Floating fan power generation efficiency evaluation method suitable for engineering design

Abstract

The invention provides a floating fan power generation efficiency evaluation method suitable for engineering design, and is suitable for the technical field of offshore power generation equipment. The method comprises the steps of floating body motion solving, fan aerodynamic performance simulation, overall calculation area setting and power generation efficiency calculation, the motion law of a tower bottom point is obtained through a potential flow method, and motion of a tower bottom end point is loaded into CFD solving through motion of a dynamic grid. Simulation of blade unsteady flow for controlling blade variable-pitch movement is achieved through an overlapped grid and a PID method, and the aerodynamic characteristics of the floating fan under the action of waves are truly reflected; according to the method, the unsteady flow process of the fan is accurately simulated through CFD, meanwhile, influences caused by floating body movement, fan yawing and fan propeller pitch changes are considered, compared with a traditional fan blade power method, the three-dimensional effect of the blade is considered, and calculation is more accurate; the problem of two-phase flow generated when the movement of the floating body in the wave is solved through a CF D method is avoided, consumption of computing resources is reduced, and solving is faster.

Description

Technical Field

[0001] The invention relates to the technical field of offshore power generation equipment, and in particular to a method for evaluating power generation efficiency of a floating wind turbine suitable for engineering design. Background Art

[0002] As offshore wind energy development gradually deepens, floating wind turbines have attracted widespread attention due to their applicability in deepwater areas. However, the working environment of floating wind turbines is relatively complex. Not only do they need to cope with variable wind speed conditions, but they also have to face the influence of ocean dynamic factors such as waves and tides. When using numerical methods to design and optimize floating wind turbines, the interaction between waves, air, and floating bodies must be fully considered, which places extremely high demands on the calculation method and the computing power of the computer.

[0003] At present, the fully coupled analysis method based on CFD is one of the most accurate ways to analyze the working state of floating wind turbines. This method can provide detailed flow field information, including key parameters such as airflow velocity distribution, pressure field, turbulence intensity, etc., by numerically simulating the interaction between waves, air and floating bodies. It can also accurately predict the dynamic response of floating bodies, including six-degree-of-freedom displacement and motion. Therefore, the fully coupled analysis method can accurately evaluate the power generation efficiency of floating wind turbines. However, the main disadvantage of the fully coupled analysis method is its huge amount of calculation and long calculation time, which makes it difficult for this method to meet the needs of rapid iterative design in engineering practice.

[0004] In order to overcome this problem, researchers have explored a series of alternative solutions, among which simplified methods such as the actuation line model, the actuation surface model, and the volume force model have been widely used. The core idea of ​​these methods is to approximate the dynamic behavior of the wind turbine blades through simplified mathematical models, thereby greatly reducing the computational complexity. For example, the actuation line model regards the blade as a series of discrete point sources distributed on the line, each of which exerts a force that interacts with the local airflow; the actuation surface model further regards the blade as a continuous surface, and simulates the dynamic effect of the blade by controlling the velocity distribution on the surface; and the volume force model directly applies a volume force related to the blade rotation in the fluid domain, thereby replacing detailed blade geometry modeling. Although these methods perform well in improving computational efficiency, they have certain limitations in dealing with the three-dimensional effects of blades, such as blade tip vortices, interference between blades, and other complex flow phenomena that often cannot be accurately described.

[0005] The fully coupled analysis method based on CFD uses two-phase flow numerical simulation methods (VOF or level-set methods, etc.) to simulate the movement of floating bodies in waves, which consumes a lot of computing resources. This patent solves the movement of floating wind turbines in waves through the potential flow method, which simplifies the solution of the movement problem in waves and avoids the large amount of computing resources required to solve the two-phase flow problem based on the CFD method.

[0006] Therefore, it is necessary to propose a more efficient analysis method that can achieve fast calculation while ensuring a certain accuracy, so as to facilitate the rapid iteration of the optimal design of floating wind turbines in engineering. Summary of the invention

[0007] The purpose of the present invention is to solve the problems of large amount of calculation and long calculation time of the fully coupled analysis method and large limitations and poor calculation accuracy of the existing alternative methods. A floating wind turbine power generation efficiency evaluation method suitable for engineering design is proposed. While having high calculation accuracy, it can achieve fast calculation and can be widely used in the field of offshore power generation equipment technology.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] S101, solving the motion of floating body;

[0010] The floating body motion solution includes establishing the motion equation of the floating wind turbine in the time domain.

