Numerical investigation of scour downstream of piano key Weirs using Flow-3D software

In this research, the numerical simulation of the scouring of the downstream bed of two types of trapezoidal and triangular piano key series in the same geometric and hydraulic conditions has been done using the Flow-3D numerical model. To carry out the calibration process of the desired numerical model, the laboratory study of Ghodsian et al. (2021) was used in the conditions of sediment transfer. After the software calibration, the accuracy of the R2 criterion for the longitudinal profile of scour and the maximum depth of scour downstream of the weir was equal to 0.9338 and 0.873, respectively. Eighteen numerical simulations for scour downstream of two types of trapezoidal and triangular piano key weirs were carried out under the conditions of changes in discharge and depth of abutment, and the local changes of scour in a trapezoidal piano key weir at a depth of 0.05, 0.075 and 0.1 meters and all three The flow rate of 25, 35 and 45 liters second was observed less than the weir of the triangular piano key. By doubling the depth of the weir in the trapezoidal weir up to 29% and in the triangular weir up to 26.6%, the scour depth decreases. Also, with a 44% decrease in discharge at a constant depth of the aquifer, a 40% and 37.4% decrease in the maximum scour hole depth was observed in the trapezoidal and triangular weir, respectively. The increase in the depth of the floodplain causes the loss of energy of the falling jets from the weir, and by reducing the capacity of the bed sediments carried by the water flow, it causes a decrease in the maximum scour depth downstream of the desired weirs. It was observed that with the increase of the flow through both types of trapezoidal and triangular piano key weirs in the condition of constant depth of the abutment, the scour rate in the sedimentary bed for both types of weirs approaches.