A. L. De Bortoli

Multigrid based aerodynamical simulations for the NACA 0012 airfoil

The major considerations in the design of effective methods for computational aerodynamics are the capability to treat flows over complex geometrical shapes with proper representation of shock waves, discontinuities and viscous effects. The present work extends the numerical method used to solve compressible flows for the solution of almost incompressible fluid flow. The technique is based on the finite volume explicit Runge-Kutta multistage scheme with central spatial discretization in combination with multigrid and preconditioning. The discretization used follows the cell-centered arrangement of the control volume for the flow variables. Numerical tests are carried out for Mach numbers ranging from 0.8 to 0.002 and the results are found to compare well with analytical/experimental data available in the literature. A spectral radii comparison is also presented and helps to understand what the preconditioning really does with the characteristic variables. Besides, some solutions presented here were obtained for parameter values excluded from the range found in the literature (such as Mach 0.002 over the NACA 0012 airfoil) employing the same preconditioning technique.

Bioethanol combustion based on a reduced kinetic mechanism

Bioethanol is a fuel additive or a fuel substitute that has the benefit of being cleaner and price competitive with gasoline. Therefore, we develop a reduced kinetic mechanism capable of modeling the ethanol combustion and the generation of the combustion products

A new reduced kinetic mechanism for turbulent jet diffusion flames of bioethanol

\text{H}_{2}\text{O},~\text{CO}_{2},~\text{CO},~ \text{H}_{2},~ \text{C}_{2}\text{H}_{4}

Large eddy simulation of a confined jet diffusion flame using a finite difference method

and OH. Based on a mechanism composed by 372 reversible elementary reactions among 56 reactive species, we propose a reduction strategy to obtain an eight-step mechanism for the ethanol. The reduction strategy consists in estimating the order of magnitude of the reaction rate coefficients, defining the main chain, applying the steady-state and partial equilibrium hypotheses, and justifying the assumptions through an asymptotic analysis. The main advantage of the obtained reduced mechanism is the decrease of the work needed to solve the system of chemical equations proportionally to the number of elementary reactions present in the complete mechanism. Numerical tests are carried out for a jet diffusion flame of ethanol and the results compare well with available data in the literature.

Development of a reduced mechanism for ethanol using directed relation graph and sensitivity analysis

This work presents analytical and numerical results for the two dimensional molecular mixing and chemical reaction processes using a vortex formulation. The particular model studied here is the single-step, irreversible, exothermic Arrhenius type reaction cA + cB → cP, in an incompressible fluid under Neumann boundary conditions. We establish the existence of a unique classical solution considering the weak coupling of the reactants via advection by a independently developing velocity, and we prove the existence and uniqueness of the solution via a semigroup formulation and the maximum principle. For the numerical solution a second order accurate spatial finite difference scheme is used with a second order accurate Runge-Kutta method for the time step. The behaviour of the concentrations cA and cB, the temperature, the reaction rate, and product concentration cP, are obtained over a wide range of Reynolds and Damkohler numbers.

Analytical‐Numerical Solution of a H2/N2 Flame Using the Reichardt’s Equation

In the last years, the understanding of the biofuels combustion processes has been facilitated through the progress of asymptotic methods, due to the difficulty of simulating the large number of reactions and species involved in the combustion. To model the molecular mixing and the combustion of a turbulent jet diffusion flame of bioethanol was using a model based on the equations of Navier-Stokes, mixture fraction, mole fraction of species and enthalpy, which are written following the large-eddy simulation approach. The Eulerian formulation is used to solve the equations governing the gas phase. The effect of the droplets of the liquid phase is considered by the introduction of appropriate source terms in the equations of the gas phase. To decrease the stiffness of the reactive system of equations, a reduced kinetic mechanism of bioethanol is developed. The reduced mechanism obtained is tested to simulate a turbulent jet diffusion flame and the results compare favorably with data found in the literature. The reduced mechanism can facilitate the work of researchers in this field, because the methodology developed allows decreasing considerably the time needed to obtain reasonable results for confined turbulent jet diffusion flames of bioethanol.

Numerical simulation of biological base pairs considering geometric and energetic criteria

The aim of this work is the development of a numerical technique for the reduction of reaction mechanisms of common hydrocarbon and oxygenated fuels, such as methane, ethylene, propane, methanol and ethanol, using steady‐state and partial equilibrium assumptions. Numerical tests are carried to establish the basic chain for each fuel as well as to determine the amount of small products of combustion, whose concentration depends on the turbulent mixing and needs to be controlled due to environmental restrictions. The results are in agreement with data in the literature.

Boundary Layer Control by Means of Plasma Actuators

The aim of this work is the development of a low cost numerical technique for confined jet diffusion flames. A convenient formulation based on the mixture fraction for fluid flow and on flamelet models combined with the presumed probability density function for the chemistry is chosen. Numerical tests, for the governing equations discretised by the finite difference explicit Runge-Kutta multistage scheme, were carried out for turbulent, nonpremixed, nonreacting propane-jet flow and for Sandia D flame for reasonable values of gaseous hydrocarbon chemistry. The developed methodology, based on the low Mach number formulation, allows to decrease considerably the time needed to obtain reasonable results for a confined jet diffusion flame.