Multi-scale dynamics at the turbulent/non-turbulent interface of jets and plumes
Lead Research Organisation:
Imperial College London
Department Name: Civil & Environmental Engineering
Abstract
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Publications
Brizzolara S
(2021)
Transition from shear-dominated to Rayleigh-Taylor turbulence
in Journal of Fluid Mechanics
Cimarelli A
(2021)
Spatially evolving cascades in temporal planar jets
in Journal of Fluid Mechanics
Neamtu-Halic M
(2021)
Role of vortical structures for enstrophy and scalar transport in flows with and without stable stratification
in Journal of Turbulence
Neamtu-Halic M
(2020)
Connecting the time evolution of the turbulence interface to coherent structures
in Journal of Fluid Mechanics
Van Reeuwijk M
(2020)
Unified description of turbulent entrainment
in Journal of Fluid Mechanics
| Description | The aim of this project was to improve our understanding of turbulent entrainment and use this to improve its parameterisation. Entrainment is a key component to many environmental and industrial flows, but is subject to substantial uncertainty. We pursued a three-pronged approach: 1) to study multi-scale properties from the Reynolds-averaged perspective; 2) to study the behaviour of the TNTI from an instantaneous and local perspective; and 3) develop new and improved turbulence parameterisations and test these for realistic flows. For approach 1, we provided the DNS data which was analysed by our colleagues from Cardiff. Approach 2 was the main topic of this part of the project. Approach 3 is led by our colleagues in Cardiff, and is still in progress. To date, one journal paper has appeared from approach 1, with one further publication under review and one in preparation. The first paper (Cimarelli et al, 2021) performs a multi-scale analysis on the interface of a turbulent jet, and shows reverse cascade mechanisms near the turbulent-nonturbulent interface (TNTI) that are found to be responsible for the generation of long and wide structures in the interface region. This simulation creates important understanding that can be used to model turbulence near the TNTI. The papers that are under review consider the coherent structures that form in the temporal jet, and how entrainment is affected by heat, i.e. the extension to a turbulent plume. Four papers have been published on approach 2. We did some fundamental work to be able to describe global and local entrainment in a single framework (Van Reeuwijk, 2021). The second paper, which is in collaboration with ETH Zurich, looks at creation mechanisms for surface area near the TNTI and how these are related to coherent structures near the interface (Neamtu-Halic et al, 2020, 2021). The creation of surface area is intimately connected to the rate at which plumes and jets entrain. The entrainment rate is an important parameter to understand, since it it is directly associated with energy loss and dilution. We considered several flow types: unsteady jets/plumes, inclined gravity currents and Rayleigh-Taylor flow (Brizzolara et al. 2021). There is currently one paper in preparation that focuses on two-point correlations relative to the TNTI for the temporal jet. For approach 3, we created a dataset for plumes in cross-flow that is currently being analysed by our colleagues in Cardiff and will be used to study LES parameterisations for TNTIs. The first paper on this topic is imminent for submission. - |
| Exploitation Route | The unified description of turbulent entrainment will be useful to people working in different fields, and will be of use to quantify entrainment in more complex environments, e.g. those with wind, turbulence or both. The multi-scale analysis that was conducted by our colleagues in Cardiff provides important new information into the behaviour of turbulence near TNTIs. This approach can be and should be applied to other canonical flows, as it is a versatile tool to understand multi-scale interactions in non-homogeneous flows. The work on TNTIs demonstrates new approaches to analyse the TNTI and we expect that other researchers will apply these methods to other problems. |
| Sectors | Aerospace, Defence and Marine,Environment |
| Title | A unified model that links local and global entrainment |
| Description | Turbulence is characterized by a large range of active scales, ranging from large integral length scales to small dissipative scales. In this theoretical paper, we connect global (large-scale) entrainment to local (small-scale) entrainment in a single framework. The significance of the work is that it provides a universal definition of entrainment and a quantitative manner to calculate its magnitude. |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2021 |
| Provided To Others? | Yes |
| Impact | The theory provides new insight into unsteady plumes and has since been instrumental to study turbulent plumes in cross-flow (Jordan et al, 2021). It highlights the complexities of environments that are turbulent, and this work has provided the framework necessary to explore turbulent-turbulent entrainment e.g. in the context of turbulent fountains and clouds. Jordan, O.H., Rooney, G.G., Devenish, B.J., Van Reeuwijk, M. (2021) Under pressure: turbulent plumes in a uniform crosswind. J. Fluid Mech. 932, A47 |
| URL | https://doi.org/10.1017/jfm.2020.836 |
| Title | Database for the unsteady turbulent planar jet |
| Description | We created a large database of 3D snapshots that document the evolution of a temporal line jet that develops in time. We have performed three independent realisations of this flow with different initial conditions in order to improve the statistical accuracy of this flow. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2020 |
| Provided To Others? | Yes |
| Impact | This rich dataset provides fully resolved flow-fields of a temporally evolving planar jet. It has been used to study the two-point correlation budgets, allowing detailed analysis of the turbulent-nonturbulent interface. The work forms the basis of two other papers that are currently under review. |
| Title | Database for the unsteady turbulent plume |
| Description | We created a large database of 3D snapshots that document the evolution of a temporal planar plume. We have performed three independent realisations of this flow with different initial conditions in order to improve the statistical accuracy of this flow. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2022 |
| Provided To Others? | Yes |
| Impact | We are currently preparing a paper that analyses the two-point correlation budgets of this flow, similar to the jet. The novelty in this work is that the buoyancy is two-way coupled with the velocity field, substantially complicating the flow physics. |
| Description | Prof. Markus Holzner |
| Organisation | Swiss Federal Institute for Forest, Snow and Landscape Research |
| Country | Switzerland |
| Sector | Public |
| PI Contribution | We provided datasets of turbulent-nonturbulent interfaces, which were analysed by the Swiss team using their unique analyses. The papers were written jointly |
| Collaborator Contribution | The Swiss team used their work on exact coherent structures to provide new insights into the flow physics near turbulent-nonturbulent interfaces. |
| Impact | It has led to a number of publications, some of which have appeared, some of which are still in the pipeline. |
| Start Year | 2019 |