Falling Objects into Water

Falling Objects into Water CFD Simulation, Dynamic Mesh, ANSYS Fluent Training

Description

This project simulates the fluid flow generated by two cubes falling into water using the dynamic mesh method in ANSYS Fluent. The 2D geometry was designed in Design Modeler, with two cubes positioned within a square domain, set to fall into the underlying fluid under gravitational acceleration. The domain was meshed in ANSYS Meshing, totaling 8,727 elements, with a transient solver enabled given the dynamic mesh approach required for this problem.

Methodology

In problems where mesh cell location and shape change over time, the dynamic mesh model is essential to prevent severe deterioration in element quality. Smoothing and remeshing methods regenerate higher-quality elements as the original mesh becomes distorted and unsuitable for continued calculation.

The two cubes begin at rest in the air above the domain; once the simulation starts, they fall and collide with the free surface separating water and air, with this two-phase behavior captured using the VOF multiphase model. A UDF governs the cubes' motion toward the water surface based on gravitational acceleration, while turbulence is resolved using the standard k-epsilon model.

Conclusion

Results include 2D contours of velocity, pressure, turbulent viscosity, and streamlines throughout the domain. As the cubes move downward and generate a sloshing effect, pressure rises progressively along their path of movement, peaking sharply at the tank's corners and at the cubes' own sharp edges, while dropping to a minimum along the cubes' vertical faces — a direct result of flow separation induced by their motion through the fluid.

The kinetic energy contour further reveals elevated average kinetic energy concentrated around the cubes, driven by the vortices generated as they move through the fluid — a clear sign of increased turbulence resulting from the falling motion. These wake regions are also clearly visible in the accompanying streamline and vector plots, illustrating how the cubes' descent reshapes the surrounding flow field.