An Irregularly Portioned FDF Solver for Turbulent Flow Simulation

A new computational methodology is developed for large eddy simulation (LES) with the filtered density function (FDF) formulation of turbulent reacting flows. This methodology is termed the "irregularly portioned Lagrangian Monte Carlo finite difference" (IPLMCFD). It takes advantage of modern parallel platforms and mitigates the computational cost of LES/FDF significantly. The embedded algorithm addresses the load balancing issue by decomposing the computational domain into a series of irregularly shaped and sized subdomains. The resulting algorithm scales to thousands of processors with an excellent efficiency. Thus it is well suited for LES of reacting flows in large computational domains and under complex chemical kinetics. The efficiency of the IPLMCFD; and the realizability, consistency and the predictive capability of FDF are demonstrated by LES of several turbulent flames

Progress Toward Affordable High Fidelity Combustion Simulations Using Filtered Density Functions for Hypersonic Flows in Complex Geometries

Significant progress has been made in the development of subgrid scale (SGS) closures based on a filtered density function (FDF) for large eddy simulations (LES) of turbulent reacting flows. The FDF is the counterpart of the probability density function (PDF) method, which has proven effective in Reynolds averaged simulations (RAS). However, while systematic progress is being made advancing the FDF models for relatively simple flows and lab-scale flames, the application of these methods in complex geometries and high speed, wall-bounded flows with shocks remains a challenge. The key difficulties are the significant computational cost associated with solving the FDF transport equation and numerically stiff finite rate chemistry. For LES/FDF methods to make a more significant impact in practical applications a pragmatic approach must be taken that significantly reduces the computational cost while maintaining high modeling fidelity. An example of one such ongoing effort is at the NASA Langley Research Center, where the first generation FDF models, namely the scalar filtered mass density function (SFMDF) are being implemented into VULCAN, a production-quality RAS and LES solver widely used for design of high speed propulsion flowpaths. This effort leverages internal and external collaborations to reduce the overall computational cost of high fidelity simulations in VULCAN by: implementing high order methods that allow reduction in the total number of computational cells without loss in accuracy; implementing first generation of high fidelity scalar PDF/FDF models applicable to high-speed compressible flows; coupling RAS/PDF and LES/FDF into a hybrid framework to efficiently and accurately model the effects of combustion in the vicinity of the walls; developing efficient Lagrangian particle tracking algorithms to support robust solutions of the FDF equations for high speed flows; and utilizing finite rate chemistry parametrization, such as flamelet models, to reduce the number of transported reactive species and remove numerical stiffness. This paper briefly introduces the SFMDF model (highlighting key benefits and challenges), and discusses particle tracking for flows with shocks, the hybrid coupled RAS/PDF and LES/FDF model, flamelet generated manifolds (FGM) model, and the Irregularly Portioned Lagrangian Monte Carlo Finite Difference (IPLMCFD) methodology for scalable simulation of high-speed reacting compressible flows

Applied Filtered Density Function

An overview is presented of recent advances in the filtered density function (FDF) modeling and simulation of turbulent combustion. The review is focused on the developments that have facilitated the FDF to be broadly applied in large eddy simulation (LES) of practical flows. These are primarily the development of a new Lagrangian Monte Carlo solver for the FDF, and the implementation of this solver on Eulerian domains portrayed by unstructured grids. With these developments, it is now much easier to apply FDF for predictions of reacting flows in complex geometrical configurations

VS-FMDF and EPVS-FMDF for Large Eddy Simulation of Turbulent Flows

The first part of this dissertation is concerned with implementation of the joint ``velocity-scalar filtered mass density function'' (VS-FMDF) methodology for large eddy simulation (LES) of Sandia Flame D. This is a turbulent piloted nonpremixed methane jet flame. In VS-FMDF, the effects of the subgrid scale chemical reaction and convection appear in closed forms. The modeled transport equation for the VS-FMDF is solved by a hybrid finite-difference/Monte Carlo scheme. For this flame (which exhibits little local extinction), a flamelet model is employed to relate the instantaneous composition to the mixture fraction. The LES predictions are compared with experimental data. It is shown that the methodology captures important features of the flame as observed experimentally. In the second part of this dissertation, the joint ``energy-pressure-velocity-scalar filtered mass density function'' (EPVS-FMDF) is developed as a new subgrid scale (SGS) model for LES of high-speed turbulent flows. In this model, the effects of compressibility are taken into account by including two additional thermodynamic variables: the pressure and the internal energy. The EPVS-FMDF is obtained by solving its modeled transport equation, in which the effect of convection appears in a closed form. The modeled EPVS-FMDF is employed for LES of a temporally developing mixing layer

A Hybrid Filtered Density Function Spectral-Element Large Eddy Simulator

This dissertation is focused on the development of a hybrid scheme, combining the spectral-element method (SEM) solver with a Lagrangian Monte Carlo (MC) filtered density function (FDF) simulator for large eddy simulation (LES) of turbulent flows. The methodology is shown to be suitable for LES, as a larger portion of the resolved energy is captured as the order of spectral approximation increases. The consistency and the overall performance of the SEM-MC solver, and the realizability of the simulated results are demonstrated via LES of a temporally developing mixing layer under both non-reacting and reacting conditions. The effects of grid resolution and polynomial order ($h-p$ refinement), and ensemble average size ($\Delta_E$) are studied. The computational scheme is fully parallelized via the message passing interface (MPI) methodology

Integrated Waste Management

This book reports research on policy and legal issues, anaerobic digestion of solid waste under processing aspects, industrial waste, application of GIS and LCA in waste management, and a couple of research papers relating to leachate and odour management