Design method for rotating wheel of ultrahigh-water-head small-flow pump turbine

Abstract

The invention relates to a method for designing a runner of an ultrahigh-water-head small-flow pump turbine, which aims at solving the problems of distributed energy consumption in situ and difficulty in site selection of a pumped storage power station, designs the runner of the ultrahigh-water-head small-flow pump turbine, draws up basic parameters of the small pumped storage power station, and utilizes the preliminarily drafted basic parameters to design the runner of the ultrahigh-water-head small-flow pump turbine. And calculating main geometric parameters of the runner blade, then verifying working parameters of the runner blade until the geometric parameters meeting design requirements are obtained, finally obtaining the boundary dimension and the blade shape of the runner blade, optimizing the parameters by utilizing numerical simulation, and designing the ultrahigh-water-head small-flow pump turbine runner. The method is simple, construction of the pumped storage power station can be accelerated, in-situ absorption of distributed energy is achieved, particularly, construction of a micro-grid can be accelerated, stability and reliability of power supply of a power system are improved, site selection difficulty of the small pumped storage power station and reservoir capacity are greatly reduced, the operation requirement of a user is met, and the method is suitable for popularization and application. And the method has obvious social and economic benefits.

Description

Technical Field

[0001] The invention relates to the field of pump turbine design for a pumped storage power station, in particular to a design method for a runner of an ultra-high head and small flow pump turbine. Background Art

[0002] Under the dual carbon goals, distributed renewable energy is developing rapidly, but current challenges with its intermittent and unstable consumption continue to hinder its development. Pumped storage, as a mature energy storage technology, offers advantages such as large-scale storage, high-efficiency energy conversion, long-term storage, and environmental sustainability. It is rapidly developing alongside the growth of new energy. The "Pumped Storage Industry Development Report 2023" reveals that China has approximately 823 million kilowatts of planned pumped storage power stations. By 2023, 5.15 million kilowatts of new installed capacity will be commissioned, bringing the total installed capacity in operation to 50.94 million kilowatts, including 12 million kilowatts under construction. While the scale of pumped storage continues to grow, it still cannot fully meet the needs of the rapid development of renewable energy. Pumped storage development is lagging behind due to issues such as site selection and construction timelines. Converting pumping stations or hydropower stations into pumped storage is a key means of accelerating its development. To address the local consumption of distributed renewable energy, the construction of ultra-high-head, low-flow pump-turbine systems at selected locations is imperative.

[0003] As a type of small pumped-storage power station, ultra-high-head, low-flow pump-turbines have unique fluid parameter characteristics, making project site selection less constrained by geographical conditions. Compared with conventional pumped-storage power stations, they can significantly reduce reservoir capacity and shorten construction periods, accelerating the development of pumped storage and effectively addressing the problem of on-site renewable energy consumption. Current research on pump-turbines focuses on ultra-high head and large capacity, with less research on ultra-high-head, low-flow pump-turbines. As their core energy conversion component, the runner must surpass the dynamic characteristics of conventional pump-turbine runners to meet demand. Therefore, developing a design method for ultra-high-head, low-flow pump-turbine runners is of great significance for improving their optimization design theory and promoting practical engineering applications. However, no relevant public reports have been published to date. Summary of the Invention

[0004] In response to the aforementioned situation and to overcome the shortcomings of the existing technology, the present invention aims to provide a design method for an ultra-high-head, low-flow pump-turbine runner that effectively addresses the problem of on-site consumption of distributed renewable energy. This method reduces the difficulty of site selection for small pumped-storage power stations, provides technical support for ultra-high-head, low-flow runner design, and accelerates the construction of pumped-storage power stations, thereby accelerating the development of a new power system based primarily on renewable energy.

[0005] To achieve the above purpose, the technical solution provided by the present invention is a method for designing a runner of a super-high head and small flow pump-turbine. Aiming at the problem of local consumption of distributed energy and difficulty in site selection of pumped storage power stations, a runner of a super-high head and small flow pump-turbine is designed. First, the design parameters of the super-high head and small flow pump-turbine are determined, namely, the design flow Q, the head H. P and rated speed n, and then based on the conventional pump turbine design principles, determine the runner low-pressure side diameter D1, runner high-pressure side diameter D2, guide vane height b0, runner inlet placement angle β1, runner outlet placement angle β2, blade wrap angle and the geometric parameters of the number of blades Z, and then calculate its specific speed n based on the above parameters sq and n st , speed coefficient K P and K T , unit flow n 11 and unit speed Q 11 , and then verify it based on the relevant parameters and experience curves of multiple high-head pumped storage power stations. If it does not meet the design requirements, the hydraulic parameters are designed again and verified again. This cycle is repeated until the design requirements are met, and the runner of the ultra-high-head and small-flow pump-turbine is obtained.

