A hydrodynamic model for calculating the pressure jump on the leeward slope of a roof during a horizontal air flow that is directed to its slope is proposed for the first time. The model takes the formation of vortices in a viscous layer of an air flow that decelerates in the flow direction into account. When a vortex departs from the viscous layer, flow acceleration occurs at the underlying surface, leading to a considerable pressure drop and to tearing the roof off. It is shown that the negative pressure jump at a site that is adjacent to the roof ridge can be decelerated by several percent with a decreased friction factor and an increased length of the portion of the roof where air flows without separation. A method for considerably reducing the pressure drop is proposed for the first time, viz., the installation of expanding air ducts on the roof, within which a compensatory pressure jump occurs. The results are verified by laboratory studies.
47.20.Ib Instability of boundary layers; separation
47.27.N- Wall-bounded shear flow turbulence
Department of Physics, Moscow State University, Moscow, 119991 Russia