DANS model for vegetated open channel flows

ABSTRACT

A novel Double Averaged Navier-Stokes equation model has been developed to simulate flows in vegetated open channels. Turbulence is modelled by the Spalart-Allmaras closure with a modified length scale, which is dependent on a zero-plane displacement parameter relating to the vegetation characteristics. The dispersive stress is modelled by a sub-length scale closure and the secondary current effect is modelled by a phenomenological expression. The simulation results show that the model is accurate for flows over vegetation with areal density ranging from 170 m^–2 to 12,000 m^–2. The computed dispersive stress and velocity dip are in reasonable agreement with the available experimental data. The effects of porosity and dispersive stress on the mean velocity and Reynolds stress are found to be minor. The model works well for gradually-varied flow over vegetation and predicts accurately the Manning roughness coefficient for flows over vegetation with low to high areal density.

Keywords:

• DANS model
• numerical model
• open channel flow
• turbulence closure
• vegetated flow

Additional information

Funding

This work was supported by a grant from the Research Grant Council of the Hong Kong Special Administrative Region [grant number 5200/12E].