Hydraulic turbine and forward design method thereof

Abstract

The application discloses a kind of impeller of hydraulic turbine and its forward design method, comprising: (1) from the extension direction of impeller inlet to outlet, the impeller blade is divided into front end and rear end;Front end is formed when the angle of installation is inlet installation angle, that is, inlet twist angle;Rear end is formed when the angle of installation is outlet installation angle, that is, outlet twist angle;(2) with the performance of hydraulic turbine as optimization target, according to the shape of volute and the flow law of outflow, the inlet twist angle and outlet twist angle of impeller matched with volute outflow are calculated;(3) according to the working condition of hydraulic turbine, verify and correct inlet twist angle and outlet twist angle;(4) then according to the iteration principle of positive and negative problem, determine the twist angle variation law of the overcurrent interface direction between impeller blade streamline direction and vertical streamline.The application improves turbine energy characteristics by optimizing the inlet twist angle of impeller blade, improves the utilization rate of existing pressure energy.

Description

Technical Field

[0001] This invention relates to the field of turbomachinery technology, and in particular to an impeller for a hydraulic turbine and its forward design method. Background Technology

[0002] A pump is a reversible rotating machine. When a pump operates in reverse as a turbine, it is called a pump-as-a-turbine (PAT), a type of hydraulic turbine. In forward operation, low-pressure liquid enters the impeller through the suction inlet. The impeller's rotation does work on the liquid, converting the pump shaft's rotational mechanical energy into the liquid's pressure and kinetic energy. The volute collects the high-speed fluid and further converts the liquid's kinetic energy into pressure energy. The high-pressure fluid is discharged from the volute outlet. In reverse operation, the internal flow direction is opposite to the pump's flow direction. High-pressure liquid enters through the volute, impacting the impeller's rotation and doing work on it. The liquid's pressure energy is converted into the shaft's rotational mechanical energy, and finally, the liquid flows out from the impeller outlet.

[0003] Centrifugal pumps operating in reverse to power turbines are commonly used in chemical, petroleum, and other industrial applications, as well as in energy recovery systems and micro-scale (less than 100kW) hydropower development. Generally, most pumps are simply reverse-engineered versions of the original pump, where the liquid flows directly from the volute outlet to the impeller inlet during turbine operation. However, the impeller design of this type of pump only considers the pump's operating conditions and not the turbine's. The blade inlet torsion angle cannot adequately match the turbine's operating conditions, resulting in generally low turbine efficiency and a narrow high-efficiency range. Furthermore, the pump's performance in reverse operation is often unknown, making operating parameters difficult to predict and leading to inaccurate turbine selection.

[0004] Chinese patent document CN112861279A discloses a design method for a turbine impeller in a membrane-based seawater desalination energy recovery integrated machine. This method involves reducing the rated design flow rate while keeping other design parameters constant to perform hydraulic design of the turbine impeller. The main steps of the hydraulic design are: reducing the rated design flow rate of the turbine while keeping other design parameters unchanged; converting these parameters to pump operating conditions; and then, based on the pump design method, determining the pump inlet diameter D1, pump outlet diameter D2, pump outlet width b2, pump inlet and outlet angles, and the number of blades to perform the pump's hydraulic design. This invention can improve the efficiency and operational safety and stability of the turbine-type seawater desalination integrated machine under various operating conditions.

[0005] Chinese patent document CN106844905A discloses an optimization design method for hydraulic turbine impellers. It employs a two-tiered optimization approach with primary and secondary objectives. The optimization of the secondary objective functions accelerates the convergence of optimization variables to the optimal solution, improving the accuracy and speed of multi-constraint optimization. The optimization of the secondary objective functions utilizes a genetic optimization algorithm, starting from a surface rather than the traditional point-based approach, thus improving computational efficiency compared to traditional hydraulic optimization design methods. The optimization of the primary objective function employs a multi-island genetic algorithm, increasing the multi-peak search capability of the optimization algorithm and mitigating the impact of local convergence on the optimization process to some extent.

[0006] Existing impeller design technologies mainly improve turbine performance by optimizing blade shape, adding guide vanes, and rounding the impeller. There are few proposals to redesign impellers specifically for hydraulic turbines to significantly improve turbine performance. Summary of the Invention

[0007] This invention provides a forward design method for hydraulic turbine impellers, which improves turbine energy characteristics and increases the utilization rate of existing pressure energy by optimizing the inlet torsion angle of the impeller blades.

