Form Drag of Fences Placed in Disturbed Turbulent Boundary Layers

Abstract

Wind tunnel studies on the drag characteristics of solid and porous fences placed in the turbulent boundary layer disturbed by the presence of an upstream fence are reported. The analysis of the data reveals that the outer region of the approach velocity profile also influences the drag, contrary to the implication from the relationship of Ranga Raju et al. that only the velocity distribution in the inner region is of consequence so far as the drag is concerned. A unique relationship has been obtained for the drag coefficient based on the average velocity over the height of the fence in terms of the porosity, the shape factor of the approach boundary layer, and an additional parameter characterizing the approach velocity distribution over the height of the fence. This relationship is valid for 2D solid and porous fences placed in a flow with a zero pressure gradient for the cases of disturbed and undisturbed boundary layers developed over smooth, transitional, and rough surfaces.