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http://hdl.handle.net/11422/18
2024-03-20T10:00:08ZNew methodologies for machine learning assisted turbulence based on the transport equations for the Reynolds stress tensor and the Reynolds force vector
http://hdl.handle.net/11422/22093
Title: New methodologies for machine learning assisted turbulence based on the transport equations for the Reynolds stress tensor and the Reynolds force vector
Author(s)/Inventor(s): Macedo, Matheus de Souza Santos
Advisor: Thompson, Roney Leon
Abstract: The long lasting demand for better turbulence models and the still prohibitively computational cost of high- delity uid dynamics simulations, like DNS and LES, have led to a rising interest in coupling available high- delity datasets and popular, yet poor, RANS simulations through Machine Learning techniques. These techniques use noble sources as training targets for predicting quantities to be propagated by RANS equations. Many of the recent advances used the Reynolds stress tensor as the target for these corrections. More recently, an alternate methodology used the divergence of the Reynolds stress, denominated the Reynolds Force Vector, computed indirectly by manipulating mean momentum balance, as the target for the Machine Learning techniques. An unexplored strategy in this e ort is to use transport equations for turbulent quantities fueled by Machine Learning predicted source terms. In this context, two new methodologies were proposed, one using a transport equation for the Reynolds Stress and another one using a transport equation for the Reynolds Force Vector. The combination of these transport equations along with the momentum balance and a pressure coupling formed two data-driven turbulence models. Neural Networks were trained using DNS data to predict the source terms of each equation. Subsequently, both proposed models were employed to correct the turbulent ow on a square-duct. Reasonable results were obtained by both datadriven turbulence models, consistently recovering the secondary ow on the duct, which was not present in the baseline simulations that used the κ - model. Results from both methods were compared with alternate strategies previously presented in literature.
Publisher: Universidade Federal do Rio de Janeiro
Type: Dissertação2020-07-01T00:00:00ZSimulação numérica tridimensional de uma bomba MHD de corrente alternada
http://hdl.handle.net/11422/22092
Title: Simulação numérica tridimensional de uma bomba MHD de corrente alternada
Author(s)/Inventor(s): Campos, Matheus de Abreu Monteiro
Advisor: Colaço, Marcelo José
Abstract: In this work, the numerical simulation of a three-dimensional magnetohydrodynamic (MHD) pump of alternating current is made. The goal of this work is to evaluate the implications caused by the alternating current over the fluid flow and compare them with a direct current case, in which the average Lorentz force exerted by the pump is equivalent. A model for the problem is presented and computationally implemented. The computational model is validated using experimental data available in the literature. During the validation step some turbulence models are evaluated and the most suitable for the alternating current problem is selected. A group of dimensionless numbers is raised in order to improve the problem analysis and justify some simplifications done in the model. At last, a range of frequency from 1 Hz to 50 Hz is simulated. Results show that around 10 Hz there is a high concordance between velocity profiles for DC and AC equivalent cases, while for other frequencies some periodicity is observed. Heating produced by Joule effect is higher for the AC pump and may be critic for its operation. Other quantities as current density and pressure are also evaluated.
Publisher: Universidade Federal do Rio de Janeiro
Type: Dissertação2020-09-01T00:00:00ZEstudo numérico-experimental da gaseificação de pellets de bagaço de cana-de-açúcar em leito fluidizado circulante
http://hdl.handle.net/11422/22091
Title: Estudo numérico-experimental da gaseificação de pellets de bagaço de cana-de-açúcar em leito fluidizado circulante
Author(s)/Inventor(s): Medeiros, Marcelo Ricardo Queiroz
Advisor: Cruz, Manuel Ernani de Carvalho
Abstract: This Thesis object is the development of a 3-D reactive model, multiphase flow, with multiple gaseous and solid species, with heat and mass transfer and standard turbulent k- model. The objective was to predict the syngas composition generated in a circulating fluidized bed gasifier. To achieve these objectives, some activities were done: thermogravimetric analysis (TGA) for sugarcane bagasse drying and devolatilization; experimental gasification tests in a pilot plant; and CFD simulations with Euler-Euler formulation to describe the gasification process. The used methodology were: Arrhenius parameters determination for the pellets drying and devolatilization processes through TGA experiments; and gasification experiments at 850 ° C using an equivalence ratio between 0.25 to 0.29 and a mass flow with steam between biomass ratio of 0.8 to 1.2. The proposed kinetic model contained the main reactions from literature and obtained data in this thesis. The simulations boundary conditions were the non-trivial gasification tests operation conditions. Four gasification models were investigated in this work. The obtained numerical data were compared with experimental data and literature data. The gasification model with the smallest deviation compared to preliminary experimental data was used to simulate the other gasification tests. The results show the evaluation of the interest species of the generated syngas in the gasification experiments.
Publisher: Universidade Federal do Rio de Janeiro
Type: Tese2020-07-01T00:00:00ZAnálise computacional da distribuição de ar em recintos climatizados por métodos de estratificação de temperatura
http://hdl.handle.net/11422/22090
Title: Análise computacional da distribuição de ar em recintos climatizados por métodos de estratificação de temperatura
Author(s)/Inventor(s): Silva, Filipe Oliveira da
Advisor: Brum, Nisio de Carvalho Lobo
Abstract: This work aims to perform an analysis of the flow of the conditioned air supplied in climatized rooms using temperature stratification systems, such as the displacement ventilation. The efficiency of a passive chilled beam is also evaluated as a complementary method for removing sensible heat. It is proposed to evaluate, from results obtained from computational fluid dynamics (CFD), the parameters of thermal comfort in the occupied zone and the effectiveness of these air conditioning techniques, targeting the energy reduction. A validation of the CFD code and a study of the turbulence models are also presented. These air conditioning systems have been modeled and computer simulations are carried out for different scenarios.
Publisher: Universidade Federal do Rio de Janeiro
Type: Dissertação2020-04-01T00:00:00Z