Dynamic stall evaluation and prediction method for Gurney flap wind turbine airfoil

Abstract

The present invention discloses a dynamic stall evaluation and prediction method applicable to a Gurney flap wind turbine airfoil, comprising: building a dynamic aerodynamic characteristic measurement test bench in a wind tunnel test section, with an airfoil section fixedly placed in the test section; setting acquisition parameters and opening the wind tunnel; using the test device to collect dynamic and static aerodynamic data of the test airfoil section under different working conditions, and installing a Gurney flap to repeat the above test; data processing to evaluate the aerodynamic performance control effect of the Gurney flap wind turbine; using the empirical constants obtained from the test to substitute into a semi-empirical prediction model to predict the unsteady aerodynamics of the wind turbine airfoil equipped with the Gurney flap. The design of the present invention is applicable to the evaluation and prediction of the dynamic and static aerodynamic data of the airfoil under different working conditions, and evaluates the dynamic aerodynamic performance control effect of the Gurney flap from multiple angles with high accuracy, which has important engineering significance for the study of the aerodynamic characteristics of the wind turbine airfoil.

Description

Technical Field

[0001] The invention relates to the field of wind tunnel test and airfoil aerodynamic characteristic test, and in particular to a dynamic stall evaluation and prediction method suitable for a Gurney flap wind turbine airfoil. Background Art

[0002] As a renewable energy source with abundant reserves, wide distribution, huge development potential and environmental protection, the development and utilization of related technologies are in line with the beautiful vision of adjusting the energy structure, reducing greenhouse gas emissions and alleviating environmental pollution. The main forms of wind energy utilization include wind power generation, wind water lifting, wind heating, etc. Due to its significant advantages such as short infrastructure cycle, low operation and maintenance costs and excellent environmental benefits, wind energy technology has developed rapidly in the past few decades and has gradually become one of the most valuable new energy sources for development. In the actual operation of wind turbines, incoming flow turbulence, gusts, yaw and blade torsion will cause the angle of attack of each section of the blade to change continuously, and the airflow around the blade cannot be changed in real time due to the time delay effect, which leads to the occurrence of dynamic stall and aerodynamic hysteresis. Therefore, in terms of accurately predicting the aerodynamic load of the blade, the influence of dynamic stall cannot be ignored. When the airfoil undergoes unsteady motion, the aerodynamic force of the airfoil will hysteresis with the instantaneous change of the angle of attack, and its stall angle will be larger than that of static state. This phenomenon is called dynamic stall.

[0003] According to the summary of previous studies, dynamic stall involves the processes of fluid attachment, separation and reattachment on the airfoil surface. When the pitching angle of attack is small, the dynamic airfoil changes are similar to the static state, and the flow is in an attached state. When the angle of attack exceeds the static stall angle, a separation vortex appears at the leading edge of the airfoil, and a reverse flow appears at the trailing edge. As the angle of attack continues to increase, the leading edge vortex accumulates and moves chordwise, and the lift continues to increase. When the leading edge vortex surrounds the entire upper surface of the airfoil, the aerodynamic force reaches its maximum value. At this time, dynamic stall occurs, and the leading edge stall vortex begins to fall off and eventually separates from the airfoil at the trailing edge. Until the angle of attack drops to a sufficiently small level, the airflow will reattach to the airfoil. Dynamic stall can be considered to be related to the rapid change of unsteady flow. In wind tunnel tests, the dynamic stall characteristics of the airfoil can be reflected by measuring the instantaneous aerodynamic force of the airfoil during pitch oscillation. On the other hand, making minor modifications to the blades and adding additional parts is one of the best ways to improve the aerodynamic performance of wind turbines. It is necessary to conduct in-depth research on the aerodynamic changes of the airfoil when dynamic stall and Gurney flap interact. Therefore, the present invention designs a method to reveal and evaluate the dynamic stall characteristics of the Gurney flap airfoil through a wind tunnel test. According to the aerodynamic changes of the Gurney flap, a high-precision dynamic stall semi-empirical model is designed to make it suitable for aerodynamic prediction of wind turbine airfoils equipped with Gurney flaps. The obtained results are helpful to better understand and evaluate the dynamic characteristics of wind turbine airfoils equipped with Gurney flaps under high turbulence conditions.

