A micro-aerodynamic decelerator based on permeable surfaces of nanofiber mats

This work deals with nonwoven permeable light mats made of submicron-diameter nanofibers. The nanofibers were obtained through electrospinning of polymer solutions. The mats were positioned on light pyramid-shaped frames. These platforms fell freely through the air, apex down, at a constant velocity. The drag of such passive airborne platforms is of significant interest in a number of modern aerodynamics applications including, for example, dispersion of "smart dust" carrying various chemical and thermal sensors, dispersion of seeds, as well as movement of small organisms with bristle appendages. In the present work, drag is measured using the free fall method supplemented by extensive flow visualization. The effects of platform weight, average nanofiber diameter, and porosity of the nonwoven mats on the drag force are studied. The results are compared to data for the corresponding impermeable structures that are covered with plastic wrap. The data are presented in the form of standard dependencies of drag coefficient on the Reynolds number of the structure. It was found that permeable platforms with holes on the order of several microns (which is about ten times the diameter of the nanofibers) are essentially impermeable for airflow.