[0011]

[0012] Where, M is the mass matrix of the floating body, C is the damping matrix, K is the hydrostatic stiffness recovery matrix, and F is wi - Wind load, F c -Flow force, F wa - Wave load, F m - anchor chain force, solve the motion equation to obtain the center of gravity of the floating buoy (x g ,y g ,z g ) at the position of the displacement, velocity, acceleration of the three translational degrees of freedom and the rotation angle, angular velocity, angular acceleration of the three rotational degrees of freedom, wherein the motion of the three translational degrees of freedom includes longitudinal oscillation x x , swing x y and heave x z The three rotational degrees of freedom include roll r x , pitch y and bow rocker z ;

[0013] Then, the position transformation matrix T is used to transform the movement of the center of gravity into the tower bottom point (x b ,y b ,z b) movement,

[0014] (x bt ,y bt ,z bt )=T(r x ,r y ,r z ,x x ,x y ,x z ) (2)In the formula, x bt ,y bt 、z bt -The displacement of the three degrees of freedom of the bottom point of the tower over time; after derivation, the velocity and acceleration of the bottom point of the tower are further obtained;

[0015] S102, fan aerodynamic performance simulation;

[0016] The wind turbine aerodynamic performance simulation includes using dynamic grid technology to realize the movement of the tower and blades as a whole, sliding grids to simulate wind turbine rotation, and overlapping grids to realize blade pitch change;

[0017] The use of the dynamic mesh technology to achieve the overall movement of the tower and the blades includes selecting a motion calculation area that wraps the wind turbine and the tower, the motion calculation area moves with the movement of the bottom point of the tower, the movement of the bottom point of the tower is obtained by formula (2), in the CFD simulation, the movement of the motion calculation area is achieved by the dynamic mesh, the movement speed of the motion calculation area is set to the speed of the bottom point of the tower, and during the movement of the dynamic mesh, the mesh after the movement is regenerated by the mesh reconstruction technology;

[0018] The sliding grid simulation of fan rotation includes setting an oblate cylindrical region that wraps the entire fan in the area where the fan is located, generating a sliding grid in the oblate cylindrical region to form a sliding grid calculation region, setting the outer surface of the oblate cylindrical region as a sliding boundary, and rotating the sliding grid calculation region around the central axis to simulate the rotation of the fan blades;

[0019] The overlapping grids for implementing blade pitch control include setting a slender cylindrical region that wraps a single blade, setting n according to the number of blades, each slender cylindrical region and the oblate cylindrical region forming an overlapping region, generating a grid in the overlapping region to form an overlapping grid calculation region, removing the grid cells inside the blade geometry in the overlapping grid calculation region by digging, and implementing data exchange between the remaining overlapping grid calculation region and the sliding grid calculation region by an interpolation method; and implementing blade pitch control by controlling the rotation of the remaining overlapping grid calculation region around the centerline axis.

[0020] S103, overall calculation area setting;

[0021] The overall calculation area setting includes presetting the overall calculation area size according to the overall size of the fan and the tower, and adjusting it according to the flow conditions of the flow field so that the vortex at the boundary of the flow field will not affect the movement of the fan and the tower. The yaw movement of the fan is achieved through the lateral component of the air inlet wind speed;

[0022] S104, calculation of power generation efficiency;

[0023] The power generation efficiency calculation includes obtaining the pressure distribution and shear force on the blade surface through CFD simulation, integrating the force on the blade surface, and obtaining the resultant moment T(t); for each time step Δt, the average output power of the wind turbine is calculated according to the following formula:

[0024] P t =∫ t t+Δt T(t)·ω(t)dt / Δt (3)

[0025] Where P t The average power from -t to t+Δt, ω(t)-t is the wind turbine speed; then the power generation efficiency of the floating wind turbine is evaluated according to the following formula:

[0026]

[0027] Where, ρ is air density, A is swept area, and V is air inlet velocity.