[0006] The method of the present invention is simple and can accelerate the construction of pumped-storage power stations, realize on-site consumption of distributed energy, especially accelerate the construction of microgrids, improve the stability and reliability of power supply of power systems, greatly reduce the difficulty of site selection and reservoir capacity of small pumped-storage power stations, reduce construction costs, shorten construction periods and reduce water demand. The designed ultra-high head and small flow pump-turbine runner has good hydraulic performance, meets user operation requirements, and has significant social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is the design drawing of the runner blade of the present invention.

[0008] Figure 2 This is a water body model diagram of the ultra-high head and small flow pump turbine runner according to an embodiment of the present invention.

[0009] Figure 3 This is a model diagram of an ultra-high head and small flow pump turbine according to an embodiment of the present invention.

[0010] Figure 4 This is the external characteristic diagram of the optimized ultra-high head and small flow pump turbine according to an embodiment of the present invention.

[0011] Figure 5 This is a frequency domain characteristic diagram of pressure pulsation of an optimized ultra-high head and small flow pump turbine according to an embodiment of the present invention.

[0012] Figure 6This is a structural diagram of the design of the runner blades of an ultra-high head and small flow water pump turbine according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings and examples.

[0014] The typical feature of ultra-high head and small flow pump turbine is that the working head is much higher than that of conventional pump turbine, while the flow is much smaller than that of conventional pump turbine. Its dynamic performance is characterized by special head characteristics and flow characteristics, H / Q is very large, and Q / (D 2 H 1 / 2 ) is very small. It is a pump-turbine with ultra-low specific speed, relatively low unit speed and ultra-low unit flow. The geometry of its runner flow channel conforms to the characteristics of ultra-low specific speed. The ratio of the high-pressure side diameter to the low-pressure side diameter of the blade D2 / D1 is large, while the relative heights B1 / D2 and b0 / D2 of the high-pressure side of the blade and the guide vane are very small, and the runner is flat.

[0015] The present invention discloses a method for designing a runner of a super-high head and small flow pump-turbine. Aiming at the problem of local consumption of distributed energy and difficulty in site selection of pumped storage power stations, the runner of a super-high head and small flow pump-turbine is designed. First, the design parameters of the super-high head and small flow pump-turbine are determined, namely, the design flow Q, the head H. P and rated speed n, and then based on the conventional pump turbine design principles, determine the runner low-pressure side diameter D1, runner high-pressure side diameter D2, guide vane height b0, runner inlet placement angle β1, runner outlet placement angle β2, blade wrap angle and the geometric parameters of the number of blades Z, and then calculate its specific speed n based on the above parameters sq and n st , speed coefficient K P and K T , unit flow n 11 and unit speed Q 11 , and then verify it based on the relevant parameters and experience curves of multiple high-head pumped storage power stations. If it does not meet the design requirements, the hydraulic parameters are redesigned and verified again, and the cycle is repeated until the design requirements are met, resulting in the runner of the ultra-high-head, low-flow pump-turbine. The designed ultra-high-head, low-flow pump-turbine flow components, including the volute, fixed guide vanes, movable guide vanes, and tailwater pipe, do not undergo major changes. Only the runner is optimized, which specifically includes the following steps:

[0016] (1) Runner low pressure side diameter D1

[0017] The design of the low-pressure side of the runner must take into account both the cavitation characteristics of the pump working condition and the flow rate of the turbine working condition. When determining the diameter of the low-pressure side of the runner, the fluid dynamic characteristics and geometric constraints are comprehensively considered. The calculation formula is:

[0018]

[0019] Where: K0 is the low-pressure side diameter correction coefficient, and its value range is [3.5, 5.5];

[0020] (2) Runner high pressure side diameter D2

[0021] Geometric parameters such as the runner high-pressure side diameter D2 and the blade outlet angle have a decisive influence on the pump head characteristics. The calculation formula is:

[0022]

