An aerodynamic measurement platform for swept blades used in wind tunnel experiments

Abstract

The invention discloses an aerodynamic measurement platform for a bent-swept blade used in a wind tunnel experiment, comprising a grille, a wind turbine, a data collector, a grille, a hot-wire anemometer and a three-dimensional moving measurement bracket; the wind turbine comprises a bent-swept blade, a rotating wind wheel, a wind turbine tower, a micro DC motor, a supporting base plate and a six-component balance; the grille is placed at the entrance of a wind tunnel test section; the bent-swept blade is connected to the rotating wind wheel; the supporting base plate is fixed to the bottom of the wind tunnel test section, a six-component balance is placed on the supporting base plate, the wind turbine tower is placed on the six-component balance, the micro DC motor is fixed to the top of the wind turbine tower, and the rotating wind wheel is connected to the shaft of the micro DC motor; the signal output ends of the micro DC motor and the six-component balance are electrically connected to the data collector; the invention is flexible and convenient to construct, and other complex terrains and obstacles can be designed and added to the supporting base plate for experiments, so as to simulate a wind tunnel experiment of a bent-swept blade wind turbine in a real environment.

Description

Technical Field

[0001] The invention relates to the field of wind tunnel tests, and in particular to an aerodynamic measurement platform for swept blades used in wind tunnel tests. Background Art

[0002] Wind energy is energy generated by the flow of air and is a renewable energy source. Wind energy reserves are abundant and almost endless. Although only 2% of the solar energy reaching the earth can be converted into wind energy, its total amount is still very huge. The global wind energy is about 130 billion kilowatts, which is more than 10 times the total amount of exploitable hydropower on the earth, and wind energy is widely distributed. Affected by the current dual crises of energy shortage and environmental pollution, the development of pollution-free and renewable wind energy has become a strategic emerging industry actively advocated and supported by countries around the world. In the United States, the wind energy industry in Texas is booming, with 12,400 megawatts of wind power installed capacity, and the contribution of wind energy to the state's power grid is also increasing day by day. In Europe, Denmark's wind power generation accounted for 43.6% of the country's total electricity consumption in 2017, with wind power generation of 14,700 megawatts, setting a new record. By the end of the 20th century, wind power generation in Germany accounted for more than 8% of total power generation. The United Kingdom is located on the west side of the Eurasian continent and the east side of the Atlantic Ocean. It is an island country. Influenced by the North Atlantic Current, it has rich wind energy resources and its government also attaches great importance to the development of wind energy.

[0003] Blades are important components of wind turbines for capturing wind energy. However, the straight-blade wind turbines currently developed have a lower wind energy utilization rate at low wind speeds. Therefore, in order to improve the wind energy utilization rate of wind turbines in low wind speed areas, the wind turbine blades can be optimized. Inspired by the observation that birds can control their flight height and speed at will with the help of their swept-wings at low wind speeds, it is of great significance to study the aerodynamic characteristics of wind turbines with swept-blade blades at low wind speeds.

[0004] At present, there are some problems in the research on wind turbine swept blades: most of the research on wind turbines is numerical simulation calculation, and there are few experimental studies. Without experimental data for comparison, it is difficult for the research to make substantial progress and breakthroughs. The commonly used numerical calculation methods for wind turbines are not suitable for the numerical calculation of wind turbines under turbulent conditions. In the design process of swept blades, there is little research on the determination method of the sweep starting position and the tip offset. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a swept-blade aerodynamic measurement platform for wind tunnel experiments. The platform is flexible and convenient to build, and other complex terrains and obstacles can be designed and added to the supporting base plate for experiments, so as to simulate the real environment of the swept-blade wind turbine wind tunnel experiments.

[0006] The object of the present invention is achieved as follows: a swept blade aerodynamic measurement platform for wind tunnel experiments, comprising a grille, a wind turbine, a data collector, a hot wire anemometer and a three-dimensional movable measurement bracket; the wind turbine comprises a swept blade, a rotating wind wheel, a wind turbine tower, a micro DC motor, a supporting base plate and a six-component balance; the grille is placed at the entrance of the wind tunnel test section; the swept blade is connected to the rotating wind wheel; the supporting base plate is fixed at the bottom of the wind tunnel test section, a six-component balance is placed on the supporting base plate, the wind turbine tower is placed on the six-component balance, the micro DC motor is fixed at the top of the wind turbine tower, and the rotating wind wheel is connected to the shaft of the micro DC motor; the signal output ends of the micro DC motor and the six-component balance are electrically connected to the data collector; the hot wire anemometer is placed directly behind the rotating wind wheel, and the distance is adjusted in the wind tunnel by the three-dimensional movable measurement bracket.

