Study On Numerical Calculation And Experiment Of Hydraulic Machinery Cavitation

With the rapid growth of the national economy, hydraulic machinery industries have gradually entered the golden stage. Groups of the continuous large-scale projects have being implemented, which put all aspects of hydraulic machinery to a higher performance. The comprehensive performances, including the efficiency, cavitation and stability are the most tranditional and important emphases of the hydraulic machinery. Efficiency is related to the utilization of energy, cavitation is related to the life circle of hydraulic machinery, and stability is related to whether the unit is secure, and normal operation. In fact the three performance indicators are not independent, they are closely connected. From the current published research of the three areas,the field of cavitation-related is the least, and the gap between research and actual need is the greatest. The reasons for this phenomenon are lack of the complexity of the phenomenon itself and the difficulties of measurement. Although a lot of research has been made in the cavitation mechanism, the impact of cavitation development and the basic law of cavitation erosion, and some considerable progress has been won, results of these research are almost qualitative or rough quantitative analysis. In the area of accurate quantitative cavitation analysis, a breakthrough progress has not been made nearly half a century. As more and more large hydraulic turbines have been implemented, the relative strength of the runner has beening fallen, Once again the issue of cavitation has been concerned.All along, the study of the hydraulic machinery cavitation has been conducted mainly through the model test. The method is subject to the scale effect of cavitation and the restriction of experimental condition, which can not accurately reflect the emergence, development and collapse of cavitation in the prototype. In this paper, In order to more completely response the hot areas and frontier issues of current hydraulic machinery research, the numerical simulation, model and field experiments of cavitation have been adopt, some common areas of study,such as hydrofoil, pump and turbine,in the hydraulic machinery have been detailed researched. It seems to the first time to analyse cavitation like this.First of all, the status of the basic theory of cavitation ,cavitation numerical simulation and cavitation on-site monitoring has been briefly descripted. The cavitation scale effect has been detailedly discussed. The numerical simulation and the model test of cavitation have been briefly compared, and examples of the numerical simulation of cavitaion in applications have been introduced. On the current numerical simulation of cavitation, there are two most commonly used cavitation model, one is cavitation interface adaptive model, the other is VOF model. After a comparison between these two models, VOF model can be used to simulate cavitation phenomenon more reasonable.Hydrofoil flow is the basis flow of hydraulic machinery. Based on airfoil standard data and test data, a variety of common turbulence models have been detail compared on the calculation of the hydrofoil cavitation. The results show that SST model in the energy and cavitation numerical calculation of the hydrofoil has a clearly advantage. This study provides a reference for the choice of the cavitation numerical simulation turblence model in the future research.The cavitation inception ascertainment has always been a difficulty in the hydraulic mechanical design process. A usual way is to obtain the critical cavitation number through the model cavitation experiment first, then revise it by an experiential factor. The actual operation shows that the equipment cavitation is very serious by the method of setting cavitation coefficient in many cases. Numerical simulation of cavitation can intuitively reflected the occurrence and development of cavitation in the hydraulic machinery. the cavitation study of the axial pump has shown that, although the cavitation critical factor from the numerical simulation is lower than the one from model experiment, the cavitation inception is much greater than the one from model experiment. This conclution is particularly usefull in the cavitation judgement of the hydraulic machinery.In order to verify whether the hydraulic stability of the Kaplan turbine can be quantitative analysis through the unsteady calculation, the SST turbulence model has been adopted to calculate a Kaplan turbine from multi-running conditions in an unsteady state. The ends have been compared with measurement results in the power plant, which tells us that the numerical simulation can do quantitative analysis for hydraulic machinery on the actual operation.The clearance cavitation has become increasingly aroused the concern of the researchers in recent cavitation studies. In order to avoid the sharp increase in the number of grids, a simulation model has been proposed to simplify clearance cavitation simulation. The calculation shows that this approach can be relatively accurate to simulate the clearance cavitation.Hydropower plant cavitation monitoring is always a problem, which is urgent needed to be solved. In this paper, some preliminary attempt has been done. With the self-designed sound-vibration acquisition system, the cavitation signals have been collected and analyzed. Analysis results show that cavitation signal can be accurately collected, and reasonable suggestions of the Kaplan turbine running conditions can be put forward.