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The mismatch between the layout of China's economic and social development and the carrying capacity of water resources, and the uneven spatial and temporal distribution of water resources have become important factors limiting the development of some regions. General Secretary Xi Jinping clearly put forward the "water conservation priority, spatial balance, system management, two-handed efforts" water management ideas, for the new era of water management work to point out the direction, to provide a fundamental guide. Among them, "spatial balance" has shown the way to solve this "mismatch". The implementation of the national water network of major projects, is to optimize the allocation of water resources, to improve the carrying capacity of important regional water resources important initiatives. To strengthen the regional interconnection of the basin, to improve the spatial and temporal distribution of water resources is a major water diversion project is the "outline" of the national water network.
For cross-basin water diversion projects, except for some projects or parts of the area can be achieved through self-flow water transfer function, basically need to first through the pumping station for water to enhance the potential energy, and then through the aqueduct, tunnel or pipeline pumping station to enhance the water transfer to the destination, to achieve the spatial redistribution of water resources. Centrifugal pump is the "heart" of these pumping stations, only "heart" long-term efficient and stable operation, water diversion projects can be long-term health and economic operation, and continue to improve the allocation of water resources to power.
The development technology of small and medium-sized pumps used in industrial and agricultural production has been relatively mature, but the large flow rate and high head of huge centrifugal pumps used in water diversion projects should not only meet the basic requirements such as large enough hump margin, but also require high efficiency, stable operation and cavitation-free operation of pumps in full working conditions to ensure safe and economic operation, and to solve technical difficulties such as anti-sediment abrasion and large head variation. In recent years, China has made a breakthrough in the development and application of giant centrifugal pumps, but relative to the needs of major national water network projects, the investment in research and development and capacity is still insufficient.
In 2021, I received the support of three types of talents (product development talents), and led the team to develop the product that is the "heart" of the pumping station of large water diversion project - high head and high power giant centrifugal pump.
In the design of the impeller, the core component of the pump, we initially adopted the iterative design method of positive and negative problems; in the design of the flow-through components, we referred to the design means of the mixed-flow turbine. Although the centrifugal pump is the working machine and the Francis turbine is the prime mover, there are many similarities between the two in the structural forms of the flow-through parts, for example, the inlet pipe of the water transfer centrifugal pump is close to the form of the tail pipe of the turbine, the guide vane of the pump discharge diameter is close to the form of the fixed guide vane of the turbine, and the water pump pressure chamber is close to the form of the turbine worm casing. In the past 10 years, we have achieved a lot of successful performance in the design and application of mixed-flow hydraulic turbine and accumulated rich design experience. Therefore, this similarity in structural form has laid the foundation for us to initially determine the hydraulic flow path of centrifugal pumps.
However, it is also because of this accumulation that the design experience of mixed-flow turbines will be reflected in the design of centrifugal pumps from time to time. This experience is a help to the turbine design, but the centrifugal pump design may be a resistance. Some turbine design experience directly applied to the design of the pump, but counterproductive, easy to make people fall into the cage of thinking. Centrifugal pump impeller is the key component to do work on water to enhance the total energy, the diameter guide lobe is to reduce the dynamic head to reduce the loss of key components, after many attempts, we fully understand that the degree of matching between the two determines the comprehensive performance of centrifugal pumps. Only by profoundly grasping the principle of the role of each component of the centrifugal pump and the matching relationship, can we jump out of the cage and realize the true flavor.
After realizing this point, we quickly improved the design method and well grasped the matching of the core components of the centrifugal pump, and designed the giant centrifugal pump again, the efficiency level was significantly improved and the cavitation performance was greatly improved.
Although we have gradually "realized the true flavor" of centrifugal pump design and embarked on the fast track, there are still many difficulties to overcome from design to product. For example, how to solve the problem of accurate prediction of the operating characteristics of the design scheme. Accurate verification of centrifugal pump performance is usually done by the model test, but the model performance test requires processing model runners and runners, the model unit processing cycle is long, high cost, energy consumption, generally need to be carried out after the design scheme is more mature. Numerical simulation of the full flow channel based on fluid dynamics (CFD) has become the most important performance analysis tool in the pre-design stage of hydraulic machinery because of its convenience and efficiency, low cost and low energy consumption, which is also an important tool for us to judge whether the hydraulic machinery design scheme is mature. However, CFD numerical calculation cannot replace the model test at present, and its results have some errors with the model test results. The error between numerical calculation and model test results is related to the model, and also influenced by a combination of factors such as grid quality, turbulence model and other calculation methods. It takes a lot of experience to predict the model test performance by numerical calculation results before doing the test. My team and I lacked experience in the design of giant centrifugal pumps, and our experience samples were insufficient, so we also lacked experience in evaluating pump performance based on numerical simulation results.
There is no shortcut to success, and the experience samples need to be accumulated gradually from scratch by ourselves. After the first model test of high flow and high head centrifugal pump in the hydro-mechanical laboratory of the institute, we found that there were some errors in the performance estimation obtained by CFD numerical calculation in the early stage, and the efficiency of the model test was lower than expected. I took the first test result as a sample, analyzed, summarized, optimized the numerical simulation calculation method and comprehensive characteristic evaluation method, and carried out a new round of design and numerical simulation based on this, and then carried out a new round of model test. After many rounds of design and model tests, we finally successfully designed a high-flow, high-head giant centrifugal pump hydraulic model with energy characteristics of a certain specific speed reaching international first-class level!
As the technical parameters of centrifugal pumps required for different water diversion projects vary greatly, to serve the national water network well, we need to accurately understand the characteristics of each water diversion project, one stop one strategy, tailor-made. When the centrifugal pump ratio speed and other parameters vary greatly, experience samples need to be re-accumulated. Therefore, despite our successful experience, it still takes a lot of efforts to design high performance centrifugal pumps with different specific speed and make accurate performance prediction.
In addition to the difficulties in design methods and performance estimation, there are many other challenges that we have to face continuously on the way of designing giant centrifugal pumps: how to adapt the pump design to the conditions of large head variation? How to improve the stability of operation under complex incoming flow conditions? Such and such, there are still many topics we need to solve. In the next few years, only by studying these problems in depth and proposing ways to deal with them, can the products we develop really realize the transformation from partial leadership to full leadership in technology!
Although there are many problems and setbacks, I think, as a "product development" talent supported by the Institute's research funds, I will continue to sum up the lessons learned and accumulate experience. I will work together with my team to further improve the design optimization method and develop and complete several excellent hydraulic models of giant centrifugal pumps during the 14th Five-Year Plan period. I will work hard with my team to further improve the design optimization methods and develop several excellent hydraulic models of giant centrifugal pumps during the 14th Five-Year Plan period.
