Evaluation of dominant momentum transfer mechanisms across a part of the city of Abu Dhabi

Quantifying and understanding momentum transfer close to and above buildings within a city, and the mixing and transport within the Urban Canopy Layer (UCL) are important to tackle problems such as air pollution, the heat island effect and other transport phenomena. The correct temporal and spatial averaging of the Navier-Stokes equations give rise to three new terms that constitute the fluid's shear stress. The two most significant are the turbulent stress and the dispersive stress. Their relative importance has been studied in the literature but, as Manes, et al. [1] point out, analysing only the value of these stresses might be misleading for assessing the dominant momentum transfer mechanisms involved. The derivate of the turbulent and dispersive stresses dictate the Navier-Stokes equations and thus, these should be studied. Furthermore, the flow's turbulent characteristics and the turbulent stress inside the urban canopy and right above it, have been extensively studied in field campaigns, laboratory experiments and numerical simulations, although most of these studies make use of arrays of cuboids as proxies for buildings. Numerical simulation of real cities, rather than arrays of cuboids, involve much greater model complexity and computation time. A 3D steady-state Reynolds Averaged Navier-Stokes equations (RANS) simulation is conducted to derive and evaluate the dominant transfer mechanisms across a real city - Abu Dhabi.