Fig. 9

Visulization of the three-dimensional flow structures around the head geometries with the help of the \(\lambda _{2}\)-criterion for an Isovalue of \(\lambda _{2}=-(50u_{\infty })^2/C_{head}^2\) at a representative timestep during simulation for a wind speed of 10 km/h (upper row) and 20 km/h (lower row). Where \(C_{head}\) is the circumference of the head. The flow structures are additionally coloured with the vorticity around main flow direction (x-axis) to indicate the rotational direction of the vortices.