Large-Eddy Simulation of a katabatic jet along a convexly curved slope. Part 1: statistical results.

Abstract

arge Eddy Simulation is performed to study a katabatic jet along a convexly curved slope with a maximum angle of about 35.5°. The design of this numerical simulation of turbulent shear flow is discussed and a qualitative assesment of the method is proposed. The katabatic flow is artificialy generated by ground surface cooling and a stable atmospheric boundary layer with constant stratification is considered as a reference state. A quantitative statistical analysis is used to describe the present turbulent flow, with a focus on the outer-layer shear of the katabatic jet which extends about 50 m above the jet maximum. The Prandtl model for a katabatic jet is applied to the present results and revisited versions of the model found in the literature are discussed with an emphasis on specific momentum and turbulent heat diffusion. The vertical and downslope variability of the turbulent kinetic energy budget is also discussed and it is shown that advection and production contributions in the downslope direction are far from negligible in katabatic flows along curved slopes. A specific effect that the convex curvature has on the katabatic jet is one of centrifugal deceleration, and an increase of the flow?s turbulent production and turbulent intensity in the outer-layer shear. A strong thickening of the outer-layer is also observed.