Rocks ejected from a volcanic eruption often cause loss of lives and structures. Aerodynamic characteristics are needed for evaluating motions of volcanic rocks for the reduction of damage. Falling motions of volcanic rock were measured by using 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 representative of cinder and a sphere was selected as reference model. The falling motions of the models dropped down from a drone were recorded by video camera and a stand-alone measuring system that included a pressure sensor, acceleration and angular velocity sensors in the models. The motion, posture, velocity and acceleration of the model were obtained in order to measure the three-dimensional falling trajectory. The drag and the deviation angle between relative wind direction and wind force direction were examined. The variation of the drag coefficient and the deviation angle with Reynolds number was clarified.

中文翻译：

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使用煤渣模型通过自由落体实验测量空气动力学特性

从火山喷发中喷出的岩石通常会造成生命和结构损失。需要空气动力学特性来评估火山岩的运动以减少破坏。火山岩的下落运动是通过使用模拟在实验地点樱岛火山收集的煤渣构造的模型来测量的。选择两种类型，一种具有锋利的边缘，一种不具有锋利的边缘，作为煤渣的代表，并选择一个球体作为参考模型。从无人机上掉下来的模型的下落运动由摄像机和独立的测量系统记录下来，该系统包括模型中的压力传感器，加速度和角速度传感器。为了测量三维下降轨迹，获得了模型的运动，姿势，速度和加速度。检查了阻力和相对风向与风向之间的偏角。弄清了阻力系数和偏角随雷诺数的变化。