Drag and wake structure of a quasi-dandelion pappus model at low and moderate Reynolds numbers: The effects of filament width

Abstract

The aerodynamic performance and wake structure of dandelion seed pappus have been numerically studied based on a simplified quasi-dandelion pappus (QDP) model with its filaments represented by rectangular cylinders. The filament width is chosen as the major geometric parameter for investigation. A rigorous measuring strategy is developed for the identification of the recirculation region width in the wake of the QDP model. Three regimes are distinguished as the filament width increases, i.e., a dandelion-like regime, a transition regime, and a disk-like regime. In the dandelion-like regime, the recirculation region widths are relatively large and monotonously decrease with the increase in Reynolds number. In the transition regime, the recirculation region widths are moderate and first decrease sharply at low Reynolds number and subsequently maintain an approximately invariant value. In the disk-like regime, the recirculation region widths are relatively small. The Reynolds number based on the recirculation region width is defined, and its correlation to the drag coefficient in a different regime is also discussed. In addition, as the QDP model turns from the dandelion-like regime to the disk-like regime, the pressure distribution in the wake turns from the recirculation region type to the flow stagnation type. The current study may provide a reference for the design of more efficient dandelion-like aircraft.