Vertical axis fan pneumatic-wake flow coupling calculation method based on octree method

Abstract

The invention discloses a vertical axis fan pneumatic-wake flow coupling calculation method based on an octree method. The vertical axis fan pneumatic-wake flow coupling calculation method comprises the following steps: presetting initial parameters and environmental conditions of a wake flow speed and a pneumatic load; the wake flow field is divided into a near field and a far field, the wake flow velocity caused by near-field particles is directly calculated by adopting a classical Biot-Savart law, the wake flow velocity caused by far-field particles is solved by adopting an octree improved algorithm, and the aerodynamic load is calculated; the relative speed and the attack angle of the vertical axis fan blade are obtained, then the aerodynamic load on the blade is calculated, and meanwhile the induced speed, obtained through calculation, of the blade node is used for calculating the wake flow field speed in the next time step; in the wake flow module, all vortex elements perform convective motion along with the local induced velocity field, and newly released vortex elements form a new wake flow field for calculation of the next time step. The invention aims to provide a pneumatic-wake flow coupling response numerical calculation method capable of giving consideration to both precision and efficiency, and an effective numerical tool is provided for engineering application of a vertical axis fan.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of renewable energy utilization, and particularly relates to an octree-based aerodynamic-wake coupling calculation method for a vertical axis wind turbine, and particularly applies to engineering application of the vertical axis wind turbine. BACKGROUND

[0002] As one of the most potential renewable energy resources, it is important to efficiently develop and utilize wind energy. In the field of wind turbine technology, according to the arrangement direction of the rotating shaft of the wind wheel, there are mainly two technical routes of horizontal axis and vertical axis. Among them, the development process of the vertical axis wind turbine is relatively slow, but its unique structural advantages, such as low gravity center of the whole machine for easy maintenance, receiving any wind direction without yaw adjustment, and fast wake recovery for compact machine arrangement, make it show great potential value in specific application scenarios.

[0003] However, the vertical axis wind turbine is still in the research stage at present, especially in the dynamic response analysis of the mutual coupling of aerodynamic performance and wake characteristics, it has long relied on numerical methods such as computational fluid dynamics with high calculation cost, and lacks efficient special simulation tools, which restricts its engineering popularization and application. Therefore, it is urgent to develop an aerodynamic-wake coupling response numerical calculation method that can balance accuracy and efficiency, and provide an effective numerical tool for the engineering application of the vertical axis wind turbine. SUMMARY

[0004] The present application aims to overcome the deficiencies in the prior art, and provides an aerodynamic-wake coupling response numerical calculation method that can balance accuracy and efficiency, and provides an effective numerical tool for the engineering application of the vertical axis wind turbine.

[0005] To achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0006] An octree-based aerodynamic-wake coupling calculation method for a vertical axis wind turbine, comprising the following steps:

[0007] (1) The initial parameters and environmental conditions of the wake velocity and the aerodynamic load are preset;

[0008] (2) The wake module first divides the wake field into a near field and a far field, the wake velocity caused by the near field particles is directly calculated by using the classical Biot-Savart law, and the wake velocity caused by the far field particles is solved by using the octree improved algorithm, and the wake vortex induced velocity is transmitted to the aerodynamic module for calculating the aerodynamic load;

[0009] (3) The relative velocity and the attack angle of the vertical axis wind turbine blade are obtained in the aerodynamic module, and then the aerodynamic load on the blade is calculated, and the induced velocity of the blade node calculated is transmitted to the wake module for calculating the wake field velocity in the next time step;

[0010] (4) In the wake module, all vortex elements move with the local induced velocity field, and the newly released vortex elements will form a new wake field for the next time step calculation.

[0011] Further, the aerodynamic-wake coupling calculation method uses a free vortex wake method in the form of a lifting line.

[0012] Further, the initial parameters and environmental conditions in step (1) include incoming wind speed, fan speed, airfoil lift-drag coefficient table, wake truncation length, wake update length, wake dissipation coefficient, wake hysteresis coefficient, iteration residual, relaxation factor, vortex element scale coefficient, Taylor approximation order.

[0013] Further, the near-field and far-field division rule of the wake field in step (2) is: when the number of target particles is less than a specified number, it is calculated according to the near-field rule; when the number of target particles is greater than a specified number, it is judged according to the input vortex element scale coefficient; when the ratio of the distance of the target particle to the size of the current vortex element is less than the vortex element scale coefficient, it is calculated according to the near-field rule, otherwise it is calculated according to the far-field rule.

