A combined experimental and numerical investigation of premixed flame-wall interaction in turbulent boundary layers

Lead Research Organisation: Newcastle University
Department Name: Sch of Engineering

Abstract

The presence of walls alters the thermo-chemical and fluid-dynamical processes associated with turbulent premixed flames. The increasing demands for light-weight combustors make flame-wall interactions (FWI) inevitable, which influence the cooling load, thermal efficiency and pollutant emission in these applications. However, this aspect has not yet been sufficiently analysed in the existing turbulent reacting flow literature because of the challenge this poses for both experimental and numerical investigations in terms of spatial and temporal resolutions among others. Therefore, a thorough physical understanding of the FWI mechanism is necessary to develop and design more energy-efficient and environmentally-friendly combustion devices. In this project, recent advances of both high-performance computing and experimental techniques will be utilised to analyse and model premixed FWI in turbulent boundary layers (TBLs). The proposed analysis will consider different FWI configurations (based on the orientation of the mean flame normal with respect to the wall) in turbulent channel flows and unconfined boundary layers (BLs) using state-of-the-art experiments and high-fidelity Direct Numerical Simulations for different wall boundary conditions. Experiments will utilize a suite of advanced laser diagnostics, providing new simultaneous measurement capabilities. DNS will simulate the turbulent flow without any recourse to physical approximations. The fundamental physical insights obtained from DNS and experimental data will be used to develop a novel hybrid RANS/LES approach for device-scale simulation of FWI, building on expertise in the context of Flame Surface Density (FSD) and Scalar Dissipation Rate (SDR) closures for Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulations (LES). The newly-developed models will be implemented to carry out hybrid RANS/LES of experimental configurations for the purpose of model validation. The project will offer robust and cost-effective Computational Fluid Dynamics (CFD) design tools for fuel-efficient and low-emission combustion devices (e.g. gas turbines, micro-combustors and automotive engines).

Planned Impact

The major impacts of this research endeavour are summarised as follows:

(i) Development of fundamental understanding and modelling of flame-wall interaction:

The research outcomes will be disseminated through participation in international conferences (e.g. Int. Combust. Symp., Eur. Combust. Meeting, Numer. Combust. Conf. etc.) and publication in reputed scientific journals (e.g. Combust. Flame, Phys. Fluids, Combust. Sci. Tech., Combust. Theo. Modell. etc.). Moreover, the models developed during the course of this project will enhance the knowledge-base of turbulent reacting flows and predictive capability of engineering simulations, which in turn will play a key role in the design-cycle of next generation energy-efficient and environmentally friendly combustors. The DNS and experimental databases resulting from the proposed research programme will be made available to other interested researchers upon request. The Research Associates (RA) will manage a website for data-exchange and documentation, and important results will be made available for public download. A workshop on flame-wall interaction will be organised at the conclusion of the project to maximise the chances of technical dissemination, and to attract the attention of relevant industrial sectors.

(ii) Industrial combustion equipment manufacturers:

Improving the predictive abilities of flame-wall interaction will be of great benefit to these industries for the development of new generation energy-efficient and environment friendly combustors especially in the UK. Industrial colleagues will be invited to attend half-yearly progress meetings and the planned workshop so that they remain aware of the new research developments and their feedback will be taken on board during the course of the proposed research programme. A website will be maintained throughout the proposed work with information on data-exchange and documentation, and specific results will be made available for public download along with the latest findings in the open literature. It will therefore serve as an important source of information for CFD practitioners both in academia and industry.

(iii) RAs who will be engaged in this research programme:

In the proposed research programme, RAs will learn advanced techniques for CFD simulations and experimental measurements which will improve their analytical and mathematical skills. It is hoped that the experience of presenting their research in the form of peer-reviewed papers and conference presentations will make them well-rounded researchers during the course of this research programme. Moreover, the RAs will need to present their work periodically in progress review meetings and maintain a project website, which will also be beneficial for them in terms of developing project management and presentation skills. These will also help them in developing a range of transferable skills such as communication, teamwork and project management. This, in turn, will give rise to development of highly-skilled technical personnel which will be essential for the UK's financial growth.

(iv) Research group at NU and UoE:

The collaboration between NU and UOE is one of the major strengths of this project which will lead to broadening of research capabilities of all the investigators. Moreover it is expected that this project will give rise to open questions which form the basis of further research by the investigators, and the usefulness of the present project will be exploited to attract industrial and research grant funding for future follow-up projects. It is likely that the understanding gained from this project will subsequently be applied to engineering combustion applications, possibly through the Knowledge Transfer Partnership (KTP) scheme in collaboration with UK industry in future, which will also ensure effective assimilation of the new knowledge gained.

