A method for calculating aerodynamic loads on fan blades considering air compressibility, an electronic terminal and a storage medium

Abstract

The present invention provides a method for calculating the aerodynamic load of a wind turbine blade taking into account the compressibility of air, including: constructing a thrust equation for updating the axial induction factor; using the thrust equation to update the axial induction factor, and synchronously updating the tangential induction factor; and obtaining the corresponding local inflow angle, lift coefficient and drag coefficient according to the updated axial induction factor and tangential induction factor; and then calculating the aerodynamic load of the wind turbine blade; wherein the thrust equation includes: a first thrust equation constructed according to the compressible air density expression, the Euler equation and the blade element theory, and a second thrust equation constructed according to the empirical relationship between the Glauert maximum thrust coefficient and the induction factor and the blade element theory. The present invention constructs the first thrust equation taking into account the compressibility of air, and combines the existing second thrust equation to iterate a more accurate induction factor and lift and drag coefficient, so that the aerodynamic load calculation accuracy of large wind turbines is higher, which is more in line with the needs of large-scale development of wind turbines.

Description

Technical Field

[0001] The invention relates to a method for calculating the aerodynamic load of a fan blade taking into account the compressibility of air, an electronic terminal and a storage medium, and belongs to the field of wind turbine aerodynamics. Background Art

[0002] In order for large wind turbines to capture wind energy more effectively and thus increase energy output, the trend of large-scale development of wind turbines has become increasingly prominent in the wind power industry, which has led to a significant increase in blade size. The length of the blades has grown from the initial tens of meters to hundreds of meters today. As an increasingly powerful component of wind energy, offshore wind power has further promoted the increase in the length of wind turbine blades and the development of large-scale wind turbines. The traditional blade element theory BEM is based on the Bernoulli equation that air is incompressible and is only applicable to the calculation of aerodynamic loads of small and medium-sized wind turbines. However, the blade tip Mach number of the latest 22MW wind turbine model has exceeded 0.3, breaking the assumption that air is incompressible, and the traditional BEM theory is no longer applicable. There is no correction for air compressibility in the existing blade element theory, so it is urgent to develop a method for calculating the aerodynamic load of wind turbine blades that takes into account air compressibility in order to perform more accurate load calculations. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a method for calculating the aerodynamic load of wind turbine blades taking into account the compressibility of air, an electronic terminal and a storage medium. By using the Euler equation and the isentropic relationship, the calculation of the blade load takes into account the change in air density, so that the aerodynamic load calculation method can adapt to the development of large-scale wind turbines.

[0004] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0005] In a first aspect, the present invention provides a method for calculating the aerodynamic load of a fan blade taking into account the compressibility of air, comprising: constructing a thrust equation for updating the axial induction factor; updating the axial induction factor using the thrust equation, and synchronously updating the tangential induction factor; and obtaining the corresponding local inflow angle, lift coefficient and drag coefficient based on the updated axial induction factor and tangential induction factor; calculating the aerodynamic load of the fan blade based on the local inflow angle, lift coefficient and drag coefficient; wherein the thrust equation comprises: a first thrust equation constructed based on the compressible air density expression, the Euler equation and the blade element theory, and a second thrust equation constructed based on the empirical relationship between the Glauert maximum thrust coefficient and the induction factor and the blade element theory.

[0006] Furthermore, the first thrust equation is constructed according to the compressible air density expression, the Euler equation and the blade element theory, including:

[0007] Using the isentropic relationship, we can get the expression for compressible air density:

[0008] ;

[0009] In the formula, and are the atmospheric density and pressure in the initial state, is the specific heat ratio, The pressure is The corresponding air density when

[0010] Substituting the compressible air density expression into the Euler equation, we get the relationship between pressure and velocity:

[0011] ;

[0012] Integrate both sides of the above equation and get the pressure in front of the wind wheel: and the pressure behind the wind wheel They are:

[0013] ;

[0014] ;

[0015] in, and are the air velocity before and after the wind wheel, respectively, and their calculation formulas are:

[0016] ;

[0017] ;

[0018] In the formula, is the axial induction factor, is the tangential induction factor, is the incoming wind speed, is the wind wheel speed, is the local radius of the blade;

[0019] The first thrust equation established in combination with the blade element theory is:

[0020] ;

[0021] In the formula, is the reference air density for calculating the aerodynamic coefficient, is the number of leaves, is the local inflow angle, and are the local radius of the blade The local chord length and axial force coefficient at is the local radius of the blade The spanwise infinitesimal length of the blade at .

