Analytical solutions for the temperature field in a 2D incompressible inviscid flow through a channel with walls of solid fuel

A gas (oxidizer) flows between two parallel walls of solid fuel. A combustion is initiated: the solid fuel is vaporized and a diffusive flame occurs. The hot combustion products are submitted both to thermal diffusion and convection. Analytical solutions can be obtained both for the velocity and temperature distributions by considering an equivalent mean temperature where the density and the thermal conductivity are evaluated. The main effects of heat transfer are due to heat convection at the flame. Because the detailed mechanism of the diffusion flame is not introduced the reference chemical reaction is the combustion of premixed fuel with oxidizer in excess. In exchange the analytical solution is used to define an ideal quasi-uniform combustion that could be realized by an n adequate control. The given analytical closed solutions prove themselves flexible enough to adjust the main data of some existing experiments and to suggest new approaches to the problem

Estimation of Wind Tunnel Corrections Using Potential Models

The evaluation of the tunnel correction remains an actual problem, especially for the effect of tunnel walls. Even if the experimental campaign meets the basic similitude criteria (Mach, Reynolds etc.), the wall effect on the measured data is always present. Consequently, the flow correction due the limited by walls must be evaluated. Solid wall corrections refer to the aerodynamic interference between the experimental model and the walls of the wind tunnel. This interaction affects the measured forces and implicitly the angle of attack. Usually, these effects are introduced through semi-empirical correction factors which change the global measured forces. The present paper refers to the mathematical and numerical modeling of aerodynamic interferences between the experimental model and the solid walls based on the potential flow model. The main goal is to asses a method allowing an estimate of the corrections for each configuration with a minimum computational resource

Using genetic algorithms to optimize airfoils in incompressible regime

Aerodynamic optimization is a very actual problem in aircraft design and airfoils are basic two-dimensional shape forming cross sections of wings. Traditionally, the airfoil geometry if defined by a very large number of coordinates. Nowadays, in order to simplify the optimization, the airfoil geometry is approximated by a parametrization, which enables to reduce the number of needed parameters to as few as possible, while effectively controlling the major aerodynamic features. The present work has been done on the Class-Shape function Transformation method (CST) [1, 2]. Also, the paper introduces the concept of Genetic Algorithm (GA) to optimize a NACA airfoil for specific conditions. A Matlab program has been developed to implement CS into the Global Optimization Toolkit. The pressure distribution lift and drag coefficients of the airfoil geometries have been calculated using two programs. The first one is an in-house code based on the Hess-Smith [3] panel technique and on the boundary layer integral equations, while the second is an XFOIL program. The optimized airfoil has improved aerodynamic characteristics as compared to the original one. The optimized airfoil is validated using the Ansys-Fluent commercial code

On Lean Turbulent Combustion Modeling

This paper investigates a lean methane-air flame with different chemical reaction mechanisms, for laminar and turbulent combustion, approached as one and bi-dimensional problem. The numerical results obtained with Cantera and Ansys Fluent software are compared with experimental data obtained at CORIA Institute, France. First, for laminar combustion, the burn temperature is very well approximated for all chemical mechanisms, however major differences appear in the evaluation of the flame front thickness. Next, the analysis of turbulence-combustion interaction shows that the numerical predictions are suficiently accurate for small and moderate turbulence intensity

Mathematical and numerical modeling of inverse heat conduction problem

The present paper refers to the assessment of three numerical methods for solving the inverse heat conduction problem: the Alifanov’s iterative regularization method, the Tikhonov local regularization method and the Tikhonov equation regularization method, respectively. For all methods we developed numerical algorithms for reconstruction of the unsteady boundary condition imposing some restrictions for the unsteady temperature field in the interior points. Numerical tests allow evaluating the accuracy of the considered methods

Unsteady effects at the interface between impeller-vaned diffuser in a low pressure centrifugal compressor

In this paper, Proper Orthogonal Decomposition (POD) is applied to the analysis of the unsteady rotor-stator interaction in a low-pressure centrifugal compressor. Numerical simulations are carried out through finite volumes method using the Unsteady Reynolds-Averaged Navier-Stokes Equations (URANS) model. Proper Orthogonal Decomposition allows an accurate reconstruction of flow field using only a small number of modes; therefore, this method is one of the best tools for data storage. The POD results and the data obtained by the Adamczyk decomposition are compared. Both decompositions show the behavior of unsteady rotor-stator interaction, but the POD modes allow quantifying better the numerical errors

Assessment of some high-order finite difference schemes on the scalar conservation law with periodical conditions

Supersonic/hypersonic flows with strong shocks need special treatment in Computational Fluid Dynamics (CFD) in order to accurately capture the discontinuity location and his magnitude. To avoid numerical instabilities in the presence of discontinuities, the numerical schemes must generate low dissipation and low dispersion error. Consequently, the algorithms used to calculate the time and space-derivatives, should exhibit a low amplitude and phase error. This paper focuses on the comparison of the numerical results obtained by simulations with some high resolution numerical schemes applied on linear and non-linear one-dimensional conservation low. The analytical solutions are provided for all benchmark tests considering smooth periodical conditions. All the schemes converge to the proper weak solution for linear flux and smooth initial conditions. However, when the flux is non-linear, the discontinuities may develop from smooth initial conditions and the shock must be correctly captured. All the schemes accurately identify the shock position, with the price of the numerical oscillation in the vicinity of the sudden variation. We believe that the identification of this pure numerical behavior, without physical relevance, in 1D case is extremely useful to avoid problems related to the stability and convergence of the solution in the general 3D case

Assessment of three WENO type schemes for nonlinear conservative flux functions

This paper focuses on a new comparison of the behavior of three Weighted Essentially Non-Oscillatory (WENO) type numerical schemes for three different nonlinear fluxes, in the case of scalar conservation law. The analytical solution is provided for various boundary conditions. For the time integration we adopt the 4-6 stage Low-Dispersion Low-Dissipation Runge-Kutta method (LDDRK 4-6). The schemes were tested on piecewise constant function for non-periodical conditions. The assessment was performed because the specialized literature mainly presents cases favorable illustrating only to a particular method while our purpose is to objectively present the performance and capacity of each method to simulate simple cases like scalar conservation law problems. All the schemes accurately identify the position of the shock and converge to the proper weak solution for the non-linear fluxes and different initial conditions. The paper is a continuation of the efficiency and accuracy analysis of high order numerical schemes previously published by the authors [1,2]

Accurate measurements and analysis of the thermal structure of turbulent methane/air premixed flame

WOS:000377911100042International audienceThis paper provides further experimental and numerical results concerning the premix turbulent combustion of lean methane-air mixture. For V-shaped flame, the experimental data were acquired by two-dimensional Rayleigh scattering technique. The main purpose of this investigation is to obtain quantitative information on the instantaneous thermal structure of the flame front for both laminar and turbulent conditions. Four values for turbulence intensity have been considered. The flame surface density is closely related to the two-dimensional temperature gradient. For turbulent combustion, a general decreasing trend of averaged temperature gradient was observed. However, this tendency is inverted for very high turbulence intensity when the instantaneous temperature gradient presents high fluctuations. The flame front thickness PDF and the curvature PDF decrease with the turbulence intensity. The joint PDF of curvature and the maximum of the progress variable's gradient have the tendency to rotate counterclockwise with the increase of turbulence intensity. Negative curvature brings more energy in preheat zone of flame and enhances combustion; consequently the temperature gradients increase. (C) 2016 Published by Elsevier Ltd