Abstract
The internal flow of hydraulic jump is essentially an unsteady flow subjected to macroturbulent 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 author 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 the maximum instantaneous negative of pressure amplitudes on the floor is considered, in order to estimate the extreme maximum positive velocities near the bottom. A useful relationship between turbulence intensity and the pressure fluctuation coefficient was proposed from ADV velocity fluctuation for low incident Froude numbers. By means of this relationship, the value (instantaneous positive semiamplitude with 0.1% of probability to be surpassed) can be considered for the determination of the turbulent extreme velocity near the bottom, under a free hydraulic jump stilling basin with incident Froude number .
Highlights
Many researchers have studied hydraulic jump, but most of the works have focused on an integral analysis, and little is known about internal flow and turbulence characteristics
A useful relationship between turbulence intensity and the pressure fluctuation coefficient Cp was proposed from a microacoustic Doppler velocity meter (ADV) velocity fluctuation for low incident Froude numbers
As noted in the case of pressure fluctuations below hydraulic jump stilling basins, the maximum positive pressure fluctuating amplitude on the floor of a hydraulic jump is much greater than the mean square value, which is usually considered for conventional analysis of turbulence decay
Summary
Many researchers have studied hydraulic jump, but most of the works have focused on an integral analysis, and little is known about internal flow and turbulence characteristics. The mean flow analysis allows the determination of the general pattern of the flow, such as water levels, the jump length, the macroscopic quantification of energy loss, and the mean pressure field. Acoustic instruments methods were used in hydraulic jumps of low Froude number by Liu et al [2]. They used a microacoustic Doppler velocity meter (ADV) and presented data of mean velocity, turbulence intensities, and Reynolds shear stresses, along with energy dissipation rate and Kolmogorov length scale calculations
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