obstacle, the flame is distorted significantly when it approaches the obstacles, thus enhancing the flame instability and accelerating the flame transition from layer to turbulence. The relative position between the obstacle and the elbow has an obvious influence on the excitation of flame propagation. When the distance between the obstacle and the elbow is more than 6 times the diameter of the pipe, the closer the obstacle is to the ignition end, the stronger the excitation effect. When the obstacle is located behind the elbow, the excitation effect of the obstacle on the flame propagation is weak. The maximum explosive overpressure in a 90° bend is influenced by the coupling of obstacles and elbows. The research results can provide theoretical guidance for the safety and explosion protection of hydrogen transportation in industrial sites. [ABSTRACT FROM AUTHOR]

Predictions are presented of mean values of statistical variables of large-scale turbulent flow of the widely used basic k- ϵ model, and of a new model, which is based on general statistical descriptions of turbulence. The predictions are verified against published results of direct numerical simulations (DNSs) of Navier–Stokes equations. The verification concerns turbulent channel flow at shear Reynolds numbers of 950, 2000, and 10 4 . The basic k- ϵ model is largely based on empirical formulations accompanied by calibration constants. This contrasts with the new model, where descriptions of leading statistical quantities are based on the general principles of statistical turbulence at a large Reynolds number and stochastic theory. Predicted values of major output variables such as turbulent viscosity, diffusivity of passive admixture, temperature, and fluid velocities compare well with DNS for the new model. Significant differences are seen for the basic k- ϵ model. [ABSTRACT FROM AUTHOR]

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

Anthropogenic carbondioxide (CO2) emissions are a major factor in global warming, requiring significant cuts to combat climate change. A crucial technology to reduce global CO2 concentration is direct air capture (DAC) of CO2. However, existing DAC techniques are expensive because of low CO2 concentrations, and they frequently rely on fossil fuel-based energy. In this article, we investigate how wind turbines can influence local CO2 levels and potentially collaborate with DAC and other technologies. To explore this idea, we performed large-eddy simulations using two 5 MW commercial-scale wind turbines. We incorporated realistic CO2 profiles collected from 13 different global locations across different seasons. The simulations were performed under neutral atmospheric boundary layer conditions. The results demonstrate that the wake recovery mechanism of a wind turbine promotes rapid mixing of CO2 both above and below the turbine blade tips in the wind turbine wake. In cases where the initial concentrations of CO2 were elevated above the turbine, downward entrainment of CO2 occurred. Conversely, when high concentrations of CO2 were present in the lower atmosphere, wind turbines facilitated a decrease in concentration at that layer by up to 138 kg/m within the intermediate wake (within 7 diameters) of the second turbine, T2. These discoveries inspire further investigation into the potential synergies between wind turbines and DAC devices or local CO2 pollutant diverters, depending on the prevailing CO2 profile. Consequently, this article marks the initial showcase of wind turbines' capability to influence CO2 levels by creating an entrainment and removal effect. [ABSTRACT FROM AUTHOR]

The setting machine exhaust gas contains a large number of fiber particles and micro oil droplets, which are adhesive and flammable. This leads to difficulties in waste heat recovery of the exhaust gas. In this article, numerical and experimental studies of a non-uniform plate heat exchanger with dimples/protrusions for waste heat recovery of setting machines are carried out. Based on the three-dimensional fluid-thermal-structural coupling method, the regenerative process between gas and air are investigated numerically with low Reynolds number turbulence model. The effect of the structural parameters (protrusions diameters, protrusions spacing and plate spacing) and operation parameters (air inlet temperature, gas and air flow rate) on the heat transfer performance are discussed. The multi-objective optimization of the plate regenerator is conducted by Box-Behnken Design and Nondominated Sorting Genetic Algorithm II to maximize the thermal performance coefficient and minimize entransy dissipation number. It is found that when D1, H1 S1, D2, H2, S2 are 9 mm, 7 mm, 161 mm, 9 mm, 8 mm and 153 mm respectively, the heat exchanger has the best heat transfer performance. Compared with the original model, the heat transfer rate of the optimized heat exchanger is increased by 3.9%, the thermal performance coefficient of the air side and flue gas side is increased by 5.7% and 5.9% respectively, and the entransy dissipation number is reduced by 24.6%. [ABSTRACT FROM AUTHOR]

