Effects Of Atmospheric Stratification Research Articles

Effects of atmospheric stratification and jet position on the properties of early aircraft contrails

Effects of atmospheric stratification and jet position on the properties of early aircraft contrails

Numerical and Wind Tunnel Simulation Studies of the Flow Field and Pollutant Diffusion around a Building under Neutral and Stable Atmospheric Stratifications

AbstractIn this paper, the k–ε renormalization group (RNG) turbulence model is used to simulate the flow and dispersion of pollutants emitted from a source at the top of a cubic building under neutral and stable atmospheric stratifications, the results of which were compared with corresponding wind tunnel experiment results. When atmosphere stratification is stable, the separation zones on the sides and at the top of a building are relatively smaller than those under neutral conditions, and the effect of the building in the horizontal direction is stronger than that in the vertical direction. The variation in turbulent kinetic energy under stable conditions is significantly lower than that under neutral conditions. The effect of atmospheric stratification on the turbulent kinetic energy becomes gradually more prominent with increased distance. When atmosphere conditions are stable, the vertical distribution of the plume is smaller than that of neutral conditions, but the lateral spread and near-ground concentration are slightly larger than those of neutral conditions, mainly because stable atmospheric stratification suppresses the vertical motions of airflow and increases the horizontal spread of the plume.

Measurement-Based Numerical Study of the Effects of Realistic Land Topography and Stratification on the Coastal Marine Atmospheric Surface Layer

Large-eddy simulations are used to investigate the effects of coastal topography and atmospheric stratification on the coastal marine atmospheric surface layer at the Field Research Facility in Duck, North Carolina, USA. Field measurements obtained from the CASPER-EAST intensive field campaign in autumn 2015 are used to determine the inlet and lower boundary conditions. The simulations are performed using the in-house Virtual Flow Simulator code, with the simulated mean streamwise velocity component, mean temperature, Reynolds shear stress, and turbulent heat flux, shown to be in good agreement with measurements. In the coastal area, the complex coastal topography leads to an enhancement of the Reynolds shear stress for both onshore and offshore flows, while the effect of atmospheric stratification on the momentum transfer is less significant than the topography. In contrast to the momentum flux, the heat flux is influenced by both the coastal topography and stratification. For onshore flow and stable stratification, the heat flux is significantly increased near the sand dune due to the enhanced turbulence and vertical temperature gradient. For onshore flow and unstable stratification, the strong turbulent mixing tends to enhance the heat flux, but is suppressed by the reduced vertical temperature gradient, such that the magnitude of the turbulent heat flux remains almost unchanged in comparison with the upstream flow. For offshore flow in both stable and unstable stratification, the heat flux is enhanced due to the flow separation at the sand dune.

Modelling the Effects of a Vegetation Barrier on Road Dust Dispersion

Atmospheric particulate matter (PM) is a well known risk to human health. Vehicular traffic is one of the major sources of particulates in an urban setting.We study a problem of road dust dispersion. Using CFD solver based on RANS equations, we investigate the effect of a vegetation barrier on the concentration of airborne PM induced by road traffic. Simplified 2D model of a porous obstacle adjacent to a road source of two classes of particles serves as an idealization of a real-world situation.Filtering efficiency of the barrier is investigated under varying atmospheric conditions. Our model indicate that the efficiency decreases for increasing wind speed. Effect of atmospheric stratification on~the~air quality behind the barrier is shown to be highly dependent on the wind speed.

Large Eddy Simulation of wind farm aerodynamics: A review

To study wind farm aerodynamics (WFA), the Wind Power industry currently relies on simple Engineering Models (EM) that simulate wind farms using basic principles of physics and empirically established approximations. EMs are fast and accurate for an overview of WFA and gauging mean power production, but cannot resolve phenomena like wake meandering, effect of atmospheric stratification on wake development, a turbine׳s response to partial wake interaction and yawed inflows etc., and their relation with turbine loading, which require a first principle physics-based model, namely Computational Fluid Dynamics (CFD). Although advances in computer technology have promoted the application of CFD, the study of WFA is yet unworkable with Direct Numerical Simulation, which is the most comprehensive CFD technique. Thus, as a trade-off between cost and detail, researchers must resort to Large Eddy Simulation (LES) to garner thorough knowledge of WFA, which could in succession help the industry improve engineering models. This paper summarises the contributions of various LES investigations into WFA and how they have helped broaden our understanding of the subject. Additionally, the article touches upon the optimal use of LES and of the resultant data, and also the challenges faced by LES.

Adaptation of Pressure Based CFD Solvers for Mesoscale Atmospheric Problems

General purpose Computational Fluid Dynamics (CFD) solvers are frequently used in small-scale urban pollution dispersion simulations without a large extent of ver- tical flow. Vertical flow, however, plays an important role in the formation of local breezes, such as urban heat island induced breezes that have great significance in the ventilation of large cities. The effects of atmospheric stratification, anelasticity and Coriolis force must be taken into account in such simulations. We introduce a general method for adapting pressure based CFD solvers to atmospheric flow simulations in order to take advantage of their high flexibility in geometrical modelling and meshing. Compressibility and thermal stratification effects are taken into account by utilizing a novel system of transformations of the field variables and by adding consequential source terms to the model equations of incompressible flow. Phenomena involving mesoscale to microscale coupled effects can be analyzed without model nesting, applying only local grid refinement of an arbitrary level. Elements of the method are validated against an analytical solution, results of a reference calculation, and a laboratory scale urban heat island circulation experiment. The new approach can be applied with benefits to several areas of application. Inclusion of the moisture transport phenomena and the surface energy balance are important further steps towards the practical application of the method.

Acoustic sounding of wind velocity profiles in a stratified moving atmosphere.

The paper deals with analytical and numerical studies of the effects of atmospheric stratification on acoustic remote sensing of wind velocity profiles by sodars. Both bistatic and monostatic schemes are considered. Formulas for the Doppler shift of an acoustic echo signal scattered by atmospheric turbulence advected with the mean wind in a stratified moving atmosphere are derived. Numerical studies of these formulas show that errors in retrieving wind velocity can be of the order of 1 m/s if atmospheric stratification is ignored. Formulas for the height at which wind velocity is retrieved are also derived. Approaches are proposed which allow one to take into account the effects of atmospheric stratification when restoring the wind velocity profile from measured values of the Doppler shift and the time interval of acoustic impulse propagation from a sodar to the scattering volume and back to the ground.

Effects of atmospheric stratification on sonic‐boom propagation

Sonic‐boom propagation is affected by stratification, geometrical spreading, nonlinear distortion, absorption and dispersion, and turbulence. Stressed in this paper is stratification, in particular its indirect effect on distortion and absorption. The stratification of the density and sound speed leads to refraction and impedance variation, which play a major role in determining the amplitude of the waveform on the ground. Stratification, and associated spreading, can also control the amount of nonlinear distortion a sonic boom suffers. In extreme cases the amount of nonlinear distortion is finite—a phenomenon known as waveform freezing. Analysis shows that for aircraft in the lower 20 km of the atmosphere waveform freezing does not occur. Through their dependence on temperature, pressure, and humidity, absorption and dispersion are also stratified. A new time domain algorithm, based on a Burgers‐type equation, was developed to analyze the effect of the stratification of absorption [ 3275 (A) (1994)]. The code is used to predict sonic‐boom waveforms on the ground. It is demonstrated that sonic‐boom shocks are affected not just by local absorption but also by absorption along path for the past 5 km or so. [Work supported by NASA.]