[0014] Further, the classical Biot-Savart law in step (2) is specifically represented as:

[0015] (1)

[0016] wherein, represents the position vector of the source particle, represents the position vector of the target particle, represents the induced velocity, represents the vortex vector, N represents the number of particles, represents the integral along the length direction of the vortex element, represents the kernel function of the Biot-Savart law.

[0017] Further, the octree improved algorithm in step (2) is to calculate the center position of each vortex element, calculate the Taylor coefficient and matrix, and calculate according to the improved Biot-Savart law, the specific steps are as follows:

[0018] First, a large number of vortex particles are divided by a certain number of vortex elements, and the center node of each vortex element is y c The classical Biot-Savart law is used at y c :

[0019] (2)

[0020] wherein, c = {y j{j=1,2,…,Nc} is a particle swarm in a vortex cell, N c This represents the total number of vortex units. Since the first term is not affected by the properties of the source particles, it can be further simplified:

[0021] (3)

[0022] in, Represents the position vector of the source particle. Represents the position vector of the target particle. Indicates the induction velocity, Represents the vorticity vector. This represents the integral along the length of the vortex element. The kernel function representing the Biot-Savart law yields two key physical quantities: the Taylor coefficient. Moment of vortex particles :

[0023] (4)

[0024] (5)

[0025] Where k is the order of the Taylor approximation, and finally the induced velocity between vortex particles based on the octree method can be calculated by the improved Biot-Savart law as follows:

[0026] (6)

[0027] in, yes In y c Taylor coefficients of order k at point k. It is the vortex element c about its center y c The k-th order moment.

[0028] Furthermore, in step (3), the relative velocity and angle of attack are obtained in the aerodynamic module by first dividing the wind turbine blade into several micro-segments along the spanwise direction in the model. For each micro-segment, the shedding vortex and wake vortex are calculated, and then the vortex core size is calculated. Based on the airfoil lift and drag coefficient table, the relative velocity and angle of attack are calculated according to the Kutzhukovsky lift principle. The Kutzhukovsky lift principle is as follows:

[0029] (7)

[0030] in, It is aerodynamic lift. It is air density. It is relative velocity. It is the vortex ring quantity.

[0031] Further, in step (3), the circulation of the attached vortex needs to be calculated, and when the circulation residual of the attached vortex of the current and previous two iterations is less than the iteration residual input in step (1), it is judged to be converged, and the aerodynamic load of the fan is further calculated, otherwise the iteration is continued to solve.

[0032] Further, in step (4), the position of each node of the new wake vortex is obtained based on the velocity of each node of the wake vortex, and the velocity of each node of the wake vortex is the superposition of the local inflow velocity and the induced velocity of each node.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] The present application introduces an octree method to optimize the calculation process of the wake, manages the wake field in layers according to the octree structure, establishes a rule for the wake particles at different levels, and adopts approximate processing with corresponding accuracy, thereby greatly improving the calculation efficiency while ensuring the accuracy of the calculation results, realizing the rapid acquisition of the aerodynamic-wake coupling response of the vertical axis fan, and providing an effective numerical tool for the engineering application of the vertical axis fan. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The present application is a method flowchart. DETAILED DESCRIPTION

[0036] The present application will be described in detail below with reference to the accompanying drawings and embodiments.

[0037] As shown in Figure 1 An octree-based aerodynamic-wake coupling calculation method for a vertical axis fan, comprising the following steps:

[0038] (1) The initial parameters and environmental conditions of the wake velocity and the aerodynamic load are pre-set;

[0039] (2) The wake module first divides the wake field into a near field and a far field, the wake velocity caused by the near field particles is directly calculated using the classical Biot-Savart law, and the wake velocity caused by the far field particles is solved by the octree improved algorithm, and the wake induced velocity is transmitted to the aerodynamic module for calculating the aerodynamic load;

[0040] (3) In the aerodynamic module, the relative velocity and the attack angle of the vertical axis fan blade are obtained, and the aerodynamic load on the blade is calculated, and the induced velocity of the blade nodes calculated is transmitted to the wake module for the next time step calculation of the wake field velocity;

[0041] (4) In the wake module, all vortex elements move convectively with the local induced velocity field, and the newly released vortex elements form a new wake field for the next time step calculation.

[0042] The aerodynamic-wake coupling calculation method uses a free vortex wake method in the form of a lifting line. The specific steps of the embodiment are as follows:

[0043] (1) The initial parameters and environmental conditions of the wake velocity and the aerodynamic load are preset, including the incoming flow speed, the fan speed, the airfoil lift-drag coefficient table, the wake truncation length, the wake update length, the wake dissipation coefficient, the wake lag coefficient, the iteration residual, the relaxation factor, the vortex element scale coefficient and the Taylor approximation order.

