Computational Fluid Dynamics Model to Simulate Wind Flow Across a Foredune

Abstract

Coastal dunes serve as important protection against water waves, particularly during storms. Therefore, investigating the formation and migration of dunes is imperative for developing hazard management strategies to protect the mainland. The wind flow over dunes plays an important role in sediment transport around dunes, contributing to their formation and shaping over time. The interaction between dune geometry and wind velocity creates a two-way coupling effect. While experimental and field studies have been conducted to examine the impact of wind velocity and dune geometry, they are often constrained by certain limitations. Numerical methods provide a viable approach to simulate wind/air flow by solving the governing equations (Navier-Stokes equations). Computational fluid dynamics (CFD) methods are commonly employed for such simulations. The objective of this contribution is to study spatial changes in near-bed wind speed and direction across a foredune as a function of the wind approach angle and foredune geometry (height and slope of its seaward side) using OpenFOAM, an open-source code that solves the partial differential equations (PDEs) governing physical problems using the finite volume method (FVM). We first tested the model against data collected at the approximately 15-m high foredune (1:2 slope) at Egmond aan Zee, Netherlands. Consistent with the data, the model shows that the speed-up of the wind from the base to the crest of the foredune depends on the wind approach angle. The speed-up varies almost 3 times to 1 when the wind direction changes from 0 to 90 degrees. The error norm of the CFD results, when compared to the measured data, is less than 10 percent, validating the accuracy of the proposed CFD model. The model was then applied to synthetic foredune profiles, in which we varied foredune height between 6 and 25 m, and slope between 1:4 and 1:2. Our results indicate that speed-up is strongest for highest and steepest dunes. Speed-up is barely notable for dunes 6 m in height and 1:4 in slope. The results also show that the speed-up can grow up to 10 times for a dune with a height of 25 m and 1:2 slope.