title: Friction factor of two-dimensional rough-boundary turbulent soap film flows.
abstract: We use momentum-transfer arguments to predict the friction factor f in two-dimensional turbulent soap film flows with rough boundaries (an analog of three-dimensional pipe flow) as a function of Reynolds number Re and roughness r , considering separately the inverse energy cascade and the forward enstrophy cascade. At intermediate Re, we predict a Blasius-like friction factor scaling of f proportional, variant Re{-1/2} in flows dominated by the enstrophy cascade, distinct from the energy cascade scaling of Re{-1/4} . For large Re, f approximately r in the enstrophy-dominated case. We use conformal map techniques to perform direct numerical simulations that are in satisfactory agreement with theory and exhibit data collapse scaling of roughness-induced criticality, previously shown to arise in the three-dimensional pipe data of Nikuradse.
authors: Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3080, USA.
authors: Nicholas
authors: N
authors: Guttenberg
authors: Nigel
authors: N
authors: Goldenfeld