[0004] In the existing research on the dynamic stall of wind turbine airfoils, the description of the dynamic stall phenomenon and the analysis of specific influencing factors are mainly concerned, and the flow control evaluation of aerodynamic attachments and the prediction research of engineering empirical models are rarely involved; the traditional way of evaluating the aerodynamic characteristics of aerodynamic attachments is relatively simple, and generally quantitative analysis is performed by comparing the lift and drag characteristics of wind turbine airfoils with and without attachments. The existing airfoil dynamic stall prediction model needs to assign semi-empirical constants in practical applications, but due to the lack of public test data, the research on LB model aerodynamic prediction is mainly verified by NACA and S series airfoils. For the dynamic aerodynamic prediction of other types of airfoils, the semi-empirical model will have obvious shortcomings. The existing semi-empirical model lacks a specific description of the effect of the Gurney flap on the dynamic stall, and it is necessary to design and establish a prediction method for the dynamic aerodynamic force of the Gurney flap airfoil. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a dynamic stall evaluation and prediction method suitable for a Gurney flap wind turbine airfoil, so as to evaluate the dynamic aerodynamic performance control effect of the Gurney flap from multiple angles and predict the dynamic aerodynamic characteristics with high accuracy, which has important engineering significance for the study of the aerodynamic characteristics of the wind turbine airfoil.

[0006] The object of the present invention is achieved in this way: a dynamic stall evaluation and prediction method applicable to a Gurney flap wind turbine airfoil, comprising the following steps:

[0007] (1) A wind turbine airfoil dynamic stall test bench is built in a wind tunnel test section. The reference airfoil section used in the test is fixed and placed vertically in the wind tunnel test section. A grille is placed at the entrance of the wind tunnel test section to modulate the grille turbulence field simulating the actual wind conditions.

[0008] (2) Adjust the parameters of the servo motor controller to control the servo motor to determine the angle of attack of the airfoil section; set the sampling frequency and sampling time of the pressure sensor;

[0009] (3) Start the wind tunnel, adjust the frequency of the control cabinet to obtain the set wind speed, and collect dynamic and static aerodynamic data of the airfoil section under different turbulence degrees and angles of attack;

[0010] (4) closing the wind tunnel, installing a Gurney flap at the trailing edge of the pressure surface of the test airfoil, repeating step (3), and closing the wind tunnel after the test is completed;

[0011] (5) Data processing, calculating the aerodynamic force of the airfoil under various working conditions, and comparing and analyzing the aerodynamic characteristics of the airfoil after the Gurney flap is installed;

[0012] (6) Comprehensively evaluate the aerodynamic performance control effect of the Gurney flap wind turbine airfoil using weighted average;

[0013] (7) The dynamic stall characteristics of the reference airfoil are predicted by correcting the empirical constants using the semi-empirical model of parameters obtained through wind tunnel experiments;

[0014] (8) The empirical constants are corrected by the semi-empirical model of parameters obtained through wind tunnel experiments to complete the prediction of the dynamic aerodynamic characteristics of the Gurney flap wind turbine airfoil.

[0015] As a further improvement of the present invention, the reference airfoil section is manufactured by 3D printing, and three rows of pressure measuring holes are left on the upper and lower surfaces of the airfoil section. The pressure measuring holes are connected to the vent holes at the bottom of the airfoil through the internal channel of the airfoil, and a groove is left at the bottom of the reference airfoil section; the reference airfoil section is provided with a through hole that goes straight up and down at the 1 / 4 position of the leading edge; the Gurney flap adopts a rectangular cross-section and is processed by 3D printing, and grooves are provided at the upper and lower edges of the Gurney flap to be fixedly connected to the trailing edge of the reference airfoil section. The test model is reasonably designed and easy to operate. When actually conducting aerodynamic test comparisons, it is only necessary to glue the Gurney flap to the trailing edge of the airfoil pressure surface without replacing the airfoil section model, thereby improving the test efficiency.

[0016] As a further improvement of the present invention, the calculation of the aerodynamic force of the airfoil under each working condition in step (5) specifically includes: static lift-to-drag ratio, maximum lift coefficient in the pitch cycle, lift change in the pitch cycle, stability performance after stall in the pitch cycle, and safety and stability performance in the pitch cycle, wherein the stability performance M after stall and the safety and stability performance of the pitch airfoil are calculated using formula (1) and formula (2);

[0017]

[0018]

[0019] Where: α is the actual angle of attack of the airfoil, α stall is the stall angle of the airfoil, A is the oscillation amplitude of the airfoil, and the smaller the M value is, the better the stability of the airfoil after stalling. l is the lift coefficient during the pitch cycle, C m is the pitch moment coefficient during the pitch cycle, max{C l} is the maximum lift coefficient during the pitch cycle, and ζ is the aerodynamic damping coefficient, which are used to quantify the safety and stability performance of the pitch dynamic airfoil.

