7. Pressure fluctuations

Pressure fluctuations are naturally present in a hydraulic machine to a greater or lesser degree, depending on the load. They are essentially due to the two-phase nature of the flow. High-load and part-load cavitating flares can cause resonance in the hydraulic circuit and alternator if care is not taken. For this reason, detailed model tests are carried out to determine the frequency of the flare and its harmonics. Typically, the fundamental is between 0.2 and 0.3 times the wheel rotation frequency.

The pressure fluctuations measured are not only characteristics of the model tested, but also of the platform, such as: the length of the test loop pipes and their roughness, the amount of dissolved air, the dynamic behavior of the rotating parts, the Reynolds number or Froude number, etc. The pressure fluctuations measured are not only characteristics of the model...