Turbulent mixing enhancement of compact swirl puffs

Lead Research Organisation: Durham University
Department Name: Engineering


The context of the research
Pulse combustion is an intermittent combustion technique, which is characterized by the oscillatory mass flow rate accompanied by a periodic variation in temperature, pressure and velocity field, but without a reciprocating mechanism as in IC engines. It is considered to be a promising combustion technique, which promotes renewable energy sources since it can burn fuels of different quality ranging from high-grade natural gas and propane to low-grade fuels like biogas. It also has higher combustion efficiency and lower pollutant emissions, compared to conventional steady combustions like it in modern jet engine combustors. These characteristics render it an ideal candidate for sustainable development (for natural resource and environment), which is a major global challenge.

In a recent review article, it mentions that although with 80 years of R&D history, pulse combustion remains a relatively obscure technique, which requires fundamental research across a wide range of disciplines ranging from fluid mechanics to chemistry. While the research so far has mainly focused on the overall system performance, systematic studies on each of the many subsystems are still in high demand. The fluid mechanics associated with the fuel injection strategy is one of them.

The flow field associated with pulse combustion is usually highly energetic and compact, which is in the form of a turbulent puff. It propagates at a considerable self-induced velocity. In non-premix combustion applications, this results in insufficient mixing of fuel and the surrounding oxidizer and hence undesirable combustion conditions. To tackle this problem, a method to enhance such mixing efficiency is sought in the project.

Its aim and objectives
This project, from a fundamental non-reacting fluid mechanics' point of view, aims to find an optimal scalar mixing enhancement by superposing a swirl component of a variety of strengths on to the pulsed puffs. Such a hybrid injection method will introduce complex coherent turbulence structures and hence promote high mixing efficiency. It combines the advantage of swirling jet combustion, which is commonly adopted in current jet engines, and pulse combustion. A feasible static flow control strategy will also be explored in order to further enhance turbulent mixing. In order to achieve these aims, systematic experiments will be conducted using advanced laser diagnostic techniques for simultaneous measurements of velocity and scalar fields in a non-invasive way.

Its potential applications and benefits
The main application of the research is pulse combustion, whose key advantage is to reduce emission and promote renewable energy sources. These two elements are crucial for global sustainable development, especially for developing countries. In the UK, over 75% of the energy demand is provided by the combustion of fossil fuels, at the cost of emitting over 3000Kt of air pollutant each year. These pollutant plus greenhouse emissions make extra £16 billion p.a. from NHS on health care service and products. A small reduction of these emissions will bring a huge impact to the UK economy.

Planned Impact

The proposed research integrates the strengths of continuous swirling jet combustion into the pulse combustion technique, to further enhance its mixing efficiency, hence to improve its overall thermal efficiency and to reduce pollutant emissions resulting from insufficient combustion of fuels. Ultimately it leads to a wider applicability of the pulse combustion technique, which may benefit more than one type of industries. Additionally, a number of broader impacts in terms of People and Knowledge have been identified. Overall, the outcomes of the project have a broad range of beneficiaries.

1. General public: The impact of the improved pulse combustion mixing efficiency leads to an improved overall thermal efficiency of such combustion technique and a lower emission of air pollutants. Each year in the UK, over 3000Kt pollutants are produced from combustion of fossil fuels. Together with greenhouse emissions, these pollutants lead to extra expenditure of £16 billion p.a. from NHS on health care service and produces, cause an effect equivalent to 29,000 deaths and shorten everyone's life by 6 months on average. Even a small percentage reduction of these pollutants will have a huge impact to the UK's society and economy.
2. Industries involving pulse combustion: In addition to engine and electric power generation industries, who directly benefit from higher combustion efficiency and lower emissions, its application has increased significantly in industrial drying. For example, pulse combustion's excellent ability for handling heat sensitive biomaterials and high-viscosity suspensions makes it an important drying method for pharmacology (e.g. antibiotics production) and food industry (e.g. milk powder production). Its advantage of burning diversified fuels allows it to contribute significantly to the development and utilization of renewable energy resources in fields such as sewage sludge treatment and hazard solids incineration.
3. Academic community: In a recent review article in renewable energy, it mentions that the importance of improving pulse combustion efficiency necessitates a substantial community of researchers underpinning expertise from a range of different disciplines. Focusing on a fundamental aspect in fluid mechanics, this project will both springboard the applicant's early career in this area and impact on the PDRA and project students working with / in collaboration with the applicant. Making available the knowledge and understanding required to apply the flow control to enhance mixing in pulsation flows will also enable other academic researchers, in both reacting and non-reacting flow communities, to draw on this approach to get otherwise unobtainable information using the results of the proposed experimental study.
4. Outreach: The project outcomes will be disseminated to the parties mentioned above through the active outreach programmes organized by the Durham University Science Outreach Department and the Durham Energy Institute.