[0008] The technical solution of the present invention is as follows:

[0009] A forward design method for hydraulic turbine impellers includes the following steps:

[0010] (1) Along the extension direction from the impeller inlet to the outlet, the impeller blades are divided into the front end and the rear end; the angle formed when the front end is installed is the inlet installation angle, which is the inlet torsion angle; the angle formed when the rear end is installed is the outlet installation angle, which is the outlet torsion angle.

[0011] (2) Taking the performance of the hydraulic turbine as the optimization target, calculate the impeller inlet torsion angle and outlet torsion angle that match the outflow of the volute according to the shape of the volute and the outflow law.

[0012] (3) Based on the working conditions of the hydraulic turbine, inspect and correct the inlet torsion angle and the outlet torsion angle;

[0013] (4) Then, based on the iterative principle of positive and negative problems, determine the variation law of the torsion angle between the streamline direction of the impeller blade and the flow interface direction perpendicular to the streamline.

[0014] This invention aims to improve the performance of a pump reversing to power a turbine by changing the inlet and outlet torsion angle of the blades, thereby enhancing the turbine's energy characteristics and improving the utilization rate of existing pressure energy.

[0015] Step (2) includes:

[0016] (2-1) Assuming that the impeller of the hydraulic turbine has a non-impact inlet under design conditions, then the inlet torsion angle β of the blades...b1 The relative flow angle β1 with the inlet is equal to that of β b1 =β1; The inlet torsion angle β is calculated using the velocity triangle at the blade inlet. b1 :

[0017]

[0018] In the formula: Ψ1 is the axial component of the absolute velocity at the inlet, in m / s; Ψ1 is the blade inlet displacement coefficient, which can be obtained from the formula... Determine, in the formula: δ1 is the circumferential thickness of the blade inlet edge, in meters; R 1c Let be the radius of the centroid of the blade inlet edge, in meters; Z be the number of blades in the impeller; u1 be the impeller inlet circumferential velocity, in meters per second; v u1 Q is the circumferential component of the absolute velocity of the inlet, in m / s; r To calculate the flow rate, m 3 / s; D1 is the impeller inlet diameter; k1 is the volute structure coefficient; b1 is the blade inlet width; n is the impeller speed, r / min;

[0019] (2-2) Assuming the direction of the fluid outlet relative streamline is consistent with the direction of the blade outlet rib line, then the outlet torsion angle β b2 The relative flow angle β2 with respect to the outlet is equal, i.e., β b2 =β2;

[0020] Let the absolute velocity of the liquid flowing out of the hydraulic turbine impeller be the normal outlet velocity, then:

[0021]

[0022] In the formula: u1 is the axial surface velocity component of the absolute velocity at the outlet, in m / s; u2 is the circumferential velocity at the outlet, in m / s; A2 is the actual cross-sectional area of ​​the liquid flow through the impeller outlet axial surface, in m². 2 .

[0023] Step (2-1) includes:

[0024] Assuming the impeller of the hydraulic turbine has a non-impact inlet under design conditions, then the inlet torsion angle β of the blades is... b1 The relative flow angle β1 with the inlet is equal to that of β b1 =β1;

[0025] (2-1a) Measure the non-circular cross-sectional area of ​​the spiral inlet of the volute and calculate the equivalent circular radius ρ0 of the spiral inlet cross-section of the volute:

[0026]

[0027] In the formula: F is the non-circular cross-sectional area of ​​the spiral inlet of the volute, in m²;

[0028] (2-1b) Calculate the volute constant k:

[0029]

[0030] In the formula: Q r To calculate the flow rate, m 3 / s; a0 is the distance from the center of the spiral inlet section of the volute to the impeller shaft centerline, m; ρ0 is the equivalent circle radius of the spiral inlet section of the volute, m; The volute enclosure angle is °;

[0031] (2-1c) Let the volute structure coefficient be... Then k = k1Q r ;

[0032] (2-1d) The impeller inlet circumferential velocity is Where: D1 is the impeller inlet diameter, m; n is the impeller speed, r / min;

[0033] (2-1e) Assuming there is no energy conversion between the volute and the impeller, the impeller inlet velocity torque v is obtained. u1 r1 = k; when the impeller inlet diameter is D1, the impeller inlet circumferential velocity component is...