Publications

10 25 50

 
Description The discovery of the project includes:
3D DNS of premixed FWI in TBLs, including:
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1: Parameter sweep of leading variables for Head-on, Side-wall & Oblique-wall FWI for adiabatic, isothermal and conjugate heat transfer wall treatments.
2: DNS with detailed chemistry and conjugate heat transfer for selected cases identified in O1.1.
3: Utilisation of DNS for a priori assessment of RANS/LES model expressions.
Novel experimental measurements, including:
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1: A modular facility for combined experimental/numerical research of FWI in TBLs.
2: Simultaneous diagnostics exploiting new measurement capabilities that uniquely describe transi-ent wall heat flux, thermal transport, and flame dynamics for FWI in TBLs.
3: Measurements resolving key variables for RANS/LES closure models and wall functions for the validation & development of a hybrid RANS/LES approach.
Exploitation Route This project offers improved fundamental physical understanding of premixed flame-wall interaction (FWI) in turbulent boundary layers (TBLs) and its high-fidelity modelling in the context of a new hybrid RANS/LES technique. This is documented in the forms of publications arose from this project. The benefit is not limited to premixed FWIs, but will also contribute to the fundamental physical understanding and modelling of turbulent non-reacting and reacting flows in general (e.g. boundary layer transport in compressible flows, FWI in stratified flames, etc.). The novelty of this work lies in the combination of Direct Numerical Simulations (DNS) and experiments, providing new physical understandings and invaluable data, which will be used in part to develop a hybrid RANS/LES approach intended for industrial applications. As optimisation of heat loss to the wall, and flame quenching near the wall, have strong implications on energy-efficiency, reliability and environmental-friendliness in IC engines and gas turbine applications, the findings of this proposed project will play a crucial role in designing clean combustors for the future. Novel outcomes of this project include: (i) Advancements in DNS and experiments for novel analysis of FWI in TBLs; (ii) A comprehensive systematic analysis of the effects of bulk Re, wall-to-gas temperature ratio, and differential diffusion of heat and mass on premixed FWI in TBLs; (iii) Combined a priori analysis and a posteriori validations of the FSD/SDR based closures in the context of hybrid RANS/LES of premixed FWI in TBLs; (iv) Development of correlations for wall heat flux and wall-functions for turbulent premixed FWI; (v) A novel hybrid RANS/LES technique for turbulent reacting flows; (vi) Generation of numerical and experimental databases for hypothesis testing and model development.
Sectors Aerospace

Defence and Marine

Energy

 
Description The proposal falls within the scope of the Engineering theme of the EPSRC portfolio, including Fluid Dynamics and Aerodynamics and Combustion Engineering. In the Energy theme, the proposal addresses the Energy Efficiency research area (End Use Energy Demand). By 2035, the world energy demand is predicted to increase by 28%. All energy outlooks acknowledge that combustion (including bio-fuels) will play an important role in the energy sector. In particular, combustors will be made smaller (e.g. in hybrid engines and micro-combustors), where flame-wall interaction (FWI) plays a key role in engine performance, durability, and reduction of its carbon footprint. The improved physical understanding and modelling methodology for FWI in turbulent boundary layers (TBLs) are not only timely but are essential for addressing the challenges of energy efficiency and pollution control faced in the UK and worldwide. The UK is home to major automotive and gas turbine manufacturers, employing over 1M UK citizens and contributing to ~20% of UK exports. The number of vehicles/aircrafts are anticipated to nearly double in 20 years with approx. 75% of them relying on some form of combustion. Given the long-term nature of the engine design cycle, the impact of this project, in terms of new products and UK wealth creation will come to fruition in a time-scale of 5-10 years. The technological advances of this project will help in designing energy-efficient and environmentally friendly combustors, bringing a long-term benefit for society, which is consistent with the UK Government's "Road to Zero" strategy and EPSRC's "Productive and Resilient Nation" delivery plan. The CFD software community, who use state-of-the-art models in their codes to yield high-fidelity predictions, will also benefit from this project, which will be realised on a 3-10 years' time-scale. This project also lays substantial emphasis on developing highly skilled UK based personnel with cutting-edge expertise in combustion science to support future innovations, in the form of 3 Research Associates.
First Year Of Impact 2020
Sector Aerospace, Defence and Marine,Energy
Impact Types Economic