Coherent structures in cross sheared flows in weakly stratified environments
Conference Publication ResearchOnline@JCUAbstract
In this study, direct numerical simulation (DNS) has been carried out to investigate the coherent structures of cross sheared stratified (CSS) flows, in which the flow in the streamwise direction with a basic sheared flow velocity interacts with the flow in the spanwise direction with another basic sheared flow velocity in a stratified environment. One additional major governing parameter for CSS flows is the cross shear ratio ξ, which represents the relative extent of the cross shear stresses in the streamwise and spanwise directions. ξ is varied from 0 to 0.5 in the DNS runs to be in line with the available experiments, with constant Reynolds, bulk Richardson and Prandtl numbers at 1200, 0.025 and 1, respectively. In the typical case of ξ = 0.5, the coherent structures of the CSS flow consist of small spanwise eddies along with a dominant streamwise Kelvin-Helmholtz (KH) 'cat eye' eddy. These small spanwise eddies originate from the braid region of a streamwise KH eddy and extend along the streamline to the top of the next streamwise KH eddy, forming unique 'eddy wrap' structures that wrap up the entire KH eddy structures. The results also demonstrate that the transition processes to turbulence in the CSS flow instability and in the classic KH instability are distinctively different. The dependence of the occurrence of 'eddy wrap' structures in CSS flows on ξ is also examined over 0 ≤ ξ ≤ 0.5.
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AFMC 2014: 19th Australasian Fluid Mechanics Conference
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978-0-646-59695-2
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4
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Melbourne, VIC, Australia
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Australasian Fluid Mechanics Society
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Clayton, VIC, Australia
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