Experimental study of the impact of upstream mountain terrain and urban exposure on approaching wind characteristics.

The approaching wind profiles have a significant impact on the wind load of the structures as well as the urban climate, pollutant diffusion, and thermal comfort. Therefore, the study of its evolution is gaining attention as the city sparrows. This paper aims to study the effects of topography and morphology on the characteristics of the approaching wind. Wind tunnel tests were conducted to observe the mean velocity profiles downstream of three kinds of common terrain, which are roughness change from open to urban exposure, open exposure behind mountain terrain, and urban exposure behind mountain terrain. The results show that the ESDU transitional model overestimates velocity inside the IBL and underestimates IBL heights compared with experimental results. The rough exposure behind the mountain leads to smaller recirculation zones and a shorter reattachment location downstream compared with that of open exposure behind mountain. In addition, the evolution of mean velocity profiles over urban exposure behind the mountain is also compared with the results estimated according to current wind load provisions. Unfortunately, none of the current wind load provisions yields a reasonable estimation of the mean velocity profiles. The study aims to provide useful references in the study of the wind environment in mountainous urban area and the estimation of wind load on structures, as well as the future codification of wind load provisions. • New profile becomes equilibrium again at about 1175 m downstream of roughness change. • The ESDU model overestimate velocity inside the IBL and underestimate IBL heights. • Flow separates at leeward slopes between 13° and 14.5°, irrespective of roughness. • The surface roughness behind the mountain leads to smaller recirculation zones. • Current provisions lack regulations on the mean wind profile behind mountains. [ABSTRACT FROM AUTHOR]