We explore the role of intermittent aerosol forcing (e.g., injections associated with marine cloud brightening) in the stratocumulus-to-cumulus transition (SCT). We simulate a 3 d Lagrangian trajectory in the northeast Pacific using a large-eddy simulation model coupled to a bin-emulating, two-moment, bulk microphysics scheme that captures the evolution of aerosol and cloud droplet concentrations. By varying the background aerosol concentration, we consider two baseline systems – pristine and polluted. We perturb the baseline cases with a range of aerosol injection strategies by varying the injection rate, number of injectors, and the timing of the aerosol injection. Our results show that aerosol dispersal is more efficient under pristine conditions due to a transverse circulation created by the gradients in precipitation rates across the plume track. Furthermore, we see that a substantial enhancement in the cloud radiative effect (CRE) is evident in both systems. In the polluted system, the albedo effect (smaller but more numerous droplets causing brighter clouds at constant liquid water) is the dominant contributor in the initial 2 d. The contributions from liquid water path (LWP) and cloud fraction adjustments are important on the third and fourth day, respectively. In the pristine system, cloud fraction adjustments are the dominant contributor to the CRE on all 3 d, followed by the albedo effect. In both these systems, we see that the SCT is delayed due to the injection of aerosol, and the extent of the delay is proportional to the number of particles injected into the marine boundary layer. [ABSTRACT FROM AUTHOR]

A novel three-equation turbulence model has been proposed as a potential solution to overcome some of the issues related to the k–ε models of turbulence. A number of turbulence models found in the literature designed for compressed turbulence within internal combustion engine cylinders tend to exhibit limitations when applied to turbulent shear flows, such as those occurring through intake or exhaust valves of the engine. In the event that the flow is out of equilibrium where Pk deviates from ε, the turbulence models require a separate turbulence time-scale determiner along with the dissipation, ε. In the current research, this is accomplished by resolving an additional equation that accounts for turbulence time scale, τ. After presenting the rationale behind the model, its application to three types of free shear flows were given. It has been shown that the three-equation k–ε–τ model outperforms the standard k–ε model as well as a number of two-equation models in these flows. Initially, the k–ε–τ model handles the issue of the plane jet/round jet anomaly in an effective manner. Secondly, it outperforms the two-equation models in predicting the flow behavior in the case of plane wake, one that is distinguished by its weak shear form. [ABSTRACT FROM AUTHOR]

The objective of this study was to create a novel 3D coupled numerical model that explores the impact of electromagnetism on the fluctuation of the slag/steel interface during the LF refining process. To evaluate the effects of alternating current power, an AC phasor was introduced to examine the Lorentz force and Joule heating phenomena. Turbulent motion was represented using the large eddy simulation technique, while the volume-of-fluid approach was utilized to illustrate the deformation of the air/slag/steel interface. The discrete phase model and the two-way coupled Euler–Lagrange technique were employed to track the motion of gas bubbles, accounting for bubble collision, coalescence, and breakup. By comparing the simulated results with experimental data, the model's fundamental validity was confirmed. The findings emphasized the importance of concurrently considering both the electromagnetic field and the bubbly flow in the investigation of the LF refining process. It was observed that the Lorentz force played a crucial role in promoting the fluctuation of the slag/steel interface, potentially leading to the absorption of carbon by the molten steel. [ABSTRACT FROM AUTHOR]

Direct numerical simulations are performed to study temporal variations of the wall shear stresses and flow dynamics in the turbulent pulsatile pipe flow. The mechanisms, responsible for the paradoxical phenomenon for which the amplitude of the oscillating wall shear stress in the turbulent flow is smaller than that in the laminar flow for the same pulsation conditions, are investigated. It is shown that the delayed response of turbulence in the buffer layer generates a large magnitude of the radial gradient of the Reynolds shear stress near the wall, which counteracts the effect of the oscillating pressure gradient on the change of the streamwise velocity and hence reduces the amplitude of the wall shear stress. Such a delayed response consists of two processes: the delayed development of near-wall streaks and the subsequent energy redistribution from the streamwise velocity fluctuation to the other two co-existing components. This is a dynamical manifestation of the viscoelasticity of turbulent eddies. As the frequency is reduced, the variation of the friction Reynolds number results in a phase-wise variation of the time scale and intensity of the turbulence response, causing the hysteresis of the wall shear stress. Such a phase asymmetry is amplified by the increase of the pulsation amplitude. An examination of the energy spectra reveals that the near-wall streaks are stretched in the streamwise direction during the acceleration phase, and then break up into small-scale structures in the deceleration phase, accompanied by the enhanced dissipation that transforms the turbulent kinetic energy into heat. [ABSTRACT FROM AUTHOR]