[0020] As a further improvement of the present invention, the modified empirical constants in step (7) specifically include: for the correction of the pitch-up stall, due to the increase of the vortex intensity, convection will be generated in the chord direction of the airfoil, and at this time, the normal force will have an additional overshoot, and the overshoot value of the normal force in the pitch-up stage From equation (3) and equation (4), we get:

[0021]

[0022]

[0023] Where: B1 is the parameter related to the normal force overshoot value, f1 and f” are the trailing edge separation point and the final trailing edge separation point after delay correction in the semi-empirical prediction model, V x is the shape function of the moving vortex on the normal force, τ is the dimensionless time lag constant of the moving vortex, T v is the eddy current decay time constant, T vL is the dimensionless time for the eddy current to propagate along the chord length, and the subscript n represents the nth sampling moment.

[0024] As a further improvement of the present invention, the modified empirical constants in step (7) specifically include: correction of the reattachment of the airfoil during the downward pitch phase. During the reattachment of the airflow, secondary vortices will be generated and convection will occur. The hysteresis of the aerodynamic force will cause the normal force to drop additionally, thereby generating a low-pressure value. As shown in formula (5) and formula (6);

[0025]

[0026]

[0027] Where: B2 is the parameter related to the low value of normal force in the pitching stage, T r is the dimensionless time lag constant of the reattachment process, V xr is the shape function affected by the normal force during the reattachment phase of the airflow, τ r It is the dimensionless time of the vortex motion on the airfoil surface during the airflow reattachment phase of the airfoil.

[0028] As a further improvement of the present invention, in step (7), the dynamic stall characteristics of the reference airfoil are predicted, and the predicted value of the critical normal force coefficient is consistent with the normal force corresponding to the sudden change in the angle of attack of the static pitch moment of the airfoil.

[0029] As an improvement of the present invention, the prediction of the dynamic stall characteristics of the Gurney flap wind turbine airfoil in step (8) specifically includes that the increase in lift caused by the installation of the flap within a pitch oscillation cycle is regarded as the result of the combined action of the airfoil circulation and the motion vortex, as shown in formulas (7) and (8);

[0030] C circ,n =B3f″C N_gf,0 (7)

[0031]

[0032] Where: C circ,n It is defined as the normal force coefficient due to the additional increase in the amount of circulation caused by the addition of flaps, B3 is the normal force test parameter due to the additional increase in the amount of circulation, and C N_gf,0Defined as the additional normal force coefficient at the static zero angle of attack, V f is the shape function of the effect of the additional vortex motion on the normal force after the Gurney flap is installed, τ f is the dimensionless time parameter of the vortex motion caused by the Gurney flap, and B4 is the normal force test parameter of the vortex intensity increase caused by the installation of flaps.

[0033] The present invention adopts the above technical scheme, and compared with the prior art, the beneficial effects are as follows: the present invention evaluates and predicts the dynamic stall characteristics of the Gurney flap wind turbine airfoil, and provides theoretical and technical support for the design of wind turbine blades; adopts wind tunnel test as the most accurate and reliable way to verify the data, and performs dynamic stall evaluation and prediction of the wind turbine airfoil. Compared with the data obtained by numerical calculation and theoretical analysis, the experimental acquisition method is more direct and has higher accuracy; and the empirical constants obtained through the experiment can more accurately provide assistance for the determination of subsequent empirical constants.

[0034] The present invention comprehensively considers the aerodynamic variation characteristics of the wind turbine airfoil in the entire pitch motion variation range by weighted averaging of various evaluation parameters. In addition to the comparison of lift-drag coefficients, the present invention comprehensively considers the flow development law and vortex development changes, and conducts a more comprehensive comprehensive evaluation by evaluating the stall smoothing characteristics, aerodynamic stability and lift change rate, so as to evaluate the influence of the aerodynamic characteristics of the airfoil.

[0035] Regarding the value of the critical normal force in the existing semi-empirical model, this value is needed in the model to predict the occurrence of leading edge stall, that is, to judge the critical conditions for the development of vortex motion. That is, the critical normal force coefficient is considered to be close to the normal force at the static stall position, and at this time the pitch moment coefficient will also mutate. In the thicker wind turbine airfoil, the corresponding static stall angle and the sudden change angle of the pitch moment coefficient are inconsistent, and the sudden change angle of the pitch moment is obviously greater than the static stall angle. At this time, the critical normal force needs to find another suitable value. The value of the critical normal force in the present invention is consistent with the normal force corresponding to the sudden change angle of the static pitch moment of the airfoil.