[0028] As a preferred technical solution of the present invention, in step S102, the pitch angle is adjusted by a PID controller, and the change in the blade pitch angle is calculated by the following formula:

[0029]

[0030] In the formula, K p - Proportional gain of input signal, K l -Integral gain of the input signal, K d - differential gain of the input signal, N - gearbox transmission ratio, Δδ - difference between the actual speed of the fan motor and the rated speed.

[0031] As a preferred technical solution of the present invention, in step S102, the overall area size is pre-set, and a distance of 5 times the characteristic length of the object in this direction is taken as the boundary on the windward side in the downwind direction, a distance of 10 times the characteristic length of the object in this direction is taken as the boundary on the leeward side in the downwind direction, and a distance of 5 times the characteristic length of the object in this direction is taken as the boundary above, below, left and right in the crosswind direction.

[0032] The beneficial effects of the present invention are:

[0033] 1. The motion law of the bottom point of the tower is obtained through the potential flow method. The motion of the bottom point of the tower is loaded through the motion of the dynamic grid. In the CFD solution, the potential flow method solves the motion of the floating body in the wave, avoiding the two-phase flow problem caused by the CFD method to solve the motion of the floating body in the wave, reducing the demand for calculation grids, reducing the consumption of calculation resources, and solving faster;

[0034] 2. The simulation of the unsteady flow of blades that controls the pitch motion of blades is realized through overlapping grids and PID methods, which truly reflects the hysteresis effect of aerodynamic force and torque brought by the wind turbine maneuvering; CFD is used to accurately simulate the unsteady flow process of the wind turbine, while considering the effects of floating body motion, wind turbine yaw, and wind turbine pitch change. Compared with the traditional wind turbine blade dynamic method, it takes into account the three-dimensional effect of the blade and the calculation is more accurate;

[0035] 3. This method achieves rapid calculation of power generation efficiency while ensuring a certain degree of accuracy, facilitating rapid iteration of the optimal design of floating wind turbines in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a flow chart of a floating wind turbine power generation efficiency evaluation method applicable to engineering design of the present invention;

[0037] Figure 2 It is a schematic diagram of the local calculation area of ​​the present invention;

[0038] Figure 3 It is a schematic diagram of the overall calculation area of ​​the present invention;

[0039] Reference numerals in the figure: 1-tower, 2-motion calculation area, 3-sliding grid calculation area, 4-overlapping grid calculation area, 5-overall calculation area, 6-air inlet, 7-air outlet. DETAILED DESCRIPTION

[0040] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments given here are only used to illustrate and explain the present invention and cannot be used to limit the present invention. It should be noted that many specific details are set forth in the following description to facilitate a full understanding of the present invention, but the present invention may also have other embodiments and variations thereof, and therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0041] Embodiment 1: A method for evaluating the power generation efficiency of a floating wind turbine applicable to engineering design is as follows:

[0042] S101, solving the motion of floating body;

[0043] The floating body motion solution includes establishing the motion equation of the floating wind turbine in the time domain.

[0044]

[0045] Where, M is the mass matrix of the floating body, C is the damping matrix, K is the hydrostatic stiffness recovery matrix, and F is wi - Wind load, F c -Flow force, F wa - Wave load, F m - anchor chain force, solve the motion equation to obtain the center of gravity of the floating buoy (x g ,y g ,z g ) at the position of the displacement, velocity, acceleration of the three translational degrees of freedom and the rotation angle, angular velocity, angular acceleration of the three rotational degrees of freedom, wherein the motion of the three translational degrees of freedom includes longitudinal oscillation x x , swing x y and heave x z The three rotational degrees of freedom include roll r x , pitch y and bow rocker z ; The water flow force and wave load are determined according to the potential flow theory, and the SST k-ω model is used as the wind load turbulence model;

[0046] Then, the position transformation matrix T is used to transform the movement of the center of gravity into the tower bottom point (x b ,y b ,z b ) movement,

[0047] (x bt ,y bt ,z bt )=T(r x ,r y ,r z ,x x ,x y ,x z ) (2)In the formula, x bt ,y bt 、z bt -The displacement of the three degrees of freedom of the bottom point of the tower over time; after derivation, the velocity and acceleration of the bottom point of the tower are further obtained;

[0048] S102, fan aerodynamic performance simulation;

[0049] The wind turbine aerodynamic performance simulation includes using dynamic grid technology to realize the movement of the tower and blades as a whole, sliding grids to simulate wind turbine rotation, and overlapping grids to realize blade pitch change;