The acoustic characteristic of swirled and non-swirled turbulent inverse diffusion flame (IDF) for hydrogen-methane fuel is experimentally investigated with variation in Reynolds numbers (Re air) and equivalence ratios (Φ). For maintaining adequate working environment, noise characterization of hydrogen-methane fuel IDF is essential. Comparison of sound level indicates significant alteration in acoustic characteristics with change in Re air , Φ and swirl. The swirling IDF is noisier than the non-swirling IDF at the same Re air and Φ. The sound level increases by 9.9% for swirling and 10.2% for non-swirling IDFs with a surge in Re air. The variation of Φ (0.6 ≤ Φ ≤ 1.4) indicates that the noise of IDF with swirl is higher (an increase of 13.14%) than non-swirling IDF (an increase of 1.43%). Shearing of flow induced by swirl dominates sound generation. For swirling IDF, the rise in sound level is 3.67% when methane is blended with H 2 from 0% to 10%. • Effect of Swirl, momentum and hydrogen addition on acoustic of IDF is analysed. • Flow shear due to swirl increases noise levels. • Hydrogen addition enhances combustion dynamics and thus radiates large sounds. • Sound level of swirled IDF with hydrogen enhances by about 4%. [ABSTRACT FROM AUTHOR]

The efficiency of supersonic combustion is largely dependent on inlet and injection parameters. Additional energy input is required in some off-design conditions, and nanosecond discharge actuation can be a solution. In the present study, a phenomenological model of a nanosecond-pulsed surface dielectric barrier discharge (NS-SDBD) actuator was developed to analyze the combustion enhancement effect for a supersonic combustor with transverse H2 injection. A seven-reaction H2–air combustion model was adopted for the numerical simulation. Dynamic mode decomposition (DMD) was employed to acquire temperature perturbation in spatial and temporal domains. The results show that the actuator provides additional temperature-increment and species transportation through compression waves. The combustion enhancement effect is mainly attributed to the flow perturbation in the shear layer, which promotes the turbulent diffusion of fuel. Given the same power input, the combustion efficiency at the shockwave reflection point is increased by 17.5%, and the flame height is increased by 15.4% at its maximum. [ABSTRACT FROM AUTHOR]

Shear flows in turbulent fluids have been known to act as transport barriers for some time. An example of a shear flow generating mechanism is the E × B shear in plasma, which has a substantial impact on the dynamics of magnetic confinement fusion devices. The influence of this may be seen in the scrape-off layer where blobs or filaments may be sheared and velocity impacted, and in the edge and core of the plasma, where the formation of transport barriers and suppression of turbulence is strongly associated with such shearing effects. A dynamical picture of transport through these effects has been elusive—the development of a reduced model would be beneficial. We consider the application of an "observational" random walk to such transport, in order to determine whether it is a suitable approach upon which to base the development of reduced models. The observational random walk is modification of the random walk approach, introducing an intrinsic time separating observations, which reproduces the basic results of previous random walk models given a Gaussian jump function, assuming spatially homogenous jump function. We demonstrate that the jump function can be inferred from the statistics of passive particles propagated by E × B drift on a synthetic turbulence field and that the transport equation found from the jump function matches the expected diffusive transport very well. We, then, consider passive particles on simulations of the classic and modified Hasagawa–Wakatani equations in a statistical steady state for a variety of adiabaticity values and find normal transport in the near-hydrodynamic limit. When zonal flows appear, we find jump functions with non-Gaussian features, which result in transport equations with fractional differential terms in addition to, or in place of, diffusion terms. We surmise that the non-local fractional terms are related to the zonal flows acting as transport barriers. Overall, we find that the approach developed is a suitable starting point for the development of reduced models. [ABSTRACT FROM AUTHOR]

Invariant solutions of the Navier--Stokes equations play an important role in the spatiotemporally chaotic dynamics of turbulent shear flows. Despite the significance of these solutions, their identification remains a computational challenge, rendering many solutions inaccessible and thus hindering progress towards a dynamical description of turbulence in terms of invariant solutions. We compute equilibria of three-dimensional wall-bounded shear flows using an adjoint-based matrix-free variational approach. To address the challenge of computing pressure in the presence of solid walls, we develop a formulation that circumvents the explicit construction of pressure and instead employs the influence matrix method. Together with a data-driven convergence acceleration technique based on dynamic mode decomposition, this yields a practically feasible alternative to state-of-the-art Newton methods for converging equilibrium solutions. We compute multiple equilibria of plane Couette flow starting from inaccurate guesses extracted from a turbulent time series. The variational method outperforms Newton(-hookstep) iterations in converging successfully from poor initial guesses, suggesting a larger convergence radius. [ABSTRACT FROM AUTHOR]

