CN110287573A - A Model Blade Design Method Applicable to Floating Fan Scale Model Pool Test - Google Patents

Abstract

The invention provides a model blade design method suitable for floating fan scaling model pool tests, and relates to the technical field of wind power generation. The method uses a low Reynolds number airfoil to replace the airfoil used in the original fan blade, and redistributes it through an optimization algorithm. The distribution of chord length and twist angle improves the aerodynamic thrust of the model fan blades to improve the accuracy and reliability of the floating fan scale model. The present invention first obtains geometrically similar blades according to Froude's scaling law based on the real-scale fan blades; then replaces the original airfoil with a low Reynolds number airfoil, and distributes the blade torsion angle distribution through the maximum lift tracking algorithm; then adjusts based on the trial and error method The chord length of the airfoil of each section of the blade; finally, the structural shape of the blade is further optimized through local fine-tuning, and the axial thrust performance similar to that of the full-scale floating fan blade is obtained. The invention has the advantages of simple steps, clear flow, accurate and reliable.

Description

A Model Blade Design Method Applicable to Floating Fan Scale Model Pool Test

technical field

The invention relates to the technical field of wind power generation, in particular to the technical field of scaled model testing of floating wind turbines, in particular to a model blade design method suitable for scaled model pool tests of floating wind turbines.

Background technique

Nowadays, the floating wind turbine scale model pool test is considered to be the most accurate, reliable, and economically feasible method for studying the dynamics of floating wind turbines, verifying the concept of new floating platforms, and verifying numerical calculation tools.

As an organic combination of floating offshore platform technology and land-based fixed wind turbines, the pool test for floating wind turbines can gain experience and guidance from scaled model pool tests on floating offshore platforms and scaled model wind tunnel tests on wind turbines. However, there is a natural incompatibility between the similarity of the hydrodynamic Froude number of the floating platform-mooring system and the similarity of the aerodynamic Reynolds number of the wind turbine blade, which is called the Reynolds number scaling effect. It is generally believed that more attention should be paid to the hydrodynamics of the floating platform-mooring system in the tank test, and Froude's law of similarity should be effectively considered. Under Froude's similarity law, the working Reynolds number of the model fan decreased by 2-3 orders of magnitude, which made the rotor thrust of the model fan significantly lower than the theoretical value. The thrust of the wind rotor is an important incentive force affecting the motion of the floating platform. Inaccurate wind rotor thrust will inevitably lead to inaccurate evaluation of the motion performance of the floating wind turbine. Therefore, reducing the adverse effects of the Reynolds number scaling effect through relevant technical means and improving the wind rotor thrust of the model fan under the Froude scale environmental working conditions are important technologies that need to be resolved urgently in the scale model test of the floating wind turbine. question. .

Contents of the invention

In view of the above-mentioned problems of the prior art, the present invention adopts the following technical solutions to solve the above-mentioned technical difficulties:

The invention provides a model blade design method suitable for floating fan scale model pool test: firstly, according to the real-scale fan blade according to Froude's scaling law, geometrically similar blades are obtained; then the original wing is replaced with a low Reynolds number airfoil The blade twist angle distribution is assigned by the maximum lift tracking algorithm; then the chord length of each section of the blade is adjusted based on the trial and error method; finally, the blade structure shape is further optimized by local fine-tuning, and the axial direction similar to that of the full-scale floating fan blade is obtained. thrust performance.

