Complexity Forum: Ryo Onishi (Earth Simulator Centre, Japan Agency for Marine-Earth Science and Technology)
Speaker: Ryo Onishi (Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology)
Title: Inversion schemes to retrieve collision kernel values from droplet size distribution change
Collisions of small-inertia droplets are often seen in both environmental and engineering flows. Examples of droplet collisions include the growth of liquid droplets in clouds, in wet steam generators, and in spray atomization processes.
This study presents an attempt to retrieve collision kernel values from changes in the droplet size distribution due to collision growth. Original linear and nonlinear inversion schemes are presented, which use the simple a priori assumption that the total collision rate is given by the sum of the gravitational and turbulent contributions. Our schemes directly handle binned (discretized) size distributions and, therefore, do not require any assumptions on distribution functional forms, such as the self-similarity assumption. To validate the schemes, three-dimensional direct numerical simulation (DNS) of colliding droplets in steady isotropic turbulence is performed. Comparison between the retrieved collision kernels and the collision kernels obtained directly from the DNS shows that for cases with small changes in size distributions both the linear and nonlinear inversion schemes give good accuracy. However, for cases with larger changes the linear inversion scheme gives significantly larger retrieval errors, while the errors for the nonlinear scheme remain small.
Lunch group: 1