[0023] Where: k D2 is the high pressure side diameter correction factor;

[0024] (3) Guide vane height b0

[0025] The guide vane height is a key geometric parameter of the Francis pump-turbine guide vane and has a significant regulatory effect on the hydraulic performance of the unit. Its design needs to take into account the hump characteristics of the flow-head curve under pump working conditions and the flow-efficiency external characteristics under turbine working conditions. The calculation formula is:

[0026]

[0027] Where: —Guide vane height correction factor;

[0028] (4) Runner inlet placement angle β1

[0029] The low-pressure side angle of the runner blades, i.e., the runner inlet placement angle β1, is a key geometric parameter of the runner under both pump and turbine operating conditions. Its design needs to balance the flow characteristics of the two operating conditions. This angle determines the inlet attack angle characteristics under pump operating conditions and affects the draft tube flow matching under turbine operating conditions. The calculation formula is:

[0030]

[0031]

[0032] Where: V m1 is the inlet axial speed, m / s; u1 is the inlet circumferential speed, m / s; V u1 is the circumferential component of the inlet velocity, m / s; b0 is the guide vane height, m;

[0033] (5) Runner outlet placement angle β2

[0034] The high-pressure side angle of the runner blades, i.e., the runner outlet placement angle β2, is a key geometric parameter of the runner under both pump and turbine operating conditions. Its design needs to balance the flow characteristics required under both operating conditions. This angle affects both the outlet flow state under pump operating conditions and determines the inlet flow distribution under turbine operating conditions. The calculation formula is:

[0035]

[0036] Where: H t is the theoretical head, m; σ is the Stodaola slip coefficient; V m2 is the outlet axial velocity, m / s; u2 is the outlet circumferential velocity, m / s;

[0037] (6) Blade angle and blade number Z

[0038] The blade wrap angle and number of blades of a Francis pump-turbine are its core geometric parameters, which have a significant impact on the hydraulic performance under dual working conditions. Compared with conventional Francis turbines, the number of blades of Francis pump-turbines presents unique design features, which can be 6, 7 or 9 blades, using thin long lines and the wrap angle range of 90°-130°. The runner blades of ultra-high head and low flow pump-turbines have large angles. Balancing the head requirements of the pump working condition with the flow characteristics of the turbine working condition, a smaller wrap angle of 90°-110° should be selected;

[0039] (7) Verify dynamic characteristics

[0040] 1) Verify the speed and specific speed

[0041] Specific speed is the core parameter that characterizes the comprehensive performance of a pump-turbine. This parameter converts parameters such as head, head, flow rate, and speed into a single indicator by unifying the dimensions. It can be used to evaluate the energy conversion efficiency and operational stability of the unit. The calculation formula is:

[0042]

[0043] Where: η is efficiency, and its value range is [80%, 100%];

[0044] According to the statistical relationship between the pump-turbine head, head amplitude and corresponding specific speed at home and abroad, combined with the dynamic performance characteristics of ultra-high head and small flow, when the pump head is 700m, the recommended specific speed of the pump is n sq <28, the recommended specific speed value for turbine operating condition is n st <90;

[0045] According to the statistical experience of the built pumped storage power stations, the water pump operating speed coefficient is recommended to be K P <3700, turbine operating speed coefficient recommended K T<2500, the calculation formula is:

[0046]

[0047] Where: K P K is the speed coefficient of the water pump; T is the turbine operating speed coefficient; H P is the design head, m; H T is the design head, m;

[0048] 2) Verify unit parameters

[0049] Comprehensive hydraulic design parameters and pump turbine flow, speed and head, unit flow Q 11 And the unit speed n 11 The calculation formula is:

[0050]

[0051] According to the statistical experience of pump turbines with a head of 600m or more at home and abroad, combined with the dynamic performance characteristics of ultra-high head and small flow, the unit flow Q 11 <0.1m 3 / s, unit speed is 70r / min <n 11 <90r / min;

[0052] (8) Establish a three-dimensional model to achieve optimal design of the runner

[0053] A three-dimensional model of an ultra-high-head, low-flow pump-turbine was established, and CFX was used to perform numerical simulation of its entire flow path to further verify the rationality of the geometric parameter selection in the runner design. The runner geometric parameters were continuously modified and optimized, and ultimately the appropriate runner blade shape was obtained, achieving the optimal design of the runner.

[0054] The present invention can be specifically implemented by the following examples.

