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SUMMARY:Synchronized motion between elastic waves in a phononic structure 
 and fluid waves in an interfacing flow - Mahmoud Hussein (University of Co
 lorado Boulder)
DTSTART:20230525T080000Z
DTEND:20230525T084500Z
UID:TALK198904@talks.cam.ac.uk
DESCRIPTION:Flow control is a many-decades old engineering problem of a mu
 lti-disciplinary nature. It is concerned with devising passive or active m
 eans of intervention with the flow structure and its underlying mechanisms
  in a manner that causes desirable changes in the overall flow behavior. F
 or streamlined bodies cruising through a flow\, such as air or water\, the
 re is a key interest in the control of flow instabilities which manifest a
 s fluid waves. These are disturbances or fluctuations in the flow velocity
  field that if left to grow are likely to trigger transition of the flow f
 rom laminar to turbulent\, which in turn causes significant increases in s
 kin-friction drag. A rise in drag reduces the fuel efficiency in aircrafts
  and ships. It is therefore desired to device intervention methods to impe
 de the growth of these instabilities. Alternatively\, in some scenarios\, 
 the objective may be to speed up the growth of the instabilities and lamin
 ar-to-turbulent transition to prevent or delay flow separation.&nbsp\;\nIn
  recent research\, we have shown that phonon motion underneath a surface i
 nteracting with a flow may be tuned to cause the flow to stabilize\, or de
 stabilize\, as desired [Hussein et al.\, Proc. R. Soc. A\, 2015]. The unde
 rlying control mechanism utilizes core concepts from crystal physics\, pri
 marily\, the principle of destructive or constructive interferences and th
 e notion of symmetry breaking. This is realized by installing a &ldquo\;ph
 ononic subsurface&rdquo\; (PSub)\, which is an architectured structure pla
 ced in the subsurface region and configured to extend all the way such tha
 t its edge is exposed to the flow\, forming an elastic fluid-structure int
 erface. The PSub may take the form of a phononic crystal or an elastic met
 amaterial\, with finite extent\, and is typically oriented perpendicular t
 o the fluid-structure interface. It is engineered to exhibit specific freq
 uency-dependent amplitude and phase response characteristics at the edge e
 xposed to the flow. We will present results demonstrating perfectly synchr
 onized passive phased response and energy exchange between the elastic dom
 ain of a PSub and the perturbation (instability) field within an interfaci
 ng flow (e.g.\, flow in a channel retrofitted with a PSub underneath the c
 hannel walls). These results suggest a new paradigm in flow control based 
 exclusively on principles from phononics.
LOCATION:Seminar Room 1\, Newton Institute
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