[0036] The existing airfoil dynamic stall prediction model needs to assign semi-empirical constants in practical application, but due to the lack of public test data, the research on LB model aerodynamic prediction is mainly verified by NACA and S series airfoils. For the dynamic aerodynamic prediction of other types of airfoils, the semi-empirical model will have obvious shortcomings. For this reason, the present invention obtains static parameters by means of wind tunnel experiments, and assigns parameters in the semi-empirical formula to further expand its applicability, and considers the correction of pitch-up stall and re-attachment in the pitch-down stage in the existing semi-empirical model, which provides a reference for subsequent aerodynamic prediction of other airfoils.

[0037] The existing semi-empirical model lacks a specific description of the effect of the Gurney flap on the dynamic stall, and it is necessary to design and establish a prediction method for the dynamic aerodynamic force of the Gurney flap airfoil. To this end, the present invention regards the increase in lift caused by the installation of flaps within a pitch oscillation cycle as the result of the combined action of the airfoil circulation and the motion vortex according to the different stages of the development of the dynamic stall. The semi-empirical prediction model is made applicable to the wind turbine airfoil equipped with a Gurney flap, and the accuracy of the semi-empirical prediction model designed by the present invention is verified by comparing the results of wind tunnel tests, so that the model can be extended to the unsteady aerodynamic prediction of the wind turbine airfoil equipped with a Gurney flap.

[0038] For the prediction of the unsteady aerodynamics of the wind turbine airfoil equipped with a Gurney flap, the present invention uses the existing empirical model to define the trailing edge separation point reflecting the airfoil separation condition, and combines the normal force coefficient added at the static zero angle of attack moment to predict the additional aerodynamic force of the Gurney flap during the attached flow. At the moment of large angle of attack, the vortex motion intensity function characterizing the airfoil surface is combined with the trailing edge separation point reflecting the airfoil separation condition to define it, that is, it is considered that the additional normal force generated by the vortex in the flap airfoil is positively correlated with the size of the vortex convection aerodynamic hysteresis, so there is no need to add additional reference variables in the semi-empirical model, that is, on the basis of obtaining empirical constants through wind tunnel tests, the aerodynamic coefficient of the Gurney flap wind turbine airfoil can be predicted relatively simply and accurately, which is convenient for practical engineering design applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the overall process of the present invention.

[0040] Figure 2 It is a schematic diagram of the wind turbine airfoil dynamic stall test bench of the present invention.

[0041] Figure 3 It is a schematic diagram of the reference airfoil section used in the test of the present invention.

[0042] Figure 4 It is a schematic diagram of the Gurney flap in the present invention.

[0043] Figure 5 It is a schematic diagram of the connection between the Gurney flap and the reference airfoil section of the present invention.

[0044] Figure 6 The figure is a comparison of the safety and stability performance of the pitch airfoil in different turbulent conditions in the present invention.

[0045] Figure 7 It is the comparison result of the lift prediction value and the test value of the reference airfoil in the pitch cycle in the present invention.

[0046] Figure 8 The figure is a comparison result between the predicted value and the experimental value of the additional lift of the Gurney flap within the pitch cycle in the present invention.

[0047] Fig. 9 It is the predicted value of lift of the Gurney flap airfoil during the pitch cycle in the present invention.

[0048] Among them, 1 is a reference airfoil section, 1-1 is a pressure measuring hole, 1-2 is a through hole, 1-3 is a vent hole, 2 is a Gurney flap, and 2-1 is a groove. DETAILED DESCRIPTION

[0049] like Figure 1 The dynamic stall evaluation and prediction method for a Gurney flap wind turbine airfoil shown includes the following steps:

[0050] (1) A wind turbine airfoil dynamic stall test bench is built in the wind tunnel test section. The reference airfoil section used in the test is fixed and placed vertically in the wind tunnel test section. A grille is placed at the entrance of the wind tunnel test section to modulate the grille turbulence field simulating the actual wind conditions. The specific arrangement can be as follows: Figure 2 As shown. The length, width and height of the test section are 1m, 0.4m and 0.4m respectively. The airfoil used in the test is DTU-LN221, with a designed chord length of 0.15m and a span of 0.395m. The grille is placed at the entrance of the test section. Two pitot tubes are placed at the same section of the leading edge of the airfoil, 0.42m behind the grille, to record the incoming wind speed. The airfoil is also placed 0.42m behind the grille.

