Aerodynamic optimization design method for large vertical axis wind turbine wind tunnel scale model blade based on DMST theory

Abstract

The application discloses a large vertical axis fan wind tunnel scale model blade aerodynamic optimization design method based on a DMST theory, and comprises the following steps: determining scale parameters according to wind tunnel test similarity criteria; selecting an optimized airfoil with matched aerodynamic characteristics under low Reynolds number based on the lift-drag ratio characteristics of a prototype blade; constructing an aerodynamic performance model based on a double disk multi-flow management theory, calculating the theoretical thrust coefficient of the prototype and the optimized airfoil, and performing matching verification; carrying out a force-measuring and pressure-measuring test in a wind tunnel, stripping the pure thrust of the blade by subtracting the total thrust of the whole machine from the thrust vector of the tower column; and comparing and verifying the aerodynamic load matching degree by comparing the measured thrust coefficient with the theoretical thrust coefficient. The application combines airfoil optimization, DMST theory verification and wind tunnel test stripping verification, effectively eliminates the Reynolds number effect in the scale test, realizes high-precision matching of the aerodynamic load of the vertical axis fan scale model blade, and improves the reliability of the wind tunnel test data.

Description

Technical Field

[0001] This invention belongs to the field of wind power generation and structural wind engineering technology, specifically involving an aerodynamic optimization design method for blades of a scaled-down model of a large vertical axis wind turbine based on the dual-disc multi-flow management theory (DMST). It is applicable to the aerodynamic performance research and wind tunnel test verification of large vertical axis wind turbines under shutdown fault conditions or normal operation conditions. Background Technology

[0002] With the advancement of global energy structure transformation and carbon neutrality goals, vertical axis wind turbines (VAWTs) are gradually becoming an important component of distributed energy systems due to their advantages such as simple structure, ability to capture wind from any direction without a yaw mechanism, and ease of ground installation and maintenance. Wind tunnel testing is an indispensable and crucial step in the research and development and wind-resistant design of wind turbines, providing important experimental data for predicting structural loads, assessing safety, and optimizing performance.

[0003] Due to the enormous physical size of large vertical axis wind turbines, and constrained by the cross-sectional dimensions of wind tunnel laboratories and the cost of model fabrication, significant geometric scaling down of the prototype is necessary for wind tunnel testing. However, the geometrically scaled-down turbine blades, while satisfying geometric and kinematic similarity, result in a sharp decrease in the Reynolds number of the flow field. This severe "Reynolds number effect" causes significant differences in the aerodynamic characteristics (such as lift and drag coefficients) of the model blade surface compared to the prototype blade. Consequently, the aerodynamic loads experienced by the directly geometrically scaled model in wind tunnel testing are much greater than the actual loads that satisfy the scaling ratio. Specifically, at low Reynolds numbers, laminar separation is more likely to occur in the boundary layer of the airfoil surface, causing the blade aerodynamic performance to deviate significantly from the design state at high Reynolds numbers. This results in key load parameters such as thrust and torque measured in wind tunnel tests failing to accurately reflect the actual stress conditions of the prototype.

[0004] In existing technologies, thrust matching techniques for scaled-down models of horizontal axis wind turbines (HAWT) have been studied to some extent. However, vertical axis wind turbines, with their blades perpendicular to the ground, experience extremely complex unsteady aerodynamic disturbances when dealing with crosswinds, such as three-dimensional vortex evolution, flow separation, and dynamic stall. Traditional scaled-down design methods based on geometric similarity cannot effectively solve the load distortion problem of scaled-down models of vertical axis wind turbines at low Reynolds numbers. This results in test data that cannot accurately reflect the stress conditions of the prototype under extreme operating conditions, leading to significant uncertainty and risks in structural safety design.

[0005] Therefore, how to overcome the Reynolds number limitation and achieve high-precision matching between the aerodynamic load of the vertical axis wind turbine model and the theoretical load of the prototype in wind tunnel scale-down tests has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide an aerodynamic optimization design method for the blades of a scaled-down model of a large vertical axis wind turbine based on DMST theory. By selecting low Reynolds number alternative airfoils through the principle of similarity between lift and drag coefficients, and verifying the method with numerical simulation based on DMST theory, a high-precision matching between the test load of the scaled-down model and the theoretical load of the prototype is finally achieved, effectively solving the problem of aerodynamic load distortion caused by the Reynolds number effect in the scaled-down test.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for aerodynamic optimization design of blades in a scaled-down wind tunnel model of a large vertical axis wind turbine based on DMST theory includes the following steps: Step 1: Determine the scaling parameters for the wind tunnel test based on the wind tunnel test similarity criteria and the wind tunnel size and wind speed parameters; Step 2: Based on the lift-drag coefficient at the position of maximum lift-drag ratio of the prototype blade, and combined with the multi-Reynolds number analysis function of Profili software, select an optimized airfoil whose aerodynamic characteristics match those of the prototype blade at low Reynolds number. Step 3: Based on the dual-disc multi-flow theory, construct the aerodynamic performance model of the vertical axis wind turbine, calculate the theoretical thrust coefficients of the prototype airfoil and the optimized airfoil at the corresponding Reynolds number, and verify whether the aerodynamic load of the optimized airfoil satisfies the scaling ratio matching relationship. Step 4: Conduct a force-pressure test on the wind turbine in the wind tunnel. Using the total thrust and tower thrust measured on the whole turbine model, separate the pure thrust actually experienced by the blades. Step 5: Compare the measured thrust coefficient with the theoretical thrust coefficient of the prototype model calculated in Step 3 to verify the matching degree of the optimized blade aerodynamic load, thereby eliminating the Reynolds number effect in the scale test.

