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Mountainous regions occupy a significant fraction of the Earth’s continents and are characterized by specific meteorological phenomena operating on a wide range of scales. Being a home to large human populations, the impact of mountains on weather and hydrology has significant practical consequences. Mountains modulate the climate and create micro-climates, induce different types of thermally and dynamically driven circulations, generate atmospheric waves of various scales (known as mountain waves), and affect the boundary layer characteristics and the dispersion of pollutants. At the local scale, strong downslope winds linked with mountain waves (such as the Foehn and Bora) can cause severe damage. Mountain wave breaking in the high atmosphere is a source of Clear Air Turbulence, and lee wave rotors are a major near-surface aviation hazard. Mountains also act to block strongly-stratified air layers, leading to the formation of valley cold-air pools (with implications for road safety, pollution, crop damage, etc.) and gap flows. Presently, neither the fine-scale structure of orographic precipitation nor the initiation of deep convection by mountainous terrain can be resolved adequately by regional-to global-scale models, requiring appropriate downscaling or parameterization. Additionally, the shortest mountain waves need to be parameterized in global weather and climate prediction models, because they exert a drag on the atmosphere. This drag not only decelerates the global atmospheric circulation, but also affects temperatures in the polar stratosphere, which control ozone depletion. It is likely that both mountain wave drag and orographic precipitation lead to non-trivial feedbacks in climate change scenarios. Measurement campaigns such as MAP, T-REX, Materhorn, COLPEX and i-Box provided a wealth of mountain meteorology field data, which is only starting to be explored. Recent advances in computing power allow numerical simulations of unprecedented resolution, e.g. LES modelling of rotors, mountain wave turbulence, and boundary layers in mountainous regions. This will lead to important advances in understanding these phenomena, as well as mixing and pollutant dispersion over complex terrain, or the onset and breakdown of cold-air pools. On the other hand, recent analyses of global circulation biases point towards missing drag, especially in the southern hemisphere, which may be due to processes currently neglected in parameterizations. A better understanding of flow over orography is also crucial for a better management of wind power and a more effective use of data assimilation over complex terrain. This Research Topic includes contributions that aim to shed light on a number of these issues, using theory, numerical modelling, field measurements, and laboratory experiments.

Turbulent fluxes --- Downslope winds --- Large eddy simulation --- Sub-mesoscale circulations --- orographic precipitation --- Thermally-driven flows --- Horizontal inhomogeneity --- Cold air pools --- Hydraulic jumps --- mountain waves

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The air pollution problem inevitably accompanies our human activities. Severe air pollution situations have been reported, especially in emerging countries, and satisfying the air quality standards fully remains an underlying issue. Today, modeling research is one of the more valuable approaches to understanding the behavior of air pollutants, and is useful for regulation-, policy- and decision-making. Such modeling applications range, with regard to horizontal grid resolution, from a few km (local) to hundreds of km (regional), to thousands of km (global). To foster our current scientific knowledge on modeling potentialities and limitations, scientific research related to multi-scale air pollution modeling is collected in this book.

Urban pollution --- Street canyon --- Nitrate aerosol --- CFD --- Air quality --- open burning --- biomass burning --- sugarcane crops --- environmental assessment --- air quality modeling --- chemical reaction model --- urban canyon --- radiation --- mesoscale models --- reactive pollutants --- Community Multiscale Air Quality (CMAQ) --- East Asia --- Tokyo --- SO42– --- stabilized Criegee intermediates (SCI) --- wildfire plume rise --- smoke modeling --- large eddy simulation --- emissions dispersion --- WRF-SFIRE --- RxCADRE --- RePLaT-Chaos --- large-scale atmospheric advection --- chaotic advection --- stretching rate --- escape rate --- education --- CMAQ --- PM10 --- atmospheric reanalysis --- PM2.5 --- PM2.5 components --- three-dimensional chemical transport model --- model inter-comparison --- urban scale --- secondary particles --- WRF-Chem --- visibility --- eastern China --- neural network algorithm --- IMPROVE --- n/a --- SO42 --- -stabilized Criegee intermediates (SCI)

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There is overwhelming evidence, from laboratory experiments, observations, and computational studies, that coherent structures can cause intermittent transport, dramatically enhancing transport. A proper description of this intermittent phenomenon, however, is extremely difficult, requiring a new non-perturbative theory, such as statistical description. Furthermore, multi-scale interactions are responsible for inevitably complex dynamics in strongly non-equilibrium systems, a proper understanding of which remains a main challenge in classical physics. As a remarkable consequence of multi-scale interaction, a quasi-equilibrium state (the so-called self-organisation) can however be maintained. This special issue aims to present different theories of statistical mechanics to understand this challenging multiscale problem in turbulence. The 14 contributions to this Special issue focus on the various aspects of intermittency, coherent structures, self-organisation, bifurcation and nonlocality. Given the ubiquity of turbulence, the contributions cover a broad range of systems covering laboratory fluids (channel flow, the Von Kármán flow), plasmas (magnetic fusion), laser cavity, wind turbine, air flow around a high-speed train, solar wind and industrial application.