[0034] (2-1f) From steps (2-1c)-(2-1e), we get:

[0035]

[0036] The inlet torsion angle β is then calculated using the velocity triangle at the blade inlet. b1 :

[0037]

[0038] In step (3), the outlet torsion angle of the impeller is corrected based on the actual cross-sectional area A2 of the liquid flow through the impeller outlet shaft surface, including:

[0039] (3-1) Calculate the flow slip Δv according to Wiesner's formula. u2 :

[0040]

[0041] In the formula: u2 is the outlet circumferential velocity, m / s; Z is the number of impeller blades; β2 is the outlet relative flow angle, °;

[0042] (3-2) According to the impeller outlet velocity triangle, v m2 =(u2+Δv) u2 cosα2;

[0043] At this point, the cross-sectional area of ​​the water passage is A2 = 2πR2b2v m2 In the formula: R2 is the impeller outlet radius, m; b2 is the blade inlet width, m; thus, the cross-sectional area of ​​the water passage considering the flow slip of the liquid at the outlet is obtained.

[0044] The formula is based on the cross-sectional area of ​​the water passage and the relative flow angle at the outlet, taking into account the slippage of the liquid at the outlet. The corrected exit torsion angle is obtained.

[0045] Preferably, Z equals 11.

[0046] In step (4), based on the iterative principle of forward and reverse problems, and according to the calculation formulas for the inlet and outlet torsion angles, it is obtained that: along the streamline direction of the impeller blades, on the flow section perpendicular to the streamline, the impeller torsion angle of the hydraulic turbine is from the inlet torsion angle β. b1 to the exit twist angle β b2 It exhibits a monotonically decreasing linear distribution pattern.

[0047] The present invention also provides a hydraulic turbine impeller designed according to the above-described impeller forward design method.

[0048] Preferably, the impeller has an inlet torsion angle of 110° and an outlet torsion angle of 32.5°. Along the streamline direction of the impeller blades, on the flow section perpendicular to the streamlines, the torsion angle of the impeller blades exhibits a monotonically decreasing linear distribution from the inlet to the outlet torsion angle.

[0049] The impeller blades designed using the method of this invention twist only at one angle, causing the liquid to impact in only one direction. Compared to turbine blades where the inlet angle is inversely proportional to the number of stages, the impeller of this invention exhibits a gradually decreasing flow channel cross-sectional area from inlet to outlet, forming a single-form flow channel. When the pump reverses to operate as a turbine, the flow channel reverses, the inlet becomes the outlet, and the outlet becomes the inlet, with the cross-sectional area gradually increasing, ensuring both liquid flowability and high efficiency.

[0050] In this invention, the flow cross-section at the inlet of the hydraulic turbine impeller is the smallest, while the inlet torsion angle is 110°. Along the streamline direction, the radius of the flow cross-section gradually increases, meaning the area also gradually increases, while the torsion angle of the blades gradually decreases. At the outlet, the flow cross-section is at its largest, and the outlet torsion angle is 32.5°. This demonstrates that the flow channel from the hydraulic turbine impeller to the volute gradually increases, ensuring sufficient space in the high-efficiency zone.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] This invention determines the inlet torsion angle that matches the volute outflow by analyzing the flow pattern of the volute. Starting from improving the performance of the pump operating as a turbine in reverse, it proposes changing the blade inlet torsion angle to enhance turbine energy characteristics and improve the utilization rate of existing pressure energy. When the pump is operating as a turbine, the liquid, passing through the annular flow channel, only twists at one angle, impacting in the same direction, thus improving practicality and reducing costs. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the impeller structure of a traditional centrifugal pump.

[0054] Figure 2 A schematic diagram of the impeller structure of the hydraulic turbine designed for this invention;

[0055] Figure 3 A schematic diagram of the torsion angle of the impeller blades of the hydraulic turbine designed for this invention;

[0056] Figure 4 This is a schematic diagram of the forward design method for the impeller of the hydraulic turbine of the present invention.

[0057] Figure 5 This is a schematic diagram of the impeller inlet velocity triangle.

[0058] Figure 6 This is a schematic diagram of the impeller outlet velocity triangle.

[0059] Figure 7 This is a diagram showing the distribution of the torsional angle of a turbine impeller. Detailed Implementation

[0060] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0061] As attached Figure 1 As shown, the blade inlet angle of traditional pumps is 22°-30°, and the inlet angle is inversely proportional to the number of stages. The blade inlet torsion angle cannot be well matched with the turbine operating conditions, generally resulting in low turbine operating efficiency and a narrow high-efficiency range.