The invention provides a method for designing a model blade suitable for a scaled model pool test of a floating fan, comprising the following steps:

Step S1, determining the scale ratio λ according to the test conditions and performance requirements of the pool;

Step S2, according to the blade parameters of the real-scale fan, and according to Froude's law of scaling, design a geometrically similar blade FSR as the blade of the model fan;

Step S3, calculating the working Reynolds number of the blades of the model fan to obtain the Reynolds number interval, and selecting an airfoil with superior working performance in the Reynolds number interval as the working Reynolds number airfoil to replace the airfoil in the geometrically similar blade FSR type;

Step S4, calculating the aerodynamic performance parameters of the working Reynolds number airfoil, and determining the maximum lift corresponding to the angle of attack α*;

Step S5, using the maximum lift tracking algorithm MLT to distribute the distribution of the twist angle of each cross-section airfoil of the blade of the model fan;

Step S6, determining the distribution of the chord lengths of the airfoils of each section of the blade of the model fan based on the trial and error method;

In step S7, the structural shape of the blade of the model fan is optimized by local fine-tuning of the chord length and the twist angle, and a blade PSR with similar performance to the scaled model of the floating fan is obtained.

Further, the determination of the scale ratio λ in the step S1 includes the following conditional factors:

(1) The structural size of the pool, including the maximum water depth, mooring system deployment space, wave-making capacity, and flow-making capacity;

(2) The performance of the wind generation system, including the maximum wind speed and the effective coverage area of the wind field.

Further, the determination of the scale ratio λ in the step S1 also includes the following conditional factors:

(3) Basic dimensions of the floating unit, including draft;

(4) Test cost.

Further, the step S2 also includes:

S201: Determine the two-dimensional shape of the airfoil of each section of the blade of the full-scale fan;

S202: Determine the chord length and twist angle of each cross-section airfoil of the blade of the model fan, which are respectively:

β _m (μ) = β _f (μ) (2)

Wherein, the subscripts m and f represent the model fan and the real-scale fan respectively, c represents the chord length of the airfoil, β represents the twist angle of the airfoil, and μ represents the position of the section of the airfoil.

Further, the root chord of the blade of the model fan is longer than the blade tip chord; the cross-sectional twist angle of the blade of the model fan increases gradually from the blade tip to the blade root.

Further, the selection of the working Reynolds number airfoil in the step S3 includes the following steps:

S301: Calculate the working Reynolds number of the blades of the real-scale fan:

Among them, Re represents the Reynolds number; V ₀ is the incoming wind speed; ν is the air kinematic viscosity; Λ is the working wing tip speed ratio of the fan, expressed as:

Wherein, Ω is the rotating speed of the wind rotor, and R is the radius of the wind rotor of the real-scale fan;

S302: Obtain the working Reynolds number of the blades of the model fan according to Froude's scaling law:

Re _m = λ ^-1.5 Re _f (5)

S303: According to the working Reynolds number of the blades of the model fan, select an airfoil with superior working performance as the working Reynolds number airfoil;

S304: The working Reynolds number airfoil is used to replace the airfoil in the FSR of the blade with similar performance, and the chord length and twist angle of each section of the blade of the model fan remain unchanged.

Further, the step S4 also includes:

S401: Obtain the basic aerodynamic performance parameters of the working Reynolds number airfoil at the working Reynolds number, including the corresponding relationship between the lift coefficient, the drag coefficient and the airfoil angle of attack, using the numerical method or the wind tunnel test technology;

S402: Draw the corresponding relationship between the lift coefficient and the angle of attack of the airfoil at the working Reynolds number under the environmental condition of the Froude scale ratio, and obtain the maximum lift coefficient at the working Reynolds number corresponding to the angle of attack α*.

Further, the step S5 also includes:

S501: Obtain the optimal wing tip speed ratio Λ according to the wind energy coefficient curve of the real-scale fan, and use it as the design working point of the blade of the model fan;

S502: Calculate the axial induction factor a (μ) and the tangential induction factor b (μ) of each airfoil section of the blade of the real-scale fan at the design working point;

S503: Calculate the distribution of the twist angle of each section of the blade of the model fan according to the formula in formula (6):

Among them, β is the twist angle of the blade section; μ is the normalized position of the section; a and b are the axial and tangential induction factors; Λ is the optimal wing tip speed ratio, corresponding to the maximum power coefficient of the real-scale fan; α * Corresponds to the angle of attack for the maximum lift coefficient at the operating Reynolds number.

