Applications of the numerical Green's function to urban flows

Theoretical predictions about urban boundary-layer flows are difficult to obtain. As an alternative to three-dimensional CFD simulations, vortex interactions can be analysed with the numerical Green's function. The Green's function characterises the strength and scale of vortex interactions and reflects the influence of the boundaries. Using the numerical Green's function, the regime transitions from isolated roughness to wake interference and wake interference to skimming flow are determined. There is good agreement with large-eddy simulations and the transition values reported in the literature. Applications to step-up and step-down canyons will also be described.