Abstract
Falling properties of cinder models, non-simple shaped objects, were measured and three-dimensional falling trajectories were obtained by using video movies. Aerodynamic characteristics of cinder models were examined by the trajectory. The falling models imitated the configuration of cinders collected at the site of the experiment, Sakurajima volcano. Two types, one with sharp edges and one without sharp edges, were selected as representatives and a sphere was selected as reference model. The results showed that the drag coefficient varied with the falling velocity becoming smaller as the velocity increased. When the models fell with terminal velocity, the drag coefficients of the cinder models without and with sharp edges were about 0.5 and 0.6, respectively. The drag coefficient of the sphere model was about 0.3.