One of the major factors controlling the phase partitioning in mixed‐phase cloud is entrainment mixing, but it is still poorly understood. In this study, the liquid‐ice mass partitioning across the edge of shallow to moderately deep cumulus clouds are analyzed using airborne measurements. The results show the concentration and water content of both liquid and ice decrease toward the cloud edge. However, the liquid mass fraction remains similar across the cloud. The mechanism responsible for the phase partitioning is that extreme inhomogeneous entrainment‐mixing dominates. This is evident as both the droplet and ice sizes remain similar with changing concentrations. The comparison between the time scale of turbulent mixing and the phase relaxation time of water also suggests the turbulence strength is too low to homogenize the cloud. The findings from this study improve our understanding on the role of entrainment in phase partitioning, and are useful in evaluating model simulations. Plain Language Summary: In mixed‐phase clouds, the coexistence of liquid and ice has significant impacts on the cloud lifecycle and radiative properties, but the phase partitioning in mixed‐phase cloud is still not fully understood. In cumulus clouds, one of the major factors controlling the microphysics across cloud edges is the entrainment of dry air into cloud. During the mixing process, the liquid‐ice partitioning is determined by the mixing type (homogeneous or inhomogeneous), the evaporation (growth) of liquid, and sublimation (growth) of ice. Currently, there is a lack of observational evidence for the main mixing mechanism that controls the phase partitioning. In this study, the liquid‐ice mass partitioning across the edge of shallow to moderately deep cumulus clouds are analyzed using airborne in situ measurements. The results show the liquid mass fraction remains similar across the cloud, and inhomogeneous mixing dominates the phase partitioning. The results improve our understanding on the role of entrainment, and are useful in evaluating model simulations. Key Points: Liquid‐ice mass partitioning across the edges of cumulus clouds is characterized using airborne in situ measurementIn most of the clouds, the liquid and ice water content decrease toward the edge, while liquid mass fraction remains similarThe inhomogeneous mixing dominates the phase partitioning across the cloud edges [ABSTRACT FROM AUTHOR]

The dynamic conformal transformation method has been generalized for the first time to numerically simulate the capillary wave turbulence of a liquid surface in the plane symmetric anisotropic geometry. The model is strongly nonlinear and involves effects of surface tension, as well as energy dissipation and pumping. Simulation results have shown that the system of nonlinear capillary waves can pass to the quasistationary chaotic motion regime (wave turbulence). The calculated exponents of spectra do not coincide with those for the classical Zakharov–Filonenko spectrum for isotropic capillary turbulence but are in good agreement with the estimate obtained under the assumption of the dominant effect of five-wave resonant interactions. [ABSTRACT FROM AUTHOR]

The effect of particle activity on collective excitations in active fluids of microflyers is studied. With an in silico study, we observed an oscillating breakdown of equipartition (uniform spectral distribution) of kinetic energy in reciprocal space. The phenomenon is related to short-range velocity–velocity correlations that were realized without forming of long-lived mesoscale vortices in the system. This stands in contrast to well-known mesoscale turbulence operating in active nematic systems (bacterial or artificial) and reveals the features of collective dynamics in active fluids, which should be important for structural transitions and glassy dynamics in active matter. [ABSTRACT FROM AUTHOR]

Near-surface oceanic turbulence plays an important role in the exchange of mass, momentum, and energy between the atmosphere and the ocean. The climate modifying the air–sea CO 2 transfer rate varies linearly with the surface turbulent kinetic energy dissipation rate to the 1 / 4 power in a range of systems with different types of forcing, such as coastal oceans, river estuaries, large tidal freshwater rivers, and oceans. In the first part of this paper, we present a numerical study of the near-surface turbulent kinetic energy spectra deduced from a direct numerical simulation (DNS) compared to turbulent kinetic energy spectra deduced from idealized infrared (IR) images. The DNS temperature fields served as a surrogate for IR images from which we have calculated the underlying kinetic energy spectra. Despite the near-surface flow region being highly anisotropic, we demonstrated that modeled isotropic and homogeneous turbulence spectra can serve as an approximation to observed near-surface spectra within the inertial and dissipation ranges. The second part of this paper validates our numerical observations in a laboratory experiment. In this experiment, we compared the turbulent kinetic energy spectra near the surface, as measured using a submerged shear sensor with the spectra derived from infrared images collected from above the surface. The energy dissipation measured by the shear sensor was found to be within 20% of the dissipation value derived from the IR images. Numerically and experimentally, we have demonstrated that IR-based and remote measurement techniques of the aquatic near surface offer a potentially accurate and non-invasive way to measure near-surface turbulence, which is needed by the community to improve models of oceanic air–sea heat, momentum, and gas fluxes. [ABSTRACT FROM AUTHOR]

We carry out direct numerical simulation (DNS) of turbulent flow in rough pipes. Two types of irregular roughness are investigated, namely a grit-blasted and a graphite surface. A wide range of Reynolds numbers is tested, from the laminar up to the fully rough regime, attempting to replicate Nikuradse's pioneering study. Despite the large relative roughness, outer-layer similarity is achieved at high Reynolds number as hypothesised by Townsend, with deviations from the smooth wall case of 4 % for the grit-blasted surface and 13 % for the graphite surface. This makes it possible to define a roughness function and the equivalent sand-grain roughness. The results are compared with those obtained in plane channels, with small differences pointing to the residual influence of the duct cross-sectional shape in the presence of relatively large roughness. The computed friction factors behave similar to those Nikuradse's chart, with differences in terms of the friction factor in the laminar region and of the critical Reynolds number, which are partly absorbed by using the hydraulic radius as reference length scale. The distributions of the velocity fluctuations intensities point to a isotropisation of turbulence in the near-wall region resulting from the roughness, with influence of the roughness geometry. Comparison of the computed equivalent sand-grain roughness height suggest that existing correlations suffer from poor predictive power, at least for surfaces with large relative roughness. [ABSTRACT FROM AUTHOR]

