Wind speed correction method with similar thrust under scale based on Froude criterion

Abstract

The invention discloses a wind speed correction method based on similar thrust under a Froude criterion reduced scale, and belongs to the technical field of test methods. The method comprises the following steps: acquiring a wind speed-thrust relation under a wind tunnel test by using a Froude criterion scaling model; fitting a wind speed-thrust curve by using an exponential function; converting the target thrust and the corresponding wind speed into a model scale according to a Froude criterion; determining a model wind tunnel test wind speed when the thrust under the target blade pitch angle is similar; calculating the ratio of the model wind tunnel test wind speed under similar thrust to the model wind speed after Froude scale reduction, and obtaining a wind speed scale correction coefficient; the correction coefficient is applied to a model test, and the multi-physics field test requirement is met. According to the method, the defects that the thrust is inconsistent and the wind-induced vibration physical process is distorted due to the fact that the Froude criterion and the Reynolds criterion cannot be met at the same time in a fan model test are overcome, and theoretical support and technical means can be provided for multiple fields such as floating fans and the like.

Description

Technical Field

[0001] The present invention belongs to the field of floating wind turbine tests, and particularly relates to a wind speed correction coefficient based on thrust similarity and its working method for physical model tests of floating wind turbines. Background Art

[0002] As an important technology for developing marine renewable energy, offshore floating wind power has attracted much attention in recent years due to its advantages such as stable resources and less land occupation. However, compared with onshore wind power, the related technologies of offshore wind power are still immature. Especially in the structural design of floating wind turbines, there are still many technical problems in the evaluation and optimization of their aerodynamic performance. Therefore, it is urgent to verify the structure and performance of floating wind turbines through physical model tests to promote the development of this field.

[0003] In physical model tests, to ensure the similarity of floating bodies and wave loads, it is necessary to satisfy the Froude criterion for scaling. However, after scaling the wind turbine according to the Froude criterion, it is difficult to ensure the consistency of wind action for aerodynamic loads. In current floating wind turbine model tests, usually, methods such as those disclosed in Chinese Patent Publication No.: CN119227542A are adopted. The strategy of selecting low Reynolds number airfoils and using the NSGA-Ⅲ algorithm is used to adjust parameters such as airfoil parameters, chord length, and pitch angle, so as to achieve the matching of model thrust, torque and target thrust and torque under different wind speed scales and improve the accuracy of the test. However, this method cannot satisfy the Froude criterion, and there are a series of problems such as limited application range after blade optimization and distortion of the physical process of wind-induced vibration. In short, there are many contradictions and deficiencies in the traditional test methods for wind force similarity. After scaling the model according to the Froude criterion, by measuring the wind speed-thrust relationship through wind tunnel tests and correcting the wind speed according to the thrust similarity criterion, the problems of small applicable range of modifying blade parameters, flow field distortion, and inconsistent wind-induced vibration phenomenon with the real physical process in the traditional test methods are solved. This test method significantly improves the accuracy of physical model tests of floating wind turbines and restores the real physical process in actual engineering to a certain extent. Summary of the Invention

[0004] (a) The technical problems solved by the present invention are as follows:

[0005] In view of the problems in the prior art that in the model test of a floating wind turbine, after optimizing the blade parameters to meet the similarity of wind action, the flow field is distorted and the real physical process of wind-induced vibration is difficult to reproduce, the present invention provides a wind speed correction method based on thrust similarity under Froude criterion scaling. Existing methods usually directly optimize the blade parameters to meet the similarity of wind force, but due to ignoring the non-linear characteristics of the aerodynamic performance of the wind turbine blades and the influence of the complex flow field, their application range is narrow and the flow description is insufficient, thus affecting the reliability of test data and the effect of model tests. Therefore, the present invention proposes a method of measuring the relationship between wind speed and thrust through experiments and correcting the wind speed scale ratio in combination with the Froude criterion, so as to achieve a greater degree of restoring the real physical process, meet the comprehensive research of multiple physical fields, and provide scientific support for the model test of floating wind turbines.

