Study On Characteristics Of Fluctuating Wall-Pressure And Its Similarity Law

In recent years, as a continual construction of high dams, it is paid more attention to that the protective structures of energy dissipators failed during the flood discharge. Associated with this process are severe pressure fluctuations which must be a matter of concern in the structural design of the protective structures of energy dissipators. The study on the pressure fluctuations had achieved great success in the past years, but because of the lack of sufficient theoretics, hydraulic model experiments however play an important role in the design of the protective structures. A similarity law of the pressure fluctuations is a key criterion that ensures the safety of the results measured from the model being transformed to the prototype. As to the characteristics of the propagation of the pressure wave within the contraction joints, theoretical calculation can only solve the simple boundary condition problems, and the experiment results are not enough at present. To resolve the above problems, this paper will discuss the following things:(1) Based on Navier-Stokes equation and theory of vorticity transport, the genesis and mechanism of the pressure fluctuations is discussed, and its similarity law is derived.(2) It is analyzed in the paper of the characteristics of the amplitude value of the pressure recorded in the experiments. It consists of the computation of average, standard deviation, skewness, kurtosis, probability density function and characteristic function of the pressure data, etc. From the results, a similarity law of the amplitude value of the pressure is discussed.(3) It is analyzed in the paper of the characteristics of the correlation and spectrum of the pressure recorded in the experiments. It consists of the computation of autocorrelation, integral time-scale, spatial correlation, integral length-scale, and power spectral density function of the pressure data, etc. From the results, a similarity law of the correlation and spectrum of the pressure is discussed.(4) It is analyzed in the paper of the characteristics of the propagation of the pressure wave within the contraction joints recorded in the experiments. It consists of the spatial distribution of the point pressure fluctuations within the joints and the influence of joints width, point pressure fluctuations on the slabs upper faces and lower faces, hydrodynamic loads, uplift loads, transform between point pressures and forces, etc.(5) Finally, a numerical calculation using large eddy simulation equation is carried out to computing the pressure fluctuations in the hydraulic jump, and its computing results is compared with the results from the experiments.From the above study, it can be drawn that in the hydraulic jumps and plunge pools, the similarity law of the pressure fluctuations obeys the Froude law. The propagation form of the pressure fluctuations in the joints is pressure wave. It has the similar spatial distribution of the pressure fluctuations between the upper faces and lower faces of the slabs. The attenuation of the pressure amplitude increases directly with the joint width.