**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, *Pittsburgh Supercomputing Center*

J. H. Chen, J. C. Sutherland, *Sandia National Laboratories*

*Summary*

***The present project is a multi-institution collaborative effort aimed
at adapting a high-fidelity turbulent reacting flow solver called S3D to
terascale, massively parallel, computer technology. 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 S3D software is enhanced with new
numerical and physical modeling capabilities; it is also modified to
become object-oriented and fit into an advanced software environment
based on an adaptive mesh refinement framework called GrACE and the
Common Component Architecture (CCA).***

**1. Introduction**

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 (*NO~x~*, soot) from
turbulent combustion systems.

**2. Scientific software developments**

The effort leverages an existing DNS capability, named S3D, developed at
Sandia National Laboratories. 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 new numerical developments includes: an implicit/explicit
operator-splitting technique for efficient time integration; a modified
inflow boundary scheme for acoustically-smooth turbulence forcing; and a
pseudo-compressibility method for more efficient computation of slow
flow problems. The list of new physical modeling developments includes:
a thermal radiation capability; a soot formation capability; and a
Lagrangian particles capability to simulate dilute liquid fuel sprays.

The new S3D software has also been modified to fit into GrACE, an
advanced parallel computing framework targeted for adaptive mesh
refinement applications. Our project has developed a library of wrappers
to fit the S3D Fortran 90 environment into the C++ GrACE framework. Our
effort is now focused in making S3D 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 \[2\]. 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 \[1\]).

**3. New combustion science**

The new DNS solver is currently used in a series of demonstration
studies selected for both their technical challenge and scientific
value. The list of ongoing pilot studies includes: the simulation of
turbulent ethylene-air counter-flow diffusion flames (to study flame
extinction phenomena and edge-flame dynamics); the simulation of a
turbulent ethylene-air jet diffusion flame near a solid wall (to study
flame-wall interactions and the associated wall heat transfer); the
simulation of turbulent auto-ignition for a population of vaporizing
liquid fuel (n-heptane) droplets (to study spray auto-ignition in
homogeneous charge compression ignition -- HCCI -- engines)

\[1\] 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://cfrfs.ca.sandia.gov/>

![](media/image1.png){width="3.5in" height="2.347916666666667in"}

![](media/image2.png){width="3.5in"
height="2.3409722222222222in"}*Figure 1.* Instantaneous variations of
fuel mass reaction rate (top) and temperature (bottom) during the
simulation of a turbulent reacting wall boundary layer*.*

**For further information on this subject contact:**

Prof. A. Trouvé

Dept. of Fire Protection Engineering

University of Maryland, College Park, MD 20742

Project web site: http://scidac.psc.edu/