CN105626573A - Designing method of fish-friendly axial flow pump based on fish survival rate prediction - Google Patents

Abstract

The invention provides a design method of a fish-friendly axial flow pump based on the prediction of fish survival rate, which uses a mathematical model to predict the relationship between pump design parameters and fish passing survival rate, and thus guides the axial flow pump's fish Class friendly design. The mathematical model mainly includes the impact probability of the leading edge of the blade and the impact fatality rate. The impact probability is the ratio of the time for fish to pass through the flow section at the leading edge of the blade to the time required for the impeller to rotate a blade distance, the impact mortality rate and the impact speed, fish The class length is related to the thickness of the leading edge of the blade, and the impact velocity is taken as the velocity component vertical to the leading edge. The design of the fish-friendly axial flow pump includes: the use of two-blade impellers to reduce the impact probability of the leading edge of the blades, the use of linearly swept and forward-extending blade leading edges to reduce the impact fatality rate, and the design of the airfoil parameters can ensure good hydraulic performance. The fish survival rate prediction model proposed by the invention has a high degree of agreement with the experimental value, and the fish-friendly axial-flow pump guided to design can greatly reduce the fish mortality rate.

Description

A Design Method of Fish-Friendly Axial Flow Pump Based on Prediction of Fish Survival Rate

technical field

The invention relates to the technical field of hydraulic machinery, in particular to a design method of a fish-friendly axial flow pump based on fish survival rate prediction, which is suitable for the design of large and medium-sized axial flow pumps through which various types of fish pass.

Background technique

Pumping stations are widely used in flood control and drainage as well as agricultural irrigation. In many domestic coastal cities along rivers and low-lying countries in Europe, the amount of pumping stations is very large. But a negative impact is that fish stocks in rivers and oceans will suffer inevitable damage and death when passing through the pumping station, which will affect the migration and migration of fish. As early as 2000, the European Parliament issued a directive to protect fish habitats, including providing unimpeded migration for fish. The EU Water Framework Directive also emphasized the importance of transforming various water barriers into fish-friendly ones. In 2010, regulations to strengthen the remediation of endangered fish species will also be enforced in EU countries. Under the background that many countries attach importance to ecological protection, the development of fish-friendly pumps and pumping stations has also received more and more attention.

After searching, there is no mathematical model for predicting the survival rate of relevant fish after passing through the axial flow pump. In the design methods related to axial flow pumps, almost all of them are to improve pump efficiency, pump stability, sewage passing capacity or under multiple working conditions. The design methods of operation, such as the patented technologies with publication numbers CN102748300A, CN104005983A, and CN103452912A, do not consider that live fish will pass through the pump in actual operation, and optimize the design of a fish-friendly pump. Publication number is that the patent technology of CN104613001A proposes the eco-friendly axial flow pump structure that can pass fish, but does not provide design method. Therefore, existing design methods do not address the important ecological issue of improving fish survival.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a design method of a fish-friendly axial flow pump based on the prediction of fish survival rate, so as to improve the survival rate of fish passing through the large and medium-sized axial flow pump and avoid fish damage and death.

The technical solution of the present invention is: a design method of a fish-friendly axial flow pump based on the prediction of fish survival rate, using a mathematical model to predict the survival rate of fish passing through the axial flow pump, and obtaining the blade design parameters and fish survival rate The relationship between these factors guides the design of fish-friendly axial flow pumps. The mathematical model mainly includes the prediction of blade leading edge impact probability and impact fatality, with emphasis on the selection of impact speed. The design of the fish-friendly axial flow pump is based on a mathematical model, using a two-blade impeller to reduce the impact probability of the leading edge of the blade, and using a linear forward-swept and forward-extending blade leading edge to reduce the impact fatality rate.

The mathematical model considers the fish as a one-dimensional linear rigid object, without subjective movement, and without relative slippage with the liquid flow, and the common axial velocity of the fish with a length L _fish and the liquid flow is v _m1 , then the fish The time required for the species to pass through the flow section at the leading edge of the blade is t _fish , Q is the pump flow rate, R ₁ and R ₂ are the radii at the hub and rim of the blade leading edge, respectively.

