Assessment of the Impact of a Low-Rise Flat Roofed Building on Ambient Wind Conditions

Abstract

Small wind turbines (SWT), representing a relatively new technology in the field of renewable energies, exhibit potential for a notable contribution to a sustainable urban energy supply accelerated by international climate agreements [1]. However, many uncertainties remain regarding site assessment, especially in the built environment. Wind conditions in areas below 30 m above ground, where small wind turbines are preferably installed, are affected by complex aerodynamic effects. Urban areas feature conditions often not considered by common CFD models and calculations. This paper focuses on the impact of low-rise flat roof buildings on the ambient wind flow. Contrary to other investigations on wind flow around complex obstacles relying on numerical fluid flow simulations or scaled wind tunnel experiments, the performed investigation relies on measurements over a flat-roofed building. The data acquired over a span of 7 months by several 3D-ultrasonic anemometers at the Lichtenegg test site (Lower Austria) was examined. In order to determine the impact of the building on ambient wind conditions, the horizontal and vertical wind velocity, turbulence intensity and direction scatter at several locations were compared to the uninfluenced inflow conditions. Moreover, in addition to the commonly calculated horizontal turbulence intensity, the vertical turbulence intensity was considered to gain a deeper understanding for the occurring aerodynamic effects. The measurement results indicate that some locations on or around the building are not suited for installing wind turbines, while others show increased wind potential compared to undisturbed wind stream. Based on findings obtained by the wind assessment, recommendations for ideal placing of small wind turbines on low-rise buildings are given.