Wind shear wind speed extrapolation calculation method based on neutral equivalent wind speed

Abstract

The invention relates to a wind shear wind speed extrapolation calculation method based on a neutral equivalent wind speed. The method comprises the following steps: (1) determining input wind speed measurement data; (2) classifying the atmospheric stability, and converting the wind speed at each moment into an equivalent wind speed in a neutral state; (3) performing extrapolation wind speed calculation according to the neutral equivalent wind speed; and (4) outputting an extrapolated wind speed result, and calculating wind shear. According to the method, the wind speed extrapolation error is effectively reduced, the wind speed extrapolation calculation is more accurate, and particularly, the method has outstanding performance in complex terrains or marine environments.

Description

Technical Field

[0001] The invention relates to the technical field of wind resource assessment and wind farm planning, and in particular to a wind shear speed extrapolation calculation method based on neutral equivalent wind speed. Background Art

[0002] In wind farm planning and wind resource assessment, it is crucial to accurately predict wind speed and wind power density at hub height. Traditional wind shear calculation methods mostly use logarithmic wind speed profiles or power law profiles, which have low accuracy under complex terrain and changeable meteorological conditions. In addition, existing wind shear models often assume that the atmosphere is in a neutral stratification, but in fact, the thermal and dynamic characteristics of the atmosphere will change with terrain and weather conditions, affecting the vertical distribution of wind speed. Therefore, it is necessary to introduce neutral equivalent wind speed to improve the wind shear extrapolation model to improve the accuracy of wind speed prediction. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a wind shear speed extrapolation calculation method based on neutral equivalent wind speed with high accuracy and strong applicability.

[0004] In order to solve the above problems, a method for calculating wind shear speed extrapolation based on neutral equivalent wind speed is provided in the present invention, comprising the following steps:

[0005] ⑴ Determine the input wind speed measurement data according to the following formula;

[0006]

[0007] Where: z is the height above the ground, m; v is the wind speed at height z, m / s; k is the Kalman constant, which is 0.4; v * is the friction speed, m / s; is the wind profile stability correction function; v z is the measured wind speed at the wind measurement height z, m / s;

[0008] ⑵ Classify the atmospheric stability and convert the moment-by-moment wind speed into the equivalent wind speed under neutral conditions;

[0009] ⑶According to the neutral equivalent wind speed v 1n Extrapolate wind speed v according to the following formula hub calculate:

[0010]

[0011] Where: Z hub is the hub height, m; z0 is the surface roughness length, which represents the influence of surface characteristics on the height change of wind speed; a=0.0185; g is the acceleration of gravity; z1 is the known height; v1 is the wind speed at height z1, m / s;

[0012] ⑷Output the extrapolated wind speed result and calculate the wind shear.

[0013] In the step ⑴ The relationship with different stabilities is:

[0014]

[0015] In the formula: β = 5;; L is the Monin-Obukhov length, a stability parameter characterizing the atmospheric stability state; v * is the friction velocity, m / s; is the mean potential temperature between two height levels; k is the Kalman constant, with a value of 0.4; g is the acceleration due to gravity; H s is the sensible heat flux, characterizing the intensity of heat exchange between the earth's surface and the atmosphere; z is the height above the ground, m; ρ is the air density, kg / m 3 ; C p is the specific heat, J / (kg.°C); ΔT is the temperature difference between two height levels, °C; Δz is the height difference between two height levels, m.

[0016] Based on the Monin-Obukhov length, when -500 ≤ L ≤ 0, unstable; when 0 < L ≤ 500, stable; when 500 < L, neutral.

[0017] The v * is calculated according to the following formula:

[0018] v * 2 = C d .U 10 2 , and

[0019] In the formula: C d is the drag coefficient; U 10 is the average wind speed at a height of 10 m.

[0020] The present invention has the following advantages compared with the prior art:

[0021] 1. The traditional power-law and logarithmic extrapolation methods do not fully consider the dynamic changes of surface roughness and atmospheric stability, resulting in large errors under complex terrain and variable meteorological conditions. The present invention uses neutral equivalent wind speed and atmospheric stability correction to effectively reduce the wind speed extrapolation error and make the wind speed extrapolation calculation more accurate, especially outstanding in complex terrain or marine environments.

