Flow over a simple hill and its impact on wind speed, variability, and turbulence

Highly variable winds in complex terrain, together with high dependence of the fire spread rate on the slope inclination, make prediction of the fire behavior in sloped terrain very difficult. In general, enhanced fire spread rate in uphill direction is attributed to the effect of fire-induced convection, and flames tilting. However, not too much attention has been paid toward understanding basic effects of the flow over a hill on the fire spread, in terms of the topographically induced wind speed variability and turbulence.

In this study we perform numerical simulation of the flow over the isolated Askervein Hill, using the University of Utah LES model. We evaluate our model using available data set from the Askervein experiment (Taylor and Teunissen 1983), and investigate the topographically-induced flow features, potentially important in terms of the fire propagation. In particular, we analyze streamlines structure at various vertical levels, surface flow pattern, and spatial distribution of the surface wind speed variability at various time scales. Finally, we investigate potential effect of the topographically-modified flow on the variability in the fire line intensity.