Further, the step S6 also includes:

S601: Adjust the chord length of each section of the blade of the model fan:

c _m (μ)=K(μ)·c _f (μ) (7)

Wherein, the chord length of each section of the blade of the model fan is multiplied by a same proportional coefficient on the basis of the chord length of the geometrically similar blade FSR, namely:

K(μ)≡K (8)

S602: Obtain the optimal proportionality coefficient K by trial and error, and determine the distribution of the chord lengths of the airfoils of each section of the blade of the model fan.

Further, the step S7 also includes:

S701: According to the nacelle design of the scale model of the floating fan, obtain the connection form and connection size between the hub of the nacelle and the blade of the model fan;

S702: Adjust the size of the root cylindrical area of the blade of the model fan according to the connection size;

S703: Establish a three-dimensional model of the blades of the model fan, and perform slight adjustments to further optimize the structural shape of the blades of the model fan.

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

1. The present invention replaces the original airfoil with an airfoil with a lower working Reynolds number, which can greatly eliminate the negative impact of the Reynolds number scaling effect, and has the advantages of high efficiency and remarkable effect;

2. The present invention optimizes the torsion angle distribution of the blade through the maximum victory tracking algorithm MLT, which has the advantages of simple and easy-to-understand algorithm and high execution efficiency;

3. The process of the present invention is clear and easy to implement, which is convenient for relevant researchers to design and develop a set of model fan blades suitable for floating fan scale model pool tests with reference to the proposed method.

Description of drawings

Fig. 1 is the flow chart of the model blade design method of the present invention;

Fig. 2 is the schematic diagram of the chord length and twist angle distribution of each section of the obtained blade of the present invention;

Fig. 3 is a schematic diagram of thrust coefficients of original scale fan blades, geometrically similar blades and performance similar blades of the present invention;

Fig. 4 is a spanwise load distribution diagram of the original scale fan blade, the geometrically similar blade and the performance similar blade of the present invention.

Detailed ways

The following describes a preferred embodiment of the present invention with reference to the accompanying drawings to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned herein.

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Fig. 1 is a kind of flow chart of the model blade design method that is applicable to floating fan scale model pool test of the present invention, and described method comprises the following steps:

Step S1, determining an appropriate scale ratio λ according to the pool test conditions and performance requirements;

Step S2, according to the parameters of the real-scale fan blades, and according to Froude's law of scaling, a geometrically similar blade design (FSR) is obtained;

Step S3, calculate the Reynolds number range of the airfoil in the model test, and select a suitable low Reynolds number airfoil accordingly, and replace the airfoil in the geometrically similar blade FSR with the low Reynolds number airfoil.

Step S4, calculating the aerodynamic performance parameters of the low Reynolds number airfoil, and calculating its maximum lift corresponding to the angle of attack α*.

Step S5, on the basis of geometrically similar blades FSR, distribute the twist angle distribution of each cross-section airfoil of the model blade through the maximum lift tracking algorithm (MLT).

Step S6, determine the chord length distribution of each section airfoil of the model blade based on the trial and error method.

In step S7, further optimize the blade structure and shape through local fine-tuning, and obtain performance-similar blades (PSR) of the scale model of the floating fan.

In the above technical solution, the basis for determining the scale ratio in step S1 includes: (1) the basic structural dimensions of the test pool, such as the maximum water depth, mooring system deployment space, wave-making capacity, flow-making capacity, etc.; Wind system performance, such as maximum wind speed, effective coverage area of wind field, etc.; (3) basic size of floating platform, such as draft, etc.; (4) test budget, generally speaking, the larger the model size, the higher the corresponding test cost high. After comprehensive consideration of various factors, a reasonable model test scale ratio is determined, which is denoted as λ.

In the above technical solution, the design of the geometrically similar blade FSR in step S2 mainly includes:

S201: Determine the two-dimensional shape of the airfoil of each section of the blade. According to the cross-sectional shape of the large floating fan blades, keep the shape unchanged and directly scale it.

