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SUMMARY:Sharks\, Aeroplanes and the Rotating-Disk Boundary Layer - Prof. P
 eter Thomas
DTSTART:20160422T120000Z
DTEND:20160422T130000Z
UID:TALK64840@talks.cam.ac.uk
CONTACT:Antoine Debugne
DESCRIPTION:The classic belief that surface roughness inevitably increases
  the skin-friction drag that acts on bodies moving through a fluid has bee
 n superseded [1\,2]. The right sort of roughness [3] can reduce drag. Evol
 ution discovered this long before Engineers did and equipped sharks with r
 ough skin. The challenge that remains for the Engineer is to establish wha
 t type of roughness exactly is energetically beneficial in the context of 
 any particular technological\, engineering application and then attempt to
  exploit this in industry.\n\nI will summarize results of our programme [4
 \,5] investigating the effects of surface roughness on the stability of th
 e boundary-layer flow over a rotating disk. This flow represents a generic
  example of a general class of boundary layers that share the common chara
 cteristic of a cross-flow velocity component. Boundary layers of this type
  exist\, for instance\, on highly-swept wings of aircraft. All such bounda
 ry layers display similar laminar-turbulent transition characteristics. Ou
 r results [4\,5] reveal stabilising\, that is energetically beneficial\, e
 ffects on the dominant instability mode responsible for transition in thes
 e boundary layers. Our goal is to develop theoretical methods to enable th
 e design of energetically optimal surface roughness for laminar-flow contr
 ol in the context of new\, passive drag-reduction techniques for boundary 
 layers with a cross-flow component.\n\nReferences:\n[1] Sirovich\, L. & Ka
 rlson\, S. 1997 Turbulent drag reduction by passive mechanisms\, Nature 38
 8\, 753. \n[2] Choi\, K.-S.\, 2006 The rough with the smooth\, Nature 440\
 , 754. \n[3] Carpenter\, P.W. 1997 The right sort of roughness\, Nature 38
 8\, 713. \n[4] Cooper\, A.J.\, Harris\, J.H.\, Garrett\, S.J.\, Özkan\, M
 . & Thomas\, P.J. 2015 The effects of anisotropic and isotropic roughness 
 on the convective stability of the rotating-disk boundary layer\, Phys. Fl
 uids. 27\, 014107. \n[5] Garrtett\, S.J.\, Cooper\, A.J.\, Harris\, J.H.\,
  Özkan\, M.\, Segalini\, A. & Thomas\, P.J. 2015 On the stability of von 
 Kármán rotating-disk boundary layers with radial anisotropic surface rou
 ghness\, Phys. Fluids. 28\, 014104
LOCATION:LR6\, Inglis Building\, CUED.
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