Francisco José de Souza

Large Eddy Simulations of a Hydrocyclone

Subgrid-scale modeling, which characterizes Large Eddy Simulation (LES), has been used to predict the behavior of a water-fed hydrocyclone operating without an air core. The governing equations were solved by a fractional step method on a staggered grid. The Smagorinsky subgrid-scale model was employed to account for turbulent effects. Numerical results actually capture the main features of the flow pattern and agree reasonably well with experiments, suggesting that LES represents an interesting alternative to classical turbulence models when applied to the numerical solution of fluid flows within hydrocyclones.Copyright

A Numerical Analysis of the Turbophoresis in a Turbulent Gas-Particle Flow

Gas-particle flows are very commonly found in pharmaceutical, chemical and petroleum industries. The optimization of the operations involved normally requires a detailed knowledge of the very intrinsic phenomena that take place within the equipment handling the mixture. Once multiphase flows have peculiar characteristics, their behavior should be extensively evaluated. One of these characteristics is the turbophoresis, which occurs in turbulent confined gas-solid flows. The dispersed phase concentrates at the walls and forms a segregated particle flow, where high mass-loading effects become important. Thus, in this work the Euler/Lagrange approach to three-dimensional unstructured meshes is used to numerically assess the turbophoretic effect. The influence of the coupling between phases (two- and four-way coupling) and wall roughness are taken into account. Results show that the particle deposition depends on the coupling and wall roughness. Four-way coupling effects are observed to increase the turbophoresis phenomenon and modify the gas phase dynamics.Copyright

Modelling and simulation of a compression cylinder-piston system with combustion reaction

In flammable gases, due to the energy stored in its molecular bonds, the construction of systems to transform the chemical energy into mechanical energy was possible. These systems were named motor. With the combustion reaction, a high rate of energy is supplied to the system in the form of heat. Expanding it suddenly and due to the action of an external force against this expansion, the movement becomes oscillatory. Within this context, the present paper contributes to the computational simulation and study of sensitivity of the velocity of the piston, the temperature and the density of the gas in the combustion process, in an integral formulation, given equations for mass, energy, momentum and molar concentration balance. The Arrhenius’ equation, numerical methods for solving differentials equations system and integral formulation using Reynolds Transport Theorem (RTT) are also used. The study is done gradually in order to understand in detail all the variables from ideal conditions. The gas is assumed to be ideal, the cylinder is perfectly sealed and the flow is assumed to be instantaneously homogeneous. The system works as a set containing gas, which is compressed by an external force. Initially, there is no friction and the system is considered adiabatic. So it was possible to understand the variation of the parameters in a model that does not lose energy. Conversely, it is conservative. The final system has friction between the piston and the cylinder wall, change of heat through the wall of the system and combustion reaction, then comparison and analysis were done. The first model response is an oscillatory system with perpetual motion, because there is no dissipation and energy is always constant. The last model response is also oscillatory, but the system tends to be static, due to the non conservation of energy. Heat transfer through the cylinder walls was observed and the temperature oscillates, tending to the prescribed temperature. As a response the density decreases, showing that the volume of the system increases, characterizing the behavior of the pressure and temperature of an ideal gas. When the chemical reaction of combustion is added, there is a very sudden increase of the temperature and volume of the system, because the rate of energy was very high.

Particle-Induced Flow Reattachment in a Diffuser

In this work, a numerical investigation on the gas-particle flow in a vertical diffuser is carried out. This study was motivated by the experimental work of Kale and Eaton [1], who noticed that the fully attached flow in a diffuser in the freeboard region of a particle bed would become detached if no particles were present. It was concluded at the time that this effect was not caused by the high inlet turbulence levels, but rather by the particles. With the goal to better understand the interactions between the particles and the fluid in a diffuser, simulations of a dilute particle-laden gas flow in a vertical diffuser are run using the Euler/Lagrange approach. The model, which includes interparticle collisions, the particle influence on the gas phase and wall roughness effects, is first validated based on experimental results from a horizontal channel and a vertical diffuser for both the continuous and dispersed phases at different mass loadings. Investigations on the effects of particles at different mass loadings and wall roughness on the diffuser flow are then carried out. It has been found that, even at moderate mass loadings, particles can significantly affect the diffuser flow pattern, and actually reattach the otherwise separated flow under some conditions. It has also been found that wall roughness plays a very important role in homogenizing the particle distribution at the diffuser section. The resulting more uniform concentration and velocity profiles can then reenergize the otherwise separated boundary layer and reattach it to the wall. The mechanism for the flow reattachment owing to the particle flow and the high wall roughness is investigated and an explanation is proposed.Copyright

Parametric Analysis of Different Nacelle Positions in the DLR-F6 Model by Means of the CFD++ Code

The integration of engines into the aircraft involves many important aspects. These aspects can be investigated by means of wind tunnel experiments or numerical simulations. The main goal of this study is to analyze the effects of different nacelle positions on the aerodynamic coefficients and pressure distributions through numerical simulations. The aircraft geometry investigated is the DLR-F6 configuration. The nacelle is changed from the original configuration to four different positions, which are characterized by distances in the longitudinal and vertical directions. High-quality hexahedral grids are used in the CFD calculations. In order to evaluate the effects of the nacelle shift, all simulations are carried out in the same conditions and the drag, lift and pressure coefficients are evaluated numerically. Interesting results are obtained. The lift coefficient is shown to be more sensitive to variations of nacelle position than the drag coefficient. Based on the simulation results, it can be inferred that the optimum position for the nacelle, among those investigated, is the most forward one.