Modeling method for blade structure of axial flow fan of nuclear power station

Abstract

The invention belongs to the technical field of axial flow fans, and particularly relates to a modeling method for a blade structure of an axial flow fan of a nuclear power station, which comprises the following steps: selecting a basic model, and amplifying the basic model by an amplification coefficient x to obtain a target model; introducing a Reynolds number correction factor KRe, and adjusting the blade chord length of the target model through the Reynolds number correction factor KRe to obtain a blade chord length parameter C new; the blade mounting angle of the target model is adjusted through the Reynolds number correction factor KRe, a blade mounting angle parameter beta new is obtained, the blade is equally divided into n areas from the blade root to the blade tip, and a mounting angle adjusting rule is established; performing gradient optimization on the blade thickness of the target model to obtain a thickness distribution function t (r) of the blade in the spanwise direction; the blade structure modeling of the target model is completed; according to the method, the efficiency and the service life of the amplified fan can be optimized, and technical guidance is provided for how to develop fans of different sizes.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of axial flow fans, and particularly relates to a modeling method for an axial flow fan blade structure for a nuclear power station. BACKGROUND

[0002] The axial flow fan is widely applied to a ventilation and cooling system in a nuclear power station, and its core performance depends on the matching design of an impeller size and airflow. In the prior art, a model amplification method is often used for quickly developing fans of different sizes, but simple equal proportion scaling will cause problems such as Reynolds number difference and blade boundary layer separation. The fan obtained after equal proportion scaling has low actual working efficiency due to insufficient aerodynamic performance matching, and is difficult to meet the use requirements. At present, some people have conceived to optimize the working efficiency of the fan by adjusting the blade installation angle, but have not mentioned how to determine the angle to be adjusted in a certain rule or calculation manner. In actual use, it is found that the fan obtained after equal proportion scaling also has problems of stress concentration or fatigue fracture of the blade, which affects the service life of the fan and is difficult to meet the high requirements of the nuclear power station on safe and reliable operation. SUMMARY

[0003] In order to solve the problems in the prior art, the application provides a modeling method for an axial flow fan blade structure for a nuclear power station, which can optimize the efficiency and service life of the amplified fan, provides technical guidance for how to develop fans of different sizes, and meets the requirements of the nuclear power station on safe and reliable operation.

[0004] The specific technical scheme adopted by the application is: A modeling method for an axial flow fan blade structure for a nuclear power station, which is characterized by comprising the following steps: S1, selecting a basic model, amplifying the basic model with an impeller diameter D0 by a magnification factor x to obtain a target model with an impeller diameter D1; S2, introducing a Reynolds number correction factor K Re , and adjusting the blade chord length of the target model by the Reynolds number correction factor K Re to obtain a blade chord length parameter C 新 ; S3, adjusting the blade installation angle of the target model by the Reynolds number correction factor K Re to obtain a blade installation angle parameter β 新 , and equally dividing the blade from a blade root to a blade tip into n regions to establish an installation angle adjustment rule β(r); S4, gradient optimizing the blade thickness of the target model to obtain a thickness distribution function t(r) of the blade along the spanwise direction; S5, obtaining the blade chord length parameter C 新 and the blade installation angle parameter β 新The blade structure of the target model is completed by the installation angle adjustment rule β (r) and the thickness distribution function t (r).

[0005] The calculation formula of the Reynolds number correction factor is , where Re 原 is the Reynolds number of the basic model, and Re 新 is the Reynolds number of the target model.

[0006] The blade chord length parameter of the target model is C 新 =C 原 ×K Re , where C 原 is the blade chord length of the basic model.

[0007] The blade installation angle parameter of the target model is β 新 =β 原 +Δβ×(1-K Re ), where β 原 is the blade installation angle of the basic model, and Δβ is the installation angle compensation amount.

[0008] The installation angle compensation amount is , where n 新 is the impeller speed of the target fan, n 原 is the impeller speed of the basic model, Q 新 is the air volume of the target fan, Q 原 is the air volume of the basic model, the value range of k is 0.5-2.0, and the value range of m is 0.1-0.5.

