Short-term measurements of airflow and turbulence in two street canyons in Manchester

Ultrasonic anemometers have been used to make measurements of airflow and turbulence in two urban street canyons in Greater Manchester, UK. This paper concentrates mostly on results from one—an asymmetrical city centre canyon with complex building geometry, building heights up to 28 m and busy traffic. Data was recorded for a total of five working weeks in four separate periods in 2001 at one roadside location at a range of heights from 2 to 18 m. This data was supplemented by a series of mobile measurements at 2–4 m height at 18 different roadside locations within the same canyon. Although some features of a vortex-flow, as assumed in some (but by no means all) numerical models, was observed, other important flow features were found which, although canyon-specific, nevertheless indicate the ways in which flow in all real canyons may differ from the assumptions implicit in some models. Of particular importance were lateral channelled flow and sheltering in perpendicular flow. Profiles of turbulence are presented along with a simple model relating turbulence to wind speed and traffic flow rate. A strong influence of traffic on vertical turbulence production was found in a layer no deeper than 3 m. This influence was absent in measurements in a traffic-free suburban canyon.