Derivation of a decorrelation timescale depending on source distance for inhomogeneous turbulence in a shear dominated planetary boundary layer

In the literature there exists a variety of pollution of dispersion models and in general, Lagrangian stochastic models are efficient and fundamentals tools in the investigation and study of turbulent diffusion phenomenon in the planetary boundary layer. The LAMBDA model is one of them. In this study, the influence of decorrelation time scales in the LAMBDA model under neutral conditions is evaluated. To this end a new parameterization of decorrelation time scales is proposed and validated. This method is based on the Eulerian velocity spectra and a formulation of the evolution of the Lagrangian decorrelation timescales. A spectral distribution of an Eulerian velocity profile and a formulation of the evolution of Lagrangian decorrelation timescales under neutral conditions is used as the forcing mechanisms (shear-dominated boundary layer) for the turbulent dispersion. The model performance was established by comparing the levels of ground-level concentrations of the tracer gas with experimental results from the classical Prarie Grass experiment

Investigation With Large-eddy Simulation of the Sea Breeze Regimes

Neste trabalho, investigam-se as interações entre a brisa marítima e a turbulência sobre a Terra empregando uma simulação dos grandes turbilhões (LES). Os resultados mostram que o modelo LES é capaz de similar um regime de brisa Mar-Terra-Mar

Flow in the wake of wind turbines : turbulance spectral analysis by wind tunnel test

The interaction between the incident wind and wind turbines in a wind farm causes mean velocity deficit and increased levels of turbulence in the wake. The turbulent flow is characterized by the superposition of wind turbine wakes. In this work, the technique of turbulence spectral evaluation for reduced scale models in a boundary layer wind tunnel is presented, and different measurements of velocity fluctuations are analysed. The results allow evaluating the spectrum for different frequency ranges and the differences of the spectral behaviour between the incident wind and the turbine wake flow

Wind tunnel experiments with neutral and convective boundary layer stabilities

The present contribution reports on the status of the STROMA experiment. As a novelty a new experimental setup in a wind tunnel allows to simulate different stability regimes with vertical heat flux in either direction. This is accomplished upon inserting a metal sheet equipped with Peltier elements into the floor of the experimental section II of the Prof. Joaquim Blessmann wind tunnel at LAC-UFRGS (Porto Alegre, Rio Grande do Sul state, Brazil). We show results and compare findings for two velocity magnitudes (1 Hz and 4 Hz) and with neutral and convective stability regime. Effects in the turbulent velocity field are presented with its dependence on height

Fluctuating velocity measurements in the turbulent wake of a wind turbine model

An experimental study of the turbulent wake of a wind turbine model was realized at the “Joaquim Blessmann” wind tunnel of the UFRGS. The turbine model was developed at the Universidade de Caxias do Sul and it represents a three blade turbine characterized by a NACA 4412 aerodynamic profile. Measurements of the velocity fluctuations were realized by hot wire anemometry. Complexity of the turbulent flow is evaluated by mean and fluctuating velocity profiles. The influence of the incident flow turbulence and the flow reconstructing process are analysed by the measurement results

Analysis of thermal and roughness effects on the turbulent characteristics of experimentally simulated boundary layers in a wind tunnel

The aim of this paper is to analyse the thermal effects in a wind tunnel experiment to simulate the planetary boundary layer (PBL). Experiments were performed in the wind tunnel of the Laboratory of Constructions Aerodynamics at the Federal University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul State, Brazil. This wind tunnel is a closed return low-speed wind tunnel specifically designed for dynamic and static studies on civil construction models. As a novelty, one of the experimental sections of the wind tunnel was equipped with a metal sheet with Peltier elements coupled to it. In other words, thermal effects generating new flow patterns become feasible and open pathways to compare wind tunnel simulations to those in the PBL. Furthermore, measurements obtained with the smooth floor of the wind tunnel were repeated under the same conditions with the addition of the roughness in the floor, and the mechanical turbulence generated by the surface roughness significantly amplified the exchange of momentum and heat between the regions located in vertical direction of the wind tunnel boundary layer. In the presence of turbulent heat flux near the surface, thermal effects contribute to the increase of the turbulence intensity. Turbulent energy spectra for flow velocities and different heights were obtained using the Hilbert–Huang transform method, and the observed convective turbulence energy spectra behavior reproduced those measured in an unstable surface PBL

Validação de uma Nova Função de Autocorrelação para Descrever o Meandro do Vento Horizontal

O objetivo deste trabalho é  validar experimentalmente uma nova função de autocorrelação para o fenômeno de meandro do vento.

Employing wind tunnel data to evaluate a turbulent spectral model

In this study, spectra obtained from wind tunnel data are compared with a model that describes observed atmospheric neutral spectra. The investigation points out that there is a good conformity between both spectra for the whole turbulent frequency domain. This result is significative since that the spectral model was obtained using only turbulent quantities measured in the planetary boundary layer. This similitude occurring with wind tunnel and atmospheric data furnishes a way to obtain connections between wind tunnel and atmospheric turbulent observations. The results, presented in this analysis, confirm the hypothesis that turbulence parameters observed in wind tunnel, can simulate real wind data measured in atmosphere

Turbulent coeficients identification under convective and neutral condittions

An inverse analysis is used to identify the vertical eddy coefficient. The inverse solution is performed minimizing an objective function: the square difference between experimental and model data added to a regularization function. Three different optimization methods are utilized. The inverse methodology is tested with synthetic data corruped with white Gaussian noise. RESUMO: Uma análise inversa é realizada para identificar o coeficiente de difusão vertical. A solução inversa é obtida minimizando uma função objetivo, a diferença quadrática entre dados experimentais e do modelo matemático, associados a uma função de regularização. Três métodos de otmização são utilizados. A metodologia inversa é testada com dados sintéticos perturbados por um ruído branco gaussiano, simulando dados experimentais

Derivation of an eddy diffusivity depending on a source distance for vertically inhomogeneous turbulence in a convective boundary layer

Accounting for the current knowledge of the convective boundary layer structure and characteristics, a new formulation for the eddy diffusivities to be used in atmospheric dispersion models has been derived. That is, expressions for the eddy diffusivities, depending on source distance, for inhomogeneous turbulence are proposed. The classical statistical diffusion theory, the observed spectral properties, and observed characteristics of energycontaining eddies are used to estimate these parameters. In addition, a vertical eddy diffusivity was introduced into an air pollution model, validated with the data of Copenhagen experiments, and compared with an improved Gaussian model. The results of this new method are shown to agree with the measurements of Copenhagen and also with those of the Gaussian model. Furthermore, the current study suggests that the inclusion of the memory effect, important in regions near an elevated continuous point source, improves the description of the turbulent transport process of atmospheric contaminants. The major advance shown in this paper is the necessity of including the downwind distance-dependent eddy diffusivity in air quality modeling, and it is demonstrated that such theory would suggest that it should yield better results than the asymptotic solution alone. It, in fact, does yield better results in the near and intermediate fields