[0022] Furthermore, the second thrust equation constructed according to the empirical relationship between the Glauert maximum thrust coefficient and the induction factor and the blade element theory includes:

[0023] The thrust coefficient is obtained according to the empirical relationship between the Glauert maximum thrust coefficient and the induction factor:

[0024] ;

[0025] Calculate the local radius of the blade The thrust of the wind wheel ring is:

[0026] ;

[0027] The second thrust equation established is:

[0028] ;

[0029] In the formula, is the Prandtl tip correction factor, is the local radius of the blade Relative wind speed.

[0030] Furthermore, the use of the thrust equation to update the axial induction factor and the synchronous updating of the tangential induction factor includes: setting the axial induction factor and tangential induction factor The initial value of

[0031] One iteration calculation includes:

[0032] According to the axial induction factor and tangential induction factor Calculate the local inflow angle and angle of attack , the formula is:

[0033] ;

[0034] ;

[0035] In the formula, is the local pitch angle of the blade;

[0036] According to the preset angle of attack-aerodynamic coefficient table, the angle of attack The corresponding lift coefficient and drag coefficient ;

[0037] According to the local inflow angle , lift coefficient and drag coefficient Calculation of the tangential force coefficient and axial force coefficient ;

[0038] The formula is:

[0039] ;

[0040] ;

[0041] According to the local inflow angle and the tangential force coefficient Update tangential induction factor , the formula is:

[0042] ;

[0043] In the formula, For the degree of reality;

[0044] Based on the above parameters, the axial induction factor is updated, including:

[0045] In response to the current axial induction factor , calculate the axial induction factor using the first thrust equation ;

[0046] In response to the current axial induction factor , the axial induction factor is calculated using the second thrust equation ;

[0047] The iterative calculation is terminated in response to satisfying the iterative termination condition. When the iterative calculation is terminated, the values ​​of the local inflow angle, the lift coefficient and the drag coefficient are obtained.

[0048] Furthermore, the Newton iteration method is used to solve the axial induction factor.

[0049] Further, the calculating of the aerodynamic load of the fan blade according to the local inflow angle, lift coefficient and drag coefficient includes:

[0050] The lift and drag of the airfoil at different positions of the blade are:

[0051] ;

[0052] ;

[0053] The axial force and tangential force at different spanwise positions of the blade are:

[0054] ;

[0055] ;

[0056] In the formula, is the lift coefficient, is the resistance coefficient.

[0057] In a second aspect, the present invention provides an electronic terminal, comprising a processor and a memory connected to the processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the steps of the method described in the first aspect are performed.

[0058] In a third aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] The method for calculating the aerodynamic load of fan blades considering the compressibility of air provided by the present invention takes into account that when the fan blades are long, the linear velocity at the blade tip position is large, and the air density will change with the air flow velocity. Therefore, the present invention establishes a first thrust equation considering the compressibility of air, and uses it in combination with the second thrust equation of the prior art to iteratively calculate more accurate parameter data for calculating the aerodynamic load of the fan blades, thereby making the calculation accuracy of the aerodynamic load of large fans higher and more in line with the needs of large-scale development of wind turbines. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is a flow chart of a method for calculating aerodynamic loads of fan blades taking into account air compressibility provided in Example 1 of the present invention;

[0062] Figure 2 is a schematic diagram of the change of air density along the span direction of the IEA 15MW wind turbine blade in Example 4 of the present invention;

[0063] Figure 3 The figure is a graph of blade axial force and tangential force of an IEA 15MW wind turbine at a tip speed of 95m / s calculated using the method proposed in the present invention, and a comparison with CFD simulation results;