The modeling of fluids in the supercritical regime is addressed at conditions characteristic of liquid-propelled rocket engines, whose increasing performance demands paved the way for supercritical conditions. In the present document, nitrogen is used as a surrogate for the commonly encountered oxygen-hydrogen mixture so that turbulence mixing can be looked into without influences from combustion and chemically reacting effects. The temperature field validation on nitrogen coaxial injection at supercritical conditions, with high-velocity ratios (outer-to-inner), where the main (inner) stream is recessed relative to the outer stream, is of paramount importance in the flame stabilization operation of liquid rocket motors. The temperature field is analyzed taking into account varying momentum and velocity ratios, whose increased leads to a reduction of potential core lengths, increasing jet spreading. The results also depict a fundamental influence of thermal effects, dominating over the transport of momentum. The experimental data and large eddy simulation solvers from the literature agree with the estimate of injection velocities at several conditions and comparable to the space shuttle main engine pre-burner. • Transcritical and supercritical injection is studied for single-species coaxial nitrogen injection, taking into account injector heat transfer. • Extension of Banuti and Hannemann analysis, detailing the temperature field. • Characterization of the temperature field at supercritical and transcritical conditions. [ABSTRACT FROM AUTHOR]

Concrete pipes are used widely in sewage pipeline networks due to their superior stiffness, bearing capacity, and low price. However, as the service age increases, the microorganisms inside the pipeline react with the concrete pipe walls and induce concrete pipe wall corrosion. Microbiologically induced corrosion (MIC) is serious corrosion in concrete sewage pipe walls, resulting in a reduction of the wall's thickness and causing the cover soil above the buried pipeline to collapse. The real-time corrosion in concrete sewage pipe walls was simulated in this study. A numerical simulation of the MIC in concrete sewage pipes was performed using the software COMSOL Multiphysics, in which the randomness of the MIC was considered by introducing the random distribution of concrete porosity and corrosive substance concentration; the influence of the turbulence and the transfer rate of H2S were considered by zoning the section of the pipe wall. Combined with the probability density evolution theory, a probability model is proposed to predict the maximum corrosion depth of the concrete sewage pipe wall. The results show that the maximum corrosion depth in the pipeline is more likely to occur in the vicinity of the sewage level and the pipe crown, and its dispersion increases with time and decreases as corrosive substance concentration increases. After verification, the model presented can be used to predict the time-dependent reliability and the service life of concrete sewage pipes. [ABSTRACT FROM AUTHOR]

In high dam construction projects in China, stilling basin design with an abrupt bottom drop is sometimes introduced to reduce the bottom velocity and pressure loads by generating A-type hydraulic jumps. Although the stilling basin design is not new, A-type hydraulic jumps have not been studied taking into account the air entrainment and evolution of internal air–water flow structures. This paper presents an experimental study of self-aerated A-type jumps in terms of bubble transport and free-surface fluctuations over the bottom drop. Four Froude numbers from 4.1 to 10.3 are tested for three drop heights, in addition to the flat-bottom case. Compared to the classic hydraulic jumps, A-jumps are observed with longer jump lengths and weaker free-surface fluctuations. The downward deflection of the jet-shear flow and formation of a bottom roller in the step cavity require a modification to the analytical expression of velocity and void fraction distributions. The relationship between the bubble diffusivity and jump spreading rate differs from that in classic hydraulic jumps, suggesting a faster expansion of the bubble diffusion layer than the turbulent shear flow downstream of the drop, especially for large drop heights. At large approach velocities, the reattachment of the deflected jet-shear flow to the lowered bed may cause a local rise in bubble counts downstream the bottom roller. Further increase in drop height results in a W-jump with overwhelming bottom roller over the surface roller and an arced surface jet, which is beyond the scope of this study. [ABSTRACT FROM AUTHOR]

