Generation of large-scale swirling flows and vortex breakdown in multifan wind facilities

With the recent growing interest in Advanced Air Mobility (AAM), the need to test and validate the flyability of these vehicles in vortical winds has become imperative for manufacturers and regulatory agencies (FAA). Multifan wind facilities (windshapers) are now commonly used to test free-flying vehicles in repeatable and controllable wind patterns. In particular, large-scale swirling flows can be generated using multiple windshapers set at an angle with respect to each other. The swirling flow morphology can be finely tuned by adjusting the azimuthal and axial flow conditions. For suitable flow regimes, vortex breakdown has been observed. The vortex bursting phenomenon can be explored with high precision and controllability thanks to the degrees of freedom in regulating the various flow components. In the present experimental setup, the onset of vortex breakdown occurs at a fixed critical value for the ratio of the rotational to the axial volume fluxes. The phenomenon exhibits no hysteresis.