Ground vortex aerodynamics under crosswind conditions

An experimental study was performed to investigate ground vortex formation under crosswind conditions using stereoscopic particle image velocimetry and in-duct total pressure measurements. The effect of velocity ratio, non-dimensional height, approaching boundary layer thickness and yaw angle are assessed using vortex strength and in-duct distortion descriptors. The flow-field is characterized by a single ground vortex which increases in strength as the velocity ratio is reduced. The vortex characteristics depend on the ground clearance with a stronger vortex observed at lower intake heights. For a high ground clearance, the vortex strength reaches a local maximum before reducing towards zero as the capture streamtube no longer interacts with the ground plane. At a low ground clearance, the vortex strength is strong enough to induce a lip separation. The approaching boundary layer thickness has no notable influence on the vortex characteristics. Reducing the intake yaw angle from a crosswind to a headwind configuration leads to a monotonic decrease in vortex strength with the data following a sin3(ψ) relationship, where ψ is the yaw angle. The distortion coefficient was also monotonic with yaw angle; however, the dependence was sin6(ψ).