Three-dimensional wake dynamics behind a tapered cylinder with large taper ratio
We have performed direct numerical simulations of flow past a tapered circular cylinder during the early transition to three dimensions for two successive taper ratios (TR) of 20 and 12.5. Our results indicate the random occurrence of vortex splits and dislocations as the topology of the shedding si...
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description | We have performed direct numerical simulations of flow past a tapered circular cylinder during the early transition to three dimensions for two successive taper ratios (TR) of 20 and 12.5. Our results indicate the random occurrence of vortex splits and dislocations as the topology of the shedding signature. In particular, we observe oblique cellular shedding with multiple spanwise patterns and oppositely oriented oblique cells in the shed structure. Unlike flow imposed shear, the vortex formation length becomes sensitive to the taper ratio, which removes oblique frequency waves noticed for lower shear rate. The local Strouhal frequency (Stz) at the higher TR case exhibits a decreasing trend with remarkably smaller finite jumps at the cell boundaries and is found close to uniform cylinder flow. The wavelet analysis reveals the narrowing of the spectrum at a lower TR. A higher TR case shows a distinctly regular and evenly spaced spectrum which does not reach the maximum Stz, making it a rare event. The present results show that tapering causes the appearance of a secondary motion, which completely reverses at the downstream cylinder wake. Our numerical calculations show that pressure has an indirect role in the growth of the secondary instabilities, where isobars align along with the taper profile. The geometrically induced shear promotes greater mixing in the near wake, and we found that the maximum cross-stream velocity never exceeds 10% of the mean flow even with the steepest TR. The streamwise growth of the defect layer is slower for increasing TR and reaches an early saturation. Although the velocity deficit is higher at the steepest TR, it causes a delay in the momentum recovery along the streamwise direction. The shape factor for the lower TR case shows a delay in the laminar–turbulent transition. Finally, our global stability analysis results employing dynamic mode decomposition revealed a nonlinear dynamical system with spanwise dissipation of the dynamic modes. |
doi_str_mv | 10.1063/5.0010960 |
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Our results indicate the random occurrence of vortex splits and dislocations as the topology of the shedding signature. In particular, we observe oblique cellular shedding with multiple spanwise patterns and oppositely oriented oblique cells in the shed structure. Unlike flow imposed shear, the vortex formation length becomes sensitive to the taper ratio, which removes oblique frequency waves noticed for lower shear rate. The local Strouhal frequency (Stz) at the higher TR case exhibits a decreasing trend with remarkably smaller finite jumps at the cell boundaries and is found close to uniform cylinder flow. The wavelet analysis reveals the narrowing of the spectrum at a lower TR. A higher TR case shows a distinctly regular and evenly spaced spectrum which does not reach the maximum Stz, making it a rare event. The present results show that tapering causes the appearance of a secondary motion, which completely reverses at the downstream cylinder wake. Our numerical calculations show that pressure has an indirect role in the growth of the secondary instabilities, where isobars align along with the taper profile. The geometrically induced shear promotes greater mixing in the near wake, and we found that the maximum cross-stream velocity never exceeds 10% of the mean flow even with the steepest TR. The streamwise growth of the defect layer is slower for increasing TR and reaches an early saturation. Although the velocity deficit is higher at the steepest TR, it causes a delay in the momentum recovery along the streamwise direction. The shape factor for the lower TR case shows a delay in the laminar–turbulent transition. Finally, our global stability analysis results employing dynamic mode decomposition revealed a nonlinear dynamical system with spanwise dissipation of the dynamic modes.