[0051] The airfoil section used in the aerodynamic characteristics test is as follows: Figure 3 As shown, the reference airfoil section 1 uses the surface pressure measurement method to perform aerodynamic analysis. The reference airfoil section 1 is manufactured by 3D printing. Three rows of pressure measuring holes 1-1 are left on the upper and lower surfaces of the airfoil section. The pressure measuring holes 1-1 are connected to the vent holes at the bottom of the airfoil through the internal channel of the airfoil, and a groove is left at the bottom of the airfoil section. The airfoil section is provided with a vertical straight-through hole 1-2 at the quarter position of the leading edge. From the leading edge point to the position of 90% of the relative chord length, 38 pressure measuring holes 1-1 are arranged on the suction surface and the pressure surface, a total of 61 pressure measuring holes are arranged and extended to the vent holes 1-3 at the bottom position in the internal channel. The mutual interference between adjacent vent holes 1-3 is reduced by uniform arrangement. The measured pressure is tightly connected to the pressure scanning valve through a plastic hose with an inner diameter of 1.1 mm connected to the vent hole. During the measurement process, ensure that there is no airflow leakage in each plastic hose.

[0052] The Gurney flap used in the test is Figure 4 As shown, the Gurney flap 2 has a rectangular cross section, a rectangular shape, is manufactured by 3D printing, has a height of 1.5% relative chord length (2.25 mm), a thickness of 0.75% relative chord length (1.1125 mm), and a length of 25 cm. It is processed by 3D printing. At the same time, in order to increase the contact area between the Gurney flap and the trailing edge of the airfoil, grooves 2-1 are provided at the upper and lower edges of the Gurney flap 2 to be fixedly connected to the trailing edge of the reference airfoil section 1. The schematic diagram is shown in FIG. Figure 5 shown.

[0053] (2) Adjust the parameters of the servo motor controller to control the servo motor to determine the angle of attack of the airfoil section; and set the sampling frequency of the pressure sensor to 333.3 Hz and the sampling time to 30 s;

[0054] (3) Start the wind tunnel, adjust the frequency of the control cabinet to obtain a set wind speed of 15m / s, and collect dynamic and static aerodynamic data of the airfoil section by changing the grid to collect turbulence of 0.5%, 6.35% and 10.18%. Specifically, the static working condition is 0° to 28° (interval 2°); the dynamic working condition is oscillation amplitude A = 10°, average angle of attack α mean =10°, reduced frequency K=0.0167;

[0055] (4) closing the wind tunnel, installing a Gurney flap at the trailing edge of the pressure surface of the test airfoil, repeating step (3), and closing the wind tunnel after the test is completed;

[0056] (5) Data processing, calculation of the aerodynamic force of the airfoil under various working conditions, including: static lift-to-drag ratio, maximum lift coefficient during the pitch cycle, lift variation during the pitch cycle, stability performance after stall during the pitch cycle, safety and stability performance during the pitch cycle, and comparative analysis of the aerodynamic characteristics of the airfoil after the Gurney flap is installed;

[0057] The stability performance M after stall and the safety stability performance of the pitch airfoil are calculated using equations (1) and (2);

[0058]

[0059]

[0060] Where: α is the actual angle of attack of the airfoil, α stall is the stall angle of the airfoil, A is the oscillation amplitude of the airfoil, and the smaller the M value is, the better the stability of the airfoil after stalling. l is the lift coefficient during the pitch cycle, C m is the pitch moment coefficient during the pitch cycle, max{C l} is the maximum lift coefficient during the pitch cycle, and ζ is the aerodynamic damping coefficient, which are used to quantify the safety and stability performance of the pitch dynamic airfoil.

[0061] The results of the stability performance M after stall are shown in Table 1, which lists the stability performance of the lift coefficient after stall in various working conditions. It can be seen from the table that, as a flow control component installed on the trailing edge of the airfoil, the Gurney flap has little effect on the airfoil after separation stall and does not show any advantage. The installation of the Gurney flap will reduce the stability performance of the lift coefficient after stall. With the increase of turbulence intensity and the increase of pitch motion amplitude, the value representing the stability performance tends to increase, but at higher turbulence intensity, the difference between the Gurney flap airfoil and the reference airfoil will decrease.

