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SUMMARY:The internal structure\, and entrainment\, of turbulent fountains 
 - Henry Burridge (Imperial College London)
DTSTART:20230616T114500Z
DTEND:20230616T124500Z
UID:TALK200656@talks.cam.ac.uk
CONTACT:Paras Vadher
DESCRIPTION:Results are presented based on data from high-fidelity DNS sim
 ulations of a turbulent forced fountain (Re0 = 1\,667\, Fr0 = 21). Within 
 a quiescent environment\, of uniform density\, a steady flow of relatively
  dense fluid is forced vertically upwards (from a circular source). These 
 flows rise up as a negatively buoyant jet\, and after some distance the bu
 oyancy reverses the flow causing it to fall back and form a downflow. For 
 sufficiently long observations\, the flow is statistically steady\, and th
 e fountain is characterised by the downflow enshrouding the dense upflowin
 g jet-like core\, atop of which sits a highly periodic unstable region of 
 flow that forms the fountain cap. Consideration of the physics identifies 
 that these fountains exhibit entrainment (herein the transfer of mass\, mo
 mentum\, buoyancy or other scalars by either mean or turbulent flow proces
 ses) across at least three physically meaningful interfaces. At the founta
 in outer boundary\, entrainment occurs across a turbulent/non-turbulent in
 terface. Internally the flow can be divided\, based on the loci of points 
 of zero mean vertical velocity\, into an upflow and a downflow\; or into a
 n inner and outer flow\, based on the loci of point of zero mean mass tran
 sport\, i.e. a separatrix. Both of these internal boundaries are turbulent
 /turbulent interfaces\, at which entrainment driven by turbulent flow proc
 esses dominates the classical mean flow entrainment. Reynolds averaging th
 e data\, we show that existing models of fountains fail to capture these i
 mportant internal entrainment processes\; conditionally averaging the data
  shows great promise for accurately capturing these dynamics over much of 
 the fountain height. Understanding and modelling the fountain cap region r
 emains an outstanding challenge.\n
LOCATION:JDB Seminar room
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