Adriane Prisco Petry

Large eddy simulation of three-dimensional turbulent flows by the finite element method

The main objectives of this work are the formulation, implementation and applications of a numerical algorithm to simulate turbulent, incompressible, isothermal flows. The transient three-dimensional flow is analyzed using an explicit Taylor-Galerkin scheme and the finite element method with hexahedrical eight-node element. Turbulence is simulated using Large Eddy Simulation. For sub-grid scales two models were implemented, the classical Smagorinskys model and the dynamic eddy viscosity model. For the second filtration, which is necessary in the dynamic model, a new method was developed based on independent finite elements that involve each node in the original mesh. The implemented scheme is efficient and good results with low additional computational cost were obtained. Results for two classical problems, the driven cavity and the backward facing step are presented. Comments about the model applicability for flows with high Reynolds numbers are also presented.

Estudio Numérico de Flujos Turbulentos Isotérmicos en Canales y Flujos Laminares con Convección Mixta en Cavidades

A numerical study about three-dimensional steady state turbulent channel flows and laminar transient cavity flows with mixed convection heat transfer has been done. The solution of the conservation equations is obtained by means of Finite Element Method and Taylor-Galerkin explicit scheme. Large Eddy Simulation is employed for the treatment of turbulence. For the isothermal case, flows with Re = 3300 were simulated using the Smagorinsky and Dynamical subgrid models. The latter model allowed improving the average velocity profiles as well as turbulence statistics. The transient velocity and temperature fields were compared with results of the literature, leading to a deviation lower than 6%.

A Numerical Study of the Influence of Temperature Fluctuations in the Thermal Radiation Field

The present paper performs a numerical study of the influence of fluctuations on the temperature field over the thermal radiation field with the purpose to simulate the effect of Turbulence-Radiation Interactions (TRI). To evaluate the behaviour of the divergence of radiative heat flux for a flame in a cylindrical cavity, four temperature profiles are imposed: an average temperature profile and other three with 10%, 20% and 30% of turbulence intensity. The radiative transfer equation is solved using the discrete ordinates method (DOM) and the participating medium is treated as a gray gas. The results achieved demonstrate that the fluctuations of temperature profiles increase significantly the mean divergence of the radiative heat flux in comparison with the average temperature profile, reaching to approximately 20% for the profile with 30% of turbulence intensity.

INFLUÊNCIA DO REFINAMENTO DA MALHA NOS COEFICIENTES DE ARRASTO, SUSTENTAÇÃO E TORQUE ESTÁTICO DE UMA TURBINA SAVONIUS DE ÚNICO ESTÁGIO

Este trabalho apresenta o estudo numerico computacional do escoamento de ar sobre um rotor eolico de eixo vertical baseado no modelo Savonius, em condicoes estaticas, afim de comparar os efeitos gerados nos coeficientes de arrasto, sustentacao e torque ao ser variado o refinamento da malha empregada no dominio computacional, para diferentes angulacoes de incidencia de vento. Foi necessario construir um modelo numerico representativo da turbina em questao, considerando o efeito da turbulencia. O software GAMBIT ® foi utilizado para confeccionar o dominio computacional, definir as condicoes de contorno e criar duas diferentes malhas, sendo uma definida como grosseira e outra refinada. O software FLUENT ® foi empregado para realizacao da simulacao numerica baseada no Metodo dos Volumes Finitos, adequando a metodologia utilizada em outros trabalhos, afim de obter os coeficientes de arrasto, sustentacao e torque, e compara-los com a literatura existente. O escoamento e incompressivel, permanente e turbulento. As equacoes de conservacao de massa e quantidade de movimento medias no tempo (Reynolds Averaged Navier-Stokes) sao resolvidas atraves do metodo dos volumes finitos. Com relacao ao fechamento da turbulencia e aplicado o modelo k - ω SST. A cada simulacao, o ângulo das pas em relacao a incidencia de vento e alterado em 30o, de 0 o a 150o. Foram realizadas 6 simulacoes para cada malha. Comprovou-se que a utilizacao de uma malha com maior numero de elementos e estruturada proxima as paredes do rotor tem extrema importância na convergencia dos coeficientes para resultados validos e com boa concordância com os valores obtidos por outros autores. Palavras-chave: Simulacao Numerica, turbina Savonius, coeficientes estaticos, ângulo de incidencia, refinamento da malha.

EXPERIMENTAL EVALUATION OF THE AERODYNAMIC PERFORMANCE OF TURBINES SMALL WIND CONFECTIONED IN PROTOTYPING 3D

This paper presents the evaluation of wind tunnel two small wind turbines features five blades. To this end, using 3D prototyping, builds up a model in reduced scale, which was first evaluated using Optimal Blade Betz and Optimal Blade Betz Modified. Before evaluating equipment as the velocity distribution was determined in the tunnel cross section through a Pitot tube. With the known tunnel velocity profile, it determined the static torque of the model with the use of a digital torquimeter coupled to the machine shaft, which recorded readings for all speed ranges from 1 m/s to 10 m/s. Also with the torquimeter assessed the influence of the angular position of the blades in the measured torque. Therefore, they are designed mobile in the hub, allowing vary their angle in the outflow, thereby changing the angle of attack and therefore the produced torque. Employs a photo tachometer for measuring the rotation of the model in free spin. With the data, determines the static torque curve and the RPM curve as a function of incident speed. Through experimental determination of the incident velocity profile and the velocity profile in the aerodynamic wake of each turbine is evaluated the variation of the amount of movement of the outflow is determined by the power extracted rotors for free rotation. This study is the first experimental stage for determining the power curve. The second phase will comprise the experimental determination of the dynamic torque with and without charging. The experimental results demonstrate torque and power good approximation to the results obtained by evaluation by analytical element of the paddle method. The turbine constructed with Optimal Betz Blades presented static torque 17.8% higher than constructed with the Modified Blades and extracted 22% more power outflow.

Guidance on choosing a measuring instrument for indoor particle pollution studies

The possibility of acquiring real-time concentration data is leading many indoor air quality and health researchers to the use of particle measuring instruments instead of the classic filtration approach. This paper summarizes a checklist of characteristics that have to be considered on the selection of such instruments and checks the compliance of three air monitoring devices suitable for environmental exposure researches. An evaluation table with desirable instrument technical, economic, and logistics characteristics was summarized in a checklist, and spec sheets of three air monitoring devices suitable for environmental exposure researches were checked. Technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. Only one instrument was in comply with it. A popular air monitoring device among environmental exposure researchers was checked and it failed the accuracy check. When selecting a particle measuring instrument, technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. When selecting an instrument for a study, a lack of information on the quality of results is a strong indication that it should not be considered, as studys response may be compromised.The possibility of acquiring real-time concentration data is leading many indoor air quality and health researchers to the use of particle measuring instruments instead of the classic filtration approach. This paper summarizes a checklist of characteristics that have to be considered on the selection of such instruments and checks the compliance of three air monitoring devices suitable for environmental exposure researches. An evaluation table with desirable instrument technical, economic, and logistics characteristics was summarized in a checklist, and spec sheets of three air monitoring devices suitable for environmental exposure researches were checked. Technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. Only one instrument was in comply with it. A popular air monitoring device among environmental exposure researchers was checked and it failed the accuracy check. When selecting a particle measuring instrument, technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. When selecting an instrument for a study, a lack of information on the quality of results is a strong indication that it should not be considered, as studys response may be compromised.