[0009] In step S3, the blade is equally divided into n regions from the blade root to the blade tip, R is the impeller radius, r is the radius of a certain region, and the installation angle adjustment rule of each region is , where β 根 is the blade root installation angle of the target model, β 根 is greater than the blade root installation angle of the basic model, β 尖 is the blade tip installation angle of the target model, and β 尖 is less than the blade tip installation angle of the basic model.

[0010] The thickness distribution function of the target model blade along the span is , where t根 t is the blade root thickness of the impeller of the target model 尖 t is the blade tip thickness of the impeller of the target model 根 = (1.1-1.4) t 原 ; t 尖 = (0.8-0.96) t 原 , t 原 is the blade thickness of the base model at the corresponding radial position.

[0011] The beneficial effects of the present application are: The present application improves the aerodynamic efficiency of large-size fans, especially the energy conversion rate under high pressure difference conditions, by scaling up the size of the base model by the same ratio, dynamically adjusting the blade installation angle and the gradient design after the blade, enhances the blade structural strength, avoids the risk of stress concentration or fatigue fracture caused by scaling up the model, and also expands the applicable working condition range to adapt to different industrial scenarios with different air volume and pressure requirements.

[0012] The method of the present application provides technical guidance on how to quickly develop fans of different sizes, enabling staff to quickly obtain the blade structure modeling of the scaled-up fan, engineers do not need to repeatedly calculate, and the development cycle of large-size fans is shortened, the design risk is reduced, and reliable technical support is provided for the large-scale and precise development of nuclear power station axial flow fans. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is the front view of the impeller; Figure 2 is the top view of the impeller; Figure 3 is a non-linear distribution diagram of the blade wrap angle; Figure 4 is a non-linear distribution diagram of the blade installation angle; Figure 5 is a blade thickness gradient distribution diagram; In the drawings, 1 is a hub, and 2 is a blade. DETAILED DESCRIPTION

[0014] The present application will be further described below in conjunction with the drawings and specific embodiments: In specific embodiments, the present application relates to a modeling method for the blade structure of a nuclear power station axial flow fan, which is characterized by comprising the following steps: S1, selecting a base model, scaling up the base model of the impeller diameter D0 by a scaling factor x to obtain a target model of the impeller diameter D1, in this embodiment, scaling up the No. 12 model to the No. 13.3 target model by x, the impeller diameter D0 of the base model is 1.2 m, the impeller diameter D1 of the target model is 1.33 m, then x is D1 / D0 = 1.108.

[0015] S2, introducing a Reynolds number correction factor K Re , the Reynolds number correction factor K Re is calculated by , Adjust the blade chord length of the target model by the Reynolds number correction factor to obtain the blade chord length parameter C 新 = C 原 × K Re , Where Re 原 is the Reynolds number of the base model, Re 原 = ρV0D0 / μ; Re 新 is the Reynolds number of the target model, Re 新 = ρV1D1 / μ; C 原 is the blade chord length of the base model; The chord length is a core parameter that affects the blade airflow capture capacity and boundary layer development. By adjusting the chord length, the influence of Reynolds number change on the boundary layer can be compensated to ensure that the aerodynamic efficiency of the target model matches that of the base model.

[0016] S3, adjust the blade installation angle of the target model by the Reynolds number correction factor to obtain the blade installation angle parameter β 新 = β 原 + Δβ× (1-K Re ), Where β 原 is the blade installation angle of the base model, and Δβ is the installation angle compensation amount; The installation angle compensation amount Δβ is usually determined based on the impeller speed (n) and operating conditions (such as air volume Q), and is dynamically determined by the following method: Establish a speed-condition-Δβ mapping table or an empirical formula based on the test data or CFD simulation results of the base model; It can be preliminarily estimated by the following formula: Where n 新 is the impeller speed of the target fan, n 原 is the impeller speed of the base model, Q 新 is the air volume of the target fan, Q 原 is the air volume of the base model, and k has a value range of 0.5-2.0 and m has a value range of 0.1-0.5.