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Description This project has resulted in 3 journal publications so far, and another 2 manuscripts are currently under review. Amongst the 3 published paper, one has been selected as Editor's Pick in Physics of Fluids.

We found that firstly, 3D printed swirlers are suitable for generating swirling pulsatile or continuous turbulent flows in an easiest compared to other alternative methods. Secondly, as swirl strength increases, the maximum energy attainable in a leading structure, which is able to propagate further by its self-induced velocity, decreases. This suggests that there is an optimal swirl strength which balances the momentum delivery and mixing intensity. This is being processed at the moment. Thirdly, it opens up an important question about what will happen in successive pulsatile swirling trains, which has also initiated an international research collaboration with US; see below.

The TomoPIV technique applied in the project has been used to develop a novel pressure field determination algorithm using data assimilation. This technique essentially combines experimental technique and CFD. It uses experimental data to correct CFD hence optimises both. Then some quantities, like pressure, which cannot be directly measured from experiments non-invasively, can now be calculated. It demonstrates it robustness over all the available pressure determination techniques. This technique will be applied not only to the Engineering community, but also to biomedical community, eg cardiovascular flow dynamics.

The PDRA working on this project will take an Assistant Professorship at Shanghai Jiaotong University (top 3 in China) after the current post. The collaboration on the current project will continue as a collaboration with China even without the support of EPSRC. In addition, the project has initiate an international collaboration with US and the research will be extended to pulsatile swirling jets. An EPSRC grant application has been submitted and is currently under review by the EPSRC-NSF joint programme.

The project has trained 4 undergraduate students via their final year research projects, who are or will work in UK Engineering industries R&D departments. One PhD student, two international visiting PhD students, two international intern students. They have already generated, or started to generate further research publications. One research collaboration has been funded by UK Fluids Network. The facility has been used as showcase on a number of open days to attract A-level pupils to take engineering as their degree.
Exploitation Route The academic impact are disseminated in top journals in the field. Three have been published and another two are being reviewed.

In addition to the original objectives, further goals have been achieved. These include a new pressure determination technique, visiting PhD students involvement and further major grant applications.

The research outcome will continue being further disseminated in future conferences as oral presentations by either the PI or the PDRA, where EPSRC will be acknowledged.

As the PDRA takes the Assistant Professor post at Shanghai Jiaotong University, the research out come has been disseminated in Chinese community by the PDRA and will also create a new research area in the community, eg additional publications will be made.

A website is currently being constructed by the PI to publish the key finds of the current project and help further disseminate the research outcome.
Sectors Chemicals,Energy,Healthcare

Description It has been used in the following areas 1. general education purpose. The findings has been used in an undergraduate course where the potential application of continuous/pulsatile swirling flow is discussed 2. student final year projects to explore complex fluid mechanics 3. on open days to attract pupils to study engineering, especially in energy area. 4. attracted one PhD student, two international visiting PhD students and one UK visiting PhD student
First Year Of Impact 2019
Sector Education
Impact Types Societal