[0008] Furthermore, in step one, the method for determining the various scaling parameters of the wind tunnel test is as follows: Obtain the geometric parameters and operating environment wind speed of the prototype vertical axis wind turbine; set the wind speed scaling ratio based on the cross-sectional area of ​​the wind tunnel test section and the maximum wind speed. and geometric scaling ; The geometric scaling ratio The determination needs to take into account both the size of the wind tunnel test section and the blockage ratio. Constraints; The blocking ratio calculation formula is: in: The projected area of ​​the model along the windward direction; This represents the cross-sectional area of ​​the wind tunnel test section; Wind load scaling ratio of the experimental scaled model The calculation formula is: in: This refers to the wind speed scaling ratio; This is the air density ratio.

[0009] Furthermore, in step two, the method for selecting an optimized airfoil whose aerodynamic characteristics match those of the prototype blade at low Reynolds numbers is as follows: Extracting the prototype's airfoil at high Reynolds numbers Lift coefficient at the bottom With drag coefficient With angle of attack The change curve data; At a given low Reynolds number Within the specified range, using the multi-Reynolds number analysis function of Profili software, the lift coefficient of the aerodynamic characteristic curves of each airfoil in the candidate airfoil library is calculated. With drag coefficient ; The optimal replacement airfoil for low Reynolds number was selected based on the following criteria: it meets the drag coefficient requirement. and Under the condition that the difference is less than the set first threshold range, the lift coefficient and The difference is also less than the set second threshold range.

[0010] Furthermore, in step three, the method for verifying whether the aerodynamic loads of the optimized airfoil satisfy the scaling ratio matching relationship is as follows: S31: Discretize the swept region of the vertical axis wind turbine rotor into multiple adjacent flow tube units, and divide each flow tube into two cascaded actuator disks in the upwind and downwind regions; the induced velocities of each flow tube in the upwind and downwind regions are respectively represented by... and This indicates that the middle section is balanced by wind speed. express; S32: The average force acting on the rotor along the incoming flow direction is calculated using the momentum theorem, and the average force acting on the blade airfoil is calculated using the blade element theorem; the force balance equations are solved simultaneously and iteratively to obtain the velocity induction factor along the incoming flow direction, and then the thrust and torque of the wind turbine in operation or shutdown state are obtained to obtain the thrust coefficient. and torque coefficient ; S33: Load factor matching verification, defining the relative error of the thrust factor. Relative error of torque coefficient : in: The thrust coefficient of the prototype airfoil at high Reynolds numbers; To optimize the thrust coefficient of the airfoil at low Reynolds numbers; The torque coefficient of the prototype airfoil at high Reynolds numbers; To optimize the torque coefficient of the airfoil at low Reynolds numbers; like and This confirms that the low Reynolds number airfoil can be used as a scaled-down model blade for wind tunnel testing; if or If so, return to step two to adjust the weights or expand the candidate airfoil library for re-screening; where: and These are the preset engineering tolerance limits for the thrust coefficient and torque coefficient, respectively.

[0011] Furthermore, in step S32, the method for obtaining the thrust and torque of the wind turbine in operation or shutdown states based on the dual-disc multi-flow management theory includes the following steps: S321: Calculate the aerodynamic force of a single leaf element: for any altitude of chord length is The blade element, at a given azimuth angle Below, local relative wind speed for: in: The local relative wind speed sensed by the blade micro-element; The local inflow velocity is recorded on the disk in the upwind area as follows. In the downwind area of ​​the board, it is recorded as ; The radius of rotation of the wind turbine; Let be the linear velocity of the rotation of the blade element; The azimuth angle of the blade; The lift coefficient of an airfoil is obtained using aerodynamic airfoil data. and drag coefficient Calculate the normal coefficient and tangential coefficient : in: Angle of attack, i.e., local relative wind speed The angle between the blade chord and the blade chord; The normal and tangential force components on the leaf element are as follows: in: and For a blade element at a specific azimuth angle The instantaneous normal force and instantaneous tangential force experienced at that moment; air density; This is the chord length of the blade; The height of the selected blade element; S322: Calculate instantaneous values ​​of aerodynamic thrust and torque: a single blade at a specific azimuth angle. At that time, the instantaneous thrust contribution of the current flow tube in the wind direction is: For those with A wind turbine with 10 blades, in a space with a width of The height is Inside the flow tube; the time-averaged aerodynamic thrust acting on the flow tube is: in: For a single blade passing through the azimuth angle At that time, the instantaneous thrust component generated along the direction of the incoming wind; This refers to the infinitesimal element of the average thrust acting on a specific flow tube, calculated based on leaf element theory. This represents the total number of blades on the wind turbine. and This represents the boundary of the azimuth integral interval corresponding to the flow tube; The instantaneous torque generated by a single blade in this micro-element segment for: The time-averaged torque contribution within this flow tube section is: S323: Execute the DMST dual-disc thrust iterative solution process: In the upwind region, the free-flow wind speed is... The induced velocity when passing through the upper half of the plate is The speed at which it leaves the first actuation plate and enters the intermediate balance zone is The momentum thrust of the upwind flow tube is: in: The axial induction factor in the upwind region; The wind speed in the equilibrium zone between the upwind and downwind areas; Let be the current windward cross-sectional area of ​​the flow tube; air density; The mean aerodynamic thrust of the blade element in the upwind region is: in: For the leaf element micro-element in the upwind area at a specific azimuth angle The instantaneous normal force experienced at that time; For the leaf element micro-element in the upwind area at a specific azimuth angle The instantaneous tangential force experienced at that time; Through residual iteration, let Solve for the actual flow tube in the upwind region Thus, the total thrust in the upwind region is obtained. and torque contribution ; In the downwind area, the equilibrium zone speed As the new free-flow velocity, the induced velocity when passing through the lower half of the disk is: The final wake velocity is The momentum thrust of the flow tube in the downwind region is: in: The axial induction factor in the downwind region; The final wake velocity of the airflow after passing through the entire wind turbine; The mean aerodynamic thrust of the blade element in the downwind region is: in: For leaf element micro-elements in the downwind area at a specific azimuth angle The instantaneous normal force experienced at that time; For leaf element micro-elements in the downwind area at a specific azimuth angle The instantaneous tangential force experienced at that time; make The iterative solution yields the value of each flow tube in the downwind region. Thus, the total thrust in the downwind region is obtained. and torque contribution ; S324: Calculate the total thrust, torque, and dimensionless coefficients of the wind turbine: Total thrust acting on the entire vertical axis wind turbine. The sum of the upwind thrust and the downwind thrust: Thrust coefficient for: Total torque for: Torque coefficient for: in: This refers to the sweeping area of ​​the wind turbine.