${\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}}}{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}$

The impeller speed is Nr/min, the time required for an impeller with n blades to rotate through a blade distance s is t _blade , r is the radius of any point on the leading edge of the blade, and u is the circumferential speed of the blade.

${\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 60</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 60</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; N</span>}}$

The leading edge impact probability is obtained by the ratio of t _fish to t _blade

To limit the leading edge strike probability to 100%, P _strike = min[1,P' _strike ]

After being hit by the leading edge of the blade, some fish will die. The most important factor affecting the ratio f _strike is the impact velocity v. The impact velocity selected by the present invention is the velocity component of the vertical leading edge, and the circumferential velocity of the blade is respectively taken as the vertical leading edge component of direction cosα and the component of the axial velocity of the liquid flow in the direction perpendicular to the leading edge cosβ performs vector superposition, that is, is the angular velocity vector, r is the radius of any point on the leading edge, α is the angle between the blade tangential velocity direction and the vertical leading edge direction on the front view, is the axial velocity vector of the liquid flow, and β is the angle between the axial velocity direction of the liquid flow and the direction perpendicular to the front edge on the axial plane projection.

Averaging the impact velocity integral over the leading edge

According to the data analysis of the pump station monitoring, the relationship between the strike fatality rate f _strike and the average strike velocity v _a , fish length L _fish , and blade leading edge thickness d, a and b are coefficients, and the values are as follows

Fish survival rate C＝1-P _strike f _strike

The leading edge of the blade is linearly swept forward, and the degree of its forward sweep Defined as the angle from the leading edge rim to the leading edge hub in the front view of the impeller, satisfying The forward sweep form is defined as the change rate k ₁ of the forward sweep angle α with the leading edge radius R, satisfying that k ₁ is a constant; the forward extension degree E is defined as the distance between the leading edge rim and the leading edge hub in the axial plane projection diagram of the impeller The axial distance satisfies 0.2R ₂ <E<0.4R ₂ , and the forward extension form is defined as the change rate k ₂ of the axial distance L of the leading edge with the radius R, satisfying that k ₂ is a constant.

The fish-friendly axial flow pump design method generates complete blades by designing cross-sectional airfoils of the blades on cylindrical surfaces with different radii.

The chord length l of the airfoil of different sections of the blade is 1.6R ₂ at the hub, and increases linearly to 3R ₂ at the rim.

The axial velocity of the liquid flow at different sections of the blade is Considering the volumetric efficiency η _v and the blade displacement coefficient ψ, the volumetric efficiency takes a fixed value of 0.98, and the value of the blade displacement coefficient increases linearly from 0.87 at the hub to 0.95 at the rim.

The circumferential velocity component of the blade outlet liquid flow at different sections of the blade is Using 1.5 to 1.7 times the design head H, the value of hydraulic efficiency η _h decreases linearly from 0.9 at the hub to 0.86 at the rim, and the circulation correction factor ξ linearly increases from 0.8 at the hub to 1 at the middle section, and then linearly Increased to 1.25 at the rim, u is the peripheral speed of the blade.

blade inlet angle The additional angle increases linearly from 1° to 3° at the hub, and v _m1 is the axial velocity component of the blade inlet liquid flow.

blade exit angle The additional angle is always 1°, and v _m2 is the axial velocity component of the blade outlet liquid flow.

Blade chord angle β _L =(β ₁ +β ₂ )/2.

According to the degree of leading edge sweep For the forward-swept form k ₁ , the degree of forward extension E and the forward-extended form k ₂ , the airfoil is offset accordingly in the airfoil development diagram to form a linear forward-swept forward-extended blade leading edge.

Beneficial effects of the present invention:

(1) The mathematical model for predicting the survival rate of fish after passing through the axial flow pump has been verified by experiments to accurately reflect the relationship between pump design parameters and fish survival rate, and can guide the design of fish-friendly axial flow pumps. According to the mathematical model, the number of blades and the rotating speed are the most important factors affecting the impact probability of the leading edge of the blade, and the impact speed is the most important factor affecting the impact fatality.

