PRESSURE AND VELOCITY FLUCTUATIONS IN STILLING BASINS

The internal flow of hydraulic jump is essentially an unsteady flow subjected to macro turbulent random fluctuations and it was not known enough. Then, for the fluctuating motion interpretation, the experimental research on the associated turbulence must be necessary. The authors developed in the past extensive laboratory research for the instantaneous pressure field determination by means of pressure transducers and new introductory experiments on velocity fluctuations by means of the ADV technique. The experimental study of the instantaneous pressure field was based on the knowledge of several statistical parameters of amplitudes and frequencies as functions of the Froude Number but for this paper only the root mean square of pressure and velocity amplitudes is considered. Following previous experimental conclusions, the tests were accomplished for incident Reynolds Number R, up to 100,000 for incident Froude Numbers F-1 = 3 and F-1 = 5. Experimental data on turbulence intensity decay downstream the stilling basin obtained by means of direct velocity fluctuations and calculated through pressure fluctuations amplitudes measured below free or submerged hydraulic jumps stilling basins were,used. A useful relationship between turbulence intensity and the pressure fluctuation coefficient Up is proposed. As velocity fluctuations cannot be measured with precision in the upstream region of the hydraulic jump with the ADV equipment, these results obtained by extrapolation of the pressure fluctuations are presented.