Improving the Performance of a Reduced-Order Mass-Consistent Model for Urban Environments and Complex Terrain With a Higher-Order Geometrical Representation

Solid structures (buildings and topography) act as obstacles and significantly influence the wind flow. Because of their importance, faithfully representing the geometry of structures in numerical predictions is critical to modeling accurate wind fields. A higher-order geometry representation (the cut-cell method) is incorporated in the mass-consistent wind model, Quick Environmental System (QES)-Winds. To represent the differences between a stair-step and the cut-cell method, an urban case study (the Oklahoma City JU2003 experiments) and a complex terrain case (from the MATERHORN campaign) are modeled in QES-Winds. Comparison between the simulation results with the stair-step and cut-cell methods and the measured data for sensors close to walls and buildings showed that the sensitivity of the cut-cell method to changes in resolution is less than the stair-step method. Another way to improve the effects of solid geometries on the flow is to correct the velocity gradient near the surface. QES-Winds solves a conservation of mass equation and not a conservation of momentum equation. This means that QES-Winds overestimates velocity gradients near the surface which leads to higher rates of scalar transport. The near-surface parameterization is designed to correct the tangential near-surface velocity component using the logarithmic assumption. Results, including the near-wall parameterization, are evaluated with data from the Granite Mountain case (the MATERHORN campaign), which indicates that the parameterization slightly improves the performance of the model for cells near the surface. The new geometry representation and near-wall parameterization added to a mass-consistent platform, enhances the model's ability to simulate the effects of solid geometries on wind fields.