(2) A fish-friendly axial flow pump is designed based on the mathematical model of fish survival rate prediction. The two-blade impeller can greatly reduce the impact probability of the blades. Compared with the low-speed impeller to reduce the impact probability, it can ensure a higher head; The linear sweep forward can greatly reduce the impact velocity at each point of the leading edge, thereby reducing the impact fatality rate. Predicted by the mathematical model, the fish survival rate of the axial flow pump under the same design parameters (outer diameter, rotational speed, flow rate, head, etc.) will be increased by more than 50% after the fish-friendly design.

(3) When the present invention is designing blade airfoil parameters, the value of chord length l can reduce the cascade denseness, control the axial height of the blade on the one hand, reduce the work area of the blade on the other hand, and reduce the hydraulic loss; adopt 1.5 ~ 1.7 times the design head to calculate the blade outlet angle β ₂ , to make up for the lack of liquid flow deflection caused by the small chord length value.

Description of drawings

Figure 1 is a side view of a standard axial flow pump impeller.

Figure 2 is a front view of a standard axial flow pump impeller.

Fig. 3 is a schematic diagram of a mathematical model for predicting fish survival rate.

Figure 4 is a schematic diagram of the axial velocity decomposition of the mathematical model for fish survival rate prediction

Figure 5 is a schematic diagram of the peripheral velocity decomposition of the mathematical model for fish survival rate prediction

Fig. 6 is a schematic diagram of an impeller of a fish-friendly axial flow pump.

Figure 7 is a front view of the impeller of the fish-friendly axial flow pump.

Fig. 8 is a projection view of the axial plane of the impeller of the fish-friendly axial flow pump.

Figure 9 is a schematic cross-sectional view of the blade.

Fig. 10 Expanded view of blade section airfoil.

Reference numerals are explained as follows: 1—the hub of the axial flow pump, 2—the leading edge of the blade, 3—the blade, 4—the trailing edge of the blade, and 5—the flow cross section at the leading edge of the blade.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

The mathematical model for predicting fish survival rate is illustrated by Fig. 1 to Fig. 5 . Fig. 1 is a side view of a standard axial flow pump impeller, and Fig. 2 is a front view of a standard axial flow pump impeller, with its blades (3) unfolded in a plane, as shown in Fig. 3 . Considering the fish as a one-dimensional linear rigid object with no subjective movement and no relative slippage with the liquid flow, the time for the fish to pass through the flow section (5) at the leading edge of the blade is t _fish , and the impeller rotates one blade The required time is t _blade , and the ratio of the two can obtain the strike probability P' _strike of the blade leading edge. Among the fish hit by the leading edge (2) of the blade, some fish will die, the ratio f _strike is related to the impact velocity v and the ratio of fish length L _fish to the thickness d of the leading edge (2) of the blade, according to the pump The regression analysis of the data monitored by the station obtained f _strike to predict the mortality of fish after being hit. For the leading-edge sweeping blade, the impact velocity v should take the velocity component of the vertical leading edge. In the schematic diagram of axial velocity decomposition in Figure 3, take the vertical component In the schematic diagram of peripheral velocity decomposition in Figure 4, take the vertical component will vector and After the superposition, the impact velocity distribution of each point on the front edge is obtained, and the average impact velocity v _a can be obtained after the integral is averaged. The prediction model has been verified by experiments and can accurately reflect the relationship between the design parameters of the pump and the survival rate of fish. According to the mathematical model, the number of blades and the rotational speed are the most important factors affecting the probability of blade impact, and the blade impact speed is the most important factor affecting the blade impact mortality. most important factor. And the use of two-blade impeller can greatly reduce the probability of blade impact, compared with the use of low-speed impeller to reduce the impact probability, it can ensure a higher head; the linear forward sweep and extension of the leading edge (2) of the blade can greatly reduce the impact speed of each point on the leading edge , thereby reducing the impact fatality rate.