[0012] Furthermore, the efficiency of wind turbines in extracting wind energy is measured by the power coefficient, which in a dimensionless system is transformed into: in: This is the power coefficient, i.e., wind energy utilization rate; For the tip speed ratio, This represents the ratio of the fan speed to the incoming air velocity. Let be the linear velocity of the rotation of the blade element; The free-flow wind speed in the upwind area.

[0013] Furthermore, in step four, the method for separating the actual pure thrust experienced by the blade is as follows: The whole-machine force-pressure measurement model includes blades, connecting rods, and tower columns, but does not consider the thrust on the connecting rods; The total thrust of the model under different overall wind direction angles was measured in a wind tunnel using a high-frequency base force balance. ; Pressure testing was conducted by installing pressure measuring tubes on the tower column to obtain the resistance experienced by the tower column. ; The pure thrust acting on the actual blade is separated by vector subtraction. , is represented as: .

[0014] Furthermore, in step five, the measured thrust coefficient is compared with the theoretical thrust coefficient of the prototype model calculated in step three. The method to verify the matching degree of the optimized blade aerodynamic load is as follows: Based on the blade thrust measured by the original airfoil scaled-down model and the optimized airfoil scaled-down model, and the reference area of ​​the scaled-down model, the measured thrust coefficient of different models in wind tunnel tests was calculated. The measured thrust coefficient is compared with the theoretical thrust coefficient obtained by numerical simulation in step three to verify the degree of matching between the aerodynamic load of the optimized blade under low Reynolds number conditions and the prototype under high Reynolds number conditions. This verifies whether the optimized airfoil can eliminate the Reynolds number effect in the scaled-down test compared to the original airfoil scaled-down model.

[0015] The beneficial effects of this invention are as follows: This invention presents an aerodynamic optimization design method for blades of a scaled-down wind tunnel model of a large vertical axis wind turbine based on DMST theory. Through a complete closed loop integrating airfoil optimization, DMST theory verification, and wind tunnel stripping verification, the following technical effects are achieved: (1) Eliminate load distortion caused by Reynolds number effect: In response to the problem of sharp drop in Reynolds number in vertical axis wind turbine scaling test, the aerodynamic performance of the scaling model was fundamentally improved by selecting an optimized airfoil with aerodynamic characteristics matching at low Reynolds number. (2) Achieve high-precision matching of aerodynamic loads: Calculate the theoretical thrust coefficients of the prototype and optimized airfoil at the corresponding Reynolds number using DMST theory, and verify them quantitatively through relative error scalar to ensure that the theoretical scale matching relationship is met. (3) Accurately obtain pure blade thrust: By using the vector stripping method of total thrust of the whole machine and tower thrust, the aerodynamic interference of non-blade components such as tower is eliminated, and accurate measured thrust data of blades is obtained; (4) Form a complete verification closed loop: Compare and verify the measured thrust coefficient with the DMST theoretical calculation results to ensure that the aerodynamic load of the optimized blade at low Reynolds number is highly matched with that of the prototype at high Reynolds number, thereby effectively eliminating the Reynolds number effect in the scaled-down test and providing a systematic and verifiable optimization design method for the scaled-down model test of large vertical axis wind turbines.

[0016] In summary, this invention presents an aerodynamic optimization design method for blades of a scaled-down model of a large vertical axis wind turbine based on DMST theory. By selecting alternative airfoils with low Reynolds numbers through the principle of similarity between lift and drag coefficients, and verifying the method through numerical simulation using DMST theory, a high-precision matching between the test load of the scaled-down model and the theoretical load of the prototype is finally achieved, effectively solving the problem of aerodynamic load distortion caused by the Reynolds number effect in the scaled-down test. Attached Figure Description

[0017] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 A schematic diagram of the force-pressure measurement model of a vertical axis fan; (a) front view; (b) top view; Figure 2 This is a flowchart of the aerodynamic optimization design method for a scaled-down model blade of a large vertical axis wind turbine based on DMST theory, as described in this invention. Figure 3 A comparison of lift and drag coefficients between the prototype airfoil NACA0018 and the scaled-down optimized airfoil ONERA_OA206; (a) lift coefficient; (b) drag coefficient; Figure 4 Schematic diagrams of scaled-down airfoil cross-sections for NACA0018 and ONERA_OA206; (a) ONERA_OA206; (b) NACA001; Figure 5 A comparison chart of thrust coefficients for different airfoil models. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0019] In this embodiment, the proposed aerodynamic optimization design method for scaled-down wind tunnel models of large vertical axis wind turbines based on DMST theory is applied. A 35kW large vertical axis wind turbine is used as the research object, with its prototype blades adopting the NACA0018 symmetrical airfoil. The rotor radius is 4.33m, the blade height is 12m, the tower height is 8m, the tower diameter is 0.9m, the rotor radius is 5m, and the swept area is 120m². 2 The aim is to address the Reynolds number effect problem in scaled-down wind tunnel tests at shutdown (0 rpm). The force-pressure measurement model of the entire vertical axis wind turbine used is as follows: Figure 1 As shown.

