Abstract：In order to explore the overflow capacity of each part of the right-angle broken line weir(front weir, side weir and back weir)when the length of the weir body changes under free outflow conditions, a mathematical model of a right-angle polyline weir was established by FLOW-3D software. The RNG k-ε turbulence model and the TruVOF free surface tracking method were used to calculate the data of nine groups of right-angle polyline weirs with different lengths and positions of the side weirs. Furthermore, the changes law of the overflow capacity of the front, side and back weirs under the same head conditions was analyzed. The results show that with the increase of the length of the side weir, the overflow capacity of the side weir increases, however the increase relatively slows down. Meanwhile, the overflow capacity of the front weir and the back weir decreases, but the decrease range in capacity of the back weir is bigger than that of the front weir. With the change of the side weir position(the length of the front weir increases and the length of the back weir decreases), the overflow capacity of the side weir increases, showing a trend of first increasing and then decreasing, while the overflow capacity of the front weir and the back weir has a non-linear positive correlation with their own length. On this basis, the flow calculation equation for different weir lengths at the leading edge of the overflow under the change of relative head at the top of the weir is fitted. It is concluded that the maximum overflow capacity is reached when the side weir of the right-angle polyline weir is located at 0.45 times the channel width, and the increase of overflow capacity tends to level off when the side weir length of the right-angle polyline weir reaches 1.30 times the channel width.