Based on the mathematical model of fish survival rate prediction, the leading edge (2) of the blade is linearly swept forward, and the three-dimensional schematic diagram of the fish-friendly axial flow pump impeller is shown in Figure 6. Specifically, the degree of forward sweep Defined as the angle from point Y at the leading edge rim to point G at the hub of the leading edge in front view 7 of the impeller, satisfying The form of the sweep is defined as the rate of change of the sweep angle α with the radius R of the leading edge Satisfy that k ₁ is a constant The degree of protruding E is defined as the axial distance from point Y at the rim of the leading edge to point G at the hub of the leading edge in the projection of the impeller shaft surface in Figure 8, which satisfies 0.2R ₂ <E<0.4R ₂ , and the protruding form is defined as the front The rate of change of the axial distance L of each point on the edge with the radius R It is satisfied that k ₂ is a constant E/(R ₂ -R ₁ ).

The fish-friendly axial flow pump design method generates complete blades by designing the cross-sectional airfoils of the blades on cylindrical surfaces with different radii. The airfoil parameters of different sections are designed by the streamline method, and the smaller value of the chord length l (1.6R ₂ ～3R ₂ ) can reduce the denseness of the cascade. On the one hand, the axial height of the blade is controlled, and on the other hand, the work area of the blade is reduced. Reduce the hydraulic loss, at this time the blades do less work and the deflection of the liquid flow is insufficient. Use 1.5 to 1.7 times the design head to calculate the circumferential velocity component v _u2 of the blade outlet liquid flow, and the circulation correction coefficient ξ increases linearly from 0.8 at the hub to the middle section 1, then linearly increased to 1.25 at the rim.

In order to design the leading edge of the linearly swept forward blade, the airfoil of each section of the blade is offset accordingly, and the offset is determined by the degree of forward sweep of the leading edge It is determined by the form of forward sweep k ₁ , the degree of forward reach E and the form of forward reach k ₂ . Specifically, with linear forward sweep forward (k ₁ , k ₂ is a constant), the degree of forward sweep is 60°, and the protruding degree E is 0.3R ₂ as an example. Figure 9 is a schematic diagram of the blade section. It is offset by 20° against the direction of impeller rotation (horizontal to the right in the figure), and 0.1R ₂ along the direction of liquid flow (vertical upward in the figure), and other sections are offset in the same way to form a linear forward sweep. leading edge of the blade. The fish survival rate prediction model proposed by the invention has a high degree of agreement with the experimental value, and the fish-friendly axial-flow pump guided to design can greatly reduce the fish mortality rate.

Claims (4)

