The long range persistence of wakes behind a row of roughness elements

• Published in: Journal of fluid mechanics Vol. 644; pp. 123 - 163
• Main Authors: GOLDSTEIN, M. E., SESCU, ADRIAN, DUCK, PETER W., CHOUDHARI, MEELAN
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.02.2010
• Subjects: Boundary layer; Exact sciences and technology; Flow velocity; Fluid dynamics; Fluid mechanics; Fundamental areas of phenomenology (including applications); Physics; Reynolds number; Surface roughness; Transition to turbulence; Turbulent flow; Turbulent flows, convection, and heat transfer; Rough wall; Digital simulation; Scaling laws; Roughness; Wakes; Modelling; Transition flow; Periodic configuration; Boundary layers; Turbulent laminar transition
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/S0022112009992102

We consider a periodic array of relatively small roughness elements whose spanwise separation is of the order of the local boundary-layer thickness and construct a local asymptotic high-Reynolds-number solution that is valid in the vicinity of the roughness. The resulting flow decays on the very short streamwise length scale of the roughness, but the solution eventually becomes invalid at large downstream distances and a new solution has to be constructed in the downstream region. This latter result shows that the roughness-generated wakes can persist over very long streamwise distances, which are much longer than the distance between the roughness elements and the leading edge. Detailed numerical results are given for the far wake structure.