[0017] The blade installation angle parameter β 新is a blade global installation angle adjustment reference value, used to compensate the aerodynamic performance deviation caused by the change of Reynolds number.

[0018] The installation angle directly determines the angle of attack of the airflow entering the blade. The installation angle is increased by the Reynolds number correction factor in the application, which can reduce airflow separation and ensure the efficiency of the blade in diverting airflow. The blade is radially divided into five regions from the blade root to the blade tip, r / R is 0.2, 0.4, 0.6, 0.8 and 1 respectively, wherein R is the impeller radius, and r is the radius of a certain region. An installation angle adjustment rule is established for each region (r / R) , Wherein, β 根 is the blade root installation angle of the target model, the difference between β 根 and the blade root installation angle of the base model is 2°-3°, which enhances the anti-separation ability, β 尖 is the blade tip installation angle of the target model, the difference between the blade tip installation angle of the base model and β 尖 is 1°-1.5°, which suppresses the wake vortex shedding; the difference between the blade root installation angle of the base model and β 根 , and the difference between the blade tip installation angle of the base model and β 尖 can be further verified and determined by CFD simulation and test.

[0019] The blade is adjusted globally, and then optimized again according to the radial position, further optimizing the aerodynamic load and flow separation at different radial positions, so that the airflow of the impeller in the whole radial direction is in the high-efficiency working interval, meeting the working condition requirements of large flow and high pressure of the nuclear power station fan, and further improving the stability of the operation efficiency; it can also effectively enhance the structural strength of the blade and avoid stress concentration.

[0020] S4, the thickness of the blade of the target model is gradient optimized to obtain the thickness distribution function of the blade along the span direction (radial direction) , Wherein t 根 is the blade root thickness of the impeller of the target model, t 尖 is the blade tip thickness of the impeller of the target model; the magnification factor in this embodiment is 1.108, t 根 =1.3t 原 , t 尖 =0.9t 原 , the thickened blade root can significantly improve the bending strength and avoid stress concentration, while the thinned blade tip makes the airflow disturbance at the blade tip more smooth, reduces the inertial load, and reduces noise and vortex loss; t 原 is the blade thickness of the base model at the corresponding radial position (r / R).

[0021] S5、According to the blade chord length parameter C 新 , the blade installation angle parameter β 新 , the installation angle adjustment rule β(r) and the thickness distribution function t(r), wherein β(r) and β 新 are the main variable parameters, and other parameters such as C 新 , t(r) and the like can also be fine-tuned, and a CFD (Computational Fluid Dynamics) and FEA (Finite Element Analysis) coupled simulation is adopted, with the aerodynamic efficiency η, the noise level L p , and the maximum stress σ max of the basic machine type as the optimization targets, and through a genetic algorithm iteration of 20-30 rounds, the optimal parameter combination is determined, the blade structure modeling of the target machine type is completed, and the structure of the impeller of the target machine type is as shown in Figure 1 , Figure 2 If the basic machine type does not have corresponding aerodynamic efficiency η, noise level L p , and maximum stress σmax data, the industry standards or design requirements can be referred to.

[0022] The role of each optimization target is as follows: Aerodynamic efficiency η (maximization): Ensure the energy conversion rate of the fan under high pressure difference working conditions; Maximum stress σ max (minimization): Avoid stress concentration or fatigue fracture of the blade, and improve the service life; Noise level L p (minimization): Reduce the noise of the fan in operation to meet the environmental requirements of nuclear power plants.

[0023] The specific steps are as follows: S5-1, Obtain parameters and set genetic algorithm Obtain parameters: Since the value range of k is 0.5-2.0 and the value range of m is 0.1-0.5, based on this, a reasonable search range of Δβ is set, and Δβ is taken as the main variable; the blade chord length parameter C 新 , the thickness distribution function t(r) and the like are obtained from the basic machine type.

