Published online by Cambridge University Press: 25 May 2009
A model of hairy medium is developed using a homogenized approach, and the fluidflow around a circular cylinder partially coated with hair is analysed by meansof numerical simulations. The capability of this coating to adapt to thesurrounding flow is investigated, and its benefits are discussed in the contextof separation control. This fluid–structure interaction problem is solvedwith a partitioned approach, based on the direct resolution of theNavier–Stokes equations together with a nonlinear set of equationsdescribing the dynamics of the coating. A volume force, arising from thepresence of a cluster of hair, provides the link between the fluid and thestructure problems. For the structure part, a subset of reference elementsapproximates the whole layer. The dynamics of these elements is governed by aset of equations based on the inertia, elasticity, interaction and losseseffects of articulated rods. The configuration chosen is that of thetwo-dimensional flow past a circular cylinder at Re = 200, a simple and well-documented test case. Aerodynamicsperformances quantified by the Strouhal number, the drag and the maximum lift inthe laminar unsteady regime are modified by the presence of the coating. A setof parameters corresponding to a realistic coating (length of elements,porosity, rigidity) is found, yielding an average drag reduction of 15% and adecrease of lift fluctuations by about 40%, associated to a stabilization of thewake.
Movie 1. Top frame: instantaneous vorticity contours of the motion past a ciliated cylinder. Blue colours denote clockwise vorticity. Only reference cilia are shown in the figure, modeling a dense coating which self-adapts to the surrounding flow. Bottom frames display the time history of the drag and lift coefficients with solid lines (dashed lines represent the case without actuators).
Movie 2. Time history of the vertical velocity contours in the developed, periodic regime. Blue colours denote velocity directed from the top towards the bottom. The motion of the reference cilia is displayed in the top frame. The bottom frame shows scaled vectors of the force produced by the coating, which counteracts the mouvement of the fluid.