[0062] Table 1 Stable performance after pitch cycle stall

[0063]

[0064] Regarding the safety and stability of the airfoil, the present invention uses ζ in formula (2) to characterize the work done by the pitch airfoil on the surrounding flow field during the motion cycle. The area formed by the pitch moment moving in the counterclockwise direction will produce positive aerodynamic damping, and vice versa. When ζ is a negative value, the airfoil is considered to be unstable. When ζ is a positive value, the pitch airfoil is considered to be safe and stable. Figure 6 The following is a comparison chart of the aerodynamic damping coefficient at three different turbulence intensities. In all cases, ζ will deflect positively as the turbulence increases. When the turbulence intensity is 6.35% and 10.35%, installing a Gurney flap will cause the aerodynamic damping coefficient of the DTU-LN221 airfoil to shift positively, making the airfoil more stable. When the turbulence intensity is 6.35%, compared with the baseline airfoil condition, the installation of the Gurney flap causes the aerodynamic damping coefficient to increase by 33.33% (light stall condition) and 58.33% (deep stall condition), respectively. When the turbulence intensity is 10.18%, the corresponding increases are 32.20% (light stall condition) and 34.13% (deep stall condition), respectively.

[0065] (6) Comprehensively evaluate the aerodynamic performance control effect of the Gurney flap wind turbine airfoil; consider the aerodynamic change characteristics of the wind turbine airfoil in the entire pitch motion change range, and adopt the form of weighted average. In the implementation of the present invention, the evaluation parameters specifically include: static lift-to-drag ratio, maximum lift coefficient in the pitch cycle, lift change in the pitch cycle, stability performance after stall in the pitch cycle, and safety and stability performance in the pitch cycle. The comparison of the above parameters can more comprehensively describe the effect of Gurney on dynamic stall, and can be comprehensively evaluated by allocating weights and weighted average. According to actual work, the above five parameters can be set to 30%, 30%, 15%, 15% and 15% in turn, and then quantitatively evaluated.

[0066] (7) The empirical constants are corrected by the parameter semi-empirical model obtained through the wind tunnel experiment to predict the dynamic stall characteristics of the reference airfoil. In the implementation of the present invention, the LB dynamic stall semi-empirical model currently used in engineering practice is taken as an example;

[0067] The pitch-up stall is corrected because the disturbance in the airfoil boundary layer takes a limited time to make the vortex strong enough, causing the leading edge pressure coefficient to exceed the critical value, resulting in dynamic stall. For this reason, in the prediction of the dynamic stall characteristics of the reference airfoil in step (7), when the pitch-up stall occurs, due to the increase in intensity, convection will occur in the chord direction of the airfoil, and the normal force will have an additional overshoot at this time. The overshoot value of the normal force in the pitch-up stage is It can be given by formula (3) and formula (4):

[0068]

[0069]

[0070] Where: B1 is the parameter related to the normal force overshoot value, f1 and f” are the trailing edge separation point and the final trailing edge separation point after delay correction in the semi-empirical prediction model, V x is the shape function of the moving vortex on the normal force, τ is the dimensionless time lag constant of the moving vortex, T v is the eddy current decay time constant, T vL is the dimensionless time for the eddy current to propagate along the chord length; the subscript n represents the nth sampling moment. At this time, B1 takes the value of 1.5, T v The value is 6.0, T vL The value is 2.0.

[0071] At the same time, during the airfoil pitch-down stage, secondary vortices will be generated and convected during the reattachment of the airflow. The hysteresis of the aerodynamic force will cause the normal force to drop additionally, thereby generating a low value. For this reason, the dynamic stall characteristics of the reference airfoil are predicted in step (7). During the airfoil pitch-down stage, secondary vortices will be generated and convected during the reattachment of the airflow. The hysteresis of the aerodynamic force will cause the normal force to drop additionally, thereby generating a low value. It can be shown as formula (5) and formula (6);

[0072]

[0073]

[0074] Where: B2 is the parameter related to the low value of normal force in the pitching stage, T r is the dimensionless time lag constant of the reattachment process, V xr is the shape function affected by the normal force during the reattachment phase of the airflow, τ ris the dimensionless time of the vortex motion on the airfoil surface during the airflow reattachment stage of the airfoil; at this time, B2 takes the value of 3.0, T r The value is 10.0;

[0075] In addition, the predicted value of the critical normal force coefficient in the dynamic stall characteristics prediction of the reference airfoil is consistent with the normal force corresponding to the sudden change in the static pitch moment angle of attack of the airfoil. Figure 7 As shown, Figure 7 The comparison results of the benchmark airfoil test value and the original LB model and the modified model prediction value when TI = 10.18% (oscillation amplitude 10°, average angle of attack 10°, reduction frequency 0.0167). The comparison found that the modified LB model prediction value in the working conditions involved in the figure is closer to the wind tunnel test value than the original LB model, especially in the area before the flow reattachment in the pitch-up stall and the pitch-down phase.