non-locality --- hybrid (U)RANS-LES --- channel flow --- thermodynamics --- Lévy noise --- non-local theory --- low speed streaks --- drop breakage --- pipe flow boundary layer --- bifurcation --- Langevin equation --- attached and separated flows --- anomalous diffusion --- kinetic theory --- stochastic processes --- self-organisation --- spatiotemporal chaos --- chaos --- bifurcations --- turbulent flow --- Lyapunov theory --- Rushton turbine --- turbulence --- intermittency --- information length --- denoise --- microcavity laser --- free vortex wake --- IDDES methodology --- local intermittency --- control strategy --- population balance equation --- Tsallis entropy --- coherent structures --- Fokker-Planck equation --- energy cascade --- fluid dynamics --- high efficiency impeller --- fractals --- large eddy simulation --- shear flows --- heat transport --- multifractal --- drop coalescence --- continuous wavelet transform --- T-junction --- scaling properties --- floating wind turbine --- scaling --- fractional Fokker–Plank equation --- magnetic confinement fusion --- multi-scale problem --- coherent structure --- solar wind --- trailing-edge flap --- turbulent transition --- turbulent boundary layer --- complex dynamics --- statistical mechanics

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This reprint focuses on experiments, modellings, and simulations of heat transfer and fluid flow. Flowing media comprise single- or two-phase fluids that can be both compressible and incompressible. The reprint presents unique experiments and solutions to problems of scientific and industrial relevance in the transportation of natural resources, technical devices, industrial processes, etc. In the presented works, the formulated physical and mathematical models together with their boundary and initial conditions and numerical computation methods for constitutive equations lead to solutions for selected examples in engineering.

hydraulic transients --- water hammer --- viscoelasticity --- cross-section change --- fluidic oscillator --- bending angle --- frequency --- pressure drop --- peak velocity ratio --- aerodynamic analyses --- unsteady Reynolds-averaged Navier-Stokes equations --- natural convection --- van der Waals gas --- analytical solution --- heat transfer in non-Newtonian slurry --- damping of turbulence --- Nusselt number for slurry --- heat pipe heat exchanger --- wickless heat pipe --- heat transfer --- individually finned tubes --- heat transfer analysis --- non-contacting mechanical face seal --- variable order derivative integral transform --- ribbed channel --- large eddy simulation --- immersed boundary method --- conjugate heat transfer --- thermal conductivity ratio --- retarded strain --- cavitation --- unsteady friction --- method of characteristics --- vortex generator --- arrangement --- numerical simulation --- plate-fin and tube heat exchanger --- air-side Nusselt number --- different heat transfer coefficient in particular tube row --- mathematical simulation --- CFD simulation --- labyrinth seal --- leakage --- design method --- kinetic energy --- inverse problem --- steam turbines --- gas turbines --- fluid-flow machines --- electric vehicle --- battery thermal management system --- optimization --- lattice Boltzmann method --- hydrostatic transmission --- hydrostatic transmission start up --- hydraulic drive --- n/a

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This Special Issue, consisting of 14 papers, presents the latest findings concerning both numerical and experimental investigations. Their aim is to achieve a reduction in pollutant emissions, as well as an improvement in fuel economy and performance, for internal combustion engines. This will provide readers with a comprehensive, unbiased, and scientifically sound overview of the most recent research and technological developments in this field. More specific topics include: 3D CFD detailed analysis of the fuel injection, combustion and exhaust aftertreatments processes, 1D and 0D, semi-empirical, neural network-based control-oriented models, experimental analysis and the optimization of both conventional and innovative combustion processes.

homogeneous charge compression ignition (HCCI) --- exhaust gas recirculation (EGR) --- dual-fuel --- dimethyl ether (DME) --- exhaust emission --- co-combustion --- dual fuel --- combustion stability --- coefficient of variation of IMEP --- probability density of IMEP --- 0D model --- predictive model --- tumble --- turbulent intensity --- spark-ignition engine --- engine geometry --- AdBlue® injection --- large eddy simulation --- Eulerian–Lagrangian approach --- thermal decomposition --- wall–film formation --- conversion efficiency --- hybrid electric vehicle --- real driving emissions --- fuel consumption --- vehicle performance --- electric supercharger --- Lambda-1 engine --- 48 V Mild Hybrid --- electrically assisted turbocharger --- variable geometry turbocharger-exhaust gas recirculation --- oxygen concentration --- active disturbance rejection control --- model-based --- control --- diesel engine --- ANN --- physics-based model --- semi-empirical model --- CNG --- diesel fuel --- dual fuel engine --- rate of heat release --- ignition delay --- burn duration --- exhaust gas emission --- camless --- electromagnetic variable valve train --- magnetorheological buffer --- soft landing --- solenoid injectors --- indirect-acting piezoelectric injectors --- direct-acting piezoelectric injectors --- engine-out emissions --- combustion noise --- diesel engines --- pollutant emission reduction --- mixing process --- advanced injection strategy --- varying injection rate --- engine torque estimation --- GDI engines --- extended state observer --- online performance --- torque --- nitrogen oxide emissions --- model-based control --- engines --- numerical simulation --- pollutant emissions prediction --- computational fluid dynamics