Cavitation is a phenomenon with both positive and negative effects and with dynamic manifestations in hydraulic, food, chemical and other machinery. This article deals with the detection and dynamic behavior of cavitation clouds in water flows through a rectangular cross-section convergent-divergent nozzle. Cavitation was measured by methods applicable in engineering practice. Pressure, flow rate, noise, vibration, and amount of air dissolved in the liquid were measured and cavitation region was recorded with a high-speed camera. Evaluation of acquired images in connection with measured pressure pulsations and mechanical vibrations was performed with the use of the FFT method. In certain cases, dimensionless parameters were used to generalize the measurements. The results will be used to specify multiphase mathematical cavitation model parameters.
Noise belongs among the negative phenomena in our environment and can have a negative effect on human health. Excessive noise occurs in many areas, e.g. in transport, aeronautics and during manufacturing processes. It is often necessary to meet specified noise limits. Acoustic measurements are carried out in many cases, e.g. in order to evaluate the sound absorption properties of investigated materials and acoustic conditions in a given environment. Measurements of extremely low sound pressure levels can be used to describe the acoustic environment in an acoustic laboratory or to measure noise emissions from quiet machines and equipment. Furthermore, measurements of extremely low noise levels are limited by the thermal noise of the measurement chain. If the sound pressure levels are lower than the thermal noise of the measurement chain, then the measurement is not correct. This paper describes the measurement of extremely low sound pressure levels using an improved correlation function method.
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