[0064] Figure 4 The figure is a graph of blade axial force and tangential force of an IEA 15MW wind turbine at a tip speed of 130m / s calculated using the method proposed in the present invention, and a comparison with CFD simulation results. DETAILED DESCRIPTION

[0065] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Example

[0066] Figure 1 The flowchart of the method for calculating the aerodynamic load of a fan blade considering the compressibility of air provided in this embodiment is shown. This flowchart only shows the logical sequence of the method described in this embodiment. In other possible embodiments of the present invention, different methods may be used without conflict. Figure 1 The steps shown or described are accomplished in the order shown.

[0067] like Figure 1 As shown, this embodiment provides a method for calculating the aerodynamic load of a fan blade taking into account the compressibility of air, including:

[0068] Construct the thrust equation to update the axial induction factor;

[0069] The axial induction factor is updated by using the thrust equation, and the tangential induction factor is updated synchronously; and the corresponding local inflow angle, lift coefficient and drag coefficient are obtained according to the updated axial induction factor and tangential induction factor;

[0070] The aerodynamic load of the fan blade is calculated according to the local inflow angle, lift coefficient and drag coefficient.

[0071] Specifically, in this embodiment, two thrust equations are constructed according to whether the momentum theory is applicable, namely: a first thrust equation constructed according to the compressible air density expression, the Euler equation and the blade element theory, and a second thrust equation constructed according to the empirical relationship between the Glauert maximum thrust coefficient and the induction factor and the blade element theory.

[0072] The construction of the first thrust equation takes into account the influence of the air flow velocity on the surface of the wind turbine blade on the air density. The air density at different local radius positions of the blades is different, which will cause the aerodynamic load of the blades to change. In this case, the first thrust equation is used to update the axial induction factor, and then update other related data.

[0073] The construction process of the first thrust equation includes:

[0074] Using the isentropic relationship, we can get the expression for compressible air density:

[0075] ;

[0076] In the formula, and are the atmospheric density and pressure in the initial state, is the specific heat ratio, The pressure is The corresponding air density when

[0077] Substituting the compressible air density expression into the Euler equation, we get the relationship between pressure and velocity:

[0078] ;

[0079] Integrate both sides of the above equation and get the pressure in front of the wind wheel: and the pressure behind the wind wheel They are:

[0080] ;

[0081] ;

[0082] in, and are the air velocity before and after the wind wheel, respectively, and their calculation formulas are:

[0083] ;

[0084] ;

[0085] In the formula, is the axial induction factor, is the tangential induction factor, is the incoming wind speed, is the wind wheel speed, is the local radius of the blade;

[0086] The first thrust equation established in combination with the blade element theory is:

[0087] ;

[0088] In the formula, is the reference air density for calculating the aerodynamic coefficient, is the number of leaves, is the local inflow angle, and are the local radius of the blade The local chord length and axial force coefficient at is the local radius of the blade The spanwise infinitesimal length of the blade at .

[0089] When the momentum theory is not applicable, the second thrust equation is used to update the calculation of the axial induction factor. The construction process of the second thrust equation includes:

[0090] The thrust coefficient is obtained according to the empirical relationship between the Glauert maximum thrust coefficient and the induction factor:

[0091] ;

[0092] Calculate the local radius of the blade The thrust of the wind wheel ring is:

[0093] ;

[0094] The second thrust equation established is:

[0095] ;

[0096] In the formula, is the Prandtl tip correction factor, is the local radius of the blade Relative wind speed.

[0097] Example 2

[0098] Based on Example 1, this example adds a process of updating the axial induction factor and the tangential induction factor, which specifically includes:

[0099] Before the iterative calculation begins, set the initial values ​​for the axial induction factor and the tangential induction factor. An iterative calculation includes:

[0100] According to the axial induction factor and tangential induction factor Calculate the local inflow angle and angle of attack , the formula is:

[0101] ;

[0102] ;

[0103] In the formula, is the local pitch angle of the blade.

