CFD study on effect of catchment area on hydraulic performance of subsurface flow constructed wetland
The subsurface flow wetland was simulated by using a commercial computational fluid dynamic code,Fluent(Fluent Inc.,Version 6.2.16).The media constructed in the wetland was modeled by the porous media and the particle trajectory model was introduced to discuss the effect of two types of catchment area,the layer pattern and protector pattern on the hydraulic performance of the wetland.The simulation results confirmed that dispersion was an important factor for hydraulic efficiency while mean residence time changed little in all reviewed cases.For the type of layer pattern,the smaller the ratio of media resistance of purge and catchment area,the bigger the effect of their changes on hydraulic efficiency.With the increase of catchment height,the dispersion of flow increased and the hydraulic efficiency of the wetland decreased accordingly.For the type of protector pattern,with the decrease of catchment breadth,hydraulic efficiency could be improved and the effect of resistance ratio on hydraulic efficiency could be weakened.The effect of catchment height on the performance of the wetland was slight and with the increase of catchment height,hydraulic efficiency was improved slightly and when the height increased to the top of the wetland,the effect of resistance ratio on hydraulic efficiency decreased further.As compared with the layer pattern catchment area,the wetland with the protector pattern catchment area had high hydraulic efficiency and by decreasing catchment breadth,hydraulic efficiency could be improved and the effect of resistance ratio on hydraulic efficiency could be weakened.Therefore,the protector pattern catchment area was better than the layer pattern.