Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet
The dynamics of the coherent structures in a turbulent three-dimensional wall jet with an exit Reynolds number of 250,000 were investigated using the Snapshot Proper Orthogonal Decomposition (POD). A low-dimensional reconstruction using the first 10 POD modes indicates that the turbulent flow is dom...
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| Format: | Article |
| Language: | English |
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MDPI AG
2021-01-01
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| Series: | Fluids |
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| Online Access: | https://www.mdpi.com/2311-5521/6/1/35 |
| _version_ | 1797413410469576704 |
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| author | Lhendup Namgyal Joseph W. Hall |
| author_facet | Lhendup Namgyal Joseph W. Hall |
| author_sort | Lhendup Namgyal |
| collection | DOAJ |
| description | The dynamics of the coherent structures in a turbulent three-dimensional wall jet with an exit Reynolds number of 250,000 were investigated using the Snapshot Proper Orthogonal Decomposition (POD). A low-dimensional reconstruction using the first 10 POD modes indicates that the turbulent flow is dominated by streamwise vortex structures that grow in size and relative strength, and that are often accompanied by strong lateral sweeps of fluid across the wall. This causes an increase in the bulging and distortions of streamwise velocity contours as the flow evolves downstream. The instantaneous streamwise vorticity computed from the reconstructed instantaneous velocities has a high level of vorticity associated with these outer streamwise vortex structures, but often has a persistent pair of counter-rotating regions located close to the wall on either side of the jet centerline. A model of the coherent structures in the wall jet is presented. In this model, streamwise vortex structures are produced in the near-field by the breakdown of vortex rings formed at the jet outlet. Separate structures are associated with the near-wall streamwise vorticity. As the flow evolves downstream, the inner near-wall structures tilt outward, while the outer streamwise structures amalgamate to form larger streamwise asymmetric structures. In all cases, these streamwise vortex structures tend to cause large lateral velocity sweeps in the intermediate and far-field regions of the three-dimensional wall jet. Further, these structures meander laterally across the jet, causing a strongly intermittent jet flow. |
| first_indexed | 2024-03-09T05:17:28Z |
| format | Article |
| id | doaj.art-bbfb05660b04470284268fc2a72de128 |
| institution | Directory Open Access Journal |
| issn | 2311-5521 |
| language | English |
| last_indexed | 2024-03-09T05:17:28Z |
| publishDate | 2021-01-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Fluids |
| spelling | doaj.art-bbfb05660b04470284268fc2a72de1282023-12-03T12:44:05ZengMDPI AGFluids2311-55212021-01-01613510.3390/fluids6010035Coherent Streamwise Vortex Structure of a Three-Dimensional Wall JetLhendup Namgyal0Joseph W. Hall1Hydropower Research & Development Centre, Druk Green Power Corporation Limited, Thimphu 1351, BhutanDepartment of Mechanical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, CanadaThe dynamics of the coherent structures in a turbulent three-dimensional wall jet with an exit Reynolds number of 250,000 were investigated using the Snapshot Proper Orthogonal Decomposition (POD). A low-dimensional reconstruction using the first 10 POD modes indicates that the turbulent flow is dominated by streamwise vortex structures that grow in size and relative strength, and that are often accompanied by strong lateral sweeps of fluid across the wall. This causes an increase in the bulging and distortions of streamwise velocity contours as the flow evolves downstream. The instantaneous streamwise vorticity computed from the reconstructed instantaneous velocities has a high level of vorticity associated with these outer streamwise vortex structures, but often has a persistent pair of counter-rotating regions located close to the wall on either side of the jet centerline. A model of the coherent structures in the wall jet is presented. In this model, streamwise vortex structures are produced in the near-field by the breakdown of vortex rings formed at the jet outlet. Separate structures are associated with the near-wall streamwise vorticity. As the flow evolves downstream, the inner near-wall structures tilt outward, while the outer streamwise structures amalgamate to form larger streamwise asymmetric structures. In all cases, these streamwise vortex structures tend to cause large lateral velocity sweeps in the intermediate and far-field regions of the three-dimensional wall jet. Further, these structures meander laterally across the jet, causing a strongly intermittent jet flow.https://www.mdpi.com/2311-5521/6/1/35wall jetturbulent flowcoherent structure |
| spellingShingle | Lhendup Namgyal Joseph W. Hall Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet Fluids wall jet turbulent flow coherent structure |
| title | Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet |
| title_full | Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet |
| title_fullStr | Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet |
| title_full_unstemmed | Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet |
| title_short | Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet |
| title_sort | coherent streamwise vortex structure of a three dimensional wall jet |
| topic | wall jet turbulent flow coherent structure |
| url | https://www.mdpi.com/2311-5521/6/1/35 |
| work_keys_str_mv | AT lhendupnamgyal coherentstreamwisevortexstructureofathreedimensionalwalljet AT josephwhall coherentstreamwisevortexstructureofathreedimensionalwalljet |