A numerical simulation of overlay effect of rigid vegetation in a straight open channel by OpenFOAM

In order to understand the mechanism of flow patterns in vegetated channels, the flow located in a rectangular channel was numerically investigated by using OpenFOAM software. Firstly, two solvers of that software (i.e. icoFoam and pimpleFoam) were used to calculate the velocity profiles in both longitudinal and cross-sectional directions for four selected sections in a rectangular channel with a square cylinder. By comparing the simulation results with the available data, the icoFoam solver with a better performance (six Percent Error) was selected for the next developed model. A new model was then created with two tandem square cylinders with spacing ratios of two and a half and five. Flow patterns, velocity distribution and pressure characteristics in the channel with different inlet flow velocities were investigated for two cases. It was observed that a flow field disturbance occurred in all simulations and the current changed from steady state to unsteady one at a critical velocity. This instability occurred in a distance between the cylinders for the spacing ratio of five at an average Reynolds number of eight, while for the ratio of two and a half it is occurred at an average Reynolds number of 32. The maximum values ​​of longitudinal and transverse velocity timelines in a period of 200 seconds for four states (including two Reynolds numbers and two different spacing ratios) were plotted in two spatial ranges and fully investigated. According to the results, it can be said that the overlap has an important role on the flow characteristics in tandem arrangements and by increasing the distance ratio between the cylinders by 55 percent, the critical velocity value decreases by 74 percent.