Turbulent flow and monami in aquatic canopy with various plant flexibility

The hydrodynamics of aquatic canopy plays an important role in many coastal and estuary processes. We have developed a numerical tool to simulate the interaction between aquatic canopy and turbulence. The hydrodynamics of each plant in the canopy is resolved by an immersed boundary method. This method does not require a priori constant drag coefficient, which is required by classical canopy model and can be inaccurate as we show in our cases. With this numerical tool, we ran six cases to study the influence of plant flexibility on the turbulent aquatic canopy flow. The plant flexibility ranges from absolute rigid to extremely flexible. For all the cases, the vertical streamwise velocity profiles in the mixing layer are self-similar, though the velocity profile above the velocity inflection point does not follow the hyperbolic tangent velocity profile of pure mixing flow. For the flexible canopy, one cannot neglect the momentum transport by the Reynolds stress in the lower part of the canopy, as well as the momentum transport by the dispersive flux throughout the canopy, while it is not the case in the rigid canopy. In the TKE budget of the flexible canopy flow, the plant waving effect induced by the correlation between plant waving and drag force is a weak sink term in the lower canopy and a strong source term in the upper canopy. We also measured the dispersion relation of the canopy waving motion (monami) and found that the wave speed of the high-wavenumber component depends on the plant flexibility.