Numerical Investigation of Flow Field subject to Vibrating structure

Hydraulic turbines are subject to both high-cycle and low-cycle fatigue during power generation. Currently, the key challenge is the credible estimation of the added mass, natural frequencies and hydrodynamic damping. The natural frequency is dependent on the flow conditions in the turbine. It is difficult to estimate the vibration characteristics for prototypes due to involved complexities in the design phase. To understand the flow physics and associated mechanical characteristics of the turbine blade, a hydrofoil test rig was developed at the Waterpower laboratory at NTNU. Measurements were conducted at different flow conditions. Strong vibrations were experienced during the lock-in condition. The lock-in condition is within the range of flow velocities that generally exist in prototype turbines. The operational range of the test rig is average inlet velocities between 0 and 40 m/s, and the lock-in phenomena was present at velocities between 10 and 12 m/s with the original hydrofoil. The main objective of the current study is to investigate the lock-in frequency with respect to different trailing edge profiles. The original hydrofoil with available measurement data was selected to validate the numerical model. Then, the modified trailing edge profiles were used to push the lock-in condition to a lower flow rate (velocity). By changing the trailing edge profile, it is expected that the lock-in condition may be pushed down by approximately 22 %.