Terascale High-Fidelity Simulations of Turbulent Combustion with Detailed Chemistry

A. Trouvé, University of Maryland
H. G. Im, University of Michigan
C. J. Rutland, University of Wisconsin
R. Reddy & R. Gomez, Pittsburgh Supercomputing Center
J. H. Chen, S. D. Mason, J. C. Sutherland, Sandia National Laboratories

Summary

The present project is a multi-institution collaborative effort aimed at adapting an existing high-fidelity turbulent reacting flow solver called S3D for efficient implementation on terascale massively parallel processors (MPP) computers. S3D adopts the direct numerical simulation (DNS) approach: DNS is a unique tool in combustion science proposed to produce both high-fidelity observations of the micro-physics found in turbulent reacting flows as well as the reduced model descriptions needed in macro-scale simulations of engineering-level systems. The new MPP S3D software is modified to become object-oriented and fit into an advanced software environment based on an adaptive mesh refinement (AMR) framework called GrACE and the Common Component Architecture (CCA).

Direct numerical simulation (DNS) is a mature and productive research tool in combustion science that is based on first principles of continuum mechanics. Because of its high demand for computational power, current state-of-the-art DNS remains limited to small computational domains (i.e. weakly turbulent flows) and to simplified problems corresponding to adiabatic, non-sooting, gaseous flames in simple geometries. The objective of this research project is to use terascale technology to overcome many of the current DNS limitations and allow for first-principles simulations of pollutant emissions (NOx, soot) from turbulent combustion systems.

The effort leverages an existing DNS capability, named S3D, developed at Sandia National Laboratories and a collaborative effort between Sandia and the Pittsburgh Supercomputing Center for efficient implementation of S3D on massively parallel computers. S3D is a compressible Navier-Stokes solver coupled with an integrator for detailed chemistry (CHEMKIN-compatible), and is based on high-order finite differencing, high-order explicit time integration, conventional structured meshing, and MPI-based parallel computing implementation. The objective here is to both re-design S3D for effective use on terascale high-performance computing platforms, and to enhance the code with new numerical and physical modeling capabilities. The list of proposed numerical developments includes: an implicit/explicit additive Runge-Kutta method for efficient time integration; an immersed boundary method to allow for geometrical complexity; and an adaptive mesh refinement (AMR) capability to provide flexible spatial resolution. The list of proposed physical modeling developments includes: a thermal radiation capability; and a multi-phase capability including soot particles and liquid fuel droplets.

The new MPP S3D software is currently being modified to be object-oriented and fit into an advanced software framework, known as the Grid Adaptive Computational Engine (GrACE). GrACE is a MPP framework targeted for AMR applications and includes load-balancing capabilities. In addition, S3D will be made compliant to a software interoperability standard, the Common Component Architecture (CCA) developed by the SciDAC ISIC in Ref. [1]. The CCA environment will allow exchanging software components developed by different teams working on complementary tasks. It will allow in particular the re-use of components developed by a separate Sandia-led research project called CFRFS [2]. The CFRFS project is closely related to, and coordinated with, the present effort, and focuses for instance on developing an AMR component. This exchange of software components between different projects is a unique feature allowed by the SciDAC structure that promotes interactions between different teams of application scientists (our project and CFRFS [2]) and between application scientists and computer scientists (our project, CFRFS and the CCA ISIC [1]).

We plan to demonstrate the performance and capabilities of the new DNS solver in a series of demonstration studies selected for both their technical challenge and scientific value. This includes: the simulation of compression-ignition of a gaseous or liquid, hydrocarbon fuel in a turbulent inhomogeneous mixture; and the simulation of NOx and soot emissions from hydrocarbon-air turbulent jet diffusion flames. Figure 1 illustrates the current S3D capability. Such DNS simulations provide unique insights into the physics of turbulence-flame interactions (for instance flame extinction events in Fig. 1) and are believed to be key contributors to achieving the improved level of understanding required for better designs of low-emission engineering combustion systems.

[1] Armstrong, R. C., et al., "Center for Component Technology for Terascale Simulation Software", SciDAC Integrated Software Infrastructure Center (ISIC), http://www.cca-forum.org/ccttss/

[2] Najm, H., et al. "A Computational Facility for Reacting Flow Science", SciDAC project, http://www.ca.sandia.gov/cfrfs

Figure 1. Two-dimensional DNS of a turbulent methane-air flame using detailed chemistry, GRI-Mech 3.0. The plots of intermediate species (CH₃O, HO₂, O) and fuel consumption rate vCH4 highlight regions undergoing extinction due to flow-induced excessive straining.

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