S202: Determine the chord length and twist angle of the airfoil of each section of the blade. Large floating fan blades often have the characteristics of longer blade root chord and shorter blade tip chord. At the same time, it is often accompanied by an increasing section twist angle from the tip to the root. The chord length and twist angle of each blade section of geometrically similar blades are:

β _m (μ) = β _f (μ) (2)

In the formula, the subscripts "m" and "f" represent the model fan and the original scale fan, respectively. c is the chord length of the airfoil, β is the twist angle of the blade section, and μ is the position of the airfoil section.

In the above-mentioned technical scheme, the low Reynolds number airfoil selection in step S3 mainly includes:

S301: Calculate the working Reynolds number of the original scale floating fan blade:

Among them, Re represents the Reynolds number; V ₀ is the incoming wind speed; ν is the air kinematic viscosity; Λ is the working wing tip speed ratio of the fan, expressed as:

Among them, Ω is the speed of the wind rotor; R is the radius of the wind rotor of the original scale fan.

S302: According to Froude's scaling law, obtain the working Reynolds number of the model fan blade:

Re _m = λ ^-1.5 Re _f (5)

It can be seen that the working Reynolds number of the model fan is significantly lower than that of the original scale fan. If the blade airfoil of the original scale fan is used, the thrust of the model fan rotor will drop significantly, which has a huge deviation from the theoretical value.

S303: According to the working Reynolds number of the model fan, select an airfoil with superior working performance in this Reynolds number range, such as the SD2030 airfoil, and call it a low Reynolds number airfoil.

S304: Replace the airfoil in the FSR with the selected low Reynolds number airfoil, keeping the chord length and twist angle of each section of the blade unchanged.

In the above technical solution, the main content of step S4 is:

S401: Use effective numerical techniques or wind tunnel test techniques to obtain the basic aerodynamic performance parameters of the low Reynolds number airfoil at the working Reynolds number, such as the corresponding relationship between lift coefficient, drag coefficient and airfoil angle of attack.

S402: Draw the corresponding relationship between the lift coefficient and the angle of attack of the low Reynolds number airfoil under the environmental conditions of the Froude scale ratio, and obtain the corresponding angle of attack of the maximum lift coefficient under the working Reynolds number, which is denoted as α*.

In the above technical solution, the basic idea of the maximum lift tracking algorithm MLT in step S5 is: due to the sharp drop in Reynolds number, the aerodynamic lift of each blade section in the FSR is much smaller than the theoretical value. In order to make full use of the aerodynamic lift resources of each section of the model blade, all sections of the guide blade work at the maximum lift, thereby improving the aerodynamic lift of the model blade to a certain extent.

The corresponding main content is:

S501: Obtain the optimal wing tip speed ratio Λ according to the wind energy coefficient curve of the real-scale fan, and use it as the design working point of the model blade;

S502: Obtain the axial induction factor a(μ) and tangential induction factor b(μ) of each airfoil section of the real-scale fan blade at the working point through a reliable numerical calculation method;

S503: Calculate and obtain the twist angle distribution of each section of the model blade according to the following formula:

In the formula, β is the twist angle of the blade section; μ is the normalized position of the section; a and b are the axial and tangential induction factors; Λ is the optimal wing tip speed ratio, which corresponds to the maximum power coefficient of the real-scale fan; α* is the angle of attack corresponding to the maximum lift coefficient at the working Reynolds number.

In the above technical solution, step S6 mainly includes: adjusting the chord length of each section of the model blade:

c _m (μ)=K(μ)·c _f (μ) (7)

A convenient way to deal with it is to multiply the chord length of all sections by the same proportional coefficient on the basis of the FSR chord length, namely:

K(μ)≡K (8)

Through trial and adjustment step by step, the optimal proportional coefficient K is obtained.