[0007] In order to ensure the performance, load and stability of the wind turbine generator set, the swept blades include multiple forward swept blades and multiple backward swept blades; the sweeping direction of the forward swept blades is the same as the rotation direction of the rotating wind wheel, and the sweeping direction of the backward swept blades is opposite to the rotation direction of the rotating wind wheel.

[0008] In order to meet higher wind energy conversion efficiency, the tip offset of the forward swept blade is 0.1, and the sweep start position is 0.2; the tip offset of the backward swept blade is 0.2, and the sweep start position is 0.4.

[0009] As a further limitation of the present invention, the micro DC motor is fixed to a reserved groove behind the hub of the rotating wind wheel through a copper coupling, and is connected to the tower through a clamping groove.

[0010] In order to facilitate the installation of the test platform, the support base plate is detachably fixed to the bottom of the wind tunnel test section by bolts, and the six-component balance is connected to the support base plate by bolts.

[0011] In order to calibrate the hot-wire anemometer to measure wind speed, thereby avoiding measurement deviations caused by temperature drift and zero-point drift as much as possible, the hot-wire anemometer is connected to the wind turbine via a Pitot tube.

[0012] The present invention adopts the above technical scheme, and compared with the prior art, the beneficial effects are as follows: the platform of the present invention is flexible and convenient to build, and other complex terrains and obstacles can be designed and added to the supporting base plate for experiments, so as to simulate the wind tunnel experiment of the swept-blade wind turbine in the real environment; the supporting base plate can be installed and disassembled in the wind tunnel only by bolts, which is convenient and flexible; the thrust data of the model wind turbine is measured by a six-component balance, the six-component balance is connected to the supporting base plate by bolts, and the six-component balance and the micro DC motor used in the experiment are electrically connected to the data collector, so that the aerodynamic characteristic curve of the model slightly curved blade wind turbine can be accurately measured; the wind turbine blade determines the performance, load and stability of the wind turbine generator set, and further research is needed for the wind turbine blade suitable for low wind speed. The present invention calculates the offset of each blade section from the aerodynamic centerline through parametric modeling, selects the ratio of the tip offset to the radius, the ratio of the sweep starting radial distance to the radius and the equation of the sweep strength, and designs multiple slightly curved wind turbine blades for aerodynamic optimization design to meet higher wind energy conversion efficiency. A six-component balance is used to measure the thrust data of the model wind turbine. Taking into account the bending and sweeping of the blades at the relative radius position, the frontal pressure in the rotation direction of the blades is decomposed, reducing the resistance during rotation. The bending deformation near the tip of the blade can reduce the axial thrust and the peak value of the axial force, which can increase the output power at low wind speeds. Therefore, the six-component balance is fixedly placed under the tower of the model wind turbine, and the six-component balance is electrically connected to the data collector, and the data collector is electrically connected to the host computer, so that real-time thrust data can be read on the host computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the test platform of the present invention.

[0014] Figure 2 Schematic diagram of the swept blade design of the present invention.

[0015] Figure 3 Structural diagram of the curved blade of the present invention.

[0016] Figure 4 The wake flow field result diagram measured by hot wire in the present invention.

[0017] Figure 5 Power coefficient variation curve diagram of the blade and the swept blade in the present invention.

