

Artikel
First instability of the flow of shearthinning and shearthickening fluids past a circular cylinder
Författare: 
Lashgari, I., Pralits, J. O., Giannetti, F., Brandt, L.B. 
Dokumenttyp: 
Artikel 
Tillstånd: 
Publicerad 
Tidskrift: 
Journal of Fluid Mechanics 
Volym: 
701
201227 
År: 
2012 
AbstractThe first bifurcation and the instability mechanisms of shearthinning and shear thickening fluids flowing past a circular cylinder are studied using linear theory and nu merical simulations. Structural sensitivity analysis based on the idea of a "wavemaker" is performed to identify the core of the instability. The sheardependent viscosity is modeled by the Carreau model where the rheological parameters, the powerindex and the material time constant, are chosen in the range 0.4 ≤ n ≤ 1.75 and 0.1 ≤ λ ≤ 100. We show how shearthinning/shearthickening effects destabilize/stabilize the flow dramatically when scaling the problem with the reference zero shearrate viscosity. These variations are ex plained by modifications of the steady base flow due to the sheardependent viscosity; the instability mechanisms are only slightly changed. The characteristics of the base flow, drag coefficient and size of recirculation bubble are presented to assess shearthinning effects. We demonstrate that at critical conditions the local Reynolds number in the core of the instability is around 50 as for Newtonian fluids. The perturbation kinetic energy budget is also considered to examine the physical mechanism of the instability.

