Objectives  In order to study the unsteady hydrodynamic performance of turbines under changing current conditions,

  Method  this paper uses the Dynamic Fluid Body Interaction(DFBI) method based on an overset grid to simulate the unsteady hydrodynamic performance of turbines under different flow conditions.

  Results  The results show that the DFBI method based on an overset grid can realize the monitoring of such transient parameters as speed, torque and flow field in the three stages of starting, acceleration and stabilization of the turbine during start-up. The power coefficient of the turbine has a peak value near the design flow rate of 1.2 m/s. Under dynamic conditions, the average energy efficiency of the turbine is about 0.181, which is about 33% lower than the designed flow rate of 1.2 m/s.

  Conclusions  The numerical simulation method used in this paper can monitor the hydrodynamic performance of passively rotating turbines under real current conditions, and changes in the characteristic parameters of the turbine flow field and power output under passive rotation conditions, which can play an important role in guiding actual engineering design.