Method for establishing bionic vertical axis wind turbine model

Abstract

The invention discloses a method for establishing a bionic vertical axis wind turbine model, and relates to a model establishing method. The invention aims to solve the problem of low power generation efficiency caused by limitation of blades of the conventional vertical-axis wind turbine. The method comprises the following steps: step 1, selecting an NACA0021 airfoil profile as a blade profile; 2, the shape of a front edge protrusion of the fan blade is a sine curve, and the section contour of a convex peak is obtained by converting a basic airfoil; step 3, dividing the computational domain into an external fixed domain and an internal rotating domain; 4, the flow field of the wind turbine is calculated through ANSYS Fluent software; and 5, verifying the accuracy of the numerical simulation of the vertical axis wind turbine. The invention belongs to the technical field of bionic vertical axis wind turbines.

Description

Technical Field

[0001] The invention relates to a model building method and belongs to the technical field of bionic vertical axis wind turbines. Background Art

[0002] Due to the increasing consumption of non-renewable resources such as oil and coal and serious problems such as environmental pollution caused by mineral fuel power generation, more and more countries have invested a lot of manpower and funds in the research and application of renewable resources; wind energy is a low-cost, clean, environmentally friendly, convenient, and "inexhaustible" energy, and is the most promising renewable resource for development and utilization in the near future.

[0003] At present, wind turbines mainly include horizontal axis wind turbines and vertical axis wind turbines. Compared with horizontal axis wind turbines, vertical axis wind turbines are characterized by a rotating axis perpendicular to the ground, a rotating plane of the wind rotor parallel to the wind direction, a constant force direction during rotation, no need for a windward adjustment system, high reliability, longer fatigue life than horizontal axis generators, and vertical axis wind turbines can be placed far below the wind rotor or even on the ground, making them easy to install and maintain.

[0004] Among them, the Darrieus wind turbine belongs to the vertical axis wind turbine generator, which is mainly composed of rotor blades, gearbox, generator, cable, top and bottom rotor center, etc. The upper part of the blade is connected to the top rotor center, and the lower part is connected to the bottom rotor center. The rotation of the rotor blade drives the vertical axis to rotate. After the gearbox changes speed, the shaft transmits power to the generator, thereby realizing the function of power generation. Since the horizontal radius of the wind turbine rotor blade is large and the shaft is high, in order to solve the strength problem caused by the strong wind force during the rotation process, the top is fixed to the ground with a cable, which causes a certain degree of waste of local space; and the main tower support bearing needs to bear huge radial and axial loads, and the up and down vibration will also produce a series of alternating loads; in addition, once the power generation equipment fails, maintenance and overhaul are more troublesome, and there are problems such as long time and low efficiency.

[0005] At present, this type of vertical axis wind turbine has matured and has advantages such as simple structure and low cost. However, the biggest problem is that due to the structural limitations of the blades, the power generation efficiency is low, especially for large-power generator sets, the material and structural costs are greatly limited. Summary of the invention

[0006] The present invention aims to solve the problem that the existing vertical axis wind turbine has low power generation efficiency due to the limitation of blades, and further proposes a method for establishing a bionic vertical axis wind turbine model.

[0007] The technical solution adopted by the present invention to solve the above problems is: the steps of the present invention include:

[0008] Step 1. Select NACA0021 airfoil as the blade profile;

[0009] Step 2: The shape of the convexity on the leading edge of the fan blade is a sine curve, and the cross-sectional profile of the convex peak is obtained by transforming the basic airfoil;

[0010] Step 3, dividing the computational domain into an external fixed domain and an internal rotating domain;

[0011] Step 4: Calculate the wind turbine flow field using ANSYS Fluent software;

[0012] Step 5: Verify the accuracy of the vertical axis wind turbine numerical simulation.

[0013] Furthermore, the blade chord length of the blade profile in step 1 is c=0.265m, the blade height is H=1.2m, and the blade rotation radius is R=1m.

[0014] Furthermore, the transformation method of the peak cross-sectional profile is as follows:

[0015]

[0016] In formula (1), (x k ,y k ) is the coordinate of the maximum thickness point of the airfoil, and A is the amplitude of the bulge.

[0017] Furthermore, in step 3, the rotation radius of the rotating domain is 1.2R, the height of the rotating domain is the same as the blade height, which is H, the left inlet of the fixed domain is a semicircle with a radius of 10R, and the fixed domain outlet is 30R away from the rotating domain. In order to consider the influence of the tip vortex in the study, the calculation domain height is greater than the blade height and is set to 2H.

[0018] Furthermore, the turbulence model in step 4 adopts the k–ωSST model widely used in the numerical simulation of vertical axis wind turbines. Incompressible air is selected as the flow medium, and the fluid density is set to 1.225 kg / m 3 The calculation time step is set to the time required for the blade to rotate 1°, 40 iterations are set in each time step, and the total physical calculation time is set to the time required for the wind turbine blade to rotate 16 times.