[0055] The Qilian Mountains at the junction of Gansu and Qinghai are generally high in elevation, with peaks mostly above 4,000 meters and large valley drops. The Hexi Corridor along its eastern side leads the nation in wind and photovoltaic resources, and has great potential for distributed energy development. Ultra-high head and low flow pumped storage projects can be planned to serve the local consumption and transmission channels of new energy in Northwest China, and enhance the consumption capacity of wind and solar power. This area is selected as a site for the construction of an ultra-high head and low flow pumped storage power station. The temporary values ​​of the hydraulic parameters of the pump and turbine are: design flow Q P 1.475m 3 / s, pump head H P is 700m, the rated speed of the unit is n r The speed is 2900r / min and the power is about 9.12MW.

[0056] The models of all flow components except the runner are established according to the flow characteristics of conventional ultra-high head pumped storage power stations, including the volute, fixed guide vanes, movable guide vanes, and tailwater pipe. The design of the runner part includes the following steps:

[0057] (1) Runner low pressure side diameter D1

[0058] The design of the low-pressure side of the runner must take into account both the cavitation characteristics of the pump working condition and the flow rate of the turbine working condition. When determining the diameter of the low-pressure side of the runner, the fluid dynamic characteristics and geometric constraints should be comprehensively considered. In this embodiment, the efficiency index is mainly considered. The low-pressure side diameter correction coefficient K0 is 3.758, which is substituted into Formula 1 to obtain the D1 value;

[0059]

[0060] (2) Runner high pressure side diameter D2

[0061] Geometric parameters such as the runner high-pressure side diameter D2 and the blade outlet angle have a decisive influence on the pump head characteristics. The pump operating speed n is obtained from formula 13. sq 25.88 mm 3 / s, substitute into formula 3 to get the high pressure side diameter correction factor k D2 Since the runner high-pressure side diameter D2 is related to the turbine operating flow, in order to meet the dynamic characteristics of the ultra-high head and small flow pump-turbine, the runner high-pressure side diameter D2 is reduced accordingly, and a larger D2 / D1 (>2) is satisfied to meet the characteristics of the ultra-low specific speed pump-turbine;

[0062]

[0063] (3) Guide vane height b0

[0064] The guide vane height is a key geometric parameter of the Francis pump turbine guide vane and has a significant regulatory effect on the hydraulic performance of the unit. Its design must take into account the hump characteristics of the flow-head curve under pump conditions and the flow-efficiency characteristics under turbine conditions. The runner should meet the characteristics of ultra-low specific speed pump turbines, with a smaller blade height b o / D2(<0.07), so substitute the parameters into Equation 4 and Equation 5 and increase the b0 value appropriately;

[0065]

[0066] Where: —Guide vane height correction factor;

[0067] (4) Runner inlet placement angle β1

[0068] The low-pressure side angle of the runner blades, or the runner inlet placement angle β1, is a key geometric parameter for the runner under both pumping and turbine conditions. Its design must balance the flow characteristics required for both conditions. This angle determines the inlet angle of attack for pumping conditions and influences the draft tube flow compatibility for turbine conditions. The calculation formula is:

[0069]

[0070] Middle: V m1 is the inlet axial speed, m / s; u1 is the inlet circumferential speed, m / s; V u1 is the circumferential component of the inlet velocity, m / s; b0 is the guide vane height, m;

[0071] (5) Runner outlet placement angle β2

[0072] The runner blade high-pressure side angle, or the runner outlet placement angle β2, is a key geometric parameter for both pump and turbine operation. Its design must balance the flow characteristics required for both conditions. This angle influences both the outlet flow state in pump operation and the inlet flow distribution in turbine operation. The calculation formula is:

[0073]

[0074] Where: H t is the theoretical head, m; σ is the Stodaola slip coefficient; V m2 is the outlet axial velocity, m / s; u2 is the outlet circumferential velocity, m / s;

[0075] Substituting the parameters and correcting them by adding the positive angle, the optimized inlet and outlet angles of the blades on each flow surface are shown in Table 1.

[0076] Table 1 Blade inlet and outlet angles of each flow surface

[0077]

[0078] Note: β1 = β′1 + Δβ1, β2 = β′2 + Δβ2, β1 and β2 are the corrected inlet and outlet angles. The recommended values ​​of the inlet and outlet angles Δβ1 and Δβ2 are 0° to 3°.