[0062] The key to the forward impeller design technology of hydraulic turbines lies in the inlet and outlet torsion angles when the pump is reverse-rotating as a turbine. (See attached image) Figure 2As shown, several blades (3) of the same shape are arranged between the front cover plate (2) and the rear cover plate (4). The blades are divided into two ends—the front end and the rear end—extending from the impeller inlet to the outlet. The angle formed by the front end when it is installed is the inlet installation angle, and the angle formed by the rear end when it is installed is the outlet installation angle. When the pump reverses to run as a turbine, the inlet and outlet directions are reversed, the front end is the outlet, and the rear end is the inlet. At this time, the inlet installation angle and the outlet installation angle are determined by the hydraulic turbine-specific impeller design method. The volute changes from a pressure chamber to a water inlet chamber, and the liquid flows from the impeller to the volute. Turbine impeller design determines the inlet torsion angle that matches the volute outflow by understanding the flow law of the volute outflow. This invention proposes to improve the turbine energy characteristics by changing the blade inlet torsion angle, starting from improving the performance of the pump in reverse turbine operation. As shown in the attached figure Figure 3 As shown, the inlet torsion angle β of the hydraulic turbine impeller designed in this invention is... b1 The angle is 110°, compared to the 22°-30° blade inlet angle of traditional pumps (e.g., Figure 1 The impeller (as shown) has been enlarged considerably and is in the form of forward-curved blades; while the corrected outlet torsion angle is 32.5°.

[0063] The turbine impeller design process of this invention is as follows: Figure 4 As shown, the specific steps include:

[0064] The inlet energy of the hydraulic turbine impeller is provided by the volute casing. According to the design method of hydraulic turbine-specific impellers, the equivalent circle radius of the spiral inlet section of the volute casing is first calculated:

[0065]

[0066] Where: F is the non-circular cross-sectional area of ​​the spiral inlet of the volute, in m²;

[0067] Then, according to the formula:

[0068]

[0069] To calculate the volute constant k, where: Q r To calculate the flow rate, m 3 / s; a0 is the distance from the center of the spiral inlet section of the volute to the impeller shaft centerline, in meters; ρ0 is the radius of the circular section of the spiral inlet of the volute, in meters; The volute enclosure angle is (°).

[0070] make:

[0071] Where: k1 is the volute structure coefficient.

[0072] It is then easy to see that k = k1Q r .

[0073] The impeller inlet circumferential speed is In the formula, u1 is the impeller inlet circumferential velocity, m / s; D1 is the impeller inlet diameter, m; and n is the impeller rotational speed, r / min.

[0074] Assuming there is no energy conversion between the volute and the impeller, the impeller inlet velocity torque v can be obtained. u1 r1 = k. When the impeller inlet diameter is D1, the impeller inlet circumferential velocity component is... In the formula v u1 Let be the circumferential component of the absolute velocity of the inlet, in m / s.

[0075] And because k = k1Q r ,so

[0076] Then, the velocity triangle at the blade inlet (as shown in the attached diagram) Figure 5 (As shown) The inlet torsion angle is calculated using the following formula:

[0077]

[0078] in: b1 is the blade inlet width, m; β1 is the inlet relative flow angle, (°); v m1 u1 is the axial component of the absolute velocity at the inlet, in m / s; u1 is the circumferential velocity at the impeller inlet, in m / s; v u1 Ψ1 is the circumferential component of the absolute velocity at the inlet, in m / s; Ψ1 is the blade inlet displacement coefficient, which can be expressed by the formula... Determine, in the formula: δ1 is the circumferential thickness of the blade inlet edge, in meters; R 1c Z is the radius of the centroid position of the blade inlet side generatrix, in meters; Z is the number of blades in the impeller.

[0079] Assuming that under design conditions, the turbine impeller has a non-impact inlet, and the inlet angle of the blades is equal to the inlet relative flow angle, i.e., β b1 =β1, where β b1 The inlet torsion angle (when the pump is running in reverse, °) is the angle of rotation.

[0080] Let the absolute velocity of the liquid flowing out of the turbine impeller be the normal outlet velocity (as shown in the attached figure). Figure 6 As shown), from the formula:

[0081]

[0082] The relative flow angle β2 at the outlet can be calculated, where β2 is the outlet relative flow angle (°); v m2 u1 is the axial surface velocity component of the absolute velocity at the outlet, in m / s; u2 is the circumferential velocity at the outlet, in m / s; A2 is the actual cross-sectional area of ​​the liquid flow through the impeller outlet axial surface, in m².2 .

