Author(s): Raul Antonio Lopardo, Maria Cecilia Lopardo
Keywords: Macroturbulence; Stilling basin; Baffle blocks; Physical model; Cavitation;
Abstract: The first prototype measurements of pressure fluctuations on baffle blocks were recorded more than 35 years ago at the Salto Grande Dam stilling basin, on Uruguay River. By means of the prototype data acquisition under flood conditions, it was possible to verify the real magnitude of the pressure fluctuations induced by macroturbulence in the basin. In particular, cavitation due to instantaneous depressions caused by low frequency pulses with mean pressures even higher to the atmospheric pressure was detected. Based on this research it was possible to demonstrate that in hydraulic jump stilling basins, Froudian physical models are excellent tools if their length scale does not exceed 1:50, the minimum flow depth is 3 cm and the incident Reynolds number is over 105. The model-prototype comparison shows excellent agreement to simulate the fluctuating pressures amplitudes and the dominant frequencies induced by the flow, with a similar shape of the power spectra. Recently, instantaneous pressures were measured in the physical model 1:40 of the Gatún Dam (Panamá) by the same experimental technique. For the maximum flood registered at the prototype, near 20% over the design discharge, “cavitation tendency” was detected in very few points of few blocks in the model. These blocks had "low pitting" in the concrete at prototype. These results also demonstrate the compatibility between data of "tendency to cavitation by pressure pulses" p0.1% in a Froudian model and the real behavior in prototype of a historical structure, after more than a century of operation under extreme conditions.