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Multispecies mixing processes play an important role in many engineering, biological, and environmental applications. Since simulating mixing flows can be useful to understand its physics and to study industrial issues, this work aims to develop the basis of a methodology able to simulate the physics of multiple-species mixing flows, using a hybrid large eddy simulation/Lagrangian filtered density function (FDF) method on an adaptive, block-structured mesh. A computational model of notional particles transport on a distributed processing environment is built using a parallel Lagrangian map. This map connects the Lagrangian information with the Eulerian framework of the in-house code MFSim, in which transport equations are solved. The Lagrangian composition FDF method, through the Monte Carlo technique, performs algebraic calculations over an ensemble of notional particles and provides composition fields statistically equivalent to those obtained by finite volume numerical solution of partial differential equations. Finally, to maintain high accuracy in the system of stochastic differential equations solver when an adaptive mesh refinement environment is used, a methodology for ensuring mass conservation is developed to preserve at least the statistical moments up to order two, even in the case of annihilation or cloning of a large number of notional particles in one time step, ensuring the applicability of Lagrangian FDF methods in dynamically adaptive grid refinement.

Hydropower plant (HPP) operation may influence downstream flow regimes, which can affect the fish movement. In South America, tailrace fisheries are often killed or injured when interacting with spillways and turbines. Hydrodynamic flow-pattern studies are essential to facilitate mitigation. We developed a computational fluid dynamics model to investigate flow downstream of Três Marias HPP (Brazil). Included in the model were the draft tubes, tailrace and a 3-km river reach. We simulated a common scenario consisting of three active turbines on the right side of the powerhouse (109.6, 108.0 and 108.0m3s–1) and three inactive turbines, by using Ansys Fluent (ver. 12). We identified a straight discharge plume from the right-most turbine that was constrained by the right-side wall. Further, there was the generation of significant plumes from Turbines 2 and 3. The maximum velocities in these plumes appears not to be a barrier for Pimelodus maculatus and Prochilodus costatus, because their prolonged swimming speeds for their maximum total length were higher than the modelled velocities. The results will support mitigation decisions such as fish passage and turbine-screen design in this particular HPP and may be a model for further studies in the South America.

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Evaporation of liquid droplets in high temperature gas environment is of great importance in many engineering applications. Accurate droplet evaporation predictions are crucial in modeling spray combustion, since it is considered a rate limiting process. For this reason, the present dissertation aims are, first, to implement and validate Lagrangian droplet evaporation models that are usually used in spray calculations, including equilibrium and non-equilibrium formulations, and, second, to use these models to pursue a deeper insight on the physical phenomena that may be involved in droplet evaporation processes. In order to validate and assess these theoretical model predictions, an in-house code was developed and diameter evolution results from the numerical simulations are compared to experimental data. First, the model performance is evaluated for water in a case of low evaporation rate and, then, it is evaluated for n-heptane in moderate and high evaporation rates using recent experimental data acquired with a new technique. The Abramzon-Sirignano model is the only one which does not overestimate the evaporation rate for any ambient condition tested, when compared with experimental rate. From the results, it is also revealed that, when a correction factor for energy transfer reduction due to evaporation is incorporated in the classical evaporation model, the predictions from this model and the nonequilibrium one cannot be differentiated, even if the initial droplet diameter is small. Furthermore, the incorporation of natural and forced convection effects on the droplet evaporation rate, by using an empirical correlation, is investigated, showing that including the Grashof number into the Ranz-Marshall correlation actually overestimates the evaporation rate for atmospheric pressure. Finally, the effects of ambient conditions on ethanol evaporation are investigated. Under ambient temperatures higher than the threshold temperature, the evaporation rate is enhanced with the increase of ambient pressure, contrary to what happens for cases when the ambient temperature is lower than the threshold temperature.

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