[0006] (b) To achieve the above object, the technical solution of the present invention is as follows:

[0007] A wind speed correction method based on thrust similarity under Froude criterion scaling. Aiming at the deficiencies in the prior art, the purpose of the present invention is to provide a test working method for floating wind turbines that meets the similarity of wind action and the Froude criterion. On the basis of meeting the similarity of wind action, through the wind speed scale ratio correction coefficient, under the requirements of geometry, mass, and stiffness that meet the Froude scaling criterion of the wind turbine, the goal of difficult-to-achieve thrust similarity is made up for, the physical process of wind-induced vibration is reproduced, and the requirements of the multi-physical field test of floating wind turbines are met.

[0008] This test working method includes the following steps:

[0009] The first step is to obtain the wind speed-thrust relationship under wind tunnel test by using the Froude criterion scaled model

[0010] Design the model of the floating wind turbine according to the Froude criterion scaling, conduct a wind tunnel test on the model, record the thrust values at different wind speeds and blade pitch angles of the wind turbine, and obtain the wind speed-thrust relationship at different blade pitch angles of the model in the wind tunnel test.

[0011] The second step is to fit the wind speed-thrust points at different blade pitch angles obtained from the wind tunnel test with an exponential function to obtain a wind speed-thrust curve

[0012] According to the wind tunnel test data, use the exponential function to fit the relationship between wind speed and thrust at different blade pitch angles, and determine the wind speed-thrust function relationship at different blade pitch angles.

[0013] y = a * x b

[0014] Among them, y represents thrust, a and b represent constants, and x represents wind speed.

[0015] Step 3: Convert the target thrust and the corresponding wind speed to the model scale according to the Froude criterion

[0016] Step 4: Determine the wind tunnel test wind speed of the model when the thrust is similar at the target blade pitch angle

[0017] Select the wind speed - thrust function relationship established in the wind tunnel test with the blade pitch angle corresponding to the thrust at the target blade pitch angle, and obtain the corresponding wind tunnel test wind speed of the model after converting the target thrust to the model scale according to the corresponding wind speed - thrust function

[0018] Step 5: Calculate the ratio of the wind tunnel test wind speed of the model under similar thrust to the model wind speed after Froude scaling to obtain the wind speed scale correction coefficient

[0019] Determine the ratio of the wind tunnel test wind speed of the model determined based on the principle of thrust similarity to the wind speed corresponding to the scaling according to the Froude criterion, which is the wind speed scale correction coefficient at this blade pitch angle

[0020]

[0021] Where: C V is the wind speed scale correction coefficient at this scale, V m,等推力 is the model wind speed in the wind tunnel test under the premise of meeting the similarity of the target thrust, V m,Froude is the wind speed obtained by converting the prototype wind speed to the model scale according to the Froude criterion

[0022] Step 6: Apply the correction coefficient to the model test to meet the requirements of multi - physical - field tests

[0023] Apply the wind speed scale correction coefficient to the model wind speed to ensure that the wind speed in the multi - physical - field test of the floating wind turbine meets the principle of thrust similarity, thereby improving the reliability of the model test results

[0024] (c) The beneficial effects of the present invention are as follows:

[0025] 1) The present invention provides a test method that meets the premise of thrust similarity and the Froude similarity criterion. It retains the consistency of the blade angle of attack and airfoil parameters with the prototype. Therefore, under the premise of thrust similarity, to a certain extent, it retains the random volatility under the prototype turbulent conditions. The non - uniformity of the turbulence and the transient wind speed changes will generate random loads on the blades and the tower, thus causing random fluctuations

[0026] 2) By using the test method with this wind speed scale correction coefficient, the angle - of - attack distribution of the wind turbine is closer to the actual working conditions of the prototype, making the trailing - edge vortex shedding frequency and characteristics of the blade remain consistent. The trailing - vortex shedding will form periodic aerodynamic loads on the tower and the blade, causing periodic vibrations

[0027] 3) The motion of the floating wind turbine platform will change the relative wind speed and angle of attack of the blades, thereby modulating the aerodynamic load; at the same time, the wind-induced vibration affects the platform motion. The wind speed scale correction method truly preserves the blade parameters, so as to reflect the true characteristics of the coupling effect of aerodynamics and structural dynamics in the prototype.

