Comparison of Measured and Numerically Modeled Wind in the Rancho Bernardo Trails Community

Wildfires have caused devastating damage to wildlife, structures, and human lives. Here in southern California, catastrophic wildfires are greatly influenced by the Santa Ana winds. Research is being funded by the National Institute of Standards and Technology (NIST) to study the wind patterns in the Rancho Bernardo Trails neighborhood which burned catastrophically in 2007.;Wind speeds, directions, temperature, and humidity in the Rancho Bernardo Trails were monitored at 17 different locations to determine how wind moves through this community of hills and canyons, and ultimately to understand quantitatively the effects of Santa Ana Winds on wildfires.;A Sonic Detecting and Ranging Unit (SoDAR) is set-up northeast of the community to measure incoming and exiting winds by emitting beep-like sounds so wind speeds can be measured at different altitudes. The experimental data collected by the SoDAR was used as boundary conditions for simulations ran using NIST's Fire Dynamics Simulator (FDS). A grid convergence study was performed in FDS using a 1.2 x 1.2 km terrain map of the Trails community with a westerly boundary condition. Boundary layer profiles were compared at each location in the domain where actual instruments exist in the community. The FDS results of the three differently sized computational grids showed that there was grid independence at most of the measurement sites. However, there were a few select instances where each grid was not in agreement.;Case studies were performed on tracked Santa Ana events in FDS. The FDS model was set-up using a 1.2 x 1.2 km terrain map of the community with a time dependent boundary condition obtained from measured SoDAR data during a Santa Ana event. Wind speeds and directions were recorded at actual instrument locations in the domain. Data extracted from these heights in the model were then compared to experimental data. The comparison of the model and experimental results showed that the locations relatively close to the boundary condition inlet displayed wind behavior dominated by the boundary condition. The locations relatively far from the inlet displayed wind behavior on par with the experimental data.