Investigation Into The Cavitation Noise In Grooves Of Spool Valve

Nowadays, the environmental and comfortable performances of machinery are becoming increasingly the focus of attention and a crucial force to promote the development of engineering and science. For sure, the fluid power technology should follow this development direction, in which the noise control is one of key fundamental research subjects. The flow-induced vibration fields are the source of noise in essence. At present, the deep understanding of the hydraulic valve noise based on investigating into the flow is still lack, mainly because of the complicated flow in the small size internal flow passage of hydraulic valves.In this thesis, Computational fluid dynamic (CFD), theoretical analysis and extensive experimental approaches including the pressure distribution measurement, the visualization of cavitating flow and the external sound noise frequency analysis were used to investigate the noise characteristics of the grooves in spool valve. A new test rig used to measure the pressure distribution in groove has been proposed, thus the mechanism of the noise differences related to the different grooves can be investigated. It was found that both the grooves with a passage of same cross-section areas and the grooves with large sloping angel can be used to reduce the cavitation noise levels effectively because these two type groove configurations can increase the pressure distribution in groove. Another interesting result is that the steady flow force in spool valve consisting of groove changes with the shift of the flow direction on the groove pass. In the converging flow direction, the value of the flow force is small, and furthermore its direction tends to open the valve in middle range of valve openings. An interpretation was proposed that the bubble growth process is determined mainly by the pressure distribution in grooves and the bubble maximum size just before collapse is the most important factor to the sound noise level. The research results presented in this thesis have showed the importance in both practice and theory for the improvement of the low-noise performance of the grooves in hydraulic valve.In chapter 1, the aim and significance of this thesis was presented. The history and current research progress on the noise of hydraulic pumps and valves were reviewed. As one of the most important source of noise in hydraulic components, the research works and current progresses on cavitation and cavitation noise was specially summarized. The application of CFD and flow field experimental approach to investigate the hydraulic component was summarized. Lastly, the main research subjects were presented.In chapter 2, the mechanism of noise in hydraulic valve was analyzed using the sound radiation principle and the bubble dynamics. Furthermore, a simple model of sound pressure to evaluate the cavitation noise was put forward. From the model, it can be found that the bubble size is the most crucial factor for the sound pressure level.In chapter 3, a novel apparatus to measure the pressure distribution in grooves on spoolvalve and the cavitating flow visualization model that was identical with the prototype were introduced. The experimental apparatus and system to investigate the groove noise were described in detail. The uncertainty in the experimental measurement was analyzed.In chapter 4, the features of groove configurations and flow passage areas were analyzed. The whole type of grooves can be generally categorized into two typical types, grooves with a passage of same cross-section area and the sloping grooves. The new concept of the shift of orifice location and multi-stage orifice in grooves was proposed. The steady flow force in spool valve consisted of grooves has been investigated by CFD, theoretical analysis and experimental approaches. The results show that the force direction and value change with the shift of the flow direction in the groove pass.In chapter 5, the flow field in grooves of spool valve was investigated by CFD and pressure distribution measurement. The results show that the patterns of pre...