[0083] Typically, the number of impeller blades Z is 11, which is relatively high. The spacing between the blades is small, and the fluid is subjected to a relatively tight clamping effect from the blades. We can assume that the direction of the fluid outlet streamline is consistent with the direction of the blade outlet rib line. Then, the outlet placement angle is equal to the outlet relative flow angle, i.e., β. b2 =β2, where β b2 The outlet torsion angle (when the pump is reversed to operate as a turbine), (°).

[0084] The cross-sectional area A2 of the hydraulic turbine impeller's axial surface through which the liquid flows can be used as a correction for the impeller outlet torsional angle, according to Wiesner's formula:

[0085]

[0086] The flow slip can be calculated. In the formula, u2 is the outlet circumferential velocity (m / s); Z is the number of blades, typically 11; and β2 is the outlet relative flow angle (°). This is based on the impeller outlet velocity triangle (see attached figure). Figure 6 As shown) v m2 =(u2+Δv) u2 The cross-sectional area of ​​the water passage is A2 = 2πR2b2v. m2 In the formula, R2 is the impeller outlet radius, m; b2 is the blade inlet width, m.

[0087] This allows us to obtain the cross-sectional area that takes into account the flow slip of the liquid at the outlet, and then apply the formula for the relative flow angle at the outlet. The corrected exit torsion angle can be obtained.

[0088] Therefore, the inlet torsion angle β of the designed impeller blades can be calculated. b1 The angle is 110°, which is much larger than the 22°-30° blade inlet angle of traditional pumps, and the impeller is of the forward-curved blade type; while the corrected outlet torsion angle is 32.5°.

[0089] It can be observed that when the pump is reversed for turbine operation, the impeller blades designed accordingly only twist at one angle, and the liquid impacts in only one direction. Compared to the turbine blades, where the inlet angle is inversely proportional to the number of stages, the impeller's flow channel cross-sectional area gradually decreases from the inlet to the outlet, forming a single-form flow channel. When the pump is reversed for turbine operation, the flow channel reverses, the inlet becomes the outlet, and the outlet becomes the inlet, and the cross-sectional area gradually increases, ensuring both liquid flowability and high efficiency.

[0090] Based on the iterative principle of forward and reverse problems, and according to the formula for calculating the inlet and outlet torsion angles, it can be found that along the streamline direction, at the flow section perpendicular to the streamline, the hydraulic turbine impeller torsion angle changes from β... b1to β b2 It exhibits a monotonically decreasing linear distribution pattern, as shown in the attached figure. Figure 7 As shown, the flow cross-section is smallest at the inlet of the hydraulic turbine impeller, while the inlet torsion angle is 110°. Along the streamline direction, the radius of the flow cross-section gradually increases, meaning the area also gradually increases, while the blade torsion angle gradually decreases. At the outlet, the flow cross-section is largest, and the outlet torsion angle is 32.5°. This demonstrates that the flow channel from the hydraulic turbine impeller to the volute gradually increases, ensuring sufficient space in the high-efficiency zone.

