Predictive tools are required to be able to reduce NOx emissions, to decrease the development time and costs of new combustion systems and to improve the operability of lean-burn combustion systems. Most promising approaches to satisfy future emission levels regulations are based on lean combustion technology. However, lean combustion compromises combustor operability, including ignition, altitude re-light, pull-away, weak extinction performance and thermo-acoustic instability behaviour. Therefore it is of prime importance to evaluate the behaviour of the flame during these transient phases in the design stage and modelling tools are required. Without these tools the development of advanced combustion systems relies on many costly and time consuming rig tests. The high-fidelity simulations proposed in TIMECOP-AE are therefore a way to increase competitiveness.
The aim of the FP6 TIMECOP-AE project was to improve the necessary combustion prediction methods that enable the development of practical advanced combustion systems for future engines, with reduced emission levels and fuel consumption.
The main objective of the project was to enable European industry to design and develop innovative, optimised, low emissions combustion systems within reduced time and cost scales. This would be made possible by the development of state-of-the-art methods in the field of combustion modelling. These prediction methods would give the European industrial partners the advantage to improve in three pertinent fields:
- ability to model a wide range of operating conditions,
- ability to model and cope with transient conditions,
- ability to model and thus avoid combustion instability,
- ability to model and secure capability for altitude re-lights.
- capability to lower combustion system emission levels during the design phase,
- ability to handle different fuel chemistry and calculate biofuelled engine.
- reducing development costs by attaining higher combustion module maturity before development tests,
- allowing more efficient design optimisation.
To reach the main objective of advancing LES methods into two-phase flows for gas turbine applications, TIMECOP was divided into 4 Work Packages and the technical activity distributed as follows:
WP1 - Fundamentals
Within this work package, numerical models for two-phase flow, chemistry and ignition were developed, improved, evaluated and tested. Both Eulerian and Lagrangian two-phase models were considered, and the performances of the two approaches compared. Chemistry models were developed to application to LES. Approaches are based on the Flamelet Generated Manifold method, the Conditional Closure Model, the Field PDF method, and the Computational Singular Perturbation method. Furthermore, a specific spark ignition model has been developed. The models were implemented in numerical solvers and exploited by industrial partners.
WP2 - Validation experiments
WP2 focused on teh development and application of advanced diagnostic techniques on geometries and flow problems ranging from very well defined, easy-to-characterise, academic test cases to industrial test cases. The former tests were used to support model development, the latter to validate models in presence of complex geometries and ambiguity in boundary conditions.
WP3 - Numerical validation and implementation of fundamentals
The aim of this work package was to integrate the fundamental models into the advanced CFD methods, in order to obtain the two-phase reactive CFD capability and resolve the intrinsic unsteady behaviour of turbulent flows. To ensure the proper implementation of these new models, validations were first performed on academic experiments. Once validated, the advanced CFD methods were ready to be tested on complex 3D geometry experiments.
WP4 - Exploitation
LES of reactive two-phase flow is the next evolution in CFD methodologies applied to the conception of aeronautical engines. It should complement and eventually replace existing RANS conception techniques. The justification of this evolution resides in the fact that engine performances and transient phases are not predictable with the only use of RANS.
Within the framework of TIMECOP-AE, the LES tools have gained a new critical capability: modelling of the liquid fuel combustion process for conventional and low-emission combustors, over a wide range of operating conditions. The operating conditions include the above-mentioned transient phenomena, such as ignition or extinction. The developments achieved in the simulation tools are concerned with models for turbulence, chemistry, turbulence-chemistry interactions, and liquid spray models. The methods and models developed within TIMECOP have been evaluated against high quality validation data issued from several validation test-rigs, from academic burners designed to validate a specific model up to a generic combustor, representative of an aero-engine combustor.
The scientific production of the project is summarised here:
- 7 test-rigs
- 18 CFD codes or modules
- 94 technical deliverables validated
- 41 publications produced
TIMECOP-AE has greatly helped introduce the LES tools into the industrial environment for aero-engine design. All industrial partners have computed one of the configurations that were experimentally tested in WP2. The results proposed have clearly shown that performing LES of two-phase reactive flows in an industrial context is feasible. Previous to TIMECOP-AE project, LES was mainly used by researchers with or without a weak link with the aeronautical industry. Several research projects (PRECCINSTA, ICLEAC, MOLECULES) have helped industrials evaluate and understand the interest to adopt such LES tools to improve the conception process. However, only gaseous-fuel combustion simulations had been applied to industrial configurations. TIMECOP-AE has brought two-phase flow modelling, which is an essential feature in combustion simulation, into industrial applications. LES technique still remains to be improved in terms of robustness and computational time consumption to be routinely integrated in the industrial conception cycles. However, all aero-engine manufacturers in TIMECOP consortium have tested it, by adapting owned CFD tools to LES, by adopting research tools modified to fit the industrial needs or by testing commercially-available tools.
TIMECOP-AE has helped consolidate the requirements that LES tools should satisfy to be integrated in the aero-engine industry conception process. Models required by industry needs have been developed by the research partners of this project, integrated in the industrial tools and then evaluated by the industrials against academic and real combustor engine geometries.
Each company started to develop industrial LES related methodologies. The research effort in this field should be continued; noticeably to obtain faster solvers to fit the conception timeline of aeronautical engines and to improve the models developed in TIMECOP.