In the above technical solution, step S7 mainly includes:

S701: According to the nacelle design of the floating wind turbine scale model, the connection form and basic size of the nacelle hub and the model blade are obtained;

S702: According to the connection size, adjust the size of the cylinder area at the root of the model blade to ensure the reliability of the connection;

S703: Establish a three-dimensional model of the model blade, examine the smoothness and processing feasibility of each transition region, and make slight adjustments to further optimize the structural shape of the model blade.

Through the above-mentioned implementation method, after providing the real-scale blade chord length and torsion angle parameters, through the implementation of the above-mentioned steps and procedures, the performance-similar blade (PSR) can finally be mentioned.

Fig. 2 shows the chord length and twist angle distribution of geometrically similar blade FSR and performance similar blade PSR of the DTU 10MW reference fan. Compared with geometrically similar blades, performance-similar blades have longer chord lengths to enhance the aerodynamic lift of the model blades. At the same time, the twist angle distribution of blades with similar performance is also quite different from that of geometrically similar blades.

Fig. 3 shows the corresponding relationship between the thrust coefficient CT and the wing tip speed ratio TSR of the real-scale fan blades, geometrically similar blades and performance-similar blades. "The blade can maintain a high degree of matching in a certain range of wing tip speed ratio, and its performance is far better than that of the geometrically similar blade "FSR".

Figure 4 shows the spanwise load distribution of full-scale fan blades, geometrically similar blades, and performance-similar blades. It can be seen that the model blade "PSR, MLT" obtained based on the spanwise load matching algorithm proposed by the present invention has far superior geometry Similar to blade "FSR" performance.

The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection defined by the claims.

Claims (10)

1. a kind of model leaf design method suitable for floating blower scale model basin test, which is characterized in that it is realized Process includes the following steps:

Step S1 determines scaling factor λ according to the experimental condition in pond and performance requirement；

Step S2 designs geometric similarity blade FSR according to Fu Laode scaling law according to the blade parameter of real scale blower, Blade as model blower；

Step S3 calculates the operating Reynolds number of the blade of the model blower, obtains Reynolds number interval, in the Reynolds number interval It selects the superior aerofoil profile of working performance as operating Reynolds number aerofoil profile, replaces the aerofoil profile in the geometric similarity blade FSR；

Step S4 calculates the Aerodynamic of the operating Reynolds number aerofoil profile, determines that maximum lift corresponds to angle of attack *；

Step S5 passes through point of the torsional angle of the maximum lift tracing algorithm MLT each section aerofoil profile of blade for distributing the model blower Cloth；

Step S6 determines the distribution of the chord length of each section aerofoil profile of blade of the model blower based on trial-and-error method；

Step S7, outside the structure for optimizing the blade of the model blower by the Local uniqueness to the chord length and the torsional angle Shape obtains floating blower scale model performance similar vanes PSR.

2. it is suitable for the model leaf design method of floating blower scale model basin test as described in claim 1, it is special Sign is that the determination of scaling factor λ described in the step S1 includes the following conditions factor:

(1) structure size in the pond, including maximum water depth, anchoring system space for its deployment, make wave energy power, make stream ability；

(2) wind making system performance, including maximum wind velocity, wind field area of effective coverage.

3. it is suitable for the model leaf design method of floating blower scale model basin test as claimed in claim 2, it is special Sign is that the determination of scaling factor λ described in the step S1 further includes the following conditions factor:

(3) basic size of floating platform, including draft；

(4) experimentation cost.

4. it is suitable for the model leaf design method of floating blower scale model basin test as described in claim 1, it is special Sign is, the step S2 further include:

S201: the two-dimensional shapes of each section aerofoil profile of blade of the real scale blower are determined；

S202: the chord length and torsional angle of each section aerofoil profile of the blade of the model blower are determined, is respectively as follows:

β_m(μ)=β_f(μ) (2)

Wherein, subscript m and subscript f respectively indicate the model blower and the real scale blower, and c indicates the chord length of aerofoil profile, β table Show the torsional angle of aerofoil profile, μ is the section position of aerofoil profile.

