Simulation of cloud drop collisions in ABC flow

TL;DR

This paper demonstrates that using ABC flow as a simplified turbulence model can accurately simulate cloud drop collisions, reducing computational costs while maintaining realistic collision statistics compared to full DNS.

Contribution

The study introduces a computationally efficient method using ABC flow to replicate collision statistics of cloud drops, enabling larger and more complex simulations.

Findings

ABC flow reproduces DNS collision statistics accurately.

Simulation results are robust to parameter variations.

Method allows larger scale and more detailed cloud physics studies.

Abstract

Simulating the collision behaviour of cloud drops in a turbulent environment is numerically expensive. Because of the typical sizes of cloud drops, their motion is predominantly influenced by the smallest turbulent scales in the flow. We can exploit this property by using an Arnold--Beltrami--Childress (ABC) flow instead of a full direct numerical simulation (DNS) to simulate the turbulent effect on cloud drop collisions. This allows simulation of drop motion using much less computational resources than needed by DNS and therefore, allows for simulations with many more drops and larger model domains or more complex cloud physics. This is useful in cases where a specific process needs to be studied and the complexity and details of a realistic turbulent flow are of secondary interest. It is shown that the simulations using ABC flow can faithfully reproduce collision statistics from much more comprehensive DNS calculations when using a similar Taylor microscale and root mean square velocity in the ABC and DNS flows. The results from the ABC flow are robust to changes in these two parameters within a reasonable range, even though adjustments to the parameters can be used to further tune the results.