[0018] Among them, 1 is a grille, 2 is a wind turbine, 3 is a hot wire anemometer, 4 is a rotating wind wheel, 5 is a wind turbine tower, 6 is a micro DC motor, 7 is a supporting base plate, 8 is a six-component balance, and 9 is a Pitot tube. DETAILED DESCRIPTION

[0019] like Figure 1The aerodynamic measurement platform of a swept blade for a wind tunnel experiment shown in the figure comprises a grille 1, a wind turbine 2, a data collector, a hot wire anemometer 3 and a three-dimensional moving measurement bracket; the wind turbine comprises a swept blade, a rotating wind wheel 4, a wind turbine tower 5, a micro DC motor 6, a supporting base plate 7 and a six-component balance 8; the grille 1 is placed at the entrance of the wind tunnel test section; the swept blade is connected to the rotating wind wheel 4; the supporting base plate 7 is fixed to the bottom of the wind tunnel test section, a six-component balance 8 is placed on the supporting base plate 7, the wind turbine tower 5 is placed on the six-component balance 8, and the micro DC motor 6 is fixed on the top of the wind turbine tower 5 , the rotating wind wheel 4 is connected to the shaft of the micro DC motor 6, the micro DC motor 6 is fixed to the reserved groove behind the hub of the rotating wind wheel 4 through a copper coupling, and is connected to the wind turbine tower 5 through a clamping groove; the signal output end of the micro DC motor 6 and the six-component balance 8 is electrically connected to the data collector; the hot wire anemometer 3 is placed directly behind the rotating wind wheel 4, and the distance is adjusted in the wind tunnel through a three-dimensional moving bracket; the supporting bottom plate 7 is detachably fixed to the bottom of the wind tunnel test section by bolts, and the six-component balance 8 is connected to the supporting bottom plate 7 by bolts; the hot wire anemometer 3 is connected to the wind turbine 2 through a pitot tube 9. To facilitate the description of the establishment of a coordinate system, Figure 1 The incoming flow direction is defined as the X-axis, the direction along the wind tunnel height is defined as the Z-axis, the direction along the crosswind direction of the incoming flow is defined as the Y-axis, and D is the diameter of the wind turbine.

[0020] Specifically, the rotating wind wheel 4 is composed of a three-blade DTU-LN221 with a radius of 20 cm, the wind turbine tower 5 is composed of a steel rod with a diameter of 16 mm, the micro DC motor 6 is composed of WS-31ZYT57-R (1308B), the six-component balance 8 is ATI's GammaSI-65-5, the data acquisition device is NI's universal data acquisition device USB-6210, the hot wire anemometer 3 is DANTEC's constant temperature hot wire anemometer CTA / HWA, and the three-dimensional transfer and measurement bracket is WNMC400.

[0021] The sweeping direction of the forward curved swept blade is the same as the rotation direction of the rotating wind wheel, and the sweeping direction of the backward curved swept blade is opposite to the rotation direction of the rotating wind wheel; the tip offset of the forward curved swept blade is 0.1, and the sweep starting position is 0.2; the tip offset of the backward curved swept blade is 0.2, and the sweep starting position is 0.4.

[0022] The specific design of the swept blade can be Figure 2 As shown, the present invention adopts the equation shown in formula (1) for parameterized design.

[0023]

[0024] Where Z is the offset of the blade section from the aerodynamic centerline of the original straight blade, r r is the radial distance of the blade section, rs is the radial distance from the starting position of the sweep, R is the radius of the wind wheel, P s is the ratio of blade tip offset d to rotor radius (P s =d / R), M is the sweep mode, P r is the ratio of the radial distance of the cross section to the radius (P r =r r / R), P rs is the ratio of the sweep start radial distance to the radius (P rs =r s / R). The sweep mode M defines the sweep strength. Increasing the M value will reduce the sweep strength, while reducing the M value to close to 1 will increase the sweep strength. In order to represent the average sweep strength, the M value of the blade design of the present invention is 2. In formula (1), R×P s The tip offset is given. In order to test the power characteristics of the swept blade, two tip offsets and two swept start positions are designed, as shown in Table 1:

[0025] Table 1 Swept blade design

[0026]

[0027] There are 8 wind turbine blades in total, 4 with forward curved design and 4 with backward curved design. The offset of each airfoil section of the blade is calculated by the sweep equation, and the sweep model is built in UG, such as Figure 3 As shown, it can be seen from the figure that the sweeping direction of the forward curved swept blade is the same as the rotation direction of the wind wheel, and the sweeping direction of the backward curved swept blade is opposite to the rotation direction.