[0020] like Figure 2 As shown in the figure, this embodiment presents an aerodynamic optimization design method for a scaled-down model blade of a large vertical axis wind turbine based on DMST theory, which includes the following steps.

[0021] Step 1: Determine the scaling parameters for the wind tunnel test based on the wind tunnel test similarity criteria and the wind tunnel size and wind speed parameters.

[0022] Specifically, in this embodiment, the method for determining the various scaling parameters of the wind tunnel test is as follows.

[0023] Obtain the geometric parameters and operating environment wind speed of the prototype vertical axis wind turbine. Specifically, the geometric parameters of the prototype vertical axis wind turbine include the rotor radius. Leaf chord length and blade height The operating environment wind speed is expressed as Based on the cross-section of the wind tunnel test section Accumulate the maximum wind speed and set the wind speed scaling ratio. and geometric scaling .

[0024] Geometric scaling The determination needs to take into account both the size of the wind tunnel test section and the blockage ratio. Constraints; The blocking ratio calculation formula is: in: The projected area of ​​the model along the windward direction; This represents the cross-sectional area of ​​the wind tunnel test section.

[0025] Wind load scaling ratio of the experimental scaled model The calculation formula is: in: This refers to the wind speed scaling ratio; This is the air density ratio.

[0026] Specifically, in this embodiment, the wind speed scaling ratio for the wind tunnel test is determined to be 1:2. This parameter is set based on the wind tunnel's maximum wind speed carrying capacity, i.e. The determination of the geometric scaling ratio requires comprehensive consideration of the wind tunnel test section dimensions, model dimensions, and blockage ratio constraints. The wind tunnel blockage ratio is defined as the ratio of the model's projected area along the wind direction to the cross-sectional area of ​​the wind tunnel test section, with a limit requirement of no more than 5%. The wind tunnel test dimensions in this embodiment are as follows: Under the condition of meeting the wind tunnel blockage ratio requirements, the geometric scaling ratio is set. The determination of the air density ratio is based on the principle of air density equivalence between conventional atmospheric boundary layer wind fields and low-speed wind tunnel tests. According to similarity theory, when the geometric scaling ratio and velocity scaling ratio meet specific conditions, dynamic similarity can be achieved by maintaining constant air density. Specifically, the ratio of the air density of conventional atmospheric boundary layer wind to the air density of the wind tunnel test section is... Based on the established scaling ratio parameters, the scaling relationship of wind loads in a rigid model can be derived using dimensional analysis. According to Buckingham's π theorem, the dimensions of wind loads have a definite proportional relationship with fundamental physical quantities such as geometric dimensions, velocity, and air density. Combining the aforementioned scaling ratio setting conditions, the expression for the wind load scaling ratio can finally be established: .

[0027] Step 2: Based on the lift-drag coefficient at the position of maximum lift-drag ratio of the prototype blade, and combined with the multi-Reynolds number analysis function of Profili software, select an optimized airfoil whose aerodynamic characteristics match those of the prototype blade at low Reynolds numbers.

[0028] In this embodiment, the method for selecting an optimized airfoil whose aerodynamic characteristics match those of the prototype blade at low Reynolds numbers is as follows: extracting the prototype blade airfoil at high Reynolds numbers... Lift coefficient at the bottom With drag coefficient With angle of attack The change curve data; at a given low Reynolds number Within the specified range, using the multi-Reynolds number analysis function of Profili software, the aerodynamic characteristic curves of each airfoil in the candidate airfoil library are calculated. and , and Low Reynolds number The lift coefficient and drag coefficient were determined; the optimal replacement airfoil with a low Reynolds number was selected based on the following criteria: [the airfoil must meet the drag coefficient requirements]. and Under the condition that the difference is less than the set first threshold range, the lift coefficient and The difference is also less than the set second threshold range.

[0029] Specifically, in this embodiment, based on the measured aerodynamic parameters of the prototype airfoil at the position of maximum lift coefficient, and combined with the multi-Reynolds number analysis function of Profili software, a low Reynolds number airfoil is designed with a maximum lift coefficient close to that of the original airfoil under different angles of attack. Considering the maximum lift coefficient of NACA0018... Since the Reynolds number is 1.278, the ONERA-OA206 low Reynolds number airfoil was used in this experiment. Based on numerical simulation calculations of low Reynolds number aerodynamic characteristics, the ONERA-OA206 airfoil maintains a drag coefficient comparable to that of traditional prototype wind turbine airfoils, i.e. At that time, its maximum lift coefficient Reaching a lift-drag coefficient of 1.03, it exhibits excellent low-speed aerodynamic performance. Figure 3 shows a comparison of the lift-drag coefficients of the prototype airfoil NACA0018 and the scaled-down optimized airfoil ONERA_OA206. It can be seen that the lift-drag coefficient of ONERA_OA206 at low Reynolds numbers matches that of the prototype airfoil NACA0018 at high Reynolds numbers very well, satisfying the optimization condition of similar lift-drag coefficients. Therefore, the low Reynolds number ONERA_OA206 airfoil is selected as the optimized airfoil.

[0030] Step 3: Construct an aerodynamic performance model of the vertical axis wind turbine based on the dual-disc multi-flow theory, calculate the theoretical thrust coefficients of the prototype airfoil and the optimized airfoil at the corresponding Reynolds number, and verify whether the aerodynamic load of the optimized airfoil satisfies the scaling ratio matching relationship.

[0031] Specifically, in this embodiment, during verification, data measured at different angles of attack under Class B terrain flow fields were compared with the results of numerical simulations using Qblade software to avoid the influence of turbulence intensity and integral scale. The numerical calculations for the NACA0018 prototype scaled model and the ONERA_OA206 scaled model represent the thrust coefficients. The thrust coefficient obtained from numerical simulation of the NACA0018 prototype model is ,Will and A comparison was conducted to verify whether the optimized airfoil met the requirements and the necessity of the optimization.

