New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer
This paper serves as a summary of new discoveries by DNS for late stages of flow transition in a boundary layer. The widely spread concept “vortex breakdown” is found theoretically impossible and never happened in practice. The ring-like vortex is found the only form existing inside the flow field....
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| Format: | Article |
| Language: | English |
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Wiley
2011-01-01
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| Series: | Modelling and Simulation in Engineering |
| Online Access: | http://dx.doi.org/10.1155/2011/721487 |
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| author | Chaoqun Liu Lin Chen Ping Lu |
| author_facet | Chaoqun Liu Lin Chen Ping Lu |
| author_sort | Chaoqun Liu |
| collection | DOAJ |
| description | This paper serves as a summary of new discoveries by DNS for late stages of flow transition in a boundary layer. The widely spread concept “vortex breakdown” is found theoretically impossible and never happened in practice. The ring-like vortex is found the only form existing inside the flow field. The ring-like vortex formation is the result of the interaction between two pairs of counter-rotating primary and secondary streamwise vortices. Following the first Helmholtz vortex conservation law, the primary vortex tube rolls up and is stretched due to the velocity gradient. In order to maintain vorticity conservation, a bridge must be formed to link two Λ-vortex legs. The bridge finally develops as a new ring. This process keeps going on to form a multiple ring structure. The U-shaped vortices are not new but existing coherent vortex structure. Actually, the U-shaped vortex, which is a third level vortex, serves as a second neck to supply vorticity to the multiple rings. The small vortices can be found on the bottom of the boundary layer near the wall surface. It is believed that the small vortices, and thus turbulence, are generated by the interaction of positive spikes and other higher level vortices with the solid wall. The mechanism of formation of secondary vortex, second sweep, positive spike, high shear distribution, downdraft and updraft motion, and multiple ring-circle overlapping is also investigated. |
| format | Article |
| id | doaj-art-347ff91262764ffeb07083bb2efb4e6e |
| institution | Kabale University |
| issn | 1687-5591 1687-5605 |
| language | English |
| publishDate | 2011-01-01 |
| publisher | Wiley |
| record_format | Article |
| series | Modelling and Simulation in Engineering |
| spelling | doaj-art-347ff91262764ffeb07083bb2efb4e6e2025-02-03T01:02:25ZengWileyModelling and Simulation in Engineering1687-55911687-56052011-01-01201110.1155/2011/721487721487New Findings by High-Order DNS for Late Flow Transition in a Boundary LayerChaoqun Liu0Lin Chen1Ping Lu2Mathematics Department, University of TX at Arlington, Arlington, TX 76019, USAMathematics Department, University of TX at Arlington, Arlington, TX 76019, USAMathematics Department, University of TX at Arlington, Arlington, TX 76019, USAThis paper serves as a summary of new discoveries by DNS for late stages of flow transition in a boundary layer. The widely spread concept “vortex breakdown” is found theoretically impossible and never happened in practice. The ring-like vortex is found the only form existing inside the flow field. The ring-like vortex formation is the result of the interaction between two pairs of counter-rotating primary and secondary streamwise vortices. Following the first Helmholtz vortex conservation law, the primary vortex tube rolls up and is stretched due to the velocity gradient. In order to maintain vorticity conservation, a bridge must be formed to link two Λ-vortex legs. The bridge finally develops as a new ring. This process keeps going on to form a multiple ring structure. The U-shaped vortices are not new but existing coherent vortex structure. Actually, the U-shaped vortex, which is a third level vortex, serves as a second neck to supply vorticity to the multiple rings. The small vortices can be found on the bottom of the boundary layer near the wall surface. It is believed that the small vortices, and thus turbulence, are generated by the interaction of positive spikes and other higher level vortices with the solid wall. The mechanism of formation of secondary vortex, second sweep, positive spike, high shear distribution, downdraft and updraft motion, and multiple ring-circle overlapping is also investigated.http://dx.doi.org/10.1155/2011/721487 |
| spellingShingle | Chaoqun Liu Lin Chen Ping Lu New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer Modelling and Simulation in Engineering |
| title | New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer |
| title_full | New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer |
| title_fullStr | New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer |
| title_full_unstemmed | New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer |
| title_short | New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer |
| title_sort | new findings by high order dns for late flow transition in a boundary layer |
| url | http://dx.doi.org/10.1155/2011/721487 |
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