The Quarterly Journal of Mechanics and Applied Mathematics Advance Access originally published online on March 7, 2007
The Quarterly Journal of Mechanics and Applied Mathematics 2007 60(2):161-200; doi:10.1093/qjmam/hbm003
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The SaffmanTaylor problem for an extremely shear-thinning fluid

( Section of Theoretical Mechanics, University of Nottingham, Nottingham NG7 2RD )
Giles.Richardson{at}nottingham.ac.uk
Received 2 August 2006.
Revise 16 January 2007.
| Abstract |
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We consider a steady flow driven by pushing a finger of gas into a highly shear-thinning power-law fluid, with exponent n, in a Hele-Shaw channel. We formulate the problem in terms of the streamfunction
, which satisfies the p-Laplacian equation
(with
), and investigate travelling wave solutions in the large-n (extreme shear-thinning) limit. We take a Legendre transform of the free-boundary problem for
, which reduces it to a linear problem on a fixed domain. The solution to this problem is found by using matched asymptotic expansions and the resulting shape of the finger deduced (being, to leading order, a semi-infinite strip). The nonlinear problem for the streamfunction is also treated using matched asymptotic expansion in the physical plane. The finger-width selection problem is briefly discussed in terms of our results.