[0091] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A forward design method for a hydraulic turbine impeller, characterized in that, Includes the following steps: (1) Along the extension direction from the impeller inlet to the outlet, the impeller blades are divided into the front end and the rear end; the angle formed when the front end is installed is the inlet installation angle, which is the inlet torsion angle; the angle formed when the rear end is installed is the outlet installation angle, which is the outlet torsion angle. (2) Taking the performance of the hydraulic turbine as the optimization target, and based on the shape of the volute and the outflow pattern, calculate the impeller inlet torsion angle and outlet torsion angle that match the outflow of the volute; including: (2-1) Assuming that the impeller of the hydraulic turbine has a non-impact inlet under design conditions, then the inlet torsion angle of the blades is... β b1 Angle of relative flow to the inlet β 1. Equal, that is β b1 = β 1; Calculate the inlet torsion angle using the velocity triangle at the blade inlet. β b1 : ； In the formula: , where is the axial surface velocity component of the absolute velocity at the inlet, in m / s; Ψ 1 represents the blade inlet displacement coefficient, which can be expressed by the formula... Determine, in the formula: δ 1 represents the circumferential thickness of the blade inlet edge, in meters (m). R 1c The radius of the centroid position of the blade inlet side generatrix is ​​in meters. Z This represents the number of blades in the impeller. u 1 represents the impeller inlet circumferential velocity, in m / s; v u1 Let be the circumferential component of the absolute velocity of the inlet, in m / s; Q r To calculate the flow rate, m 3 / s; D 1 represents the impeller inlet diameter; k 1 represents the volute structure coefficient; b 1 represents the blade inlet width; n represents the impeller speed, in r / min; (2-2) Assuming the direction of the fluid outlet relative streamline is consistent with the direction of the blade outlet rib line, then the outlet torsion angle is... β b2 Angle of flow relative to outlet β 2 are equal, that is β b2 = β 2; Let the absolute velocity of the liquid flowing out of the hydraulic turbine impeller be the normal outlet velocity, then: ； In the formula: , where is the axial component of the absolute velocity at the exit, in m / s; u 2 represents the exit circumferential velocity, in m / s; A 2 represents the actual cross-sectional area of ​​the liquid flow through the impeller outlet shaft surface, in m². 2 ; (3) Based on the working conditions of the hydraulic turbine and the actual cross-sectional area of ​​the hydraulic fluid flow through the impeller outlet shaft surface. A 2. Correct the outlet torsion angle of the impeller, including: (3-1) Calculate the flow slip according to the Wiesner formula : ， In the formula: u 2 represents the exit circumferential velocity, in m / s; Z This represents the number of blades in the impeller. β 2 represents the outlet relative flow angle, in °; (3-2) According to the impeller outlet velocity triangle, we can obtain: ; At this time, the cross-sectional area of ​​the water passage is In the formula: R 2 represents the impeller outlet radius, in meters (m). b 2 represents the blade inlet width, in meters; this gives the cross-sectional area of ​​the water passage that takes into account the flow slippage of the liquid at the outlet. The formula is based on the cross-sectional area of ​​the water passage and the relative flow angle at the outlet, taking into account the slippage of the liquid at the outlet. The corrected exit torsion angle is obtained; (4) Then, based on the iterative principle of positive and negative problems, determine the variation law of the torsion angle between the streamline direction of the impeller blade and the flow interface direction perpendicular to the streamline.

2. The forward design method for the impeller of a hydraulic turbine according to claim 1, characterized in that, Step (2-1) includes: Assuming the hydraulic turbine impeller has a non-impact inlet under design conditions, then the inlet torsion angle of the blades is... β b1 Angle of relative flow to the inlet β 1. Equal, that is ; (2-1a) Measure the non-circular cross-sectional area of ​​the spiral inlet of the volute and calculate the equivalent circle radius of the spiral inlet cross-section of the volute. ρ 0: ； In the formula: F The area of ​​the non-circular cross-section of the spiral inlet of the volute is in meters. (2-1b) Calculate the volute constant k : ； In the formula: Q r To calculate the flow rate, m 3 / s; a 0 represents the distance from the center of the spiral inlet section of the volute to the impeller shaft centerline, in meters (m). ρ 0 is the equivalent circle radius of the spiral inlet section of the volute, in meters; φ 0 represents the volute wrap angle, in degrees. (2-1c) Let the volute structure coefficient ,but ; (2-1d) The impeller inlet circumferential velocity is In the formula: D 1 represents the impeller inlet diameter, in meters (m); n represents the impeller rotational speed, in r / min. (2-1e) Assuming there is no energy conversion between the volute and the impeller, the impeller inlet velocity torque is obtained. When the impeller inlet diameter is D At time 1, the circumferential velocity component of the impeller inlet is ; (2-1f) From steps (2-1c)-(2-1e), we get: ； The inlet torsion angle is then calculated using the velocity triangle at the blade inlet. β b1 : 。 3. The forward design method for the impeller of a hydraulic turbine according to claim 1, characterized in that, Z It equals 11.

4. The method for forward design of the impeller of a hydraulic turbine according to claim 1, characterized in that, In step (4), based on the iterative principle of forward and reverse problems, and according to the calculation formulas for the inlet and outlet torsion angles, it is obtained that: along the streamline direction of the impeller blades, on the flow section perpendicular to the streamline, the impeller torsion angle of the hydraulic turbine is from the inlet torsion angle. β b1 Turning angle at the exit β b2 It exhibits a monotonically decreasing linear distribution pattern.

5. An impeller for a hydraulic turbine, characterized in that, The impeller was designed according to the forward design method of the hydraulic turbine as described in any one of claims 1-4.

6. The impeller of the hydraulic turbine according to claim 5, characterized in that, The impeller has an inlet torsion angle of 110° and an outlet torsion angle of 32.5°. Along the streamline direction of the impeller blades, on the flow section perpendicular to the streamlines, the torsion angle of the impeller blades exhibits a monotonically decreasing linear distribution from the inlet to the outlet torsion angle.

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