Falling Droplet

Falling Droplet — ANSYS Fluent CFD Simulation

Description

Welcome to the Falling Droplet CFD Simulation module. This project introduces the behavior of a falling water droplet in air, using the Volume of Fluid (VOF) method in ANSYS Fluent. A single droplet falling through air is the most basic air–water interface problem there is, making it a perfect first case for multiphase flow — the droplet deforms, oscillates, and may even break up as surface tension, gravity, and air resistance act on it. Droplet dynamics of this kind underlie spray systems, inkjet printing, rainfall analysis, and atomization. As the opening project of the Multiphase Flow: Beginner CFD Training Package, it introduces the VOF method — the sharp-interface free-surface model — on the simplest possible geometry, establishing the foundation for the cases that follow.

Methodology

The simulation uses a pre-configured axisymmetric geometry representing the droplet and the surrounding air domain, with a mesh designed to capture the droplet interface and its deformation precisely. The initial droplet parameters — size, shape, and initial velocity — are configured at the start, and the surrounding air domain is defined with appropriate boundary conditions. The VOF model lies at the heart of the setup: an optimal VOF scheme is selected for stable, accurate tracking of the water–air interface as the droplet falls, and the crucial physical effects of surface tension and gravity are incorporated, since these are what govern the droplet's shape and stability. The case is solved transient to capture the time-dependent evolution of the droplet.

Analysis

Post-processing focuses on the droplet's shape evolution through time-dependent contours and animations that reveal its deformation and oscillation, with deformation metrics such as aspect ratio and oscillation frequency quantified during the fall. The results allow you to investigate how surface tension affects the droplet's ability to hold its shape or break up, and how air resistance influences its motion and terminal velocity, while the transient time-series data track the evolution of the droplet's properties and pinpoint critical stages such as potential breakup. These insights connect directly to optimizing spray and atomization systems and to improving rainfall and cloud-formation models in atmospheric science. By the end of this project, you'll be able to set up a transient VOF simulation of a falling droplet, incorporate surface tension and gravity, track the liquid–gas interface accurately, and interpret the droplet's deformation, oscillation, and stability.