When Chaos Meets Chaos - Turbulent Entrainment from a Turbulent Background
Lead Research Organisation:
Imperial College London
Department Name: Aeronautics
Abstract
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Publications
Kankanwadi K
(2020)
Turbulent entrainment into a cylinder wake from a turbulent background
in Journal of Fluid Mechanics
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509486/1 | 30/09/2016 | 30/03/2022 | |||
| 2091392 | Studentship | EP/N509486/1 | 30/09/2017 | 30/07/2021 | Krishna Kankanwadi |
| Description | The aim of this research project was to investigate the effects of background turbulence on the process of entrainment. Entrainment can be regarded as the process by which turbulent bodies of fluid grow. With regards to the effect of background turbulence on this process, there was a lack of consensus in the per-existing literature. Therefore, in this project a parametric study that independently varied all of the relevant parameters was conducted in order to ascertain the effects of background turbulence on entrainment. The two main parameters that were investigated were the intensity of the background turbulence and the length scale of the same. The project investigated this through the analysis of a cylinder wake. In the far wake region, where the wake lacks significant coherence, we were able to show that an increase in background turbulence intensity resulted in an increased inter-facial surface area. This would intuitively lead us to a conclusion that the expected entrainment rate should be increased. However, it is found that the increased entertainment that should be expected due to the increased inter-facial surface area, is overbalanced by the action of extreme yet intermittent events that result in a negative entrainment rate. An increase in the intensity of the background turbulence led to a reduction in net entrainment rate. Given that the background was sufficiently intense, such that it overpowered the wake, the wake experienced net detrainment (negative entrainment). The length scale of incoming turbulence was shown to have a negligible effect on the entrainment process in the far wake. Along with the entrainment rate, which has a direct engineering application, the structure of the inter-facial region was also investigated. It was found that regardless of the level of turbulence available in the background, the classical signature of an enstrophy jump at the interface was still present when turbulence was available on both sides of the interface. This is a very important result as it proves the existence of a turbulent-turbulent interface, something that was questioned in previous literature and even speculated that it may break down and cease to exist. Following this major finding, this interface was further investigated through the use of the enstrophy budget equation. This is a common tool of analysis when examining interfaces. It was shown that the role of viscosity, which is the most crucial method by which entrainment occurs in a non-turbulent environment, is actually subdued and not so crucial in a turbulent/turbulent interface. A turbulent/turbulent interface has rotational fluid on both sides of the interface and hence strain, through the medium of the inertial term, does most of the heavy lifting when it comes to enstrophy production in the vicinity of the interface. The final branch of our research focuses on the near field effects of free-stream turbulence on the shedding of a circular cylinder. Experimental data for this branch has been collected, although the data analysis is still ongoing and in its infancy. |
| Exploitation Route | These findings can potentially used to better design and plan for engineering applications that directly involve the interaction of several bodies of turbulent fluid. As an example, the design of a new wind farm would largely benefit with a better understanding of the growth of the wake behind each turbine. |
| Sectors | Aerospace Defence and Marine Energy Environment |
| URL | https://doi.org/10.1017/jfm.2020.755 |
| Description | Work on turbulent/turbulent entrainment will now be used to develop models for wind turbine wakes in an industrial setting. This is reflected through the collaborations with Industrial partners. |
| First Year Of Impact | 2021 |
| Sector | Aerospace, Defence and Marine,Energy,Environment |
| Impact Types | Cultural Societal Economic |
| Description | Accurate modelling of wind turbine wake spreading through consideration of realistic turbulent entrainment: revolutionising wind farm optimisation |
| Amount | £1,612,676 (GBP) |
| Funding ID | EP/V006436/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 06/2021 |
| End | 06/2026 |
| Description | Callaboration with Vestas |
| Organisation | Vestas Technology UK Ltd |
| Country | United Kingdom |
| Sector | Private |
| PI Contribution | We are developing models for wind turbine wakes based on my work in turbulent/turbulent entrainment and multi-scale generated turbulence |
| Collaborator Contribution | Providing relevant data to develop and tune the models we are developing |
| Impact | N/A |
| Start Year | 2021 |
| Description | Collaboration with Frazer Nash Consultancy |
| Organisation | Frazer-Nash Consultancy |
| Country | United Kingdom |
| Sector | Private |
| PI Contribution | We are developing models for wind turbine wakes which are of interest to clients of Frazer Nash building offshore wind farms |
| Collaborator Contribution | They will assist with disseminating our findings to industry to generate immediate impact |
| Impact | N/A |
| Start Year | 2021 |
| Description | Collaboration with University of Oldenburg |
| Organisation | Carl von Ossietzky University of Oldenburg |
| Country | Germany |
| Sector | Academic/University |
| PI Contribution | We will use the world-class facilities at Oldenburg and in return I will assist them with the implementation of my multi-scale triple decomposition analysis, published in Baj, Bruce & Buxton (2015), Baj & Buxton (2017), Baj & Buxton (2019) |
| Collaborator Contribution | Use of their world leading facilities for wind energy research |
| Impact | N/A |
| Start Year | 2021 |