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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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This Special Issue highlights the latest enhancements in the abatement of noise and vibrations in aerospace and automotive systems. The reduction of acoustic emissions and the improvement of interior cabin comfort desired by all major transportation industries, as these areas have a direct impact on customer satisfaction and, consequently, the commercial success of new products. Topics covered in this Special Issue deal with computational approaches, instrumentation and data analysis related to noise and vibrations of fixed-wing aircraft, satellites, spacecraft, automobiles, and trains, covering aerodynamically generated noise, engine noise, sound absorption, cabin acoustic treatments, duct acoustics, and vibroacoustic properties of materials. This Special Issue also focuses on industrial aspects. Existing procedures and algorithms that are useful in reaching the abovementioned objectives in the most efficient way are illustrated in the collected papers.

flexible spacecraft --- periodic disturbance compensation --- compensate torque design --- vibration attenuation --- reaction wheel. --- vibration analysis --- FEM --- multibody simulations --- Plasma flow control --- multichannel discharge --- plasma synthetic actuator --- actuator array --- analytic model --- centrifugal fan --- unsteady flow --- vibroacoustics --- fluid-structure-acoustic coupling --- optimization --- high-speed train --- pantograph --- aerodynamic noise --- large eddy simulation --- acoustic finite element method --- transonic buffet --- tangential slot --- steady and periodic blowing --- postpone of buffet onset --- buffet load alleviation --- component mode synthesis --- petrol engine --- NVH --- FRF --- leakage location --- Lamb wave --- beamforming --- spacecraft in orbit --- vibro-acoustics --- MDO --- aircraft fuselage --- aeroacoustics --- acoustics --- noise --- vibration --- aeronautics --- automotive

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sidewall quenching --- LES --- premixed methane --- flame–wall interaction --- FGM --- Lewis number --- flame curvature --- iso-scalar non-material surfaces --- turbulent premixed spherical flame --- reaction waves --- turbulent reacting flows --- turbulent consumption velocity --- bending effect --- reaction surface area --- molecular transport --- direct numerical simulations --- turbulent flame --- premixed turbulent combustion --- countergradient transport --- flame surface density --- scalar dissipation rate --- modeling --- large eddy simulation --- confined --- boundary layer flashback --- turbulent combustion --- hydrogen --- autoignition modelling --- reduced chemical kinetics --- gasoline surrogates --- engine knock --- spray combustion --- evaporative cooling --- flame surface wrinkling modeling --- thickened flame --- flamelet generated manifold --- n/a --- flame-wall interaction

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The book contains the research contributions belonging to the Special Issue "Numerical Simulation of Wind Turbines", published in 2020-2021. They consist of 15 original research papers and 1 editorial. Different topics are discussed, from innovative design solutions for large and small wind turbine to control, from advanced simulation techniques to noise prediction. The variety of methods used in the research contributions testifies the need for a holistic approach to the design and simulation of modern wind turbines and will be able to stimulate the interest of the wind energy community.

large-scale wind turbine balde --- computational aeroacoustics --- sound source detection --- low Mach number turbulent flows --- NACA0012 airfoil --- fluid–structure interaction --- wind turbine --- atmospheric boundary layer --- composite materials --- gusts --- wind energy --- actuator line method --- wind turbine simulation --- regularization kernel --- small wind turbine (SWT) --- computational fluid dynamics (CFD) --- composites --- fluid–structure interaction (FSI) --- VAWT --- gurney flap --- CFD --- RBF --- power augmentation --- Darrieus --- turbulence --- experiments --- turbine wake --- turbine size --- large-eddy simulation --- actuator surface model --- wind turbine wake --- actuator disk model --- dynamic mode decomposition --- coherent structures --- wake meandering --- vertical axis wind turbine (VAWT) --- Savonius turbine --- deformable blades --- power coefficient --- blade load --- fluid-structure interaction (FSI) --- uncertainty quantification --- blade damage --- AEP --- winglet --- computational fluid dynamics (CFD), wind energy --- renewable energy --- rotor blade --- tip vortices --- aerodynamics --- ansys fluent --- savonius turbine --- icewind turbine --- static torque --- three-dimensional simulation --- Delayed DES --- H-Darrieus --- micro wind power generation --- wind turbine control --- load mitigation --- individual pitch control --- lifting line free vortex wake --- vortex methods --- pitch --- stall --- engineering codes --- n/a --- fluid-structure interaction

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Currently, the use of computational fluid dynamics (CFD) solutions is considered as the state-of-the-art in the modeling of unsteady nonlinear flow physics and offers an early and improved understanding of air vehicle aerodynamics and stability and control characteristics. This Special Issue covers recent computational efforts on simulation of aerospace vehicles including fighter aircraft, rotorcraft, propeller driven vehicles, unmanned vehicle, projectiles, and air drop configurations. The complex flow physics of these configurations pose significant challenges in CFD modeling. Some of these challenges include prediction of vortical flows and shock waves, rapid maneuvering aircraft with fast moving control surfaces, and interactions between propellers and wing, fluid and structure, boundary layer and shock waves. Additional topic of interest in this Special Issue is the use of CFD tools in aircraft design and flight mechanics. The problem with these applications is the computational cost involved, particularly if this is viewed as a brute-force calculation of vehicle’s aerodynamics through its flight envelope. To make progress in routinely using of CFD in aircraft design, methods based on sampling, model updating and system identification should be considered.

numerical methods --- modeling --- aerodynamics --- Taylor–Green vortex --- slender-body --- neural networks --- shock-channel --- wind gust responses --- installed propeller --- bifurcation --- RANS --- wake --- multi-directional --- bluff body --- MDO --- variable fidelity --- computational fluid dynamics (CFD) --- high angles of attack --- aeroelasticity --- computational fluid dynamics --- wind tunnel --- Godunov method --- flow control --- unsteady aerodynamic characteristics --- overset grid approach --- convolution integral --- MUSCL --- DDES --- dynamic Smagorinsky subgrid-scale model --- CPACS --- flutter --- reduced-order model --- meshing --- vortex generators --- hybrid reduced-order model --- microfluidics --- Riemann solver --- characteristics-based scheme --- CFD --- wing–propeller aerodynamic interaction --- kinetic energy dissipation --- Euler --- formation --- square cylinder --- multi-fidelity --- turbulence model --- subsonic --- large eddy simulation --- after-body --- flow distortion --- VLM --- numerical dissipation --- hypersonic --- modified equation analysis --- fluid mechanics --- reduced order aerodynamic model --- p-factor --- URANS --- flexible wings --- chemistry --- detection --- microelectromechanical systems (MEMS) --- angle of attack --- sharp-edge gust --- truncation error --- aerodynamic performance --- quasi-analytical --- gasdynamics --- discontinuous Galerkin finite element method (DG–FEM) --- geometry --- S-duct diffuser