Comparison of Two-Phase and Single-Phase Hurricane Wind Loading on Coastal Structures

Tropical cyclone (TC) loading on coastal structures is typically approximated as a linear superposition of de-coupled wave and wind loading. In the young wave, high wind, and steep wave regime typical of hurricanes, phenomena such as flow separation over wave crests and injection of turbulence into the air phase due to wave breaking are expected to occur. The interactions of these different flow physics could substantially alter expected wind loading on coastal structures.

Two-phase flow simulations provide an opportunity to model fully coupled wind and wave loading on coastal structures. However, very little experimental or field data exists with which to validate these simulations. As such, in this work, we contrast a fully coupled simulation approach (where waves and wind influence each other) to a one-way coupled approach (where only waves influence wind). For both approaches, we perform Large Eddy Simulations (LES) using the CFD solver Charles and an unstructured, Voronoi mesh. The fully coupled approach uses the Accurate Conservative Diffuse Interface (ACDI) two-phase interface capturing scheme in a Volume-of-Fluid (VOF) framework (Hwang & Jain 2022) to model the interaction between wind and waves. The one-way coupled approach implements parametric forcing (Busse & Sandham 2012) adapted to vary in time in order to characterize an evolving wave field’s influence on simulated wind.

We examine momentum transfer from waves to the air phase and compare these results to theoretical expectations for young waves (Belcher & Hunt 1998). We compare mean profiles, wave-phase-averaged profiles, and turbulent statistics between the fully coupled and one-way coupled approaches. Advantages and limitations of currently available two-phase methods are highlighted to guide future development.