Ice-nucleating particle concentrations (INPCs) can spread over several orders of magnitude at any given temperature. However, this variability is rarely accounted for in heterogeneous ice-nucleation parameterizations. In this paper, we present an approach to incorporate the random variation in the INPC into the parameterization of immersion freezing and analyze this novel concept with various sensitivity tests. In the new scheme, the INPC is drawn from a relative frequency distribution of cumulative INPCs. At each temperature, this distribution describing the INPCs is expressed as a lognormal frequency distribution. The new parameterization scheme does not require aerosol information from the driving model to represent the heterogeneity of INPCs. The scheme's performance is tested in a large-eddy simulation of a relatively warm Arctic mixed-phase stratocumulus. We find that it leads to reasonable ice masses in the cloud, especially when compared to immersion freezing schemes that yield one fixed INPC per temperature and lead to almost no ice production in the simulated cloud. The scheme is sensitive to the median of the frequency distribution and highly sensitive to the standard deviation of the distribution, as well as to the frequency of drawing a new INPC and the resolution of the model. Generally, a higher probability of drawing large INPCs leads to substantially more ice in the simulated cloud. We expose inherent challenges to introducing such a parameterization and explore possible solutions and potential developments. [ABSTRACT FROM AUTHOR]

To study the mechanism by which an increase in the number of obstacles affects the propagation of hydrogen-air premixed gas explosions under a constant overall volume of obstacles, a large eddy simulation method was used to carry out numerically simulate configurations with different distribution modes of combined obstacles. The study focused on the flame structure, evolution process of overpressure dynamics, and flame-flow coupling relationship. The results showed that the flame propagation velocity and flame front area are increased during the conversion of the combined obstacles from 1-30 mm to 4–7.5 mm, while the flame front area logarithmically depends on the number of obstacles. The flames gradually develop from "corrugated flamelets" to "thin reaction zones" in different distribution modes. In addition, the results showed that although increasing dispersion increases the explosion overpressure, a critical number of obstacles likely exist. Beyond the critical point, explosion overpressure peak no longer strongly varies with the number of obstacles. Furthermore, for working configurations with different numbers of obstacles, an increase in the overall number of obstacles before reaching the same number of obstacles weakly affects the flame shape and flow rate of the flame front. This study provides theoretical guidelines for safety designs to prevent hydrogen-air premixed gas explosion in obstructed spaces. • The accuracy of some premixed combustion simulation results is verified. • Flame modes for different combined obstacles are elucidated. • The coupling relationship between the flame and flow field is analyzed. [ABSTRACT FROM AUTHOR]

A simplified and a numerical mathematical models of gas cooling and water heating in a thin turbulent bubbling layer on a tray with cross-phase flow are presented. The thermal efficiency of gas cooling is found using the ideal displacement model, and the temperature profile in the liquid phase is found from the solution of a cell model or a two-dimensional differential equation of convective heat exchange with an interfacial heat source. Examples of calculating the efficiency of water cooling of gas with different humidity on sieve and valve trays are given. The results of calculations of the thermal efficiency of gas cooling depending on the height of the gas–liquid layer, as well as on the gas velocity in the column are compared with known experimental data. Conclusions are drawn about the adequacy of the mathematical model and of the developed algorithm for calculating the heat and mass transfer characteristics of the bubbling layer. Comparative characteristics of the thermal efficiency of sieve and valve trays are given depending on the gas velocity and different heights of the liquid column. The influence of the variable mass of valves along the length of the tray on the increase in thermal efficiency is shown. Conclusions are drawn on the most efficient designs and modes of operation of bubbling trays. [ABSTRACT FROM AUTHOR]

Turbulent shear flows are abundant in geophysical and astrophysical systems and in engineering-technology applications. They are often riddled with large-scale secondary flows that drastically modify the characteristics of the primary stream, preventing or enhancing mixing, mass and heat transfer. Using experiments and numerical simulations, we study the possibility of modifying these secondary flows by using superhydrophobic surface treatments that reduce the local shear. We focus on the canonical problem of Taylor–Couette flow, the flow between two coaxial and independently rotating cylinders, which has robust secondary structures called Taylor rolls that persist even at significant levels of turbulence. We generate these structures by rotating only the inner cylinder of the system, and show that an axially spaced superhydrophobic treatment can weaken the rolls through a mismatching surface heterogeneity, as long as the roll size can be fixed. The minimum hydrophobicity of the treatment required for this flow control is rationalized, and its effectiveness beyond the Reynolds numbers studied here is also discussed. [ABSTRACT FROM AUTHOR]