[0104] According to the preset angle of attack-aerodynamic coefficient table, the angle of attack The corresponding lift coefficient and drag coefficient It should be noted that the angle of attack-aerodynamic coefficient table used in this embodiment is obtained through three-dimensional CFD simulation experiments.

[0105] According to the local inflow angle , lift coefficient and drag coefficient Calculation of the tangential force coefficient and axial force coefficient ;

[0106] The formula is:

[0107] ;

[0108] ;

[0109] According to the local inflow angle and the tangential force coefficient Update tangential induction factor , the formula is:

[0110] ;

[0111] In the formula, For reality.

[0112] According to the above parameters, the axial induction factor is updated in response to the current axial induction factor , calculate the axial induction factor using the first thrust equation ;

[0113] In response to the current axial induction factor , the axial induction factor is calculated using the second thrust equation .

[0114] The iteration is repeated until the error meets the preset accuracy requirement or reaches the preset maximum number of iteration steps, and the iteration ends.

[0115] When the iterative calculation ends, the values ​​of the current local inflow angle, lift coefficient and drag coefficient are obtained, which are used to calculate the aerodynamic loads of the wind turbine blades.

[0116] It should be noted that the Newton iteration method used in this embodiment is used to solve the axial induction factor. Other iteration methods may also be used for calculation during the specific implementation process.

[0117] Example 3

[0118] Based on Example 1, this embodiment adds a process for calculating the aerodynamic load of the wind turbine blade, which specifically includes:

[0119] The lift and drag of the airfoil at different positions of the blade are:

[0120] ;

[0121] ;

[0122] The axial force and tangential force at different spanwise positions of the blade are:

[0123] ;

[0124] ;

[0125] In the formula, is the lift coefficient, is the resistance coefficient.

[0126] Example 4

[0127] This example provides aerodynamic load data of an IEA 15MW wind turbine at blade tip speeds of 95 m / s and 130 m / s obtained using the method of the present invention. Figure 2 The figure shows the variation of air density along the span direction of IEA 15MW wind turbine blades at blade tip speeds of 95m / s and 130m / s. Figure 3 (a) and (b) are the blade axial force and tangential force under the condition of blade tip speed of 95m / s; Figure 4 (a) and (b) are respectively the axial force and tangential force of the blade under the condition of blade tip speed of 130m / s. Among them, BEM is the calculation result of the aerodynamic load of the wind turbine blade using the traditional blade element momentum theory, and the angle of attack-aerodynamic coefficient table extracted from the incompressible CFD simulation results is used for calculation; C-BEM is the calculation result of the aerodynamic load calculation method of the wind turbine blade provided by the present invention, and the angle of attack-aerodynamic coefficient table extracted from the compressible CFD simulation results is used for calculation; it can be seen that when the compressibility of air is considered, the axial force and tangential force of the blade increase, and the increase in the tip speed makes the compressibility of the air more significant. In addition, Figure 3 and Figure 4 In the present invention, the blade axial force and tangential force calculated by the aerodynamic load calculation method for the fan blade provided by the present invention are consistent with the compressible CFD simulation results, which verifies the effectiveness of the aerodynamic load calculation method for the fan blade provided by the present invention.

[0128] Example 5

[0129] This embodiment provides an electronic terminal, including a processor and a memory connected to the processor, wherein a computer program is stored in the memory. When the computer program is executed by the processor, the steps of the method for calculating the aerodynamic load of a wind turbine blade provided in any one of Embodiments 1-3 are performed.

[0130] Example 6

[0131] An embodiment of the present invention also provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, the program implements the steps of the method for calculating the aerodynamic load of a wind turbine blade provided in any one of the above embodiments 1-3, and has the corresponding beneficial effects of the execution method.

