Passive separation control using a self-adaptive hairy coating

Abstract

A model of hairy medium is developed using a homogenized approach, and the fluid flow around a circular cylinder partially coated with hair is analysed by means of numerical simulations. The capability of this coating to adapt to the surrounding flow is investigated, and its benefits are discussed in the context of separation control. This fluid–structure interaction problem is solved with a partitioned approach, based on the direct resolution of the Navier–Stokes equations together with a nonlinear set of equations describing the dynamics of the coating. A volume force, arising from the presence of a cluster of hair, provides the link between the fluid and the structure problems. For the structure part, a subset of reference elements approximates the whole layer. The dynamics of these elements is governed by a set of equations based on the inertia, elasticity, interaction and losses effects of articulated rods. The configuration chosen is that of the two-dimensional flow past a circular cylinder at Re=200, a simple and well-documented test case. Aerodynamics performances quantified by the Strouhal number, the drag and the maximum lift in the laminar unsteady regime are modified by the presence of the coating. A set of parameters corresponding to a realistic coating (length of elements, porosity, rigidity) is found, yielding an average drag reduction of 15% and a decrease of lift fluctuations by about 40%, associated to a stabilization of the wake

A Lattice Boltzmann–Immersed Boundary method to simulate the fluid interaction with moving and slender flexible objects

“…In particular, slender filament-like structures can be used as a wall coating able to influence the recirculating zones of separated flows (Favier et al, 2009;Bagheri et al, 2012).…”

Drag measurements in laterally confined 2D canopies: Reconfiguration and sheltering effect

“…46,47 There is also an increasing interest in theoretical models for drag force acting on poro-elastic systems. 19,21,[48][49][50][51] Few studies make explicit the influence of canopy density on drag. Through theoretical modelling, Gosselin and de Langre 52 investigated the effect of surface density on the Vogel exponent of a synthetic poro-elastic system.…”

The PELskin project—part I: fluid–structure interaction for a row of flexible flaps: a reference study in oscillating channel flow

“…This roll-up starts along the lateral side-walls of the cylinder and vorticity is then swept along the row of the flaps in transversal direction towards the inner part of the row, similar as in the case discussed herein. Therefore the observed travelling wave-type motion of the flaps in the cylinder wake Favier et al [2009]; Kunze and Bruecker [2012] is a result of the phase-shift between neighbouring flaps as documented herein. …”

“…Of particular interest to flow control, a wave-type motion along rows of flexible structures has been observed in the wake of bluff bodies, where such flexible structures are attached to the aft part. The hairs interact with the unsteady wake flow and show the emergence of travelling wave-like motion patterns [Favier et al, 2009]. Experimental studies of flow past cylinders with attached hairs proved the potential for these structures to modify the shedding cycle [Kunze and Bruecker, 2012].…”