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SUMMARY:Asymptotic theory for acoustic instability of premixed combustion 
 - Professor Xuesong Wu\, Mathematics\, Imperial College London
DTSTART:20131206T160000Z
DTEND:20131206T170000Z
UID:TALK48055@talks.cam.ac.uk
CONTACT:Dr C. P.  Caulfield
DESCRIPTION:Acoustic instability of premixed combustion refers to large-sc
 ale self-sustained pressure fluctuations in a combustion chamber. It is a 
 typical multi-physics\, multi-scale problem in the sense that it arises du
 e to complex interactions among chemical reaction\, heat and mass transpor
 t\, hydrodynamics and acoustics\, which take place on distinctively differ
 ent scales. Such disparity of scales presents a formidable challenge for d
 irection numerical simulations\, but can be exploited mathematically to de
 rive simplified systems. Asymptotic techniques\, such as matched asymptoti
 c expansion\, can be used to analyse the small-scale inner structure of th
 e flame\, thereby characterizing the mutual interaction between the flame 
 and the ambient flow motion. In the so-called flamelet regime\, where the 
 length scale of the flow motion is much greater than the flame thickness\,
  this leads to the classical hydrodynamic theory of premixed combustion. H
 owever\, the theory assumes that the enthalpy (temperature and the mass fr
 action of the fuel) in the oncoming mixture are steady and homogeneous\, a
 nd the spontaneous sound of the flame is not accounted for explicitly. We 
 extends the formulation by allowing for enthalpy fluctuations\, and show t
 hat unsteady combustion necessarily emits spontaneous sound\, which acts s
 imultaneously on the flame. The resulting general theory for the flame-flo
 w-acoustic interactions is applied to simple cases to provide insights int
 o fundamental mechanisms of acoustic instability of premixed combustion.
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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