We explore the role of intermittent aerosol forcing (e.g., ship tracks, or injections associated with marine cloud brightening) on the stratocumulus-to-cumulus transition (SCT). We simulate a three-day Lagrangian trajectory in the north-east Pacific using a large-eddy simulation model coupled to a bin-emulating, two-moment, bulk microphysics scheme that captures the evolution of aerosol and cloud droplet concentrations. By varying the background aerosol concentration, we consider two baseline systems - pristine and polluted. We perturb the baseline cases with a range of aerosol injection strategies by varying the injection rate, number of injectors, and the timing of the aerosol injection. Our results show that aerosol dispersal is more efficient under pristine conditions due to a transverse circulation created by the gradients in precipitation rates across the plume track. Furthermore, we see that a substantial enhancement in the cloud radiative effect (CRE) is evident in both systems. In the polluted system, the albedo effect (smaller but more numerous droplets causing brighter clouds at constant liquid water) is the dominant contributor in the initial two days. The contributions from liquid water path (LWP) and cloud fraction adjustments are important on the third and fourth day, respectively. In the pristine system, cloud fraction adjustments are the dominant contributor to the CRE on all three days, followed by the albedo effect. In both these systems, we see that the SCT is delayed due to the injection of aerosol, and the extent of the delay is proportional to the number of particles injected into the marine boundary layer. [ABSTRACT FROM AUTHOR]

Electrostatic nonlinear random Langmuir structures have been propagated in stochastic magnetospheres, clouds and solar wind. A theoretical description of Langmuir waves can be modeled by Schrödinger and Zakharov models with stochastic terms. It was explained that the stochastic parameter affects the forcing, collapsing in strongly density turbulence and density crystalline structures. The unified method has been implemented to provide new stochastic solutions for a Zakharov system in subsonic limit with noises via the Itô sense. This unified approach provides a variety of advantages, such as avoiding difficult calculations and explicitly providing pivotal solutions. It is easy to use, efficient, and precise. The induced generated energy during the collapsing of solar Langmuir wave bursts and clouds is determined by the solitonic formations. In addition, the collapsing strong turbulence or forcing density crystalline structures depend mainly on stochastic processes. Furthermore, electrostatic waves in clouds that may collapse are represented sometimes as dissipative shapes. So, the results of this investigation could be applicable to observations of energy seeding and collapsing in clouds. This energy is based on the electrostatic field and its related densities' perturbation in subsonic limits. Finally, it has been explored how noise parameters in the Itô sense affect the solar wind Langmuir waves' properties. So, the findings of this discussion may be applicable to real observations of energy collapsing and seeding in clouds. [ABSTRACT FROM AUTHOR]

Wall-bounded turbulent shear flows are known to exhibit universal small-scale dynamics that are modulated by large-scale flow structures. Strong pressure gradients complicate this characterization, however. They can cause significant variation of the mean flow in the streamwise direction. For such situations, we perform asymptotic analysis of the Navier-Stokes equations to inform a model for the effect of mean flow growth on near-wall turbulence in a small domain localized to the boundary. The asymptotics are valid whenever the viscous length scale is small relative to the length scale over which the mean flow varies. To ensure the correct momentum environment, a dynamic procedure is introduced that accounts for the additional sources of mean momentum flux through the upper domain boundary arising from the asymptotic terms. Comparisons of the model's low-order, single-point statistics with those from direct numerical simulation and well-resolved large eddy simulation of adverse-pressure-gradient turbulent boundary layers indicate the asymptotic model successfully accounts for the effect of boundary layer growth on the small-scale near-wall turbulence. [ABSTRACT FROM AUTHOR]

This paper explores the effects of an abrupt cross-section area change of gas pipes on the propagation law of explosion. For this, an explosion pipe experimental system was established, and a numerical research was conducted. By experimental and numerical simulation, the evolution of the overpressure, temperature, vorticity, and kinetic energy of shock waves of gas explosion in abrupt pipelines was investigated. This allowed us to obtain expressions for the attenuation coefficient, increase coefficient, and reflection coefficient of gas explosion overpressure. The study indicates that an abrupt increase of the pipeline cross-section area leads to a decrease of shock wave overpressure and vice versa. For a given change of cross-section area, the attenuation coefficient gradually increases as the initial peak overpressure rises, whereas the increase coefficient and reflection coefficient both present a decreasing trend. An abrupt change in the pipe structure can inhibit the propagation of gas explosion flames. The explosive gas is affected by the turbulence effect after passing through the middle large-diameter pipe, and the vorticity curve exhibits a clear peak. In addition, the large eddy motion caused by strong confinement increases the kinetic energy of the gas in pipes. The above research outcomes contribute to further enriching the basic theory of gas explosion for the study of gas explosion propagation in mining laneway. [ABSTRACT FROM AUTHOR]