[0032] In this embodiment, the steps for verifying whether the aerodynamic load of the optimized airfoil satisfies the scaling ratio matching relationship are as follows.

[0033] S31: Discretize the swept region of the vertical axis wind turbine rotor into multiple adjacent flow tube units, and divide each flow tube into two cascaded actuator disks in the upwind and downwind regions; the induced velocities of each flow tube in the upwind and downwind regions are respectively represented by... and This indicates that the middle section is balanced by wind speed. express.

[0034] S32: The average force acting on the rotor along the incoming flow direction is calculated using the momentum theorem, and the average force acting on the blade airfoil is calculated using the blade element theorem; the force balance equations are solved simultaneously and iteratively to obtain the velocity induction factor along the incoming flow direction, and then the thrust and torque of the wind turbine in operation or shutdown state are obtained to obtain the thrust coefficient. and torque coefficient .

[0035] In this embodiment, the method steps for obtaining the thrust and torque of the wind turbine in operation or shutdown state based on the dual-disc multi-flow management theory (DMST) are as follows.

[0036] S321: Calculate the aerodynamic force of a single leaf element: for any altitude of chord length is The blade element, at a given azimuth angle Regardless of whether it is in the upwind or downwind area, the first step is to determine the local relative wind speed. and attack angle : in: The local relative wind speed sensed by the blade element is the vector sum of the blade rotational linear velocity and the incoming wind speed. For local inflow velocity, in DMST, the velocity on the upwind side of the disk is denoted as . In the downwind area, it is recorded as ; The radius of rotation of the wind turbine; Let be the linear velocity of the rotation of the blade element; This is the azimuth angle of the blade.

[0037] The lift coefficient of an airfoil is obtained using aerodynamic airfoil data. and drag coefficient Calculate the normal coefficient and tangential coefficient : in: Angle of attack, i.e., local relative wind speed The angle between the blade chord and the blade chord.

[0038] The normal and tangential force components on the leaf element are as follows: in: and For a blade element at a specific azimuth angle The instantaneous normal force and instantaneous tangential force experienced at that moment; air density; This is the chord length of the blade; The height of the selected blade element is given by [reference to a specific element]. If expressed as an integral, it is represented by [reference to a specific element]. .

[0039] S322: Calculate the instantaneous values ​​of aerodynamic thrust and torque: Definition This is the azimuth angle (usually starting from a horizontal axis perpendicular to the wind direction). A single blade at a specific azimuth angle... At that time, the instantaneous thrust contribution of the current flow tube in the wind direction is: For those with A wind turbine with 10 blades, in a space with a width of The height is Inside the flow tube; the time-averaged aerodynamic thrust (averaged over one rotation cycle) experienced by the flow tube is: in: For a single blade passing through the azimuth angle At that time, the instantaneous thrust component generated along the direction of the incoming wind; This refers to the infinitesimal element of the average thrust acting on a specific flow tube, calculated based on leaf element theory. This represents the total number of blades on the wind turbine. and The boundary of the azimuth integral interval corresponding to the flow tube is defined as follows: when the disk is divided into multiple small flow tubes, each flow tube corresponds to a very small azimuth span.

[0040] The core of torque is tangential force. The torque generated on the wind turbine's main shaft. The instantaneous torque generated by a single blade in this micro-element segment. for: The time-averaged torque contribution within this flow tube section is: S323: Execute the DMST dual-disk thrust iterative solution process: According to the one-dimensional momentum theory, the cross-sectional area of ​​the flow is... The air mass flow rate of the flow tube is As air flows past the actuator disk, its velocity decreases, resulting in a reduction in momentum. The resulting thrust is: in: This is the macroscopic thrust element of the flow tube calculated based on the law of conservation of momentum; This represents the mass flow rate of the air passing through the flow tube. and The far-field wind speeds are those before and after the airflow passes through the actuator disk (impeller cross-section); This refers to the local inflow velocity, which is the actual velocity of the airflow when it reaches the blade element. Due to momentum loss, the difference between the two represents the energy extracted and thrust borne by the rotor. In DMST theory, this is divided into two processes: the upwind and downwind regions.

[0041] Specifically, in the upwind area, the free-flow wind speed is The induced velocity when passing through the upper half of the plate is The speed at which it leaves the first actuation plate and enters the intermediate balance zone is The momentum thrust of the upwind flow tube is: in: The axial induction factor in the upwind region; The wind speed in the equilibrium zone between the upwind and downwind areas; Let be the current windward cross-sectional area of ​​the flow tube; This refers to air density.

[0042] The mean aerodynamic thrust of the blade element in the upwind region is: in: For leaf element micro-elements in the upwind area at a specific azimuth angle The instantaneous normal force experienced at that time; For leaf element micro-elements in the upwind area at a specific azimuth angle The instantaneous tangential force experienced at that time.

[0043] Through residual iteration, let ,because and It contains inducing factors (By changing local wind speed) This is about The nonlinear equations are obtained. By setting residuals, the actual flow rate of each flow tube in the upwind region is solved iteratively. Solve for Then, all the flow tubes Integrating along the rotor width yields the total thrust in the upwind region. Solve for back, and All become definite values. The thrust contribution of this flow tube in the upwind region is... Torque contribution of the flow tube in the upwind region. for: In the downwind area, the equilibrium zone speed As the new free-flow velocity, the induced velocity when passing through the lower half of the disk (the second actuation disk) is: The final wake velocity is The momentum thrust of the flow tube in the downwind region is: in: The axial induction factor in the downwind region; The final wake velocity of the airflow after passing through the entire wind turbine.

[0044] The mean aerodynamic thrust of the blade element in the downwind region is: in: For leaf element micro-elements in the downwind area at a specific azimuth angle The instantaneous normal force experienced at that time; For leaf element micro-elements in the downwind area at a specific azimuth angle The instantaneous tangential force experienced at that time.