[0022] 2. The stability of the atmosphere and surface roughness are the key factors affecting the variation of wind speed with height. The present invention calculates the atmospheric stability parameter (such as the Monin-Obukhov length) and introduces a correction function The dynamic adjustment of the wind speed extrapolation model can accurately reflect the wind speed changes under unstable, stable and neutral conditions. The introduction of the roughness parameter makes the model more applicable to different terrains, such as plains, hills, forests and oceans.

[0023] 3. The present invention is based on mature physical models and empirical formulas, making the wind speed extrapolation calculation process simple and easy. In applications, the wind speed data obtained from the wind tower can be used for subsequent calculations, reducing the observation requirements and calculation complexity in practical applications and improving the overall application efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0025] Figure 1 It is a flow chart of the present invention.

[0026] Figure 2 This is a wind shear diagram between different altitudes of the present invention. DETAILED DESCRIPTION

[0027] The present invention is based on Monin Obukhov similarity theory and takes into account the dynamic changes of terrain roughness and atmospheric stability, so as to more accurately predict the wind speed at the hub height, reduce the wind speed extrapolation error, and optimize wind farm planning and wind resource utilization.

[0028] like Figure 1 As shown, a method for calculating wind shear speed extrapolation based on neutral equivalent wind speed includes the following steps:

[0029] ⑴ Determine the input wind speed measurement data according to the following formula;

[0030]

[0031] Where: z is the height above the ground, m; v is the wind speed at height z, m / s; k is the Kalman constant, which is 0.4; v * is the friction speed, m / s; is the wind profile stability correction function; v z is the measured wind speed at the wind measurement height z, m / s.

[0032] The relationship with different stability is:

[0033]

[0034] Where: β = 5; L is the Moo length, a stability parameter that characterizes the state of atmospheric stability; v * is the friction speed, m / s; is the mean potential temperature between two altitude levels; k is the Kalman constant with a value of 0.4; g is the acceleration due to gravity; H s is the sensible heat flux, characterizing the intensity of heat exchange between the surface and the atmosphere; z is the height above the ground, in m; ρ is the air density, in kg / m 3 ; C p is the specific heat, in J / (kg.℃); ΔT is the temperature difference between two altitude levels, in ℃; Δz is the altitude difference between two altitude levels, in m.

[0035] Based on the Obukhov length, when -500 ≤ L ≤ 0, it is unstable; when 0 < L ≤ 500, it is stable; when 500 < L, it is neutral.

[0036] Based on the Reynolds stress relationship, using the mean wind speed U at a height of 10 m 10 and its corresponding drag coefficient C d the friction velocity v obtained is * calculated as:

[0037] v * 2 = C d .U 10 2 and

[0038] where: C d is the drag coefficient; U 10 is the mean wind speed at a height of 10 m.

[0039] ⑵ Classify the atmospheric stability and convert the wind speed at each moment into the equivalent wind speed in the neutral state, which performs a neutral equivalent conversion on the atmospheric state at each moment;

[0040] ⑶ According to the neutral equivalent wind speed v 1n extrapolate the wind speed v according to the following formula hub Calculation:

[0041]

[0042] where: Z hub is the hub height, in m; z0 is the surface roughness length, characterizing the influence of surface characteristics on the change of wind speed with height; a = 0.0185; g is the acceleration due to gravity; z1 is the known height; v1 is the wind speed at height z1, in m / s.

[0043] ⑷ Output the result of the extrapolated wind speed and calculate the wind shear.

[0044] The specific process is as follows:

[0045] The wind speed profile model under Monin Obukhov similarity theory is:

[0046]

[0047] Where z is the height above the ground, m; v is the wind speed at height z, m / s; k is the Kalman constant, which is 0.4; v * is the friction wind speed, m / s; is the wind profile stability correction function.

[0048] Integrate the above formula to get

[0049] Assume that the wind speed at height z under neutral conditions is v zn :

[0050] From equations (2) and (3), we can get:

[0051] Where: z is the height above the ground, m; v is the wind speed at height z, m / s; k is the Kalman constant, which is 0.4; v * is the friction wind speed, m / s; is the wind profile stability correction function; v z is the measured wind speed at the wind measurement height z, m / s.