</description><identifier>ISSN: 1070-6631</identifier><identifier>EISSN: 1089-7666</identifier><identifier>DOI: 10.1063/5.0010960</identifier><identifier>CODEN: PHFLE6</identifier><language>eng</language><publisher>Melville: American Institute of Physics</publisher><subject>Circular cylinders ; Computational fluid dynamics ; Computer simulation ; Dynamic stability ; Fluid dynamics ; Fluid flow ; Isobars ; Physics ; Shape factor ; Shear rate ; Shedding ; Stability analysis ; Tapering ; Topology ; Wavelet analysis</subject><ispartof>Physics of fluids (1994), 2020-06, Vol.32 (6)</ispartof><rights>Author(s)</rights><rights>2020 Author(s). 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Our results indicate the random occurrence of vortex splits and dislocations as the topology of the shedding signature. In particular, we observe oblique cellular shedding with multiple spanwise patterns and oppositely oriented oblique cells in the shed structure. Unlike flow imposed shear, the vortex formation length becomes sensitive to the taper ratio, which removes oblique frequency waves noticed for lower shear rate. The local Strouhal frequency (Stz) at the higher TR case exhibits a decreasing trend with remarkably smaller finite jumps at the cell boundaries and is found close to uniform cylinder flow. The wavelet analysis reveals the narrowing of the spectrum at a lower TR. A higher TR case shows a distinctly regular and evenly spaced spectrum which does not reach the maximum Stz, making it a rare event. The present results show that tapering causes the appearance of a secondary motion, which completely reverses at the downstream cylinder wake. Our numerical calculations show that pressure has an indirect role in the growth of the secondary instabilities, where isobars align along with the taper profile. The geometrically induced shear promotes greater mixing in the near wake, and we found that the maximum cross-stream velocity never exceeds 10% of the mean flow even with the steepest TR. The streamwise growth of the defect layer is slower for increasing TR and reaches an early saturation. Although the velocity deficit is higher at the steepest TR, it causes a delay in the momentum recovery along the streamwise direction. The shape factor for the lower TR case shows a delay in the laminar–turbulent transition. Finally, our global stability analysis results employing dynamic mode decomposition revealed a nonlinear dynamical system with spanwise dissipation of the dynamic modes.</description><subject>Circular cylinders</subject><subject>Computational fluid dynamics</subject><subject>Computer simulation</subject><subject>Dynamic stability</subject><subject>Fluid dynamics</subject><subject>Fluid flow</subject><subject>Isobars</subject><subject>Physics</subject><subject>Shape factor</subject><subject>Shear rate</subject><subject>Shedding</subject><subject>Stability analysis</subject><subject>Tapering</subject><subject>Topology</subject><subject>Wavelet analysis</subject><issn>1070-6631</issn><issn>1089-7666</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2020</creationdate><recordtype>article</recordtype><recordid>eNqdkM1Lw0AQxRdRsFYP_gcLnhRSZ7LNpjlK8QsKeqjnZbofdmuaxN3Ukv_elBS8e5ph5sfjvcfYNcIEQYr7bAKAUEg4YSOEWZHkUsrTw55DIqXAc3YR4wYARJHKEXtfroO1ifFbW0VfV1TyPX1ZbrqKtl5HvrJrXxlOvKXGBmu47sr-YAPf-3bNSwqfdvjxQK2vL9mZozLaq-Mcs4-nx-X8JVm8Pb_OHxaJFmneJmgxL2bTnJxbpWSMQYczJ0TmjHDGTo1z5DLSAhAFAeawkn0GKY0mjQLEmN0Muk2ov3c2tmpT70LvP6p0ilkmUQrZU7cDpUMdY7BONcFvKXQKQR0KU5k6FtazdwMbtW8PUar_wT91-ANVY5z4BQgpeaU</recordid><startdate>20200601</startdate><enddate>20200601</enddate><creator>De, Arnab Kumar</creator><creator>Sarkar, Sandip</creator><general>American Institute of Physics</general><scope>AAYXX</scope><scope>CITATION</scope><scope>8FD</scope><scope>H8D</scope><scope>L7M</scope><orcidid>https://orcid.org/0000-0003-4647-954X</orcidid><orcidid>https://orcid.org/0000-0002-4442-5882</orcidid></search><sort><creationdate>20200601</creationdate><title>Three-dimensional wake dynamics