5. it is suitable for the model leaf design method of floating blower scale model basin test as claimed in claim 4, it is special Sign is that the big blade tip chord length of the blade root chord length of the blade of the model blower is short；The section torsional angle of the blade of the model blower It is incremented by from blade tip to blade root.

6. it is suitable for the model leaf design method of floating blower scale model basin test as described in claim 1, it is special Sign is, the selection of the operating Reynolds number aerofoil profile in the step S3 the following steps are included:

S301: the operating Reynolds number of the blade of the real scale blower is calculated:

Wherein, Re indicates Reynolds number；V₀For arrives stream wind speed；ν is air movement viscosity；Λ is blower work wing tip speed ratio, is indicated Are as follows:

Wherein, the wind wheel radius that Ω is wind speed round, R is the real scale blower；

S302: it is contracted according to Fu Laode than law, obtains the operating Reynolds number of the blade of the model blower:

Re_m=λ^-1.5Re_f (5)

S303: according to the operating Reynolds number of the blade of the model blower, select the superior aerofoil profile of working performance as the work Make Reynolds number aerofoil profile；

S304: replace the aerofoil profile in the performance similar vanes FSR, the leaf of the model blower with the operating Reynolds number aerofoil profile The chord length and torsional angle in each section of piece remain unchanged.

7. it is suitable for the model leaf design method of floating blower scale model basin test as described in claim 1, it is special Sign is, the step S4 further include:

S401: using value technical method or wind-tunnel technique, the operating Reynolds number aerofoil profile is obtained under operating Reynolds number Basic Aerodynamic, the corresponding relationship including lift coefficient, resistance coefficient and the aerofoil profile angle of attack；

S402: the corresponding pass of the lift coefficient-angle of attack of the operating Reynolds number aerofoil profile under Fu Laode scaling factor environmental condition is drawn System, obtains the maximum lift coefficient under operating Reynolds number and corresponds to angle of attack *.

8. it is suitable for the model leaf design method of floating blower scale model basin test as described in claim 1, it is special Sign is, in the step S5 further include:

S501: best wing tip speed ratio Λ is obtained according to the wind energy coefficient curve of the real scale blower, as the model blower Blade projected working point；

S502: axial inducible factor a (μ) of each aerofoil section of blade in the projected working point of the real scale blower is calculated With tangential inducible factor b (μ)；

S503: the distribution of the torsional angle in each section of the blade of the model blower is calculated according to the formula in formula (6):

Wherein, β is blade profile torsional angle；μ is that section normalizes position；A and b is axially and tangentially inducible factor；Λ is best Wing tip speed ratio, the Maximun power coefficient of the corresponding real scale blower；α * is that the maximum lift coefficient under operating Reynolds number is corresponding The angle of attack.

9. it is suitable for the model leaf design method of floating blower scale model basin test as described in claim 1, it is special Sign is, in the step S6 further include:

S601: the chord length in each section of blade of the model blower is adjusted:

c_m(μ)=K (μ) c_f(μ) (7)

Wherein, the chord length in each section of blade of the model blower multiplies on the basis of the chord length of the geometric similarity blade FSR With an identical proportionality coefficient, it may be assumed that

K(μ)≡K (8)

S602: by trial-and-error method, obtaining optimal Proportional coefficient K, determines the string of each section aerofoil profile of the blade of the model blower Long distribution.

10. it is suitable for the model leaf design method of floating blower scale model basin test as described in claim 1, it is special Sign is, in the step S7 further include:

S701: according to floating blower scale model cabin design, the connection of the blade of cabin wheel hub and the model blower is obtained Form and size for connection；

S702: according to the size for connection, the size of the root cylindrical region of the blade of the model blower is adjusted；

S703: establishing the leaf three-dimensional model of the model blower, and readjusted by a small margin, to advanced optimize the model wind The construction profile of the blade of machine.