The flow into and out of the turbine should be the same (the water flowing from the turbine to the engine room is very small and can be ignored), i.e. Q1=Q2 , the flow V1>V2, Q=S*V, which means the inflow. The area of channel S1 of water in the turbine is smaller than the area of channel S2 of water flowing out of the turbine.
If the cross-sectional areas of the inlet pipes and output are equal, then v1=v2
Here is the explanation.
Part of the energy of the water is converted into the kinetic energy of the turbine. easier to explain by converting potential energy into kinetic energy. The final formula is: P=9.81*Q*H*η P is the power, in KW Q is the flow rate, the unit is cubic meter/second. water height (the difference in water level between upstream and downstream), the unit is meter and η is the efficiency, which is 0.8 to 0.85.