Determination of Flow Characteristics of Mountain-Valley Systems by Numerical Modeling

Wind pressures on buildings and other structures, pedestrian level winds, wind-induced dispersion of pollutants in urban locations depend, among other factors, on the velocity profile and turbulence characteristics of the upcoming wind. These, in turn, depend on the roughness and general configuration of the upstream terrain. Consequently, wind standards and codes of practice typically assume upstream terrain of homogeneous roughness or provide explicit corrections for specific topographies such as hills or escarpments; for more complex situations they refer the practitioner to physical simulation in a boundary layer wind tunnel. The evolution of computational wind engineering makes the evaluation of wind velocities over complex terrain very attractive. In fact, significant progress has been made in the application of Computational Fluid Dynamics (CFD) for specific cases of escarpments, single and multiple hills, as well as valleys. Numerical modelling of wind flow consists of utilizing a set of differential equations (Navier-Stokes) describing the flow in a particular domain, say near an obstruction. The Reynolds-Averaged Navier-Stokes equations have been used in most of the studies dealing with wind flow over complex terrain such as that corresponding to a mountain-valley system. Turbulence of the flow is represented by a particular model, such as the well known k-ε model which is appropriate for the case of homogeneous isotropic turbulence. Descretization of the flow equations leads to a set of solvable algebraic equations. The simplification inherent in the use of algebraic equations is what makes the numerical approach so powerful and attractive. The following sections present and summarize the progress made in the numerical evaluation of wind flow over complex topographies.