Numerical simulation of turbulent exchange flow in aquatic canopies

ABSTRACT

In the present study, lock-exchange flows through rigid emergent vegetation are investigated numerically. The volume-averaged Reynolds-averaged Navier–Stokes equations and the transport equations of the renormalization group k-ε turbulence model, which include additional terms due to vegetation, are solved numerically. The drag coefficient C_D is estimated as a function of the local volume-averaged velocity, which varies in space and time. The dynamics of gravity currents in regions covered by vegetation (fully and partly) is examined. The solid volume fraction of vegetation ϕ ranges from 0.03 to 0.35. The numerical model is validated with available experimental data for sparse vegetation. The characteristics of gravity currents in dense vegetation, where there is no sufficient information, are investigated. Ιt is found that the toe velocity in the open area is influenced by the adjacent vegetation for ϕ > 0.104. The currents become drag dominated from the beginning of the exchange flow for ϕ > 0.141.

Keywords:

• Drag coefficient
• drag resistance
• gravity (density) currents
• VARANS model
• vegetated flows