[0079] (6) Blade angle and blade number Z

[0080] The blade wrap angle and number of blades in a Francis pump-turbine are its core geometric parameters, significantly impacting dual-operation hydraulic performance. Compared to conventional Francis turbines, Francis pump-turbines exhibit unique design features: typically 6, 7, or 9 blades, employing thin, long profiles and a wrap angle of 90°-130°. Ultra-high-head, low-flow pump-turbines have large runner blade angles. Balancing the required head under pumping conditions with the flow characteristics of turbine operation, a smaller wrap angle should be selected. After design optimization, this embodiment selects 7 blades with a wrap angle of 100°.

[0081] (7) Verify dynamic characteristics

[0082] 1) Verify the speed and specific speed

[0083] Specific speed is the core parameter that characterizes the comprehensive performance of a pump-turbine. This parameter converts parameters such as head, head, flow rate, and speed into a single indicator by unifying the dimensions. It can be used to evaluate the energy conversion efficiency and operational stability of the unit. Based on the statistical relationship between the head, head amplitude, and corresponding specific speed of pump-turbines at home and abroad, combined with the dynamic performance characteristics of ultra-high head and small flow rate, the recommended specific speed value for the pump operating condition is n when the pump head is 700m. sq <28, the recommended specific speed value for turbine operating condition is n st <90. Substituting each parameter into formula 13, we can get the pump operating speed n sq =25.88 mm 3 / s, turbine operating speed n st =78.54m·kW (assuming efficiency η is 90%), it is easy to see that the specific speed of the ultra-high head and small flow pump-turbine is within the recommended range;

[0084]

[0085] According to the statistical experience of built pumped storage power stations, the water pump operating speed coefficient is recommended to be less than 3700, and the turbine operating speed coefficient is recommended to be less than 2500. Substituting the design parameters into formula 14, the water pump operating speed coefficient K can be obtained. P =3522, turbine operating speed coefficient K T =2048, which is consistent with the empirical value, indicating that the rated speed of the unit is n r 2900r / min is appropriate.

[0086]

[0087] Where: K P K is the speed coefficient of the water pump; T is the turbine operating speed coefficient; H P is the design head, m; H T is the design head, m;

[0088] 2) Verify unit parameters

[0089] Based on the statistical experience of pump-turbines with a head of 600m or more at home and abroad, combined with the dynamic performance characteristics of ultra-high head and small flow, the recommended value of unit flow Q 11 <0.1m 3 / s, the recommended unit speed is 70r / min <n 11 <90r / min. Combining the above hydraulic design parameters and the pump turbine flow rate, speed and head parameters, substitute them into Equation 15 and Equation 16 to solve the unit flow rate Q 11 =0.088m 3 / s and unit speed n 11 =88.74r / min, it can be seen that the unit parameters meet the design requirements.

[0090] Unit speed calculation formula:

[0091]

[0092] Unit flow calculation formula:

[0093]

[0094] (8) Establish a three-dimensional model to achieve optimal design of the runner

[0095] A three-dimensional model of an ultra-high head and low flow pump-turbine was established, and CFX was used to perform numerical simulation of its entire flow path to further verify the rationality of the geometric parameter selection in the runner design. The runner geometric parameters were continuously modified and optimized, and finally a suitable runner blade shape was obtained to achieve the optimal design of the runner. The final model parameters are shown in Table 2.

[0096] Table 2 Hydraulic design parameters of ultra-high head and small flow pump turbine

[0097]

[0098] According to the above method, the runner of the ultra-high head and small flow pump turbine is obtained, and the runner blade design is as follows: Figure 1 As shown, the water body of the runner channel is Figure 2 As shown in the figure, the volute, fixed guide vanes, movable guide vanes, runner and tailwater pipe constitute the entire ultra-high head and small flow pump turbine. Figure 3 The components of the entire flow channel of the calculation model were divided into networks, and numerical calculations were performed using CFX to obtain the hydraulic performance of the ultra-high head and small flow pump-turbine designed using the method of the present invention.

