The Study On The Test And Chaos Identification Of The Cavitation Noise Produced By Water Jet

Cavitation is a common, extremely complicated hydraulic phenomenon. The huge energy produced by cavitation can provide a special circumstance, which is difficult to realize under ordinary conditions, for physical or chemical processes.Applied in the field of water treatment, the technology of submerge cavitating water jet features in simple construction, striking cavitating performance and high energy-exchanging ratio. Thus, it is particularly applicable to treat the water in industrial quantity. As a pure physical process, submerge cavitating water jet, in contrast to chemical treatment, will not produce any chemical by-product during the process. Generally, submerge cavitating water jet is a potential, energy-saving technique of water treatment.The key of a cavitating water jet system is the cavitating nozzle. The shape and the characteristic sizes of a nozzle greatly affect its cavitating performance. The basis for nozzle design is how to judge the cavitating performance. The performance can be determined by measuring the effect of cavitating erosion, and one of the most common experimental methods is to measure the mass loss of a trial piece due to cavitating erosion.Based on the chaos theory, the relations has been investigated among the standoff distance, the nozzle's structure and the maximum value of Lyapunov exponent of the time sequence of the cavitation noise signal produced by water jet and collected in this experiment. The objective is to try to find the relevance of cavitation properties of a nozzle to the chaotic properties of the time sequence of the cavitation noise signal.The following work has been done: introducing the theories on water jet, cavitation, nozzle and chaos; collecting the algorithms of determining characteristic parameters to reconstruct from a time sequence the phase space based on Takens theorem, and of calculating the value of Lyapunov exponent; setting up the experimental systems to produce hydraulic cavitation and to test cavitation noise; collecting time sequences of cavitation noise signals produced by nozzles of different structure at different stand-off distance by hydrophone under the same experimental conditions; calculating and analyzing the obtained time sequences in the light of chaos theory to draw the experimental conclusions. The experimental results show: given a preferable standoff, the intensity of cavitation noises collected at the target is larger than that collected at the outlet of the nozzle; the maximum values of Lyapunov exponent corresponding to the obtained time sequences are all positive, i.e. they are all chaotic sequences; the cavitation noise signal is distinct from the reverberation signal; the maximum value of Lyapunov exponent varies with the nozzle's structure, i.e. the dependence of a nozzle on initial conditions relates to the structure of itself; under the conditions of this experiment the maximum Lyapunov exponent value of the nozzleâ… is the largest; the curve of Lyapunov exponent presents, to some extent, oscillating activities; if the mean value of the Lyapunov exponent curve is taken as the maximum Lyapunov exponent and used to describe the cavitation properties of cavitation nozzle, this method is relatively more steady than traditional spectral methods; an optimal standoff exists which makes the maximum Lyapunov exponent value the largest; under the conditions of this experiment the optimal standoff of the nozzleâ… is about 35mm, the nozzleâ…¡is also about 35mm and the nozzleâ…¢is less than 35mm.