WIND FLOW AND TURBULENCE STATISTICS IN AND ABOVE AN URBAN STREET CANYON IN AKURE, NIGERIA

Abstract

This study investigates the wind flow and turbulence characteristics in and above an urban street canyon in Akure City Centre, Southwest Nigeria. The data used for this study were obtained between June 2013 – December, 2013 in the street canyon bordered by the Akure Central Mosque to the north and the Oja-Oba (Oba’s Ultra-Modern Market) to the south on Oba Adesida road, Akure with height to width ratio H/W = 12/30. Wind speed and direction were simultaneously monitored on a lamppost in the middle of the road at two levels ( in-street, 3m and roof level, 12m) within and above the canyon, using RM Young wind sentry cup-anemometer and wind vane system . Traffic count was also taken using a digital traffic counter. Data analysis was carried out using descriptive statistics in Microsoft excel. Flow channeling, recirculation and helical vortices (spiraling) are identified in the canyon for along street (220ᵒ - 250ᵒ), across street (190ᵒ - 170ᵒ) and oblique (120ᵒ - 150ᵒ), roof level flows. Turbulence kinetic energy and turbulence intensity are also observed to be strongly dependent on the roof-top wind direction within the canyon. Turbulence kinetic energy and wind speed decrease within the canyon for across street roof-top flow, while turbulence intensity increases within and above the canyon. Small changes in roof-level wind direction are found to have profound influences on the behavior of in-street flow patterns. Consequently, variability in background flow direction can lead to highly scattered in-street mean flow. Flow disturbance by vehicular traffic also appears to increase the flow complexity for low wind conditions