Inland transport is one of the modes of transport that recognizes these last year's a lot of attention. This mode of transport is known by its ecological quality in term of CO2 emission compared to road and rail transport. However, despite the reduced amount of CO2 emitted, this mode of transport still has a significant negative impact on the environment, which is the erosion of banks and the bed of inland waterways as well as the re-suspension of existing polluting particles and contaminants. This impact becomes more and more visible with the arrival of the new generation of ships with large size and their very powerful propulsive system.
The presence of suspended sediment in inland waterways leads to difficult problems for the development and maintenance of channels. To these problems are added the quality of the water. In fact, sediments trap many elements such as metals of industrial origin. There can be transport or accumulation of these pollutants which may be re-suspended under the effect of hydrodynamics of the water often disturbed by ships passage. These re-suspension can contribute to transport of pollutants from a polluted area to a unpolluted area.
The understanding and control of interactions at the water-sediment interface are extremely complex due to the presence of several processes of natures and spatio-temporal scales very different. The hydro-sedimentary processes are governed by the action of friction exerted by the water on the bed of the channel. It is generally accepted that sediment transport is carried out in two modes: bedload on the channel bed and suspension in the water.
Numerical modeling of the sediments suspension phenomena is often carried out on a large scale by models such as Saint-Venant or Boussinesq. The recourse to this type of model is mainly related to the simplifying assumptions adopted. These models use empirical formulas for estimating shear stress applied on sediments using average velocities. Recently, and thanks to the rapid development of computing resources, fully models based on Navier-Stokes equations are used to model sedimentary transport. The coupling between the fluid model and the sediments transport models can be strong (simultaneous resolution of the both equations) or weak (alternative resolution). The advantage of these models is the high precision of the shear stresses estimation on the channel bed.
Hence, in the present work a fine numerical study was conducted to assesses the impact of the inland transport on the inland waterways. The influence of the under keel clearance and the ship advance coefficient have been tested for several size of sediments. This study was carried out using a Computational Fluid Dynamics model (CFD) based on Unsteady Reynolds-Averaged Navier-Stokes (URANS) is used to simulate the flow around the ship as well as through propellers. This model is coupled with a sedimentary transport model to simulate the re-suspension of sediments. The both models were verified and validated using an experiment data. Flow is considered with free surface and highly turbulent. An inland ship with twice propellers is selected for this investigation.
KEYWORDS: Inland transport, environmental impact, Computational Fluid Dynamics (CFD), ship container, sediment resuspension, propellers effect.