behind a tapered cylinder with large taper ratio</title><author>De, Arnab Kumar ; Sarkar, Sandip</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c327t-1e179847affb2addd1f18f335fd3fde4dffaf5ac30113a0170b610766dcac1303</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2020</creationdate><topic>Circular cylinders</topic><topic>Computational fluid dynamics</topic><topic>Computer simulation</topic><topic>Dynamic stability</topic><topic>Fluid dynamics</topic><topic>Fluid flow</topic><topic>Isobars</topic><topic>Physics</topic><topic>Shape factor</topic><topic>Shear rate</topic><topic>Shedding</topic><topic>Stability analysis</topic><topic>Tapering</topic><topic>Topology</topic><topic>Wavelet analysis</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>De, Arnab Kumar</creatorcontrib><creatorcontrib>Sarkar, Sandip</creatorcontrib><collection>CrossRef</collection><collection>Technology Research Database</collection><collection>Aerospace Database</collection><collection>Advanced Technologies Database with Aerospace</collection><jtitle>Physics of fluids (1994)</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>De, Arnab Kumar</au><au>Sarkar, Sandip</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Three-dimensional wake dynamics behind a tapered cylinder with large taper ratio</atitle><jtitle>Physics of fluids (1994)</jtitle><date>2020-06-01</date><risdate>2020</risdate><volume>32</volume><issue>6</issue><issn>1070-6631</issn><eissn>1089-7666</eissn><coden>PHFLE6</coden><abstract>We have performed direct numerical simulations of flow past a tapered circular cylinder during the early transition to three dimensions for two successive taper ratios (TR) of 20 and 12.5. Our results indicate the random occurrence of vortex splits and dislocations as the topology of the shedding signature. In particular, we observe oblique cellular shedding with multiple spanwise patterns and oppositely oriented oblique cells in the shed structure. Unlike flow imposed shear, the vortex formation length becomes sensitive to the taper ratio, which removes oblique frequency waves noticed for lower shear rate. The local Strouhal frequency (Stz) at the higher TR case exhibits a decreasing trend with remarkably smaller finite jumps at the cell boundaries and is found close to uniform cylinder flow. The wavelet analysis reveals the narrowing of the spectrum at a lower TR. A higher TR case shows a distinctly regular and evenly spaced spectrum which does not reach the maximum Stz, making it a rare event. The present results show that tapering causes the appearance of a secondary motion, which completely reverses at the downstream cylinder wake. Our numerical calculations show that pressure has an indirect role in the growth of the secondary instabilities, where isobars align along with the taper profile. The geometrically induced shear promotes greater mixing in the near wake, and we found that the maximum cross-stream velocity never exceeds 10% of the mean flow even with the steepest TR. The streamwise growth of the defect layer is slower for increasing TR and reaches an early saturation. Although the velocity deficit is higher at the steepest TR, it causes a delay in the momentum recovery along the streamwise direction. The shape factor for the lower TR case shows a delay in the laminar–turbulent transition. Finally, our global stability analysis results employing dynamic mode decomposition revealed a nonlinear dynamical system with spanwise dissipation of the dynamic modes.</abstract><cop>Melville</cop><pub>American Institute of Physics</pub><doi>10.1063/5.0010960</doi><tpages>16</tpages><orcidid>https://orcid.org/0000-0003-4647-954X</orcidid><orcidid>https://orcid.org/0000-0002-4442-5882</orcidid></addata></record> |
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subjects | Circular cylinders Computational fluid dynamics Computer simulation Dynamic stability Fluid dynamics Fluid flow Isobars Physics Shape factor Shear rate Shedding Stability analysis Tapering Topology Wavelet analysis |
title | Three-dimensional wake dynamics behind a tapered cylinder with large taper ratio |
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