Local Wind Pressures for Rectangular Buildings in Turbulent Boundary Layers

Abstract

In this paper emphasis is mainly directed to external local wind pressures on isolated rectangularly-shaped bluff bodies immersed in deep turbulent boundary layer flow. A single rectangularly-shaped building in atmospheric boundary layer flow represents an idealized case. Especially in cities, buildings usually are surrounded by other structures, which may influence the local wind loads on buildings drastically. Nevertheless, knowledge of local wind loads on an isolated building, which may be considered as a reference case, is valuable for the design of cladding elements, glass panels and roof pavers. It is the objective of this paper, to provide this 'reference case'-information. Some relevant previous investigations which are concerned with local wind loads on rectangular buildings in turbulent boundary layers are mentioned. On the basis of own wind tunnel experiments properties and magnitudes of aerodynamic parameters (mean, rms, and peak pressure coefficients, spectral and probability densities) are discussed as a function of approach flow and building dimensions. l. Introduction and Background Information From aerodynamic point of view most buildings are so-called bluff or blunt bodies, in contrast to streamline bodies such as aircraft wings. When a bluff body is exposed to a flow of air which is no ideal fluid, i.e. the influence of viscosity is significant, the approaching flow is displaced, separates from the body, and free shear layers enclosing broad wakes are developing. The structure and curvature of the free shear layers separating from the body, and consequently the wake size, are strongly influenced by the turbulence of the approaching flow. Air flowing around bluff bodies results in distortion, deceleration, acceleration, separation and sometimes reattachment of flow. Turbulent boundary layer flows, i.e. the presence of a wind velocity profile and shear stress, as they are typical for natural wind, complicate the flow around bluff bodies drastically. This is illustrated in Figure 1. The afore-mentioned effects result in a distribution of flow-induced pressures acting over the body surface and a corresponding form drag. The friction drag of bluff bodies usually may be neglected for design purposes. 185