[0028] (4) Compared with the traditional method of adjusting airfoil parameters to a certain extent of wind load, which is not limited to static thrust similarity and wind action similarity under a single wind speed, the wind speed scale correction method has a wider application range and can meet the scale correction under different wind speeds. Brief Description of the Drawings

[0029] Figure 1 is the wind speed-thrust curve (converted to the prototype) obtained from the model test at the 0-degree pitch angle;

[0030] Figure 2 is the wind speed-thrust curve under prototype conditions at different pitch angles;

[0031] Figure 3 is the test point diagram of the wind speed scale correction coefficient. Detailed Implementation Manner

[0032] The above content of the present invention will be further described in detail below in conjunction with the specific implementation manner, but the scope of the present invention is by no means limited to the following examples:

[0033] Specific implementation method:

[0034] To make the above features and advantages of the present invention more obvious and understandable, a specific embodiment is given below and described in detail in conjunction with the accompanying drawings as follows.

[0035] On the premise of meeting the thrust similarity, the present invention corrects the wind speed according to the Froude criterion.

[0036] Step 1: Use the Froude criterion to scale down the model to obtain the wind speed-thrust relationship under wind tunnel test

[0037] Design the model of the floating wind turbine according to the Froude criterion for scaling, conduct wind tunnel tests on the model, adjust the blade pitch angle and wind speed of the wind turbine, and record the thrust of the wind turbine corresponding to the wind speed at different blade pitch angles of the model.

[0038] Step 2: Fit the wind speed-thrust curves at different blade pitch angles in the wind tunnel test (such as Figure 1 and Figure 2 )

[0039] Based on the measured test values of the thrust of the wind turbine corresponding to the wind speed at different blade pitch angles in Step 1. Use the exponential function to establish a fitting curve of the wind speed-thrust relationship, and establish the thrust F of the model wind turbine at different blade pitch angles θm The functional relationship with the model wind speed V m is as follows:

[0040] F m = f(θ, V m )

[0041] For example, at a blade pitch angle of 90 degrees, the established wind speed - thrust fitting function is:

[0042]

[0043] In the formula, F m,θ＝90° is the model thrust when the blade pitch angle is 90°, and V m,θ＝90° is the wind tunnel test wind speed when the blade pitch angle is 90°.

[0044] Step 3: Convert the target thrust of the prototype to the model based on the Froude criterion

[0045] According to the Froude criterion, convert the target thrust of the prototype to the model scale. The expression of the Froude number is as follows:

[0046]

[0047] In the formula, F r is the Froude number, U is the characteristic velocity, g is the acceleration due to gravity, and L is the characteristic length; when the Froude numbers are the same, the geometric scale relationship is:

[0048]

[0049] In the formula, λ is the scale factor, L m is the characteristic length of the model, and L p is the characteristic length of the prototype.

[0050] Then, to ensure the Froude numbers of the prototype and the model are the same:

[0051] F rm = F rp

[0052] From this, it is confirmed that the ratio of the model speed to the prototype speed is the square root of the scale factor λ, and the ratio of the model thrust to the prototype thrust is the cube of the scale factor λ. From the above derivation, the relationship between the prototype target thrust F p，目标 and the thrust F m，Froude at the model scale is:

[0053] F m , Froude = λ 3 F p，目标

[0054] In the formula, Fp，目标 is the prototype target thrust, F m，Froude is the design target thrust converted to the model result.

[0055]

[0056] In the formula, V p，目标 is the wind speed corresponding to the prototype target thrust, V m，Froude is the wind speed corresponding to the design target thrust converted to the model result according to the Froude criterion.

[0057] Convert the thrust and wind speed of the prototype to the thrust and wind speed under the model scale according to the above formula.