[0044] (2) The wake module first divides the wake field into a near field and a far field. The near field and the far field of the wake field are divided according to the following rules: if the number of target particles is less than a specified number, the near field rule is used for calculation; if the number of target particles is greater than the specified number, the input vortex element scale coefficient is used for judgment; if the ratio of the distance of the target particle to the size of the current vortex element is less than the vortex element scale coefficient, the near field rule is used for calculation, otherwise the far field rule is used for calculation.

[0045] The wake velocity caused by the near field particles is directly calculated using the classical Biot-Savart law, and the wake velocity caused by the far field particles is solved by the octree improved algorithm, and the induced velocity of the wake vortex is transmitted to the aerodynamic module for calculating the aerodynamic load.

[0046] The classical Biot-Savart law is specifically represented as:

[0047] (1)

[0048] wherein, represents the position vector of the source particle, represents the position vector of the target particle, represents the induced velocity, represents the vortex vector, N represents the number of particles, represents the integral along the length direction of the vortex element, represents the kernel function of the Biot-Savart law.

[0049] The octree improved algorithm successively calculates the center position of each vortex element, calculates the Taylor coefficient and the moment, and calculates according to the improved Biot-Savart law. The specific steps are as follows:

[0050] First, a large number of vortex particles are divided by a certain number of vortex elements. The center node of each vortex element is y c The classical Biot-Savart law is used at y c :

[0051] (2)

[0052] wherein, c = {yj {j=1,2,…,Nc} is a particle swarm in a vortex cell, N c This represents the total number of vortex units. Since the first term is not affected by the properties of the source particles, it can be further simplified:

[0053] (3)

[0054] in, Represents the position vector of the source particle. Represents the position vector of the target particle. Indicates the induction velocity, Represents the vorticity vector. This represents the integral along the length of the vortex element. The kernel function representing the Biot-Savart law yields two key physical quantities: the Taylor coefficient. Moment of vortex particles :

[0055] (4)

[0056] (5)

[0057] Where k is the order of the Taylor approximation, and finally the induced velocity between vortex particles based on the octree method can be calculated by the improved Biot-Savart law as follows:

[0058] (6)

[0059] in, yes In y c Taylor coefficients of order k at point k. It is the vortex element c about its center y c The k-th order moment.

[0060] (3) Obtain the relative velocity and angle of attack of the vertical axis wind turbine blades in the aerodynamic module. The method for obtaining the relative velocity and angle of attack is as follows: First, the wind turbine blades need to be divided into several micro-segments along the spanwise direction in the model. For each micro-segment, calculate the shedding vortex and wake vortex, then calculate the vortex core size, and calculate the circulation of the attached vortex. When the residual of the circulation of the attached vortex between the previous and next iterations is less than the iteration residual input in step (1), it is judged as convergence, and the aerodynamic load of the wind turbine is further calculated. Otherwise, continue iterative solution and repeat step (2). Combine the airfoil lift and drag coefficient table and calculate the relative velocity and angle of attack according to the Kutzhukovsky lift principle. The Kutzhukovsky lift principle is as follows:

[0061] (7)

[0062] where, is the aerodynamic lift, is the air density, is the relative velocity, is the vortex ring strength.

[0063] The aerodynamic load on the blade is further calculated, and the induced velocity of the blade node calculated is transmitted to the wake module for the next time step calculation of the wake field velocity.

[0064] (4) In the wake module, all vortex elements convect with the local induced velocity field, and the newly released vortex elements form a new wake field for the next time step calculation. The position of each node of the new wake vortex is obtained based on the velocity of each node of the wake vortex, and the velocity of each node of the wake vortex is the superposition of the local inflow velocity and the induced velocity of each node.

[0065] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for calculating the aerodynamic-wake coupling of a vertical axis fan based on the octree method, characterized in that: Includes the following steps: (1) Pre-set the initial parameters and environmental conditions for the wake velocity and aerodynamic load; (2) The wake module first divides the wake field into near field and far field. The wake velocity caused by near field particles is directly calculated using the classical Biot-Savart law, while the wake velocity caused by far field particles is solved by the improved octree algorithm. The wake vortex induced velocity is then transferred to the aerodynamic module for calculating aerodynamic loads. (3) Obtain the relative velocity and angle of attack of the vertical axis fan blades in the aerodynamic module, and then calculate the aerodynamic load on the blades. At the same time, transmit the induced velocity of the blade nodes obtained by calculation to the wake module for the next time step to calculate the wake field velocity. (4) In the wake module, all vortex elements undergo convective motion with the local induced velocity field, and the newly released vortex elements will form a new wake field for the calculation of the next time step.