[0132] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, electronic terminals, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0133] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for calculating the aerodynamic load of a fan blade taking into account the compressibility of air, characterized in that: include: Construct the thrust equation to update the axial induction factor; The axial induction factor is updated by using the thrust equation, and the tangential induction factor is updated synchronously; and the corresponding local inflow angle, lift coefficient and drag coefficient are obtained according to the updated axial induction factor and tangential induction factor; The aerodynamic load of the fan blade is calculated according to the local inflow angle, lift coefficient and drag coefficient; wherein the thrust equation includes: a first thrust equation constructed according to the compressible air density expression, the Euler equation and the blade element theory, including: Using the isentropic relationship, we can get the expression for compressible air density: In the formula, ρ0 and P0 are the atmospheric density and pressure in the initial state, γ is the specific heat ratio, and ρ' is the air density corresponding to the pressure P; Substituting the compressible air density expression into the Euler equation, we get the relationship between pressure and velocity: Where V is the air velocity; Integrating both sides of the above equation, we can get the pressure P1 before the wind rotor and the pressure P2 after the wind rotor respectively: Among them, V1 and V2 are the air flow rates before and after the wind rotor, respectively, and their calculation formulas are: Where a is the axial induction factor, a ′ is the tangential induction factor, v0 is the incoming wind speed, ω is the wind wheel speed, and r is the local radius of the blade; The first thrust equation established in combination with the blade element theory is: Where ρ is the reference air density for calculating the aerodynamic coefficient, B is the number of blades, φ is the local inflow angle, c and C n are the local chord length and axial force coefficient at the local radius r of the blade, respectively, dr is the spanwise microelement length of the blade at the local radius r of the blade; The second thrust equation constructed based on the empirical relationship between the Glauert maximum thrust coefficient and the induction factor and the blade element theory includes: The thrust coefficient is obtained according to the empirical relationship between the Glauert maximum thrust coefficient and the induction factor: The thrust of the wind wheel ring at the local radius r of the blade is calculated as: The second thrust equation established is: Where F is the Prandtl blade tip correction factor, v rel is the relative wind speed at the local radius r of the blade.

2. The calculation method according to claim 1, characterized in that: The method of updating the axial induction factor by using the thrust equation and synchronously updating the tangential induction factor includes: Set the axial induction factor a and the tangential induction factor a ′ The initial value of One iteration calculation includes: According to the axial induction factor a and the tangential induction factor a ′ Calculate the local inflow angle φ and the angle of attack α using the formula: α=φ-θ Where θ is the local pitch angle of the blade; According to the preset angle of attack-aerodynamic coefficient table, the lift coefficient C corresponding to the angle of attack α is obtained. l and the drag coefficient C d ; According to the local inflow angle φ, lift coefficient C l and the drag coefficient C d Calculation of the tangential force coefficient C t and axial force coefficient C n , the formula is: C n =C l cosφ+C d sinφ C t =C l sinφ-C d cosφ According to the local inflow angle φ and the tangential force coefficient C t Update tangential induction factor a ′ , the formula is: In the formula, σ is the solidity; Based on the above parameters, the axial induction factor is updated, including: In response to the current axial induction factor a≤1 / 3, the axial induction factor a is calculated using the first thrust equation; In response to the current axial induction factor a>1 / 3, the axial induction factor a is calculated using the second thrust equation; The iterative calculation is terminated in response to satisfying the iterative termination condition. When the iterative calculation is terminated, the values ​​of the local inflow angle, the lift coefficient and the drag coefficient are obtained.

3. The calculation method according to claim 2, characterized in that: The axial induction factor is solved using Newton's iteration method.

4. The calculation method according to claim 2, characterized in that: The step of calculating the aerodynamic load of the fan blade according to the local inflow angle, lift coefficient and drag coefficient comprises: The lift and drag of the airfoil at different radius positions of the blade are: The axial force and tangential force at different spanwise positions of the blade are: F N =Lcosφ+Dsinφ F T =Lsinφ-Dcosφ Where ρ is the reference air density when calculating the aerodynamic coefficient, v rel is the relative wind speed at radius r, C l is the lift coefficient, C d is the drag coefficient, c is the local chord length at radius r, and φ is the local inflow angle.

5. An electronic terminal, characterized in that: The method comprises a processor and a memory connected to the processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the steps of the method according to any one of claims 1 to 4 are executed.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

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