[0024] Genetic algorithm setting: Population size: According to the complexity of the problem, usually 50-100 individuals (each individual represents a Δβ value) are set; Encode Δβ as a binary string or a real number; Randomly generate an initial population within the search range of Δβ.

[0025] S5-2, CFD / FEA coupled simulation evaluates each individual For each individual (i.e., each Δβ value) in the population, the following coupled simulation is performed: S5-2a, Geometric model construction: Calculate β using current Δβ 新 = β 原 + Δβ × (1 - K Re )。

[0026] Combine blade chord C 新 , thickness distribution function t(r), and installation angle adjustment rule β(r) to generate a three-dimensional geometric model of the target blade model (e.g. through CAD software).

[0027] S5-2b, CFD simulation (aerodynamic performance analysis): Perform structured or unstructured meshing on the blade passage domain, ensuring near-wall mesh refinement to capture the boundary layer; Set the inlet wind speed, pressure, and turbulence model (e.g. k-ε or SST model) based on the target model's operating conditions (air volume Q 新 , rotational speed n 新 ); Use CFD software ANSYS Fluent to simulate the flow field and calculate: Aerodynamic efficiency η: calculated based on input power and output wind pressure / air volume.

[0028] Noise level L p : estimate far-field noise through an acoustic analogy model (e.g. FW-H equation); Obtain the pressure distribution, velocity field, aerodynamic efficiency η, and noise level L p of the blade surface.

[0029] S5-2c, FEA simulation (structural strength analysis): Import the pressure distribution calculated by CFD as aerodynamic load into the FEA model for load mapping; Perform solid meshing on the blade structure, focusing on the blade root and tip regions; Fix the hub connection and apply centrifugal force (based on rotational speed n 新 ) and aerodynamic load; Use FEA software ANSYS Mechanical for static analysis, calculating: Stress distribution: especially the maximum stress σ max (which is usually located in the blade root or stress concentration area); Evaluate the safety of the blade.

[0030] S5-2d, objective function calculation: Extract η, σ max , and L p values from the simulation; Construct a comprehensive objective function (fitness function), for example using the weighted sum method: Fitness = w1·η− w2·σ max − w3·L p where the weight coefficients w1, w2, w3 are adjusted according to design requirements (e.g. nuclear power plants place more emphasis on safety, giving σ max a higher weight).

[0031] S5-3, Genetic Algorithm Optimization Loop S5-3a, Fitness Evaluation: Calculate the fitness value for each individual in the population based on the results of Step 2.

[0032] S5-3b, Selection Operation: Use methods such as roulette wheel selection, tournament selection, etc. to select individuals with high fitness as parents.

[0033] S5-3c, Crossover Operation: Perform crossover (such as single-point crossover) on the selected parent individuals to generate offspring individuals. The crossover probability is usually set to 0.7-0.9.

[0034] S5-3d, Mutation Operation: Perform random mutation (such as small changes in Δβ value) on the offspring individuals to maintain population diversity. The mutation probability is usually set to 0.01-0.1.

[0035] S5-3e, New Generation Population: Replace the old population with the offspring individuals to form a new generation.

[0036] S5-3f, Iteration Check: Repeat Steps S5-2 and S5-3 for 20-30 iterations until the fitness converges (change less than a threshold value) or the maximum number of iterations is reached.

[0037] S5-4: Optimal Solution Determination and Verification Output optimal Δβ: Select the individual with the highest fitness from the final population as the optimal installation angle compensation Δβ.

[0038] Verification: Perform final CFD / FEA simulation on the blade shape corresponding to the optimal Δβ to confirm that the efficiency is improved by ≥8% and the maximum stress is reduced by ≥15%.