[0058] Step 4: Determine the wind speed of the equal-thrust model under the target thrust

[0059] According to the wind speed-thrust function at the blade pitch angle θ established in Step 2, based on the similarity of thrust, obtain F m，Froude corresponding wind speed V m，等推力 :

[0060] F m，Froude = f(θ, V m,等推力 )

[0061] Step 5: Calculate the wind speed scale correction coefficient

[0062] Correction coefficient: Define the wind speed scale correction coefficient C v as the ratio of the wind speed of the equal-thrust model to the Froude-scaled wind speed:

[0063]

[0064] Step 6. Apply the correction coefficient to the model test to meet the requirements of multi-physical field tests

[0065] Apply the wind speed scale correction coefficient to the model wind speed to ensure that the wind speed in the multi-physical field test of the floating wind turbine meets the thrust similarity principle, thereby improving the reliability of the model test results.

[0066] Figure 3 The following is an example of the test points of the wind speed scale correction coefficient obtained based on the above steps.

Claims

1. A wind speed correction method based on the Froude criterion with similar thrust under scale, characterized in that: The following steps are involved: The first step is to use the Froude criterion scaled model to obtain the wind speed-thrust relationship under the wind tunnel test; The second step is to fit the wind speed-thrust points at different blade pitch angles obtained from the wind tunnel test using an exponential function to obtain a wind speed-thrust curve. The third step is to convert the target thrust and the corresponding wind speed to the model scale according to the Froude criterion; The fourth step is to determine the model wind tunnel test wind speed when the thrust is similar under the target blade pitch angle; The fifth step is to calculate the ratio of the wind speed of the model wind tunnel test under similar thrust to the wind speed of the model after Froude scaling, and obtain the wind speed scale correction coefficient; In the sixth step, the correction coefficient is applied to the model test to meet the requirements of multi-physics field tests.

2. The method for correcting wind speed based on similar thrust under Froude criterion scale according to claim 1, characterized in that: The first step is to design a model of the floating wind turbine according to the Froude criterion, conduct a wind tunnel test on the model, record the thrust values ​​of the wind rotor at different wind speeds and blade pitch angles, and obtain the wind speed-thrust relationship of the model at different blade pitch angles in the wind tunnel test.

3. The method for correcting wind speed based on similar thrust under Froude criterion scale according to claim 1, characterized in that: The second step is as follows: according to the wind tunnel test data, the wind speed and thrust relationship under different blade pitch angles are fitted using an exponential function to determine the wind speed-thrust function relationship under different blade pitch angles; y=a*x b Among them, y represents thrust, a and b represent constants, and x represents wind speed.

4. The method for correcting wind speed based on similar thrust under Froude criterion scale according to claim 1, characterized in that: The fourth step is specifically as follows: select the wind speed-thrust function relationship established in the wind tunnel test based on the blade pitch angle corresponding to the thrust under the target blade pitch angle, and convert the target thrust into the corresponding model wind tunnel test wind speed under the model scale according to the corresponding wind speed-thrust function.

5. The method for correcting wind speed based on similar thrust under Froude criterion scale according to claim 1, characterized in that: The fifth step is specifically as follows: determine the ratio of the model wind tunnel test wind speed determined based on the thrust similarity principle to the wind speed corresponding to the scaled wind speed according to the Froude criterion, which is the wind speed scale correction coefficient under the blade pitch angle; Where: C V is the wind speed scale correction factor at this scale, V m,等推力 To meet the target thrust similarity under the premise of model wind speed in wind tunnel test, V m,Froude The prototype wind speed is converted to the wind speed at the model scale according to the Froude criterion.

6. The method for correcting wind speed based on similar thrust under Froude criterion scale according to claim 1, characterized in that: The sixth step is specifically to apply the wind speed scale correction factor to the model wind speed to ensure that the wind speed in the floating wind turbine multi-physics field test meets the thrust similarity principle, thereby improving the reliability of the model test results.

Images