Form drag of fences placed in disturbed turbulent boundary layers

Wind tunnel studies on the drag characteristics of solid and porous fences placed in the turbulent boundary layer disturbed by the presence of an upst ream fence are reported. The analysis of the data reveals that the outer re gion of the approach velocity profile also influences the drag, contrary to the implication from the relationship of Ranga Raju et al. that only the v elocity distribution in the inner region is of consequence so far as the dr ag is concerned. A unique relationship has been obtained for the drag coeff icient 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 ad ditional parameter characterizing the approach velocity distribution over t he 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 dist urbed and undisturbed boundary layers developed over smooth, transitional, and rough surfaces.