Abstract
Experimental investigations using wind and water tunnels have long been a
staple of fluid mechanics research for a large number of applications. These
experiments often single out a specific physical process to be investigated,
while studies involving multiscale and multi-physics processes are rare due to
the difficulty and complexity in the experimental setup. In the era of climate
change, there is an increasing interest in innovative experimental studies in
which fluid (wind and water) tunnels are employed for modelling multiscale,
multi-physics phenomena of the urban climate. High-quality fluid tunnel
measurements of urban-physics related phenomena are also much needed to
facilitate the development and validation of advanced multi-physics numerical
models. As a repository of knowledge in modelling these urban processes, we
cover fundamentals, recommendations and guidelines for experimental design,
recent advances and outlook on eight selected research areas, including (i)
thermal buoyancy effects of urban airflows, (ii) aerodynamic and thermal
effects of vegetation, (iii) radiative and convective heat fluxes over urban
materials, (iv) influence of thermal stratification on land-atmosphere
interactions, (v) pollutant dispersion, (vi) indoor and outdoor natural
ventilation, (vii) wind thermal comfort, and (viii) urban winds over complex
urban sites. Further, three main challenges, i.e., modelling of multi-physics,
modelling of anthropogenic processes, and combined use of fluid tunnels, scaled
outdoor and field measurements for urban climate studies, are discussed.