An asymptotic theory for the high-Reynolds-number flow past a shear-free circular cylinder

• Published in: Journal of fluid mechanics 2021-08, Vol.920, Article A44
• Main Authors: Kumar, Anuj, Rehman, Nidhil M.A., Giri, Pritam, Shukla, Ratnesh K.
• Format: Article
• Language: English
• Subjects: Aquatic reptiles; Asymptotic properties; Boundary layer equations; Boundary layers; Circular cylinders; Computational fluid dynamics; Cylinders; Differential equations; Drag; Flow; Fluid flow; Fluid mechanics; High Reynolds number; Incompressible flow; Investigations; Inviscid flow; JFM Papers; Mathematical analysis; Newtonian fluids; Nonlinear dynamics; Perturbation; Reynolds number; Self-similarity; Shear; Stagnation point; Theories; Viscosity; Vorticity
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2021.446

We present an asymptotic theory for analytical characterization of the high-Reynolds-number incompressible flow of a Newtonian fluid past a shear-free circular cylinder. The viscosity-induced modifications to this flow are localized and except in the neighbourhood of the rear stagnation point, behave like a linear perturbation of the inviscid flow. Our theory gives a highly accurate description of these modifications by including the contribution from the most significant viscous term in a correctional perturbation expansion about an inviscid base state. We derive the boundary layer equation for the flow and deduce a similarity transformation that leads to a set of infinite, shear-free-condition-incompatible, self-similar solutions. By suitably combining members from this set, we construct an all-boundary-condition-compatible solution to the boundary layer equation. We derive the governing equation for vorticity transport through the narrow wake region and determine its closed-form solution. The near and far-field forms of our wake solution are desirably consistent with the boundary layer solution and the well-known, self-similar planar wake solution, respectively. We analyse the flow in the rear stagnation region by formulating an elliptic partial integro-differential equation for the distortion streamfunction that specifically accounts for the fully nonlinear and inviscid dynamics of the viscous correctional terms. The drag force and its atypical logarithmic dependence on Reynolds number, deduced from our matched asymptotic analysis, are in remarkable agreement with the high-resolution simulation results. The logarithmic dependence gives rise to a critical Reynolds number below which the viscous correction term, counterintuitively, reduces the net dissipation in the flow field.