Mike Lijewski

CASTRO: A NEW COMPRESSIBLE ASTROPHYSICAL SOLVER. I. HYDRODYNAMICS AND SELF-GRAVITY

We present a new code, CASTRO, that solves the multicomponent compressible hydrodynamic equations for astrophysical flows including self-gravity, nuclear reactions, and radiation. CASTRO uses an Eulerian grid and incorporates adaptive mesh refinement (AMR). Our approach to AMR uses a nested hierarchy of logically rectangular grids with simultaneous refinement in both space and time. The radiation component of CASTRO will be described in detail in the next paper, Part II, of this series.

Parallelization of structured, hierarchical adaptive mesh refinement algorithms

Abstract.We describe an approach to parallelization of structured adaptive mesh refinement algorithms. This type of adaptive methodology is based on the use of local grids superimposed on a coarse grid to achieve sufficient resolution in the solution. The key elements of the approach to parallelization are a dynamic load-balancing technique to distribute work to processors and a software methodology for managing data distribution and communications. The methodology is based on a message-passing model that exploits the coarse-grained parallelism inherent in the algorithms. The approach is illustrated for an adaptive algorithm for hyperbolic systems of conservation laws in three space dimensions. A numerical example computing the interaction of a shock with a helium bubble is presented. We give timings to illustrate the performance of the method.

Nyx: A Massively Parallel AMR Code for Computational Cosmology

We present a new N-body and gas dynamics code, called Nyx, for large-scale cosmological simulations. Nyx follows the temporal evolution of a system of discrete dark matter particles gravitationally coupled to an inviscid ideal fluid in an expanding universe. The gas is advanced in an Eulerian framework with block-structured adaptive mesh refinement; a particle-mesh scheme using the same grid hierarchy is used to solve for self-gravity and advance the particles. Computational results demonstrating the validation of Nyx on standard cosmological test problems, and the scaling behavior of Nyx to 50,000 cores, are presented.

Interaction of turblence and chemistry in a low-swirl burner

New combustion systems based on ultra-lean premixed combustion have the potential for dramatically reducing pollutant emissions in transportation systems, heat, and stationary power generation. However, lean premixed flames are highly susceptible to fluid-dynamical combustion instabilities, making robust and reliable systems difficult to design. Low-swirl burners are emerging as an important technology for meeting design requirements in terms of both reliability and emissions for next-generation combustion devices. In this paper, we present simlations of a laboratory-scale low-swirl burner using detailed chemistry and transport without incorporating explicit models for turbulence or turbulence/chemistry interaction. We consider two fuels, methane and hydrogen, each at two turbulent intensities. Here we examine some of the basic properties of the flow field and the flame structure. We focus on the differences in flame behavior for the two fuels, particularly on the hydrogen flame, which burns with a cellular structures.

Parallelization of an Adaptive Mesh Refinement Method for Low Mach Number Combustion

We describe the parallelization of a computer program for the adaptive mesh refinement simulation of variable density, viscous, incompressible fluid flows for low Mach number combustion. The adaptive methodology is based on the use of local grids superimposed on a coarse grid to achieve sufficient resolution in the solution. The key elements of the approach to parallelization are a dynamic load-balancing technique to distribute work to processors and a software methodology for managing data distribution and communications. The methodology is based on a message-passing model that exploits the coarse-grained parallelism inherent in the algorithms. A method is presented for parallelizing weakly sequential loops--loops with sparse dependencies among iterations.

Tools for simulation of laboratory-scale premixed turbulent flames

We have entered a new era in turbulent combustion calculations, where we can now simulate a detailed laboratory-scale turbulent reacting flow with sufficient fidelity that the computed data may be expected to agree with experimental measurements. Moreover, flame simulations can be used to help interpret measured diagnostics, validate evolving flame theories, and generally allow exploration of the system in ways not previously available to experimentalists. In this paper, we will discuss our adaptive projection algorithm for low speed reacting flow that has helped make these types of simulations feasible, and two sets of new issues that are associated with application of this approach to simulating real flames. Using a recently computed flame simulation as an example, we will discuss issues concerning characterization of the experimental conditions and validation of the computed results. We also discuss recent developments in the analysis and interpretation of extremely large and complex reacting flow datasets, and a new approach to simulating premixed turbulent flames relevant to laboratoryscale combustion experiments-a feedback-controlled flame stabilization method.