[0039] For example, Figures 3-5 , the blade installation angle refers to the angle between the blade airfoil chord line and the rotation plane, mainly affecting the angle of attack; the blade wrap angle refers to the overall bending of the blade in the rotation direction, mainly affecting the shape of the flow passage and the airflow path; the blade thickness refers to the normal distance of the blade airfoil at a specific radial position (r / R) perpendicular to the arc line, i.e. the vertical thickness of the blade airfoil profile line, and the thickness distribution affects the shape of the flow passage and the diffuser degree, thereby affecting airflow separation, efficiency and stable working range, and thickness is the most critical factor to resist centrifugal force and aerodynamic load, directly affecting the stress level and life of the blade.

[0040] Through fan performance test, the performance of the fan directly enlarged in equal proportion and the fan obtained through the method of the application is compared, and the efficiency of the fan obtained through the method of the application is increased by greater than or equal to 8%, and the maximum stress is decreased by greater than or equal to 15%.

Claims

1. A method for designing the blade structure of an axial flow fan in a nuclear power plant, characterized in that, Includes the following steps: S1. Select the base model and multiply the base model with the magnification factor by the impeller diameter D0 to obtain the target model with impeller diameter D1. S2. Introducing the Reynolds number correction factor K Re And through the Reynolds number correction factor K Re Adjust the blade chord length of the target aircraft model to obtain the blade chord length parameter C. 新 ; S3, via Reynolds number correction factor K Re Adjust the blade installation angle of the target aircraft model to obtain the blade installation angle parameter β. 新 And divide the leaf blade into n equal regions from leaf root to leaf tip, and establish the installation angle adjustment rule β(r); S4. Perform gradient optimization on the blade thickness of the target model to obtain the blade thickness distribution function t(r) along the spanwise direction. S5. Based on the blade chord length parameter C 新 Blade installation angle parameter β 新 The blade structure design of the target aircraft model is completed by using the installation angle adjustment rule β(r) and the thickness distribution function t(r).

2. The method for designing the blade structure of an axial flow fan in a nuclear power plant according to claim 1, characterized in that: The formula for calculating the Reynolds number correction factor is as follows: ， Where Re 原 Reynolds number of the basic model, Re 新 The Reynolds number of the target aircraft model.

3. The method for designing the blade structure of an axial flow fan in a nuclear power plant according to claim 1, characterized in that: The blade chord length parameters of the target model C 新 =C 原 ×K Re , Where C 原 The blade chord length of the basic model.

4. The method for designing the blade structure of an axial flow fan in a nuclear power plant according to claim 1, characterized in that: The blade installation angle parameters of the target model b 新 =b 原 +Δβ×(1-K Re ) Where, β 原 The blade installation angle is the basic model, and Δβ is the installation angle compensation amount.

5. The method for designing the blade structure of an axial flow fan in a nuclear power plant according to claim 4, characterized in that: The installation angle compensation amount ， Where, n 新 Let n be the impeller speed of the target fan. 原 The impeller speed of the basic model, Q 新 Q represents the air volume of the target fan. 原 For the basic model's airflow, the value of k ranges from 0.5 to 2.0, and the value of m ranges from 0.1 to 0.

5.

6. The method for designing the blade structure of an axial flow fan in a nuclear power plant according to claim 1, characterized in that: In step S3, the blade is divided into n equal regions from the blade root to the blade tip, where R is the impeller radius and r is the radius of a certain region. The installation angle adjustment rules for each region are as follows. ， Where, β 根 β is the blade root mounting angle for the target aircraft model. 根 The blade root installation angle is greater than that of the basic model, β 尖 For the blade tip installation angle of the target aircraft model, β 尖 Smaller than the blade tip installation angle of the basic model.

7. The method for designing the blade structure of an axial flow fan in a nuclear power plant according to claim 1, characterized in that: The blade thickness distribution function along the span of the target aircraft model. ， Among them, t 根 For the impeller root thickness of the target model, t 尖 For the tip thickness of the impeller of the target model, t 根 = (1.1-1.4)t 原 ;t 尖 = (0.8-0.96)t 原 , t 原 This refers to the blade thickness at the corresponding radial position of the base model.

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