Research On Judging Inception Cavitation Of Runner Blade Of Model Hydraulic Turbine Based On Acoustics Method

Cavitation has a great influence on the operating stability of hydraulic turbine.The vibration will increase,and efficiency will drop when the unit operates under the condition of cavitation.The blades will even be damaged under the condition of long-term cavitation.At present,the cavitation characteristics of prototype is deduced from model tests,and the judgement of inception cavitation of model hydraulic turbine still depends on artificial ways,so the results will be as individual as the person for their different qualities and conditions of body.As a result,an objective and effective method of judging inception cavitation of model runner blade is urgently needed.The common problem from traditional analysis methods has been compared based on the acoustic characteristics of bubble caused by cavitation.Do research on the cavitation acoustic energy radiated distribution during the course of no cavitation,appearance,development and collapse of bubble,the extreme value methods had been discovered with the acoustic energy radiated distribution between the high frequency zone and the low frequency zone against cavitation coefficient.The characteristic quantities of the peak to peak value,the inflection point between of the cavitation noise power spectral density curve,the e nergy distribution tendency between the high frequency zone and the low frequency zone and the energy ratio between the high frequency zone and the low frequency zone had been found,and the mathematical models for inception cavitation of model hydraulic turbine with the extreme value method had been built based on the above 4 characteristic quantities.A cavitation monitoring system for model turbine is developed with the attracting technology mentioned above by the mathematical models from cavitation noise characteristics parameters in time and frequency domain.The data and tendency curve of the cavitation noise could be showed on the system and the cavitation data could be saved,the cavitation data and the cavitation noise saved could be rewound.The “double-blind” tests had been performed on test rig.A model Francis turbine and a model pump-turbine had been selected for turbine mode and pump mode.The test results shows that the method expounded in this paper has highly consistency compared with traditional way.The feasibility and effectiveness of the acoustic mothed for judging inception cavitation of runner blade of model hydraulic turbine have been proved by model test and it is very important on engineering for judging inception cavitation of runner blade of model hydraulic turbine.