Backscatter in stratified turbulence

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• 作者：Sina Khani^a ; ^b ; ^{sinakhani@uwaterloo.ca" class="auth_mail" title="E-mail the corresponding author} ; ^{skhani@princeton.edu" class="auth_mail" title="E-mail the corresponding author} ; Michael L. Waite^b
• 关键词：Stratified turbulence ; Direct numerical simulations ; Up- and downscale energy transfer
• 刊名：European Journal of Mechanics - B/Fluids
• 出版年：2016
• 出版时间：November-December 2016
• 年：2016
• 卷：60
• 期：Complete
• 页码：1-12
• 全文大小：2098 K

文摘

In this paper, kinetic and potential energy transfers around a spectral test filter scale in direct numerical simulations of decaying stratified turbulence are studied in both physical and spectral domains. It is shown that while the domain-averaged effective subgrid scale energy transfer in physical space is a net downscale cascade, it is actually a combination of large values of downscale and upscale transfer, i.e. forward- and backscatter, in which the forward scatter is slightly dominant. Our results suggest that spectral backscatter in stratified turbulence depends on the buoyancy Reynolds number 54615303472&_mathId=si48.gif&_user=111111111&_pii=S0997754615303472&_rdoc=1&_issn=09977546&md5=40aa94e2c52cd73be889fe545de238ac" title="Click to view the MathML source">Re_b$R{e}_b$ and the filtering scale 54615303472&_mathId=si79.gif&_user=111111111&_pii=S0997754615303472&_rdoc=1&_issn=09977546&md5=24e17b3a3f81f2fe9f81b56688180413" title="Click to view the MathML source">Δ_test${\Delta }_{test}$. When the test filter scale 54615303472&_mathId=si79.gif&_user=111111111&_pii=S0997754615303472&_rdoc=1&_issn=09977546&md5=24e17b3a3f81f2fe9f81b56688180413" title="Click to view the MathML source">Δ_test${\Delta }_{test}$ is around the dissipation scale 54615303472&_mathId=si81.gif&_user=111111111&_pii=S0997754615303472&_rdoc=1&_issn=09977546&md5=3cabcfe88292b3d36c80ab06e89cfa61" title="Click to view the MathML source">L_d$L_d$, transfer spectra show spectral backscatter from sub-filter to intermediate scales, as reported elsewhere. However, we find that this spectral backscatter is due to viscous effects at vertical scales around the test filter. It is also shown that there is a non-local energy transfer from scales larger than the buoyancy scale 54615303472&_mathId=si82.gif&_user=111111111&_pii=S0997754615303472&_rdoc=1&_issn=09977546&md5=11f286f10063caa4b8d0074103f85f98" title="Click to view the MathML source">L_b$L_b$ to small scales. The effective turbulent Prandtl number spectra demonstrate that the assumption 54615303472&_mathId=si83.gif&_user=111111111&_pii=S0997754615303472&_rdoc=1&_issn=09977546&md5=e27d28898a1ea9a83f359e6f9cb7f818" title="Click to view the MathML source">Pr_t≈1$P{r}_t\approx 1$ is reasonable for the local energy transfer.