[0052] Then, the atmospheric stability is classified and the moment-by-moment Substituting into the above formula, the moment-by-moment wind speed is converted into an equivalent wind speed under a neutral state. This equivalent wind speed performs a neutral equivalent transformation on the atmospheric state at each moment.

[0053] Secondly, the neutral equivalent wind speed is used for wind speed extrapolation, assuming that the neutral equivalent wind speed v at height z1 is known 1n , then the hub height Z hub Wind speed v hub It can be calculated logarithmically:

[0054]

[0055] Substituting formula (5) into formula (6), we get:

[0056] Finally, using the wind shear exponent α formula, substituting the extrapolated equivalent wind speed into the formula, we get:

[0057]

[0058] Substituting formula (7) into formula (8), we get:

[0059] By using the Charnock model for z0, we get:

[0060]

[0061] Figure 2 This is a graph of wind shear index between different altitude layers. The trend of wind shear index changes between different altitude differences is basically the same. The wind shear index reaches the highest value in winter, the lowest value in summer, and is relatively stable in spring and autumn. The wind shear index between 10-30 meters in altitude is most affected by atmospheric stability and has the most significant seasonal changes. The wind shear index between 30-50 meters in altitude changes relatively little with the seasons, and the wind shear index between 50-70 meters in altitude fluctuates less throughout the year. The atmospheric state is relatively stable in winter and the wind shear index is high, while the atmospheric state is relatively unstable in summer and the wind shear index is low. The greater the difference between altitude layers, the greater the difference in wind shear index between altitudes.

[0062] In summary, the present invention directly calculates the Mo'o length based on friction velocity and sensible heat flux, reflects the stable state of the atmosphere, and is suitable for rapid assessment of atmospheric stability. At the same time, the wind speed is extrapolated based on the wind shear index combined with the neutral equivalent wind speed and terrain roughness to improve the accuracy of the model, which is more suitable for wind speed extrapolation and accuracy improvement under complex terrain and variable atmospheric conditions.

Claims

1. A method for calculating wind shear speed extrapolation based on neutral equivalent wind speed, comprising the following steps: ⑴ Determine the input wind speed measurement data according to the following formula; Where: z is the height above the ground, m; v is the wind speed at height z, m / s; k is the Kalman constant, which is 0.4; v * is the friction speed, m / s; is the wind profile stability correction function; v z is the measured wind speed at the wind measurement height z, m / s; ⑵ Classify the atmospheric stability and convert the moment-by-moment wind speed into the equivalent wind speed under neutral conditions; ⑶According to the neutral equivalent wind speed v 1n Extrapolate wind speed v according to the following formula hub calculate: Where: Z hub is the hub height, m; z0 is the surface roughness length, which represents the influence of surface characteristics on the height change of wind speed; a=0.0185; g is the acceleration of gravity; z1 is the known height; v1 is the wind speed at height z1, m / s; ⑷Output the extrapolated wind speed results and calculate the wind shear.

2. The method for calculating wind shear speed extrapolation based on neutral equivalent wind speed according to claim 1, characterized in that: In the step (1) The relationship with different stability is: Where: β = 5; L is the Moo length, a stability parameter that characterizes the state of atmospheric stability; v * is the friction speed, m / s; is the average potential temperature between two altitude layers; k is the Kalman constant, which is 0.4; g is the gravitational acceleration; H s is the sensible heat flux, which represents the intensity of heat exchange between the surface and the atmosphere; z is the height from the ground, m; ρ is the air density, kg / m 3 ; C p is the specific heat, J / (kg.℃); ΔT is the temperature difference between two altitude layers, ℃; Δz is the difference between two altitude layers, m.

3. The method for calculating wind shear speed extrapolation based on neutral equivalent wind speed according to claim 2, characterized in that: Based on the Obukhov length, when -500 ≤ L ≤ 0, unstable; when 0 < L ≤ 500, stable; when 500 < L, neutral.

4. A method for calculating wind shear speed extrapolation based on neutral equivalent wind speed according to claim 1 or 2, characterized in that: The v * Calculate as follows: v * 2 =C d .U 10 2 ,and Where: C d is the drag coefficient; U 10 is the average wind speed at a height of 10m.

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