[0045] make The iterative solution yields the value of each flow tube in the downwind region. Solve for Then, the total thrust in the downwind region is obtained by integrating over all downwind flow tubes. The torque contribution of the flow pipe in the downwind region... for: S324: Calculation of total thrust, torque, and dimensionless coefficients of the wind turbine: Based on the dual-disc multi-flow tube (DMST) theory, the total thrust acting on the entire vertical axis wind turbine. The sum of the upwind thrust and the downwind thrust: Thrust coefficient for: Total torque for: Torque coefficient for: in: Total aerodynamic thrust; This is the thrust coefficient; This refers to the sweeping area of ​​the wind turbine.

[0046] The efficiency of wind turbines in extracting wind energy is measured by the power coefficient, which in a dimensionless system is converted to: in: This is the power coefficient, i.e., wind energy utilization rate; For the tip speed ratio, This represents the ratio of the fan speed to the incoming air velocity. Let be the linear velocity of the rotation of the blade element; This refers to the free-flow wind speed in the upwind area.

[0047] The prototype and scaled-down models were modeled using Qblade software, and the calculated thrust and torque coefficients are shown in Table 1. A comparison reveals that the thrust and torque coefficients of the ONERA_OA206 airfoil at low Reynolds numbers are very close to those of the NACA0018 airfoil at high Reynolds numbers, with a relatively small error scalar value. The result is within the engineering tolerance limit, meaning that the optimized airfoil can effectively replace the prototype airfoil for scale-down experiments. Preliminary numerical simulations demonstrate that the ONERA_OA206 airfoil can effectively reflect the loads experienced by the prototype model at low Reynolds numbers. The next step will be wind tunnel testing to further verify whether this optimized airfoil can replace the NACA0018 airfoil for scale-down experiments under real-world conditions.

[0048] Table 1. Thrust and torque coefficients of the prototype and scaled-down models calculated using Qblade software. S33: Load factor matching verification, defining the relative error of the thrust factor. Relative error of torque coefficient : in: The thrust coefficient of the prototype airfoil at high Reynolds numbers; To optimize the thrust coefficient of the airfoil at low Reynolds numbers; The torque coefficient of the prototype airfoil at high Reynolds numbers; To optimize the torque coefficient of the airfoil at low Reynolds numbers; like and This confirms that the low Reynolds number airfoil can be used as a scaled-down model blade for wind tunnel testing; if or If so, return to step two to adjust the weights or expand the candidate airfoil library for re-screening; where: and These are the preset engineering tolerance limits for the thrust coefficient and torque coefficient, respectively.

[0049] Step 4: Conduct a wind turbine force-pressure test in a wind tunnel. Using the measured total thrust and tower thrust of the whole turbine model, separate the pure thrust actually experienced by the blades.

[0050] In this embodiment, the method for extracting the actual pure thrust experienced by the blade is as follows: the whole-machine force-pressure measurement model includes the blade, connecting rod, and tower column; because the thrust experienced by the connecting rod is very small, it is not considered. Specifically, for this embodiment, there are two wind tunnel test models: the NACA0018 airfoil scaled-down whole-machine force-pressure measurement model and the ONERA_OA206 airfoil scaled-down whole-machine force-pressure measurement model. The models are made using carbon fiber 3D printing, and the dimensional diagrams of the two airfoil scaled-down models are shown below. Figure 4 As shown, a high-frequency base force balance was used in the wind tunnel to measure the total thrust of the model under different overall wind direction angles. To mitigate interference from the tower column, pressure testing was conducted by installing pressure measuring tubes on the column. Pressure measuring holes were placed every 20°, and a strip was installed every 70mm from bottom to top to obtain the resistance experienced by the tower column. The pure thrust acting on the actual blade can be separated by vector subtraction. , represented as: Table 2 shows the load statistics obtained from the NACA0018 airfoil scaled whole-aircraft force-pressure measurement model and the ONERA_OA206 airfoil scaled whole-aircraft force-pressure measurement model in wind tunnel experiments.

[0051] Table 2 Load statistics of different airfoil models in wind tunnel experiments Step 5: Compare the measured thrust coefficient with the theoretical thrust coefficient of the prototype model calculated in Step 3 to verify the matching degree of the optimized blade aerodynamic load, thereby eliminating the Reynolds number effect in the scale test.

[0052] In this embodiment, the method for verifying the matching degree of the aerodynamic load of the optimized blade by comparing the measured thrust coefficient with the theoretical thrust coefficient of the prototype model calculated in step three is as follows: Based on the blade thrust and the reference area of ​​the scaled-down model of the original airfoil and the optimized airfoil, the measured thrust coefficient of different models in the wind tunnel test is calculated; the measured thrust coefficient is compared with the theoretical thrust coefficient obtained by numerical simulation in step three to verify the matching degree of the aerodynamic load of the optimized blade under low Reynolds number conditions with that of the prototype under high Reynolds number conditions, thereby verifying whether the optimized airfoil can eliminate the Reynolds number effect in the scaled-down test relative to the original airfoil scaled-down model.

[0053] Specifically, for this embodiment, the theoretical thrust coefficient calculation results of the prototype model - NACA0018 airfoil at high Reynolds numbers are shown in Table 2. The thrust coefficients measured using the NACA0018 airfoil-scaled whole-aircraft force-pressure measurement model and the ONERA_OA206 airfoil-scaled whole-aircraft force-pressure measurement model are shown in Table 2. . Figure 5 The comparison chart of thrust coefficients for different airfoil models shows that the thrust coefficient measured in wind tunnel tests for the directly scaled-down NACA0018 airfoil is too high, indicating that the NACA0018 airfoil cannot be directly scaled down for testing. In contrast, the thrust coefficient measured for the optimized ONERA_OA206 airfoil is very close to the calculation result of the prototype model. Therefore, it is believed that the ONERA_OA206 airfoil can be used as an optimized choice for scaled-down wind tunnel tests of the NACA0018 airfoil.

