Wall heating effect modelling for street canyon environment prediction: Experimental and numerical investigation

Abstract

Wall heating effect has been demonstrated to be a significant factor for street canyon microclimate. To improve the accuracy and practicality of street canyon microclimate prediction, multiple surface heating schemes with the consideration of both steady and unsteady wall heating effect are provided based on measured data. Numerical simulations were performed to investigate the wall heating effect on urban street canyon environment under all these modelling schemes. A scale-down water channel experimental system was established for flow field observation and model validation. Ri and Gr number was adopted for quantitative evaluation of wall heating effect. The experimental and numerical results demonstrate that wall heating scheme profoundly affect airflow patterns and thermal environment inside street canyons. Without considering the coupling thermal effect of street canyon surfaces, buoyant flow could be underestimated in steady single-surface heating assumption especially for ground and leeward wall heating conditions. With the combined heating of ground and leeward wall, airflow rotation would be enhanced, velocity near the leeward wall and upper outflow regions in a street canyon would be increased, when the Ri < -10.5 on the ground or the Gr > 1.16 × 10¹² on the leeward, the velocity distribution is relatively stable. In contrast with steady modelling schemes, less vortices occur under continuous unsteady surface heating conditions. Due to the accurate prediction, numerical model with unsteady multi-surface heating scheme is suggested for street canyon environment assessment. The findings underscore the critical role of coupling thermal effect in shaping street canyon microclimates, providing insights for environment optimizing in dense cities.