A lean premixed ethylene–air flame in a backstep configuration is simulated on multiple grids using both direct numerical simulations (DNS) with reduced order kinetic mechanism and large eddy simulations (LES) with flamelet-based thermochemistry. The configuration includes preheated reactants and a recirculation zone that provides radicals and high temperature gases to stabilize the flame. Heat losses are present due to the proximity of cooled walls. The reacting flow obtained from DNS at different resolutions is first analyzed to investigate the property of heat transfer within the recirculation region. LES based on adiabatic flamelets with a correction of the heat capacity is then tested, and its ability to account for heat losses is compared to results obtained using a three-dimensional non-adiabatic flamelet approach. Mean fields and subgrid properties are compared to those obtained from DNS to assess the capability of the LES models. The results show that the non-adiabatic flamelet approach can predict recirculation region and temperature fields with good accuracy. The model with heat capacity correction is able to effectively correct the heat capacity behavior as observed by a priori comparisons. However, in the a posteriori context, it is observed to overestimate the temperature field, although the correct size of the recirculation region is predicted. The combined a priori and a posteriori analyses on the same configuration and at different mesh resolutions allow for a precise separation of modeling effects due to heat transfer at the wall and combustion closure, thus providing indications on the LES performance in the context of flamelets. [ABSTRACT FROM AUTHOR]

Carrier-phase direct numerical simulations (DNS) of n-heptane/air combustion with water droplet injection are reported in this paper. The influence of water droplet injection has been analyzed for statistically planar gaseous premixed flames and spray flames where the fuel is supplied in the form of monodisperse fuel droplets. The effects of water injection in both types of flames are compared, including their sensitivities on the initial diameter of water droplets. The simulations are based on an Eulerian-Lagrangian-Lagrangian approach to consider the multi-phase interaction and the simultaneous effects of n-heptane and water droplets. It is shown that the two types of flames are different in terms of several aspects. In particular, the spray flames are characterized by lower temperatures, and their propagation speed is lower than for premixed flames. The main reason for these differences lies in the gaseous equivalence ratio experienced by the reaction zone. For the cases investigated here, where the overall equivalence ratio is unity, the spray combustion occurs under predominantly fuel-lean conditions. Furthermore, the flame temperature is influenced by the initial diameter of water droplets, which affects the strength of thermal expansion within the flame. This in turn influences the evaporation characteristics of both fuel and water droplets due to different residence times within the flame. Although the effects of water droplets on the combustion mode are dependent on the relative position within the spray flame, the net effect is a partial shift from non-premixed to premixed mode. At the same time, the spray combustion occurs under relatively fuel-richer conditions with water injection and these trends appear consistently in laminar and turbulent flows. [ABSTRACT FROM AUTHOR]

The influence of the properties of the profile of a radial static electric field E(r) on the evolution of an unstable ion temperature–gradient (ITG) drift wave in a nonuniformly rotating plasma column in a magnetic field is studied. The effect of symmetry on the decrease in the level of turbulent fluctuations, which are associated with the limiting state of the ITG wave during its destruction, is discussed. The level of turbulence is estimated in the framework of approximation of finite amplitudes depending on the electric field structure. It is shown that the maximum decrease in the level of fluctuations occurs with a symmetrical configuration of the radial electric field. [ABSTRACT FROM AUTHOR]

An expression for the transverse mixing coefficient in a rectangular channel is derived to evaluate the importance of transverse turbulent diffusion. Although some formulas for the transverse mixing coefficient account for both turbulent diffusion and shear dispersion, most calculations of the transverse dispersion coefficient do not include the effect of transverse turbulent diffusion on shear dispersion. Both vertical and transverse turbulent diffusion contribute appreciably to transverse shear dispersion, and the direct contribution of transverse turbulent diffusion to transverse mixing is important for a range of conditions commonly observed in natural channels. A comparison of predicted and measured transverse mixing coefficients supports including turbulent diffusion in analyses of transverse mixing – both in its effect on shear dispersion and as a direct mechanism of transport. [ABSTRACT FROM AUTHOR]

Nepenthes alata‐inspired micro/nano‐textured lubricant‐infused surface (LIS) has shown strong potential in the fields of drag reduction (DR), anti‐biofouling, and self‐cleaning. However, its surface‐slippery property is largely degraded under turbulent shear flow conditions due to the loss of the impregnated oil. This condition inhibits its practical applications to marine vehicles. The mucus‐impregnated tissue systems of marine creatures are primarily based on fatty acid amides (FAAs), such as erucamide or oleamide, which have been commercially utilized as solid‐slip additives. A stable lubricant interface of erucamide‐PDMS composite (EPC) oleogel is formed by cross‐linking erucamide with PDMS gel network prior to infusion of silicon oil. In this study, the surface stability and lubricant retention of EPC are investigated in consideration of DR applications. The fabricated EPC‐oleogel surface exhibits shear stable DR under harsh conditions, such as high pressure, temperature, and shear flow conditions. The surface shows a shear stable DR performance of about 14% even up to a high‐speed flow of 12 ms−1, corresponding to friction Reynolds number (Reτ) of approximately 5000. The superior lubrication stability of FAA‐oleogel at the flow conditions of cruising ships ensures its strong potential for sustainable fuel economy of marine vehicles. [ABSTRACT FROM AUTHOR]