[0019] Furthermore, in step 5, the time step, total physical time, grid density, and the difference between simulation and experiment are checked, and the relationship between the power coefficient, torque coefficient, and tangential force coefficient is:

[0020]

[0021] In formulas (2), (3), and (4), C poweris the wind turbine power coefficient, TSR is the tip speed ratio, Q is the wind turbine torque, ρ is the gas density, H is the wind turbine blade height, R is the blade rotation radius, U is the mainstream flow velocity, C Q is the torque coefficient of the wind turbine, C T is the tangential force coefficient of the wind turbine, and c is the average chord length of the blade.

[0022] The beneficial effects of the present invention are as follows: the present invention aims at improving the performance of the vertical axis wind turbine blades by using a passive control method called a bionic leading edge protrusion; under the optimal tip speed ratio, the bionic blades can improve the performance of the vertical axis wind turbine by a maximum of 6.28%; the bionic protrusions form a counter-rotating flow vortex at the leading edge of the blades, and the vortex creates an upwash or downwash effect on the middle airflow; the bionic blades will bear greater tangential forces and main axis composite forces from the spanwise unevenness. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a simplified schematic diagram of a bionic vertical axis wind turbine model;

[0024] Figure 2 It is a schematic diagram of the transformation process of the convex peak profile;

[0025] Figure 3 It is a schematic diagram of the computational domain model and boundary conditions;

[0026] Figure 4 It is a schematic diagram of the computational domain grid division;

[0027] Figure 5 It is a schematic diagram for determining the total computation time and time step;

[0028] Figure 6 It is a schematic diagram of grid node distribution and grid density. DETAILED DESCRIPTION

[0029] Specific implementation method 1: Figures 1 to 6 As shown, a method for establishing a bionic vertical axis wind turbine model comprises the following specific steps:

[0030] Step 1, select NACA0021 airfoil as the blade profile; the blade chord length of the blade profile is c = 0.265m, the blade height is H = 1.2m, and the blade rotation radius is R = 1m;

[0031] Step 2: The shape of the convex peak of the leading edge of the fan blade is a sine curve, and the cross-sectional profile of the convex peak is obtained by transforming the basic airfoil; the transformation method of the cross-sectional profile of the convex peak is:

[0032]

[0033] In formula (1), (x k ,yk ) is the coordinate of the maximum thickness point of the airfoil, and A is the amplitude of the bulge;

[0034] Step 3, the computational domain is divided into a fixed domain located outside and a rotating domain located inside; the rotation radius of the rotating domain is 1.2R, the height of the rotating domain is the same as the blade height H, the left inlet of the fixed domain is a semicircle with a radius of 10R, and the fixed domain outlet is 30R away from the rotating domain. In order to consider the influence of the blade tip vortex in the study, the computational domain height is greater than the blade height and is set to 2H;

[0035] Step 4: Use ANSYS Fluent software to calculate the wind turbine flow field; the turbulence model adopts the k–ωSST model widely used in the numerical simulation of vertical axis wind turbines. Incompressible air is selected as the flow medium, and the fluid density is set to 1.225 kg / m 3 , the calculation time step is set to the time required for the blade to rotate 1°, 40 iterations are set in each time step, and the total physical calculation time is set to the time required for the wind turbine blade to rotate 16 times;

[0036] Step 5: Verify the accuracy of the numerical simulation of the vertical axis wind turbine; check the time step, total physical time, grid density, and the difference between simulation and experiment. The relationship between the power coefficient, torque coefficient, and tangential force coefficient is:

[0037]

[0038] In formulas (2), (3), and (4), C power is the wind turbine power coefficient, TSR is the tip speed ratio, Q is the wind turbine torque, ρ is the gas density, H is the wind turbine blade height, R is the blade rotation radius, U is the mainstream flow velocity, C Q is the torque coefficient of the wind turbine, C T is the tangential force coefficient of the wind turbine, is the average chord length of the blade.

[0039] Among them, the average chord length of the blade is shown in the following table:

[0040] Table 6-1Average chord length of blade

[0041]

[0042] The prototype blade is named O blade, and the blade with a protrusion amplitude of A=0.025c=a0=0.006625m and a wavelength of W=H / 3=w0=0.4m is defined as the reference blade W(A) blade. The subscripts of the W series and A series mean that the protrusion wavelength or amplitude is a multiple of the corresponding value of the reference blade. The protrusion amplitude of the WN series is w0. The meaning of the W superscript is the same as above, and the N superscript means the number of protrusions evenly distributed on the leading edge of the blade.