[0050] The use of the dynamic mesh technology to achieve the overall movement of the tower and the blades includes selecting a motion calculation area that wraps the wind turbine and the tower, the motion calculation area moves with the movement of the bottom point of the tower, the movement of the bottom point of the tower is obtained by formula (2), in the CFD simulation, the movement of the motion calculation area is achieved by the dynamic mesh, the movement speed of the motion calculation area is set to the speed of the bottom point of the tower, and during the movement of the dynamic mesh, the mesh after the movement is regenerated by the mesh reconstruction technology to avoid the negative volume of the mesh;

[0051] The sliding grid simulation of fan rotation includes setting an oblate cylindrical region that wraps the entire fan in the area where the fan is located, generating a sliding grid in the oblate cylindrical region to form a sliding grid calculation region, setting the outer surface of the oblate cylindrical region as a sliding boundary, and rotating the sliding grid calculation region around the central axis to simulate the rotation of the fan blades;

[0052] The overlapping grid realizes blade pitch change, including setting a slender cylindrical area that wraps a single blade, setting n according to the number of blades, each slender cylindrical area forms an overlapping area with the oblate cylindrical area, generating a grid in the overlapping area to form an overlapping grid calculation area, removing the grid units inside the blade geometry in the overlapping grid calculation area by digging, and realizing data exchange between the remaining overlapping grid calculation area and the sliding grid calculation area by interpolation method; the blade pitch change is realized by controlling the rotation of the remaining overlapping grid calculation area around the centerline axis, and the influence of the change of the wind turbine pitch is introduced; the pitch change adopts a PID controller to adjust the pitch angle, and the change of the blade pitch angle is calculated by the following formula,

[0053]

[0054] In the formula, K p - Proportional gain of input signal, K l -Integral gain of the input signal, K d - differential gain of the input signal, N-gearbox transmission ratio, Δδ-difference between the actual speed of the fan motor and the rated speed;

[0055] S103, overall calculation area setting;

[0056] The overall calculation area setting includes presetting the overall calculation area size according to the overall size of the wind turbine and the tower, presetting the overall area size, taking 5 times the characteristic length of the object in this direction as the boundary on the windward side in the downwind direction, taking 10 times the characteristic length of the object in this direction as the boundary on the leeward side in the downwind direction, taking 5 times the characteristic length of the object in this direction as the boundary on the up, down, left, and right sides in the crosswind direction, and then adjusting according to the flow conditions of the flow field so that the vortex at the boundary of the flow field will not affect the movement of the wind turbine and the tower, and the yaw movement of the wind turbine is realized by the lateral component of the wind speed at the air inlet;

[0057] S104, calculation of power generation efficiency;

[0058] The power generation efficiency calculation includes obtaining the pressure distribution and shear force on the blade surface through CFD simulation, integrating the force on the blade surface, and obtaining the resultant moment T(t); for each time step Δt, the average output power of the wind turbine is calculated according to the following formula:

[0059] P t =∫ t t+Δt T(t)·ω(t)dt / Δt (4)

[0060] Where P t The average power from -t to t+Δt, ω(t)-t is the wind turbine speed; then the power generation efficiency of the floating wind turbine is evaluated according to the following formula:

[0061]

[0062] Where, ρ is air density, A is swept area, and V is air inlet velocity.

[0063] In summary, the floating wind turbine power generation efficiency evaluation method applicable to engineering design of the present invention has the characteristics of low consumption of computing resources and accurate calculation results in the technical field of offshore power generation equipment.

[0064] It should be understood that the above-mentioned embodiments are one or more embodiments of the present invention, and there are many other embodiments and variations thereof based on the present invention; the variations and modifications made by ordinary technicians in this industry through the present invention without making pioneering innovations all fall within the scope of protection of the present invention.