2. The aerodynamic-wake coupling calculation method for vertical axis fans based on the octree method according to claim 1, characterized in that: The aerodynamic-wake coupling calculation method uses the free vortex wake method in the form of lift lines.

3. The aerodynamic-wake coupling calculation method for vertical axis fans based on the octree method according to claim 1, characterized in that: The initial parameters and environmental conditions in step (1) include incoming wind speed, fan speed, airfoil lift and drag coefficient table, wake cut-off length, wake update length, wake dissipation coefficient, wake hysteresis coefficient, iteration residual, relaxation factor, vortex element scale coefficient, and Taylor approximation order.

4. The aerodynamic-wake coupling calculation method for vertical axis fans based on the octree method according to claim 1, characterized in that: The rules for dividing the near field and far field of the wake field in step (2) are as follows: if the number of target particles is less than the specified number, the near field rule shall be used for calculation; if the number of target particles is greater than the specified number, the judgment shall be made according to the input vortex unit scale coefficient; if the ratio of the distance of the target particle to the size of the current vortex unit is less than the vortex unit scale coefficient, the near field rule shall be used for calculation, otherwise the far field rule shall be used for calculation.

5. The aerodynamic-wake coupling calculation method for vertical axis fans based on the octree method according to claim 4, characterized in that: The classic Biot-Savart law in step (2) is specifically expressed as follows: （1） in, Represents the position vector of the source particle. Represents the position vector of the target particle. Indicates the induction velocity, Let represent the vorticity vector, N represent the number of particles, and represent the integral along the length of the vortex element. The kernel function representing the Biot-Savart law.

6. The aerodynamic-wake coupling calculation method for vertical axis fans based on the octree method according to claim 5, characterized in that: The improved octree algorithm in step (2) involves calculating the center position of each vortex element, calculating the Taylor coefficient and moment, and performing calculations according to the improved Biot-Savart law. The specific steps are as follows: First, a large number of vortex particles are divided into a certain number of vortex units, and the central node of each vortex unit is y. c Regarding the classical Biot-Savart law in y c Taylor approximation is used here: （2） Where, c = {y j {j=1,2,…,Nc} is a particle swarm in a vortex cell, N c This represents the total number of vortex units. Since the first term is not affected by the properties of the source particles, it can be further simplified: （3） in, Represents the position vector of the source particle. Represents the position vector of the target particle. Indicates the induction velocity, Represents the vorticity vector. This represents the integral along the length of the vortex element. The kernel function representing the Biot-Savart law yields two key physical quantities: the Taylor coefficient. Moment of vortex particles : （4） （5） Where k is the order of the Taylor approximation, and finally the induced velocity between vortex particles based on the octree method can be calculated by the improved Biot-Savart law as follows: （6） in, yes In y c Taylor coefficients of order k at point k. It is the vortex element c about its center y c The k-th order moment.

7. The aerodynamic-wake coupling calculation method for vertical axis fans based on the octree method according to claim 1, characterized in that: In step (3), the relative velocity and angle of attack in the aerodynamic module are obtained by first dividing the wind turbine blade into several micro-segments along the spanwise direction in the model. For each micro-segment, the shedding vortex and wake vortex are calculated, and then the vortex core size is calculated. Based on the airfoil lift and drag coefficient table, the relative velocity and angle of attack are calculated according to the Kutzhukovsky lift principle. The Kutzhukovsky lift principle is as follows: （7） in, It is aerodynamic lift. It is air density. It is relative velocity. It is the vortex ring quantity.

8. The aerodynamic-wake coupling calculation method for vertical axis fans based on the octree method according to claim 7, characterized in that: In step (3), the circulation of the attached vortex needs to be calculated. If the residual of the circulation of the attached vortex between the previous and next iterations is less than the iteration residual input in step (1), it is judged as convergence, and the aerodynamic load of the wind turbine is further calculated. Otherwise, the iteration solution continues.

9. The aerodynamic-wake coupling calculation method for vertical axis fans based on the octree method according to claim 1, characterized in that: In step (4), the position of each node of the new wake vortex is obtained based on the velocity of each node of the wake vortex. The velocity of each node of the wake vortex is the superposition of the local incoming flow velocity and its induced velocity.

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