Abstract
Collision experiments were made on tilting and fluttering disks in a vertical wind tunnel to evaluate the effects of falling attitude and fluttering motion on the riming of snow particles. Two disks of the same diameter were supported at the ends of needles inserted in the tunnel. One was tilted or given fluttering motion, and the other was set horizontal as a reference disk. Impact was given to the disks with water droplets at various air speeds. The collection efficiency of the tilted or fluttering disk was estimated in comparison with the reference disk.
The results showed that the effects of tilting and fluttering motion on the collection efficiency of the disks for droplets depend largely on the inertia of impacting droplets. For small inertia of droplets, the collection efficiency was increased by tilting. Small droplets around a cutoff point were collected more by tilting. The fluttering motion did not affect the collection efficiency except for a case of strong fluttering motion. This result could be explained in terms of deformation of air flow near the disk due to tilting or strong fluttering motion.
For large inertia of droplets, the collection efficiency was decreased by tilting, but was not affected by fluttering motion. This result could be interpreted by the decrease in the effective cross section of the disk against the airstream due to tilting.
The collection efficiency of the rear disk surface for droplets was decreased by tilting and was slightly increased by fluttering motion.