[0028] The aerodynamic characteristics of wind turbine blades with a tip offset of 10% of the radius length and a sweep start position of 20% of the radius length are significantly improved. Regardless of whether it is a forward-swept design or a swept-back design, the thrust coefficient and power coefficient of the wind turbine are improved compared with the original straight-blade wind turbine. Among them, the forward-swept blade wind turbine with a tip offset of 10% of the radius length and a sweep start position of 20% of the radius length, namely the F2010 swept-blade wind turbine, has the largest increase in power coefficient compared with the original straight-blade wind turbine, increasing by 2.167%, and the thrust coefficient increased by 2.478%. The power coefficient of the B2010 wind turbine with swept blades also increased by 0.497%, and the thrust coefficient increased by 0.384%.

[0029] A method for testing aerodynamic performance of a wind turbine with swept blades for wind tunnel experiments, comprising:

[0030] Step 1) Designing the swept blades of a wind turbine using 3D modeling software, modeling the wind turbine tower and supporting base plate, and performing 3D printing using a 3D printer;

[0031] Step 2) constructing a swept blade aerodynamic measurement platform for wind tunnel experiments in a wind tunnel (the present invention);

[0032] Step 3) Equipment safety inspection includes: whether the fastening bolts are loose; whether the model wind turbine is fixedly installed; whether the current conditioning circuit and the speed conditioning circuit are correctly connected and operate normally, ensuring that each pipeline remains unobstructed and unblocked; ensuring that the inside of the wind tunnel is clean;

[0033] Step 4) setting the sampling frequency and sampling time of each aerodynamic characteristic measurement collector, specifically including: the sampling frequency of the power acquisition data collector is 10kHz, and the sampling time is 5s; the sampling frequency of the six-component balance is 1kHz, and the sampling time is 10s; the sampling frequency of the hot wire anemometer is 5kHz, and the sampling time is 20s;

[0034] Step 5) Start the wind tunnel and adjust the frequency of the control cabinet to obtain a wind speed of 7m / s;

[0035] Step 6) adjusting the parameters to obtain the set speed, and sequentially collecting the thrust coefficient and power coefficient of the benchmark wind turbine at multiple different speeds (corresponding to the range of blade tip speed ratio 1 to 5);

[0036] Step 7) adjusting the parameters to obtain the set speed, collecting the wake flow field distribution of the benchmark wind turbine, and closing the wind tunnel after completion;

[0037] Step 8) After repeating steps (4) and (5), adjust the parameters to obtain the set speed, and collect the thrust coefficient and power coefficient of the swept wind turbine at different speeds (corresponding to the range of blade tip speed ratio 1 to 5) in turn;

[0038] Step 9) adjusting the parameters to obtain the set speed, collecting the wake flow field distribution of the swept wind turbine when the blade tip ratio is 4.6, and closing the wind tunnel after completion;

[0039] Step 10) Compare and analyze the aerodynamic characteristics of each wind turbine under different working conditions to obtain the design of the optimal swept wind turbine.

[0040] The wind turbine power measurement in steps 6) and 8) is carried out by:

[0041]

[0042] In formula (2), ρ is the air density, U hub is the average wind speed at the center of the rotating wind rotor, r is the radius of the wind rotor, ω is the speed of the wind turbine, C pow is the power coefficient under different working conditions, T j is the instantaneous thrust corresponding to the working condition, f T (I,ω) is the relationship between the output shaft power of the generator used in the test, the output current I and the speed ω. T(I,ω)=-0.1298+0.07518I+0.001066ω+0.001606I 2 +0.001425Iω+5.25x10 -8 ω 2 .

[0043] Similarly, the thrust coefficient measurement in steps 6) and 8) is processed using formula (3);

[0044]

[0045] In formula (3), ρ is the air density, U hub is the average wind speed at the center height of the wind turbine rotor, r is the rotor radius, n is the number of thrust data collected, T j is the instantaneous thrust corresponding to the working condition, C Ti is the thrust coefficient under different working conditions.

[0046] In both steps 7) and 9), a Pitot tube calibrated hot wire anemometer is used to measure the wind speed in the wake flow field measurement, and the measuring points on the vertical plane directly behind the rotating wind rotor tower and the horizontal plane at the center height of the rotating wind rotor of the wind turbine are measured. The interval between adjacent measuring points is 5% of the relative radius of the rotating wind rotor, that is, the adjacent interval is 1 cm, and the distance between the measuring points is from the center of the rotating wind rotor to 1.5 times the relative radius of the rotating wind rotor.