[0054] This embodiment presents an aerodynamic optimization design method for blades of a scaled-down model of a large vertical axis wind turbine based on DMST theory, which can overcome the Reynolds number limitation. Specifically, by constructing a rigorous similarity ratio theory and a multi-objective optimization function that includes discretized summation of both lift and drag parameters, it overcomes the bottleneck of severe aerodynamic load distortion caused by traditional direct geometric scaling. "Aerodynamic shape replacement" ensures the consistency of the overall thrust coefficient at low Reynolds numbers. The complex dual-disk multi-flow turbine theory (DMST) containing rotationally induced components is transformed into an aerodynamic mathematical model, providing a clear algebraic balance equation between the induction factor and the local drag coefficient, offering an efficient and accurate numerical analytical basis for pre-experiment aerodynamic evaluation. In the wind tunnel physical verification stage, a clear thrust separation formula for subtracting tower interference from the overall turbine load is given, ensuring that the actual aerodynamic contribution of the optimized blade is accurately extracted and verified, greatly improving the reliability of ultimate load prediction and wind-resistant design.

[0055] The embodiments described above are merely preferred embodiments for fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. An aerodynamic optimization design method for blades of a scaled-down wind tunnel model of a large vertical axis wind turbine based on DMST theory, characterized in that: Includes the following steps: Step 1: Determine the scaling parameters for the wind tunnel test based on the wind tunnel test similarity criteria and the wind tunnel size and wind speed parameters; Step 2: Based on the lift-drag coefficient at the position of maximum lift-drag ratio of the prototype blade, and combined with the multi-Reynolds number analysis function of Profili software, select an optimized airfoil whose aerodynamic characteristics match those of the prototype blade at low Reynolds number. Step 3: Based on the dual-disc multi-flow theory, construct the aerodynamic performance model of the vertical axis wind turbine, calculate the theoretical thrust coefficients of the prototype airfoil and the optimized airfoil at the corresponding Reynolds number, and verify whether the aerodynamic load of the optimized airfoil satisfies the scaling ratio matching relationship. Step 4: Conduct a force-pressure test on the wind turbine in the wind tunnel. Using the total thrust and tower thrust measured on the whole turbine model, separate the pure thrust actually experienced by the blades. Step 5: Compare the measured thrust coefficient with the theoretical thrust coefficient of the prototype model calculated in Step 3 to verify the matching degree of the optimized blade aerodynamic load, thereby eliminating the Reynolds number effect in the scale test. In step three, the method for verifying whether the aerodynamic loads of the optimized airfoil satisfy the scaling ratio matching relationship is as follows: S31: Discretize the swept region of the vertical axis wind turbine rotor into multiple adjacent flow tube units, and divide each flow tube into two cascaded actuator disks in the upwind and downwind regions; the induced velocities of each flow tube in the upwind and downwind regions are respectively represented by... and This indicates that the middle section is balanced by wind speed. express; S32: The average force acting on the rotor along the incoming flow direction is calculated using the momentum theorem, and the average force acting on the blade airfoil is calculated using the blade element theorem; the force balance equations are solved simultaneously and iteratively to obtain the velocity induction factor along the incoming flow direction, and then the thrust and torque of the wind turbine in operation or shutdown state are obtained to obtain the thrust coefficient. and torque coefficient ; The method for obtaining the thrust and torque of a wind turbine in operation or shutdown states based on the dual-disc multi-flow management theory is as follows: S321: Calculate the aerodynamic force of a single leaf element: for any altitude of chord length is The blade element, at a given azimuth angle Below, local relative wind speed for: in: The local relative wind speed sensed by the blade micro-element; The local inflow velocity is recorded on the disk in the upwind area as follows. In the downwind area, it is recorded as ; The radius of rotation of the wind turbine; Let be the linear velocity of the rotation of the blade element; The azimuth angle of the blade; The lift coefficient of an airfoil is obtained using aerodynamic airfoil data. and drag coefficient Calculate the normal coefficient and tangential coefficient : in: Angle of attack, i.e., local relative wind speed The angle between the blade chord and the blade chord; The normal and tangential force components on the leaf element are as follows: in: and For a blade element at a specific azimuth angle The instantaneous normal force and instantaneous tangential force experienced at that moment; air density; This is the chord length of the blade; The height of the selected blade element; S322: Calculate instantaneous values ​​of aerodynamic thrust and torque: a single blade at a specific azimuth angle. At that time, the instantaneous thrust contribution of the current flow tube in the wind direction is: For those with A wind turbine with 10 blades, in a space with a width of The height is Inside the flow tube; the time-averaged aerodynamic thrust acting on the flow tube is: in: For a single blade passing through the azimuth angle At that time, the instantaneous thrust component generated along the direction of the incoming wind; This refers to the infinitesimal element of the average thrust acting on a specific flow tube, calculated based on leaf element theory. This represents the total number of blades on the wind turbine. and This represents the boundary of the azimuth integral interval corresponding to the flow tube; The instantaneous torque generated by a single blade in this micro-element segment for: The time-averaged torque contribution within this flow tube section is: S323: Execute the DMST dual-disc thrust iterative solution process: In the upwind region, the free-flow wind speed is... The induced velocity when passing through the upper half of the plate is The speed at which it leaves the first actuation plate and enters the intermediate balance zone is The momentum thrust of the upwind flow tube is: in: The axial induction factor in the upwind region; The wind speed in the equilibrium zone between the upwind and downwind areas; Let be the current windward cross-sectional area of ​​the flow tube; air density; The mean aerodynamic thrust of the blade element in the upwind region is: in: For leaf element micro-elements in the upwind area at a specific azimuth angle The instantaneous normal force experienced at that time; For the leaf element micro-element in the upwind area at a specific azimuth angle The instantaneous tangential force experienced at that time; Through residual iteration, let Solve for the actual flow tube in the upwind region Thus, the total thrust in the upwind region is obtained. and torque contribution ; In the downwind area, the equilibrium zone speed As the new free-flow velocity, the induced velocity when passing through the lower half of the disk is: The final wake velocity is The momentum thrust of the flow tube in the downwind region is: in: The axial induction factor in the downwind region; The final wake velocity of the airflow after passing through the entire wind turbine; The mean aerodynamic thrust of the blade element in the downwind region is: in: For leaf element micro-elements in the downwind area at a specific azimuth angle The instantaneous normal force experienced at that time; For leaf element micro-elements in the downwind area at a specific azimuth angle The instantaneous tangential force experienced at that time; make The iterative solution yields the flow rate of each flow tube in the downwind region. Thus, the total thrust in the downwind region is obtained. and torque contribution ; S324: Calculate the total thrust, torque, and dimensionless coefficients of the wind turbine: Total thrust acting on the entire vertical axis wind turbine. The sum of the upwind thrust and the downwind thrust: Thrust coefficient for: Total torque for: Torque coefficient for: in: The swept area of ​​the wind turbine; S33: Load factor matching verification, defining the relative error of the thrust factor. Relative error of torque coefficient : in: The thrust coefficient of the prototype airfoil at high Reynolds numbers; To optimize the thrust coefficient of the airfoil at low Reynolds numbers; The torque coefficient of the prototype airfoil at high Reynolds numbers; To optimize the torque coefficient of the airfoil at low Reynolds numbers; like and This confirms that the low Reynolds number airfoil can be used as a scaled-down model blade for wind tunnel testing; if or If so, return to step two to adjust the weights or expand the candidate airfoil library for re-screening; where: and These are the preset engineering tolerance limits for the thrust coefficient and torque coefficient, respectively.