[0099] Figure 4The figure shows the performance evolution of the ultra-high head, low-flow pump-turbine after design optimization. Under turbine operation, the optimized efficiency curve increases with increasing flow rate, with the fastest rate of increase between 0.7Q and 0.8Q, then decreasing and leveling off. The optimized power curve increases with increasing flow rate, with the rate of power growth gradually increasing. At 1.3Q, the efficiency reaches 81.31%, and the output is 10.45 MW. Under pump operation, the optimized efficiency curve first increases, then decreases, and then increases with increasing flow rate. The efficiency growth rate first increases gradually, then decreases, and then gradually increases. The optimized hump characteristic curve exhibits a better overall performance, with a smaller hump area. Starting at 0.9Q, the optimized head first decreases, then increases, and then decreases with increasing flow rate. The head curve growth rate first decreases, then increases, and then decreases. At 1.0Q, the efficiency reaches 80.64%, and the head is 721 m. In summary, the optimal operating efficiency, power and head of the optimized ultra-high head and small flow pump-turbine have been improved, the high-efficiency area has been expanded compared with before optimization, and the operating stability has been improved.

[0100] Figure 5 This figure shows the pressure pulsation characteristics of an ultra-high head, low-flow pump-turbine under design operating conditions. Under the pump's design operating conditions, the pressure pulsation amplitude in the bladeless area is large and periodic. The pressure pulsation amplitude reaches its maximum at monitoring point P6 (0.0476 kPa), with the primary frequencies being 0.5 times the rotational frequency, the blade frequency, and its multiples. The primary frequencies of pressure pulsation at monitoring point P5 are the same as those at monitoring point P6. The runner pressure pulsation amplitude is smaller, reaching 0.0304 kPa at monitoring point P7. The primary frequencies are the rotational frequency, the blade frequency, and its multiples (f / fn = 7 and 14). The pressure pulsation amplitude at monitoring point P8 is smaller than that at monitoring point P7, with the primary frequencies being the same as those at monitoring point P7. Under the turbine's design operating conditions, the pressure pulsation spectrum in the bladeless area exhibits broadband characteristics. The pressure pulsation amplitude reaches its maximum at monitoring point P5 (0.0678 kPa), with the main frequencies being the blade frequency and its multiples. The main frequencies of pressure pulsation at monitoring point P6 are the same as those at P5. The pressure pulsation amplitude at the runner is smaller, reaching 0.0081 kPa at monitoring point P7, with the main frequencies being the rotational frequency and blade frequency. The pressure pulsation amplitude at monitoring point P8 is smaller than that at monitoring point P7, with the main frequencies being the blade frequency and rotational frequency. Overall, the runner and guide vanes are well matched, the pressure pulsation amplitude is moderate, and the flow is relatively stable, indicating less flow separation within the channel, a low cavitation risk, and controllable cavitation.

[0101] In summary, the design method of the present invention obtains an ultra-high head and small flow pump-turbine runner that meets the runner design requirements, and at the same time has good hydraulic performance, meets the user's operation requirements, and reduces the problems of difficult site selection, long construction period, and high cost of conventional pumped storage power stations. It effectively solves the problem of on-site absorption of distributed renewable energy, accelerates the construction of a new power system based on new energy, and helps energy transformation and upgrading. The design method has a wide range of applications and can be applied to the pumped storage transformation of conventional axial flow turbines, diagonal flow turbines, and axial flow pumps. It will face the dual carbon goals and the "Medium- and Long-Term Development Plan for Pumped Storage (2021-2035)" provides technical support for the research and development of fluid machinery in small pumped storage power stations. It is a major innovation in ultra-high head and small flow pump-turbine runners and has significant social and economic benefits.

[0102] It should be pointed out that the above implementation examples are only used to illustrate the technical method of the present invention, rather than to limit the scope of protection of the present invention. Although the design method is described in detail using more appropriate examples, in the field of ultra-high head and small flow pump turbine design, the design scheme of the present invention is modified or replaced in the same way, and the equivalent embodiments or changes that do not deviate from the design method of the present invention are all within the scope of protection of the present invention.

Claims

1. A design method for an ultra-high head and low flow pump turbine runner, characterized in that: In order to realize the local consumption of distributed energy and the difficulty in site selection of pumped storage power station, the runner of ultra-high head and small flow pump turbine is designed. First, the design parameters of ultra-high head and small flow pump turbine are determined, namely design flow Q, head H. P and rated speed n, and then based on the conventional pump turbine design principles, determine the runner low-pressure side diameter D1, runner high-pressure side diameter D2, guide vane height b0, runner inlet placement angle β1, runner outlet placement angle β2, blade wrap angle and the geometric parameters of the number of blades Z, and then calculate its specific speed n based on the above parameters sq and n st , speed coefficient K P and K T , unit flow n 11 and unit speed Q 11 , and then verify it based on the relevant parameters and experience curves of multiple high-head pumped storage power stations. If it does not meet the design requirements, the hydraulic parameters are designed again and verified again. This cycle is repeated until the design requirements are met, and the runner of the ultra-high-head and small-flow pump-turbine is obtained.