Description Durham University Grant Seedcorn Fund
Amount £12,000 (GBP)
Funding ID 037/18-19 
Organisation Durham University 
Sector Academic/University
Country United Kingdom
Start 03/2019 
End 06/2019
Description UK Fluids Network Short Research Visit
Amount £1,000 (GBP)
Organisation UK Fluids Network 
Sector Public
Country United Kingdom
Start 10/2018 
End 10/2018
Title Complex pulsatile flow generator using novel portable 3D printed components 
Description The method is the first time of using 3D printing to design and fabricate components which are able to generate special fluid dynamic characteristics which are otherwise difficult to achieve using conventional mechanical components. These characteristics is expected to enhance scalar mixing in pulsatile turbulent flows. These components are also specially designed to be easily integrated with others and to be easily portable to the facility. The fine features of the designed the component will also be very useful for flow control purpose, which are highly sensitive to special disturbance at critical regimes in the flow field. The project also generates a novel idea of 3D flow field measurement by extending the existing Tomographic PIV to multiple viewing angles using one camera, achievable by multiple optical fibres. 
Type Of Material Model of mechanisms or symptoms - in vitro 
Year Produced 2019 
Provided To Others? Yes  
Impact The first publication is to appear in 2019. The impact will be on the use of 3D printing techniques to achieve complex flow control and manipulations. The impact on the flow measurement technique is expected to have a considerable impact, but it needs further work to continue. 
Title Using data assimilation to calculate pressure distribution from TomoPIV 
Description New algorithm for pressure field calculation from TomoPIV (three-dimensional three-component velocity field) was developed. This method shows it robustness and superior performance over all the other pressure calculation techniques. This technique essentially integrates experiments (PIV) and CFD and has a promising future in the fluid mechanics applications. 
Type Of Material Model of mechanisms or symptoms - in vitro 
Year Produced 2020 
Provided To Others? Yes  
Impact Non-invasive pressure field calculation is challenging. This technique offers the best ever pressure calculation way from velocity information, which can be obtained from PIV (2DPIV to tomoPIV). Its potential applications are in aerodynamic industries and biomedical areas. The paper has been selected as an Editor's Pick. 
Title The designed swirler angles on the generated swirl strength for both continuous and pulsatile turbulent flows 
Description We have collected a large amount of data base on the swirling strength generated from novelly designed and 3D printed swirlers. The database is for both jet like or piston-nozzle like turbulent flow generators and hence is for both continuous and pulsatile flows, which exhibits considerable differences. We have also develop a data analysis method to obtained the maximum energy obtainable for pulsatile flows with varying strengths. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Impact The impact will be on the design of swirlers to achieve swirl strength which will optimise momentum delivery and mixing strengths, primarily relevant to pulse combustion techniques. The paper has been submitted to Physics of Fluids and is currently under review. 
Title TomoPIV applied to new technique development 
Description TomoPIV, which was utilised in the project, has been used to collect volumetric velocity data. It has been used to develop a novel post-processing technique (data assimilation) to obtain pressure field in the flow. Compared to other pressure estimation techniques, data assimilation demonstrated significant advantages. 
Type Of Material Data analysis technique 
Year Produced 2020 
Provided To Others? Yes  
Impact A journal paper has been published in Physics of Fluids; see the publication section. This paper has been selected as Editor's picks. 
Description EPSRC-NSF application on turbulent puff trains 
Organisation Texas A&M University
Country United States 
Sector Academic/University 
PI Contribution This collaboration was initiated because of this EPSRC award. The award funded facility extracted a collaboration with the above mentioned partner, where experimental work will be combined with numerical simulations to look at structural interaction and promotion, energy delivery and scalar mixing optimisations in turbulent puff trains inside complex cavities. An EPSRC-NSF joint application has been generated and went through the Expression of Interest stage. We are aiming to submit the full proposal in 2019. It will be an EPSRC led project with me as PI. If successful, the award will be £276k to the PI, and $270k to the partner. Basically experimental work will be conducted here in the EPSRC funded unique facility.
Collaborator Contribution The partner will conduct high fidelity numerical simulations, to compromise the experimental work.
Impact A joint application of EPSRC-NSF scheme has been through the Expression of Interest stage and the full application will be submitted in the second half of 2019
Start Year 2018
Description collaboration with London City University 
Organisation City, University of London
Country United Kingdom 
Sector Academic/University 
PI Contribution The facility attracted research collaborator from City University London to come to conduct a one-week research. The research visit is supported by UK Fluid Network Short Reserach visit scheme. It involved the PDRA supported by the current award and a PhD student from City. The data collected is being analysed.
Collaborator Contribution A PhD students came from City University to conduct research for one week using the facility. The data collected is being analysed at City University and the outcome will be disseminated in a publication.
Impact The output is expected to appear in 2019.
Start Year 2018
Description University undergraduate internships, research projects and open days 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Undergraduate students
Results and Impact It has generated 3 undergraduate final year research projects, each spending 600 research hours using the facility funded by the award
It has attracted 2 international summer intern students from China to use the facility
It has attracted 1 visiting PhD student from China, to use the facility to conduct research which will yield research outcome, expected in 2019
It has been used as a showcase example on 2 open days, where over 50 A-level pupils and their parents presented
Year(s) Of Engagement Activity 2018,2019