Abstract: It’s one of the most important causes that pressure surge occurs in the draft tube， which results in the units operation instability and power losses. In the experimental study, the pressure surge data are acquired at 26 points from the taper pipe intake to the draft tube exit distributing at 8 sections under 6 stable operating conditions. With the FFT analysis it is analyzed that the pressure surge changing laws in the taper pipe and draft tube in time domain and frequency domain. It shows that the pressure surge is different at different position and operation conditions. In the taper pipe it is closely related to the flow field of rotating runner exit, and it is more interrelated to the draft tube form behind the elbow. These results afford reference on the draft tube design in order to improve the operation stability.

Key words: Draft tube, Hydraulic turbine, Pressure surge