Stable–streamlined and helical cavities following the impact of Leidenfrost spheres

Handle URI:
http://hdl.handle.net/10754/625635
Title:
Stable–streamlined and helical cavities following the impact of Leidenfrost spheres
Authors:
Mansoor, Mohammad M. ( 0000-0001-9196-0960 ) ; Vakarelski, Ivan Uriev ( 0000-0001-9244-9160 ) ; Marston, J. O.; Truscott, T. T. ( 0000-0003-1613-6052 ) ; Thoroddsen, Sigurdur T. ( 0000-0001-6997-4311 )
Abstract:
We report results from an experimental study on the formation of stable–streamlined and helical cavity wakes following the free-surface impact of Leidenfrost spheres. Similar to the observations of Mansoor et al. (J. Fluid Mech., vol. 743, 2014, pp. 295–326), we show that acoustic ripples form along the interface of elongated cavities entrained in the presence of wall effects as soon as the primary cavity pinch-off takes place. The crests of these ripples can act as favourable points for closure, producing multiple acoustic pinch-offs, which are found to occur in an acoustic pinch-off cascade. We show that these ripples pacify with time in the absence of physical contact between the sphere and the liquid, leading to extremely smooth cavity wake profiles. More importantly, the downward-facing jet at the apex of the cavity is continually suppressed due to a skin-friction drag effect at the colliding cavity-wall junction, which ultimately produces a stable–streamlined cavity wake. This streamlined configuration is found to experience drag coefficients an order of a magnitude lower than those acting on room-temperature spheres. A striking observation is the formation of helical cavities which occur for impact Reynolds numbers and are characterized by multiple interfacial ridges, stemming from and rotating synchronously about an evident contact line around the sphere equator. The contact line is shown to result from the degeneration of Kelvin–Helmholtz billows into turbulence which are observed forming along the liquid–vapour interface around the bottom hemisphere of the sphere. Using sphere trajectory measurements, we show that this helical cavity wake configuration has 40 %–55 % smaller force coefficients than those obtained in the formation of stable cavity wakes.
KAUST Department:
Physical Sciences and Engineering (PSE) Division
Citation:
Mansoor MM, Vakarelski IU, Marston JO, Truscott TT, Thoroddsen ST (2017) Stable–streamlined and helical cavities following the impact of Leidenfrost spheres. Journal of Fluid Mechanics 823: 716–754. Available: http://dx.doi.org/10.1017/jfm.2017.337.
Publisher:
Cambridge University Press (CUP)
Journal:
Journal of Fluid Mechanics
KAUST Grant Number:
URF/1/2621-01-01
Issue Date:
23-Jun-2017
DOI:
10.1017/jfm.2017.337
Type:
Article
ISSN:
0022-1120; 1469-7645
Sponsors:
We gratefully acknowledge support from King Abdullah University of Science and Technology (KAUST), Office of Competitive Research Funds, under grant URF/1/2621-01-01.
Additional Links:
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/stablestreamlined-and-helical-cavities-following-the-impact-of-leidenfrost-spheres/F2C8CAD3E5E95F92800AABBBD4447E3D
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division

Full metadata record

DC FieldValue Language
dc.contributor.authorMansoor, Mohammad M.en
dc.contributor.authorVakarelski, Ivan Urieven
dc.contributor.authorMarston, J. O.en
dc.contributor.authorTruscott, T. T.en
dc.contributor.authorThoroddsen, Sigurdur T.en
dc.date.accessioned2017-10-03T12:49:30Z-
dc.date.available2017-10-03T12:49:30Z-
dc.date.issued2017-06-23en
dc.identifier.citationMansoor MM, Vakarelski IU, Marston JO, Truscott TT, Thoroddsen ST (2017) Stable–streamlined and helical cavities following the impact of Leidenfrost spheres. Journal of Fluid Mechanics 823: 716–754. Available: http://dx.doi.org/10.1017/jfm.2017.337.en
dc.identifier.issn0022-1120en
dc.identifier.issn1469-7645en
dc.identifier.doi10.1017/jfm.2017.337en
dc.identifier.urihttp://hdl.handle.net/10754/625635-
dc.description.abstractWe report results from an experimental study on the formation of stable–streamlined and helical cavity wakes following the free-surface impact of Leidenfrost spheres. Similar to the observations of Mansoor et al. (J. Fluid Mech., vol. 743, 2014, pp. 295–326), we show that acoustic ripples form along the interface of elongated cavities entrained in the presence of wall effects as soon as the primary cavity pinch-off takes place. The crests of these ripples can act as favourable points for closure, producing multiple acoustic pinch-offs, which are found to occur in an acoustic pinch-off cascade. We show that these ripples pacify with time in the absence of physical contact between the sphere and the liquid, leading to extremely smooth cavity wake profiles. More importantly, the downward-facing jet at the apex of the cavity is continually suppressed due to a skin-friction drag effect at the colliding cavity-wall junction, which ultimately produces a stable–streamlined cavity wake. This streamlined configuration is found to experience drag coefficients an order of a magnitude lower than those acting on room-temperature spheres. A striking observation is the formation of helical cavities which occur for impact Reynolds numbers and are characterized by multiple interfacial ridges, stemming from and rotating synchronously about an evident contact line around the sphere equator. The contact line is shown to result from the degeneration of Kelvin–Helmholtz billows into turbulence which are observed forming along the liquid–vapour interface around the bottom hemisphere of the sphere. Using sphere trajectory measurements, we show that this helical cavity wake configuration has 40 %–55 % smaller force coefficients than those obtained in the formation of stable cavity wakes.en
dc.description.sponsorshipWe gratefully acknowledge support from King Abdullah University of Science and Technology (KAUST), Office of Competitive Research Funds, under grant URF/1/2621-01-01.en
dc.publisherCambridge University Press (CUP)en
dc.relation.urlhttps://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/stablestreamlined-and-helical-cavities-following-the-impact-of-leidenfrost-spheres/F2C8CAD3E5E95F92800AABBBD4447E3Den
dc.subjectcavitationen
dc.subjectcontact linesen
dc.subjectdrag reductionen
dc.titleStable–streamlined and helical cavities following the impact of Leidenfrost spheresen
dc.typeArticleen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.identifier.journalJournal of Fluid Mechanicsen
dc.contributor.institutionDepartment of Chemical Engineering, Texas Tech University, Lubbock, TX 79409-3121, USAen
dc.contributor.institutionDepartment of Mechanical and Aerospace Engineering, Utah State University, Logan, UT 84322-4130, USAen
kaust.authorMansoor, Mohammad M.en
kaust.authorVakarelski, Ivan Urieven
kaust.authorThoroddsen, Sigurdur T.en
kaust.grant.numberURF/1/2621-01-01en
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