An abstraction layer for efficient memory management of tabulated chemistry and flamelet solutions

Abstract

A large number of methods for simulating reactive flows exist, some of them, for example, directly use detailed chemical kinetics or use precomputed and tabulated flame solutions. Both approaches couple the research fields computational fluid dynamics and chemistry tightly together using either an online or offline approach to solve the chemistry domain. The offline approach usually involves a method of generating databases or so-called Lookup-Tables (LUTs). As these LUTs are extended to not only contain material properties but interactions between chemistry and turbulent flow, the number of parameters and thus dimensions increases. Given a reasonable discretisation, file sizes can increase drastically. The main goal of this work is to provide methods that handle large database files efficiently. A Memory Abstraction Layer (MAL) has been developed that handles requested LUT entries efficiently by splitting the database file into several smaller blocks. It keeps the total memory usage at a minimum using thin allocation methods and compression to minimise filesystem operations. The MAL has been evaluated using three different test cases. The first rather generic one is a sequential reading operation on an LUT to evaluate the runtime behaviour as well as the memory consumption of the MAL. The second test case is a simulation of a non-premixed turbulent flame, the so-called HM1 flame, which is a well-known test case in the turbulent combustion community. The third test case is a simulation of a non-premixed laminar flame as described by McEnally in 1996 and Bennett in 2000. Using the previously developed solver ‘flameletFoam’ in conjunction with the MAL, memory consumption and the performance penalty introduced were studied. The total memory used while running a parallel simulation was reduced significantly while the CPU time overhead associated with the MAL remained low.

Keywords:

• efficient tabulation
• precomputed chemistry
• scientific database
• memory management
• flamelet

Acknowledgements

This research has been funded by the Federal Ministry of Economics and Technology of Germany in the project COORVED (project number 0327865) as well as the Federal Ministry of Education and Research of Germany in the framework of Virtuhcon (project number 03Z2FN11). It was furthermore supported by the Saxon State Ministry for Economic Affairs, Labour and Transport and the European Union in the project Schlackebadvergaser für die Nutzung schwieriger Brennstoffe (project number P100092007).

Notes

1. CH₄/H₂ 50 Vol% each, with a velocity of 118 m s⁻¹.

2. With a velocity of 40 m s⁻¹.