2. The method for designing a runner for an ultra-high head and small flow pump-turbine according to claim 1, characterized in that: The following steps are involved: (1) Runner low pressure side diameter D1 The design of the low-pressure side of the runner must take into account both the cavitation characteristics of the pump working condition and the flow rate of the turbine working condition. When determining the diameter of the low-pressure side of the runner, the fluid dynamic characteristics and geometric constraints are comprehensively considered. The calculation formula is: Where: K0 is the low-pressure side diameter correction coefficient, and its value range is [3.5, 5.5]; (2) Runner high pressure side diameter D2 The calculation formula for the runner high-pressure side diameter D2 is: Where: k D2 is the high pressure side diameter correction factor; (3) Guide vane height b0 The guide vane height is a key geometric parameter of the guide vane of a Francis pump-turbine. Its design must take into account both the hump characteristics of the flow-head curve under pump conditions and the flow-efficiency external characteristics under turbine conditions. The calculation formula is: Where: —Guide vane height correction factor; (4) Runner inlet placement angle β1 The low-pressure side angle of the runner blade is the runner inlet placement angle β1. Its design needs to balance the flow characteristics requirements of the two working conditions. The calculation formula is: Where: V m1 is the inlet axial speed, m / s; u1 is the inlet circumferential speed, m / s; V u1 is the circumferential component of the inlet velocity, m / s; b0 is the guide vane height, m; (5) Runner outlet placement angle β2 The high-pressure side angle of the runner blade is the runner outlet placement angle β2. Its design needs to balance the flow characteristics requirements of the two working conditions. The calculation formula is: Where: H t is the theoretical head, m; σ is the Stodaola slip coefficient; V m2 is the outlet axial velocity, m / s; u2 is the outlet circumferential velocity, m / s; (6) Blade angle and blade number Z The blade wrap angle and blade number of a Francis pump-turbine are its core geometric parameters. Compared with conventional Francis turbines, the Francis pump-turbine has 6, 7, or 9 blades, uses a thin and long profile, and has a wrap angle range of 90°-130°. The runner blade angle of an ultra-high head and low flow pump-turbine is large. A wrap angle of 90°-110° is selected to balance the head requirement of the pump and the flow characteristics of the turbine. (7) Verify dynamic characteristics 1) Verify the speed and specific speed Specific speed is the core parameter that characterizes the comprehensive performance of the pump-turbine. The calculation formula is: Where: η is efficiency, and its value range is [80%, 100%]; According to the statistical relationship between the pump-turbine head, water head amplitude and corresponding specific speed, combined with the dynamic performance characteristics of ultra-high head and small flow, when the pump head is 700m, the pump operating specific speed n sq <28, turbine operating speed n st <90; According to the statistical experience of the built pumped storage power stations, the pump operating speed coefficient K P <3700, turbine operating speed coefficient K T <2500, the calculation formula is: K P =n sq H P 3 / 4 , K T =n st H T 1 / 2 Formula 14 Where: K P K is the speed coefficient of the water pump; T is the turbine operating speed coefficient; H P is the design head, m; H T is the design head, m; 2) Verify unit parameters Comprehensive hydraulic design parameters and pump turbine flow, speed and head, unit flow Q 11 And the unit speed n 11 The calculation formula is: According to the statistical experience of pump turbines with a head of 600m or more, combined with the dynamic performance characteristics of ultra-high head and small flow, the unit flow Q 11 <0.1m 3 / s, unit speed is 70r / min <n 11 <90r / min; (8) Establish a three-dimensional model to achieve optimal design of the runner A three-dimensional model of an ultra-high-head, low-flow pump-turbine was established, and CFX was used to perform numerical simulation of its entire flow path to further verify the rationality of the geometric parameter selection in the runner design. The runner geometric parameters were continuously modified and optimized, and ultimately the appropriate runner blade shape was obtained, achieving the optimal design of the runner.

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