[0043] The grid partitioning strategies for fixed and rotating domains are as follows: Figure 4 As shown in the figure, the blade is divided into 100 nodes along the chord direction and 65 nodes in the height direction. In order to meet the requirements of wall flow analysis accuracy in the calculation, 65 layers of boundary layer grids are arranged on the blade surface, and the height of the first layer grid is 2×10 -5 m, and the grid height growth ratio is 1.1.

[0044] The boundary conditions of the computational domain are set as follows: Figure 4 As shown in the figure, the fixed domain inlet is set as the velocity inlet, the velocity is 8m / s, the turbulence intensity is 0.5%, the fixed domain outlet is set as the pressure outlet, the boundary condition of the interface between the fixed domain and the rotating domain is set as Interface, the blades and the rotating axis in the rotating domain are set as Wall boundary conditions, and the boundary conditions of the remaining surfaces are set as Symmetry. The sliding grid method is used to simulate the rotation of the vertical axis wind turbine blades, and the tip speed ratio is defined as formula (5); the blade rotation angular velocity ω is set to 12rad / s (TSR=1.5), 17.52rad / s (TSR=2.19) and 24rad / s (TSR=3) at different tip speed ratios;

[0045]

[0046] Among them, when the blade tip speed ratio is 2.19, the monitoring results of the vertical axis wind turbine power coefficient are as follows: Figure 5 As shown in the figure, in the first three rotations of the blade, the power coefficient fluctuates greatly. In order to avoid the influence of non-convergence on the conclusion, the data of the 16th rotation are used for analysis. Figure 5 It is shown that choosing a time step of 1° can ensure the accuracy of the analysis.

[0047] To ensure the accuracy of the calculation, three sets of computational grids were used for grid independence verification. The external domain used a grid with 2.2 million grid nodes. The grid encryption strategy in the rotation domain was as follows: Figure 6As shown in the figure; the grid density of the internal rotation domain is coarse, medium and fine, with the grid numbers of 2 million, 3.7 million and 5.2 million respectively. The total number of grids for the three groups of calculations are 4.2 million, 5.9 million and 7.4 million respectively. The performance deviation of the coarse grid is caused by the insufficient number of grid nodes when the blade is located in the downstream area. The calculation results of the medium density grid and the fine density grid are compared, and it is found that their change trends are basically the same. Therefore, 5.9 million grid nodes are selected as the calculation grid.

[0048] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for establishing a bionic vertical axis wind turbine model, characterized in that: The specific steps include: Step 1. Select NACA0021 airfoil as the blade profile; Step 2: The shape of the convexity on the leading edge of the fan blade is a sine curve, and the cross-sectional profile of the convex peak is obtained by transforming the basic airfoil; Step 3, dividing the computational domain into an external fixed domain and an internal rotating domain; Step 4: Calculate the wind turbine flow field using ANSYS Fluent software; Step 5: Verify the accuracy of the vertical axis wind turbine numerical simulation.

2. A method for establishing a bionic vertical axis wind turbine model according to claim 1, characterized in that: The blade chord length of the blade profile in step 1 is c=0.265m, the blade height is H=1.2m, and the blade rotation radius is R=1m.

3. The method for establishing a bionic vertical axis wind turbine model according to claim 1, characterized in that: The transformation method of the peak cross-section profile is: In formula (1), (x k ,y k ) is the coordinate of the maximum thickness point of the airfoil, and A is the amplitude of the bulge.

4. The method for establishing a bionic vertical axis wind turbine model according to claim 1, characterized in that: In step 3, the rotation radius of the rotating domain is 1.2R, the height of the rotating domain is the same as the blade height, which is H, the left inlet of the fixed domain is a semicircle with a radius of 10R, and the outlet of the fixed domain is 30R away from the rotating domain. In order to consider the influence of the tip vortex in the study, the height of the calculation domain is greater than the blade height and is set to 2H.

5. The method for establishing a bionic vertical axis wind turbine model according to claim 1, characterized in that: The turbulence model in step 4 adopts the k–ωSST model widely used in the numerical simulation of vertical axis wind turbines. Incompressible air is selected as the flow medium, and the fluid density is set to 1.225 kg / m 3 The calculation time step is set to the time required for the blade to rotate 1°, 40 iterations are set in each time step, and the total physical calculation time is set to the time required for the wind turbine blade to rotate 16 times.

6. A method for establishing a bionic vertical axis wind turbine model according to claim 1, characterized in that: In step 5, the time step, total physical time, mesh density, and simulation and experimental differences are checked. The relationship between the power coefficient, torque coefficient, and tangential force coefficient is: In formulas (2), (3), and (4), C power is the wind turbine power coefficient, TSR is the tip speed ratio, Q is the wind turbine torque, ρ is the gas density, H is the wind turbine blade height, R is the blade rotation radius, U is the mainstream flow velocity, C Q is the torque coefficient of the wind turbine, C T is the tangential force coefficient of the wind turbine, is the average chord length of the blade.

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