1. A method for designing a fish-friendly axial-flow pump based on fish survival rate prediction, comprising the steps of: S1: Establish a mathematical model between the fish survival rate and the design parameters of the axial flow pump; S2: Optimize the parameter design of the axial flow pump based on the mathematical model between the fish survival rate and the design parameters of the axial flow pump. 2. the design method of a kind of fish-friendly axial flow pump based on fish survival rate prediction according to claim 1, is characterized in that, the mathematical model between described fish survival rate and axial flow pump design parameter The establishment method is as follows: S3: Considering the fish as a one-dimensional linear rigid object, there is no subjective movement, and there is no relative slippage with the liquid flow, the impact probability _P'strike of the leading edge of the blade (2) is the flow section where the fish passes through the leading edge of the blade (5) The ratio of the time t _fish to the time t _blade required for the impeller to rotate through a blade distance s, then: ${\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}}}{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}$ ${\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 60</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 60</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; N</span>}}$ ${{\mathrm{<span\; class="notranslate">\; P</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}}}{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; e</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; 60</span>}\mathrm{<span\; class="notranslate">\; Q</span>}}$ Among them, L _fish is the length of the fish, v _m1 is the common axial velocity component of the fish and the liquid flow at the blade inlet, Q is the pump flow rate, R ₁ and R ₂ are the radii of the hub and rim of the blade leading edge, respectively, N is the impeller speed, r/min, n is the number of impeller blades, r is the radius of any point on the leading edge of the blade, u is the circumferential speed of the blade; S4: The fish mortality f _strike after being hit by the leading edge of the blade (2) is obtained through regression analysis of the monitoring data, and the mathematical relationship between it and the design parameters of the axial flow pump is: ${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 4.8</span>}<span\; class="notranslate">\; )</span>$ ${\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}\frac{\mathrm{<span\; class="notranslate">\; v</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}$ Among them, a and b are constant coefficients, L _fish is the length of the fish, d is the thickness of the leading edge of the axial flow pump blade, v _a is the average impact velocity, and v is the impact velocity of any point on the leading edge of the blade; S5: According to step S3 and step S4, the mathematical model of fish survival rate C and axial flow pump design parameters is obtained as C=1-P _strike f _strike . 3. The design method of a fish-friendly axial flow pump based on fish survival rate prediction according to claim 2, characterized in that, in the step S4, the impact velocity v at any point on the leading edge of the blade is taken to be perpendicular to the front The velocity components of the blade edge are respectively taken as the components of the blade peripheral velocity perpendicular to the leading edge direction The component perpendicular to the leading edge direction of the axial velocity of the liquid flow Do vector superposition, that is, $v=|\stackrel{\&Right\; Arrow;}{\mathrm{\&omega;}}rco\mathrm{the\; s}\mathrm{\&alpha;}+{\stackrel{\&Right\; Arrow;}{v}}_{m1}co\mathrm{the\; s}\mathrm{\&beta;}|;$ in: is the angular velocity vector, r is the radius of any point on the leading edge, α is the angle between the blade tangential velocity direction and the direction perpendicular to the leading edge, is the axial velocity vector of the liquid flow, and β is the angle between the axial velocity direction of the liquid flow and the direction perpendicular to the front edge on the axial plane projection. 4. the design method of a kind of fish-friendly axial-flow pump based on fish survival rate prediction according to claim 1, is characterized in that, The fish-friendly axial flow pump adopts a two-blade impeller, and the leading edge (2) of the blade is linearly swept forward, and the degree of forward sweep satisfy The forward sweep form k ₁ is the rate of change of the forward sweep angle α with the leading edge radius R, and here satisfies The degree of forward extension E satisfies 0.2R ₂ <E<0.4R ₂ , the forward extension form k ₂ is the rate of change of the axial distance L of each point on the leading edge with the radius R, and k ₂ =E/(R ₂ - R ₁ ), where R ₁ and R ₂ are the radii at the hub and rim of the leading edge of the blade respectively; the chord length l of the airfoil of different sections of the fish-friendly axial flow pump blade is 1.6R ₂ at the hub , increasing linearly to 3R ₂ at the rim; The axial velocity of the liquid flow at different sections of the blade is The volumetric efficiency η _v takes a fixed value of 0.98, and the value of the blade displacement coefficient ψ increases linearly from 0.87 at the hub to 0.95 at the rim; The circumferential velocity component of the blade outlet liquid flow at different sections of the blade is Using 1.5 to 1.7 times the design head H, the value of hydraulic efficiency η _h decreases linearly from 0.9 at the hub to 0.86 at the rim, and the circulation correction factor ξ linearly increases from 0.8 at the hub to 1 at the middle section, and then linearly Increased to 1.25 at the rim; The blade inlet angle The blade inlet angle additional angle increases linearly from 1° to 3° at the hub; the blade outlet angle The additional angle of the blade outlet angle is always 1°; blade chord angle β _L = (β ₁ +β ₂ )/2; where: u is the peripheral speed of the blade, v _m1 is the axial velocity component of the blade inlet liquid flow, and v _m2 is the blade The axial velocity component of the outlet liquid flow, v _u2 is the circumferential velocity component of the blade outlet liquid flow; According to the degree of leading edge sweep For the forward-swept form k ₁ , the degree of forward extension E and the forward-extended form k ₂ , the airfoil is offset accordingly in the airfoil development diagram to form a linear forward-swept forward-extended blade leading edge.