[0076] (8) The empirical constants are corrected by the semi-empirical model of the parameters obtained by the wind tunnel experiment to complete the prediction of the dynamic aerodynamic characteristics of the wind turbine airfoil with a Gurney flap; wherein the dynamic stall characteristics of the wind turbine airfoil with a Gurney flap are predicted in the step (8), and the increase in lift caused by the installation of the flap within a pitch oscillation cycle can be regarded as the result of the combined action of the airfoil circulation and the motion vortex, which can be specifically shown in equations (7) and (8);

[0077] C circ,n =B3f″C N_gf,0 (7)

[0078]

[0079] Where: C circ,n It is defined as the normal force coefficient of the additional increase in the circulation caused by the addition of flaps. B3 is the normal force test parameter of the additional increase in the circulation, and its value is 1.0; C N_gf,0 Defined as the additional normal force coefficient at the static zero angle of attack, V f is the shape function of the effect of the additional vortex motion on the normal force after the Gurney flap is installed, τ f is the dimensionless time parameter of the vortex motion caused by the Gurney flap, B4 is the normal force test parameter of the vortex intensity increase caused by the installation of flaps, and its value is 3.0;

[0080] Similarly, in order to verify the accuracy of the prediction method of the present invention, the aerodynamic prediction value of the method of the present invention is compared with the test value. Figure 8 shown. Figure 8The comparison results of the predicted value and the experimental value of the additional lift of the Gurney flap during the pitch cycle are given (oscillation amplitude 10°, average angle of attack 10°, reduction frequency 0.0167, turbulence intensity 0.5%). It is observed that the change trend of the aerodynamic model prediction value is similar to that of the wind tunnel test value. The lift caused by the installation of flaps during attached flow is mainly attributed to the increase in circulation, so the lift change is small. With the increase of the angle of attack, the additional lift becomes dominated by the vortex motion, and the additional lift coefficient decreases until the moment when the airflow reattaches, and the additional lift increases again.

[0081] contrast Fig. 9 It can be found that the aerodynamic model can predict the lift coefficient of the Gurney flap airfoil more accurately, but there is still a small deviation between the prediction model and the experimental value in the deep stall stage. This is because the LB model itself is not accurately modeled and described in the deep stall area.

[0082] The design of the present invention is suitable for the evaluation and prediction of dynamic and static aerodynamic data of airfoils under different working conditions, and can evaluate the dynamic aerodynamic performance control effect of the Gurney flap from multiple angles with high accuracy, which has important engineering significance for the study of aerodynamic characteristics of wind turbine airfoils. The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and deformations to some of the technical features according to the disclosed technical contents without creative labor, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A dynamic stall evaluation and prediction method for a Gurney flap wind turbine airfoil, characterized in that: The following steps are involved: (1) A wind turbine airfoil dynamic stall test bench is built in a wind tunnel test section. The reference airfoil section used in the test is fixed and placed vertically in the wind tunnel test section. A grille is placed at the entrance of the wind tunnel test section to modulate the grille turbulence field simulating the actual wind conditions. (2) Adjust the parameters of the servo motor controller to control the servo motor to determine the angle of attack of the airfoil section; set the sampling frequency and sampling time of the pressure sensor; (3) Start the wind tunnel, adjust the frequency of the control cabinet to obtain the set wind speed, and collect dynamic and static aerodynamic data of the airfoil section under different turbulence degrees and angles of attack; (4) closing the wind tunnel, installing a Gurney flap at the trailing edge of the pressure surface of the test airfoil, repeating step (3), and closing the wind tunnel after the test is completed; (5) Data processing, calculating the aerodynamic force of the airfoil under various working conditions, and comparing and analyzing the aerodynamic characteristics of the airfoil after the Gurney flap is installed; (6) Comprehensively evaluate the aerodynamic performance control effect of the Gurney flap wind turbine airfoil using weighted average; (7) The dynamic stall characteristics of the reference airfoil are predicted by correcting the empirical constants using the semi-empirical model of parameters obtained through wind tunnel experiments; (8) The empirical constants are corrected by the semi-empirical model of parameters obtained through wind tunnel experiments to complete the prediction of the dynamic aerodynamic characteristics of the Gurney flap wind turbine airfoil.