2. The aerodynamic optimization design method for blades of a scaled-down model of a large vertical axis wind turbine based on DMST theory according to claim 1, characterized in that: In step one, the method for determining the various scale parameters of the wind tunnel test is as follows: Obtain the geometric parameters and operating environment wind speed of the prototype vertical axis wind turbine; set the wind speed scaling ratio based on the cross-sectional area of ​​the wind tunnel test section and the maximum wind speed. and geometric scaling ; The geometric scaling ratio The determination needs to take into account both the size of the wind tunnel test section and the blockage ratio. Constraints; The blocking ratio calculation formula is: in: The projected area of ​​the model along the windward direction; This represents the cross-sectional area of ​​the wind tunnel test section; Wind load scaling ratio of the experimental scaled model The calculation formula is: in: This refers to the wind speed scaling ratio; This is the air density ratio.

3. The aerodynamic optimization design method for blades of a scaled-down model of a large vertical axis wind turbine based on DMST theory according to claim 1, characterized in that: In step two, the method for selecting an optimized airfoil whose aerodynamic characteristics match those of the prototype blade at low Reynolds numbers is as follows: Extracting the prototype airfoil at high Reynolds numbers Lift coefficient at the bottom With drag coefficient With angle of attack The change curve data; At a given low Reynolds number Within the specified range, using the multi-Reynolds number analysis function of Profili software, the lift coefficient of the aerodynamic characteristic curves of each airfoil in the candidate airfoil library is calculated. With drag coefficient ; The optimal replacement airfoil for low Reynolds number was selected based on the following criteria: it meets the drag coefficient requirement. and Under the condition that the difference is less than the set first threshold range, the lift coefficient and The difference is also less than the set second threshold range.

4. The aerodynamic optimization design method for blades of a scaled-down model of a large vertical axis wind turbine based on DMST theory according to claim 1, characterized in that: The efficiency of wind turbines in extracting wind energy is measured by the power coefficient, which in a dimensionless system is converted to: in: This is the power coefficient, i.e., wind energy utilization rate; For the tip speed ratio, This represents the ratio of the fan speed to the incoming air velocity. Let be the linear velocity of the rotation of the blade element; The free-flow wind speed in the upwind area.

5. The aerodynamic optimization design method for blades of a scaled-down model of a large vertical axis wind turbine based on DMST theory according to claim 1, characterized in that: In step four, the method for separating the actual pure thrust experienced by the blade is as follows: The whole-machine force-pressure measurement model includes blades, connecting rods, and tower columns, but does not consider the thrust on the connecting rods; The total thrust of the model under different overall wind direction angles was measured in a wind tunnel using a high-frequency base force balance. ; Pressure testing was conducted by installing pressure measuring tubes on the tower column to obtain the resistance experienced by the tower column. ; The pure thrust acting on the actual blade is separated by vector subtraction. , represented as: 。 6. The aerodynamic optimization design method for blades of a scaled-down model of a large vertical axis wind turbine based on DMST theory according to claim 1, characterized in that: In step five, the measured thrust coefficient is compared with the theoretical thrust coefficient of the prototype model calculated in step three. The method to verify the matching degree of the optimized blade aerodynamic load is as follows: Based on the blade thrust measured by the original airfoil scaled-down model and the optimized airfoil scaled-down model, and the reference area of ​​the scaled-down model, the measured thrust coefficient of different models in wind tunnel tests was calculated. The measured thrust coefficient is compared with the theoretical thrust coefficient obtained by numerical simulation in step three to verify the degree of matching between the aerodynamic load of the optimized blade under low Reynolds number conditions and the prototype under high Reynolds number conditions. This verifies whether the optimized airfoil can eliminate the Reynolds number effect in the scaled-down test compared to the original airfoil scaled-down model.

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