The challenge of integrating complex chemistry in industrial CFD simulations

Complex chemistry effects play a predominant role in practical turbulent combustion applications. Complex phenomena, such as knock in spark-ignition engines, auto-ignition in Diesel engines or in lean premixed gas turbines can only be predicted using finite-rate chemistry of hydrocarbon fuels. But also emission predictions for soot or NOx for example require the use of detailed chemistry.

Accounting for complex chemistry in CFD simulations is not trivial, as the time and length scales involved are typically several orders of magnitude smaller than the flow scales. Typical solutions may be based on a tabulation approach, where the chemical reactions are calculated a priori and stored in a look-up table which is read by the CFD software, or a direct coupling approach, where the chemistry solver is coupled to the CFD solver. A hybrid approach, often referred to as in situ tabulation, may also be adopted.

Current trends in combustion modelling show that especially the use of look-up tables is emerging in the context of advanced combustion models. Also, the chemistry models used to create the look-up tables make use of increasingly complex chemical reaction mechanisms, developed with the latest insights on combustion chemical kinetics. Dacolt has established a proven track record in these areas with the development of custom solutions for complex chemistry & CFD.

Custom solutions for integrating complex chemistry in CFD

In order for a chosen solution to work efficiently in a given industrial environment, an integral approach is required, accounting for the following aspects:

• Chemistry model: which model is used to represent the underlying physics (thermodynamic equilibrium, homogeneous reactor, steady or unsteady laminar premixed or diffusion flames)
• CFD software: what level of access to the source code and what documentation and support is available (proprietary or Open Source CFD software)
• Turbulent combustion model: how is the interaction between the turbulent flow and chemical reactions modelled (presumed PDF model, flame surface density model, Eddy Dissipation Concept model, etc.)
• Coupling method: is there a direct coupling between the chemistry model and the CFD software or are look-up tables used
• IT environment: in what type of IT environment will the solution be implemented (operating system, networked workstations or cluster, etc.)

Dacolt has realised several custom solutions for the integration of complex chemistry in industrial CFD simulations, for various chemistry models, turbulent combustion models, CFD software packages, IT environments and coupling methods. These projects involved various programming languages like Fortran 77/90, C, C++, C# and scripting languages like Bash, Python, etc.

Dacolt can create and implement a complete solution, or develop one or several of the components, like the implementation of the turbulent combustion model, or the realisation of a custom software package for creating CFD look-up tables.

Contact us for more information on including complex chemistry in CFD simulations.