2. The dynamic stall evaluation and prediction method for a Gurney flap wind turbine airfoil according to claim 1, characterized in that: The reference airfoil section is manufactured by 3D printing, and three rows of pressure measuring holes are left on the upper and lower surfaces of the airfoil section. The pressure measuring holes are connected to the vents at the bottom surface of the airfoil through the internal channel of the airfoil, and a groove is left at the bottom of the reference airfoil section; the reference airfoil section is provided with a vertical straight through hole at the 1 / 4 position of the leading edge; the Gurney flap adopts a rectangular cross-section and is manufactured by 3D printing, and grooves are provided at the upper and lower edges of the Gurney flap to be fixedly connected to the trailing edge of the reference airfoil section.

3. The dynamic stall evaluation and prediction method for a Gurney flap wind turbine airfoil according to claim 1, characterized in that: The calculation of the aerodynamic force of the airfoil under each working condition in step (5) specifically includes: static lift-to-drag ratio, maximum lift coefficient in the pitch cycle, lift change in the pitch cycle, stability performance after stall in the pitch cycle, and safety and stability performance in the pitch cycle, wherein the stability performance M after stall and the safety and stability performance of the pitch airfoil are calculated using formula (1) and formula (2); Where: α is the actual angle of attack of the airfoil, α stall is the stall angle of the airfoil, A is the oscillation amplitude of the airfoil, C l is the lift coefficient during the pitch cycle, C m is the pitch moment coefficient during the pitch cycle, max{C l } is the maximum lift coefficient during the pitch cycle, and ζ is the aerodynamic damping coefficient, which are used to quantify the safety and stability performance of the pitch dynamic airfoil.

4. The dynamic stall evaluation and prediction method for a Gurney flap wind turbine airfoil according to claim 1, characterized in that: The modified empirical constants in step (7) specifically include: correction for the pitch-up stall. Due to the increase in vortex intensity, convection will occur in the chord direction of the airfoil. At this time, the normal force will have an additional overshoot. The overshoot value of the normal force in the pitch-up stage is It is given by equation (3) and equation (4): Where: B1 is the parameter related to the normal force overshoot value, f1 and f” are the trailing edge separation point and the final trailing edge separation point after delay correction in the semi-empirical prediction model, V x is the shape function of the moving vortex on the normal force, τ is the dimensionless time lag constant of the moving vortex, T v is the eddy current decay time constant, T vL is the dimensionless time for the eddy current to propagate along the chord length, and the subscript n represents the nth sampling moment.

5. The dynamic stall evaluation and prediction method for a Gurney flap wind turbine airfoil according to claim 1, characterized in that: The modified empirical constants in step (7) specifically include: the correction of the reattachment of the airfoil during the pitch-down phase. During the reattachment of the airflow, secondary vortices will be generated and convection will occur. The hysteresis of the aerodynamic force will cause the normal force to drop additionally, thus generating a low-profile value. As shown in formula (5) and formula (6); Where: B2 is the parameter related to the low value of normal force in the pitching stage, T r is the dimensionless time lag constant of the reattachment process, V xr is the shape function affected by the normal force during the reattachment phase of the airflow, τ r It is the dimensionless time of the vortex motion on the airfoil surface during the airflow reattachment phase of the airfoil.

6. The dynamic stall evaluation and prediction method for a Gurney flap wind turbine airfoil according to claim 1, characterized in that: In step (7), the dynamic stall characteristics of the reference airfoil are predicted, and the predicted value of the critical normal force coefficient is consistent with the normal force corresponding to the sudden change in the angle of attack of the static pitch moment of the airfoil.

7. The dynamic stall evaluation and prediction method for a Gurney flap wind turbine airfoil according to claim 1, characterized in that: The prediction of the dynamic stall characteristics of the Gurney flap wind turbine airfoil in step (8) specifically includes that the increase in lift caused by the installation of the flap within a pitch oscillation cycle is regarded as the result of the combined action of the airfoil circulation and the motion vortex, as shown in equations (7) and (8); C circ,n =B3 f″ C N_gf,0 (7) Where: C circ,n It is defined as the normal force coefficient due to the additional increase in the amount of circulation caused by the addition of flaps, B3 is the normal force test parameter due to the additional increase in the amount of circulation, and C N_gf,0 Defined as the additional normal force coefficient at the static zero angle of attack, V f is the shape function of the effect of the additional vortex motion on the normal force after the Gurney flap is installed, τ f is the dimensionless time parameter of the vortex motion caused by the Gurney flap, B4 is the normal force test parameter of the vortex strength increase caused by the installation of flaps; C vtx,n is the normal force coefficient of the change in vortex intensity caused by the installation of flaps, the subscript n represents the nth sampling moment; T f is the time constant associated with the separation point.

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