Presentation Information
[O09-P08]Restitution coefficient measurement of a dense-potato-starch-suspension droplet impacting onto a hard floor★Invited Papers
*Misato Fujimoto1, Hiroaki Katsuragi1, Hiroyuki Ebata1, Makoto Katsura1, Fumiaki Nakai1 (1.The University of Osaka)
Keywords:
Dilatant fluid,Droplet impact,Rebound behavior
Dilatant fluids, a type of non-Newtonian fluid such as concentrated porato-starch suspensions, exhibit dramatic shear thickening behavior depending on the shear strain rate [1]. The potato starch suspension used in this study is a well-known example of such dilatant fluid which behaves like a liquid under slow deformation but hardens into a solid-like state when subjected to rapid deformation such as impact. In previous study, impact experiments using a dilatant fluid have often been conducted in relatively low-concentration regimes to ensure the easy handling and observation [2], while research reporting the impact of droplets consisting of dilatant fluids (dilatant droplets) under high-concentration conditions has remained limited. In particular, the rebound behavior of the dilatant droplet impact onto a hard floor has rarely been reported in previous literature.
We performed a systematic free-fall impact experiments using a dilatant droplet consisting of dense potato-starch suspension .In the experiments, the drop height (impact velocity) and the concentration of the suspension were varied as key parameters. The impact process was observed and recorded using a high-speed camera. The drop heights were set at 6 cm, 12 cm, 24 cm, and 48 cm, while four different suspension concentrations were prepared with solid volume fractions of 0.395, 0.450, 0.471, and 0.495.
The obtained video data were processed using the OpenCV image processing library to extract the time-series data of positions and velocities of the droplet’s top point, bottom point, and center of mass. For the analysis, the first frame of each video was defined as the background. The droplet region in each subsequent frame was isolated through background subtraction, and the droplet boundaries were determined by applying binarization. The center of mass was calculated as the area centroid of the identified droplet region. Furthermore, the coefficient of restitution was estimated to quantify the rebound characteristics.
From the experiment, we found that under specific concentrations and impact velocities, the dilatant droplets exhibited a distinct rebound behavior similar to that of an elastic body. The maximum measured coefficient of restitution was 0.16, which is significantly smaller than that of typical elastic solids. Additionally, it was observed that the coefficient of restitution tended to decrease as the impact velocity increased. Based on these findings, we discussed the kinetic energy dissipation process to evaluate the transitional behavior between the elastic and plastic characteristics of dilatant droplets during the extreme short-duration impact process.
[1] H. A. Barnes, J. Rheol., 33, 329 (1989).
[2] F. Boyer et al., Phys. Rev. Fluids, 1, 013901 (2016).
We performed a systematic free-fall impact experiments using a dilatant droplet consisting of dense potato-starch suspension .In the experiments, the drop height (impact velocity) and the concentration of the suspension were varied as key parameters. The impact process was observed and recorded using a high-speed camera. The drop heights were set at 6 cm, 12 cm, 24 cm, and 48 cm, while four different suspension concentrations were prepared with solid volume fractions of 0.395, 0.450, 0.471, and 0.495.
The obtained video data were processed using the OpenCV image processing library to extract the time-series data of positions and velocities of the droplet’s top point, bottom point, and center of mass. For the analysis, the first frame of each video was defined as the background. The droplet region in each subsequent frame was isolated through background subtraction, and the droplet boundaries were determined by applying binarization. The center of mass was calculated as the area centroid of the identified droplet region. Furthermore, the coefficient of restitution was estimated to quantify the rebound characteristics.
From the experiment, we found that under specific concentrations and impact velocities, the dilatant droplets exhibited a distinct rebound behavior similar to that of an elastic body. The maximum measured coefficient of restitution was 0.16, which is significantly smaller than that of typical elastic solids. Additionally, it was observed that the coefficient of restitution tended to decrease as the impact velocity increased. Based on these findings, we discussed the kinetic energy dissipation process to evaluate the transitional behavior between the elastic and plastic characteristics of dilatant droplets during the extreme short-duration impact process.
[1] H. A. Barnes, J. Rheol., 33, 329 (1989).
[2] F. Boyer et al., Phys. Rev. Fluids, 1, 013901 (2016).