[0047] The accuracy of the wake flow field measurement of the benchmark wind turbine is verified by using equation (4) in the wake flow field measurement using a hot wire anemometer and a three-dimensional measurement device.

[0048]

[0049] In formula (4), Y is the lateral coordinate of the wake; U N0 is the dimensionless value of the average wind speed of the wake, U D is the maximum value of dimensionless wind speed loss, U D The value should be greater than 0; D r To represent 0.5U D The width of the trail at y r is the starting lateral coordinate of the wake center.

[0050] Take X=2D and blade tip speed ratio λ=4.67 as an example, Figure 4 This is the result of the wake flow field measured by hot wire in the aerodynamic performance optimization design method of the swept blade wind turbine. The swept blade is also selected with r s For example, d / r = 0.2, d / r = 0.1, and M = 2, it is found that the swept blade increases the power coefficient while the wake loss also becomes larger. Figure 5As shown in the figure, the power coefficient change curves of straight blades and swept blades show that at high tip speed ratios, the swept blades gradually increase the output power of the wind turbine. At yaw of 20°, especially under 0.5% low turbulence intensity inflow, the swept blades have a significant increase in the output power of the wind turbine. It can be seen from the figure that the output power of the swept blades and straight blades is almost the same at low tip speed ratios. As the tip speed ratio increases to a larger value, the power characteristics of the swept blade wind turbine are improved compared to the straight blade wind turbine, and the output power is increased, especially at yaw, the output power of the swept blade wind turbine increases significantly.

[0051] The present invention provides a swept-blade aerodynamic measurement platform for wind tunnel experiments. The platform is flexible and convenient to build, and other complex terrains and obstacles can be designed and added to the supporting base plate for experiments, so as to simulate the swept-blade wind turbine wind tunnel experiments in real environments.

[0052] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed in the present invention, technicians in this field can make some substitutions and deformations to some technical features therein according to the disclosed technical content without creative labor, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A swept blade aerodynamic measurement platform for wind tunnel experiments, characterized in that: It includes a grille, a wind turbine, a data collector, a hot-wire anemometer and a three-dimensional mobile measurement bracket; the wind turbine includes a curved blade, a rotating wind wheel, a wind turbine tower, a micro DC motor, a support base plate and a six-component balance; the grille is placed at the entrance of the wind tunnel test section; the curved blade is connected to the rotating wind wheel; the support base plate is fixed at the bottom of the wind tunnel test section, a six-component balance is placed on the support base plate, the wind turbine tower is placed on the six-component balance, the micro DC motor is fixed at the top of the wind turbine tower, and the rotating wind wheel is connected to the shaft of the micro DC motor; the signal output ends of the micro DC motor and the six-component balance are electrically connected to the data collector; the hot-wire anemometer is placed directly behind the rotating wind wheel, and the distance is adjusted in the wind tunnel through the three-dimensional mobile measurement bracket; The swept blades include a plurality of forward swept blades and a plurality of backward swept blades; the sweeping direction of the forward swept blades is the same as the rotation direction of the rotating wind wheel, and the sweeping direction of the backward swept blades is opposite to the rotation direction of the rotating wind wheel; The tip offset of the forward swept blade is 0.1, and the sweep start position is 0.2; the tip offset of the backward swept blade is 0.2, and the sweep start position is 0.

4.

2. The aerodynamic measurement platform for a swept blade used in a wind tunnel experiment according to claim 1, characterized in that: The micro DC motor is fixed to a reserved groove behind the hub of the rotating wind wheel through a copper coupling, and is connected to the tower through a clamping groove.

3. The aerodynamic measurement platform for swept blades used in wind tunnel experiments according to claim 1, characterized in that: The supporting bottom plate is detachably fixed to the bottom of the wind tunnel test section by bolts, and the six-component balance is connected to the supporting bottom plate by bolts.

4. The aerodynamic measurement platform for swept blades used in wind tunnel experiments according to claim 1, characterized in that: The hot wire anemometer is connected to the wind turbine through a Pitot tube.

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