Large-Eddy Simulations of the Flow Over an Isolated Three-Dimensional Hill

Atmospheric three-dimensional (3D) mean and turbulent flow over an isolated 3D hill of cosine-squared cross-section and a smooth surface are studied by large-eddy simulations validated against data from a wind-tunnel experiment. Many features of the 3D flow across the hill are identified through analyzing mean and turbulent quantities on three surfaces, including a vertical cross-section across the hilltop, and surfaces of vertical distances of 0.25h and 1.25h from the ground, where h is the hill height. Besides flow blocking and separation with a recirculation region immediately upstream and downstream of the hill, respectively, a spiral-shaped structure wandering in both the lateral and vertical directions develops, accompanied by the wake and shear regions where sweep and ejection events play different roles in momentum transfer. The secondary rotations in the wake flow as well as the inner and outer rotations associated with the core vortex are also identified, together with other features.