Jørgen R. Aarnes, Omer Babiker, Anqing Xuan, Lian Shen, Simen Å. Ellingsen
{"title":"自由表面湍流中凹陷和疤痕下的涡旋结构","authors":"Jørgen R. Aarnes, Omer Babiker, Anqing Xuan, Lian Shen, Simen Å. Ellingsen","doi":"arxiv-2409.05409","DOIUrl":null,"url":null,"abstract":"Turbulence beneath a free surface leaves characteristic long-lived signatures\non the surface, such as upwelling 'boils', near-circular 'dimples' and\nelongated 'scars', easily identifiable by eye, e.g., in riverine flows. In this\npaper, we use Direct Numerical Simulations to explore the connection between\nthese surface signatures and the underlying vortical structures. We investigate\ndimples, known to be imprints of surface-attached vortices, and scars, which\nhave yet to be extensively studied, by analysing the conditional probabilities\nthat a point beneath a signature is within a vortex core as well as the\ninclination angles of sub-signature vorticity. The analysis shows that the\nlikelihood of vortex presence beneath a dimple decreases from the surface down\nthrough the viscous and blockage layers in a near-Gaussian manner, influenced\nby the dimple's size and the bulk turbulence. When expressed as a function of\ndepth over the Taylor microscale $\\lambda_T$, this probability is independent\nof Reynolds and Weber number. Conversely, the probability of finding a vortex\nbeneath a scar increases sharply from the surface to a peak at the edge of the\nviscous layer, at a depth of approximately $\\lambda_T/4$. Distributions of\nvortical orientation also show a clear pattern: a strong preference for\nvertical alignment below dimples and an equally strong preference for\nhorizontal alignment below scars. Our findings suggest that scars can be\ndefined as imprints of horizontal vortices approximately a quarter of the\nTaylor microscale beneath the surface, analogous to how dimples can be defined\nas imprints of surface-attached vertical vortex tubes.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"11 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Vortex structures under dimples and scars in turbulent free-surface flows\",\"authors\":\"Jørgen R. Aarnes, Omer Babiker, Anqing Xuan, Lian Shen, Simen Å. Ellingsen\",\"doi\":\"arxiv-2409.05409\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Turbulence beneath a free surface leaves characteristic long-lived signatures\\non the surface, such as upwelling 'boils', near-circular 'dimples' and\\nelongated 'scars', easily identifiable by eye, e.g., in riverine flows. In this\\npaper, we use Direct Numerical Simulations to explore the connection between\\nthese surface signatures and the underlying vortical structures. We investigate\\ndimples, known to be imprints of surface-attached vortices, and scars, which\\nhave yet to be extensively studied, by analysing the conditional probabilities\\nthat a point beneath a signature is within a vortex core as well as the\\ninclination angles of sub-signature vorticity. The analysis shows that the\\nlikelihood of vortex presence beneath a dimple decreases from the surface down\\nthrough the viscous and blockage layers in a near-Gaussian manner, influenced\\nby the dimple's size and the bulk turbulence. When expressed as a function of\\ndepth over the Taylor microscale $\\\\lambda_T$, this probability is independent\\nof Reynolds and Weber number. Conversely, the probability of finding a vortex\\nbeneath a scar increases sharply from the surface to a peak at the edge of the\\nviscous layer, at a depth of approximately $\\\\lambda_T/4$. Distributions of\\nvortical orientation also show a clear pattern: a strong preference for\\nvertical alignment below dimples and an equally strong preference for\\nhorizontal alignment below scars. Our findings suggest that scars can be\\ndefined as imprints of horizontal vortices approximately a quarter of the\\nTaylor microscale beneath the surface, analogous to how dimples can be defined\\nas imprints of surface-attached vertical vortex tubes.\",\"PeriodicalId\":501270,\"journal\":{\"name\":\"arXiv - PHYS - Geophysics\",\"volume\":\"11 1\",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2024-09-09\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"arXiv - PHYS - Geophysics\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/arxiv-2409.05409\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - PHYS - Geophysics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2409.05409","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
Vortex structures under dimples and scars in turbulent free-surface flows
Turbulence beneath a free surface leaves characteristic long-lived signatures
on the surface, such as upwelling 'boils', near-circular 'dimples' and
elongated 'scars', easily identifiable by eye, e.g., in riverine flows. In this
paper, we use Direct Numerical Simulations to explore the connection between
these surface signatures and the underlying vortical structures. We investigate
dimples, known to be imprints of surface-attached vortices, and scars, which
have yet to be extensively studied, by analysing the conditional probabilities
that a point beneath a signature is within a vortex core as well as the
inclination angles of sub-signature vorticity. The analysis shows that the
likelihood of vortex presence beneath a dimple decreases from the surface down
through the viscous and blockage layers in a near-Gaussian manner, influenced
by the dimple's size and the bulk turbulence. When expressed as a function of
depth over the Taylor microscale $\lambda_T$, this probability is independent
of Reynolds and Weber number. Conversely, the probability of finding a vortex
beneath a scar increases sharply from the surface to a peak at the edge of the
viscous layer, at a depth of approximately $\lambda_T/4$. Distributions of
vortical orientation also show a clear pattern: a strong preference for
vertical alignment below dimples and an equally strong preference for
horizontal alignment below scars. Our findings suggest that scars can be
defined as imprints of horizontal vortices approximately a quarter of the
Taylor microscale beneath the surface, analogous to how dimples can be defined
as imprints of surface-attached vertical vortex tubes.