Claims

1. A floating wind turbine power generation efficiency evaluation method suitable for engineering design, characterized in that The specific steps include: S101, solving the motion of floating body; The floating body motion solution includes establishing the motion equation of the floating wind turbine in the time domain. Where, M is the mass matrix of the floating body, C is the damping matrix, K is the hydrostatic stiffness recovery matrix, and F is wi - Wind load, F c -Flow force, F wa - Wave load, F m - anchor chain force, solve the motion equation to obtain the center of gravity of the floating buoy (x g ,y g ,z g ) at the three translational degrees of freedom, displacement, velocity, acceleration and the three rotational degrees of freedom, rotation angle, angular velocity, angular acceleration, wherein the three translational degrees of freedom include longitudinal oscillation x x , swing x y and heave x z The three rotational degrees of freedom include roll r x , pitch y and bow rocker z ; Then, the position transformation matrix T is used to transform the movement of the center of gravity into the tower bottom point (x b ,y b ,z b ) movement, (x bt ,y bt ,z bt )=T(r x ,r y ,r z ,x x ,x y ,x z ) (2)In the formula, x bt ,y bt 、z bt -The displacement of the three degrees of freedom of the bottom point of the tower over time; after derivation, the velocity and acceleration of the bottom point of the tower are further obtained; S102, fan aerodynamic performance simulation; The wind turbine aerodynamic performance simulation includes using dynamic grid technology to realize the movement of the tower and blades as a whole, sliding grids to simulate wind turbine rotation, and overlapping grids to realize blade pitch change; The use of the dynamic mesh technology to achieve the overall movement of the tower and the blades includes selecting a motion calculation area that wraps the wind turbine and the tower, the motion calculation area moves with the movement of the bottom point of the tower, the movement of the bottom point of the tower is obtained by formula (2), in the CFD simulation, the movement of the motion calculation area is achieved by the dynamic mesh, the movement speed of the motion calculation area is set to the speed of the bottom point of the tower, and during the movement of the dynamic mesh, the mesh after the movement is regenerated by the mesh reconstruction technology; The sliding grid simulation of fan rotation includes setting an oblate cylindrical region that wraps the entire fan in the area where the fan is located, generating a sliding grid in the oblate cylindrical region to form a sliding grid calculation region, setting the outer surface of the oblate cylindrical region as a sliding boundary, and rotating the sliding grid calculation region around the central axis to simulate the rotation of the fan blades; The overlapping grids for implementing blade pitch control include setting a slender cylindrical region that wraps a single blade, setting n according to the number of blades, each slender cylindrical region and the oblate cylindrical region forming an overlapping region, generating a grid in the overlapping region to form an overlapping grid calculation region, removing the grid cells inside the blade geometry in the overlapping grid calculation region by digging, and implementing data exchange between the remaining overlapping grid calculation region and the sliding grid calculation region by an interpolation method; and implementing blade pitch control by controlling the rotation of the remaining overlapping grid calculation region around the centerline axis. S103, overall calculation area setting; The overall calculation area setting includes presetting the overall calculation area size according to the overall size of the fan and the tower, and adjusting it according to the flow conditions of the flow field so that the vortex at the boundary of the flow field will not affect the movement of the fan and the tower. The yaw movement of the fan is achieved through the lateral component of the wind speed at the air inlet; S104, calculation of power generation efficiency; The power generation efficiency calculation includes obtaining the pressure distribution and shear force on the blade surface through CFD simulation, integrating the force on the blade surface, and obtaining the resultant moment T(t); for each time step Δt, the average output power of the wind turbine is calculated according to the following formula: Where P t The average power from -t to t+Δt, ω(t)-t is the wind turbine speed; then the power generation efficiency of the floating wind turbine is evaluated according to the following formula: Where, ρ is air density, A is swept area, and V is air inlet velocity.

2. The method for evaluating the power generation efficiency of a floating wind turbine suitable for engineering design according to claim 1, characterized in that: In step S102, the pitch angle is adjusted by a PID controller, and the change in the blade pitch angle is calculated by the following formula: In the formula, K p - Proportional gain of input signal, K l -Integral gain of the input signal, K d - differential gain of the input signal, N - gearbox transmission ratio, Δδ - difference between the actual speed of the fan motor and the rated speed.

3. The method for evaluating the power generation efficiency of a floating wind turbine suitable for engineering design according to claim 1, characterized in that: In step S102, the overall area size is pre-set, and a distance of 5 times the characteristic length of the object in this direction is taken as the boundary on the windward side in the downwind direction, a distance of 10 times the characteristic length of the object in this direction is taken as the boundary on the leeward side in the downwind direction, and a distance of 5 times the characteristic length of the object in this direction is taken as the boundary above, below, left and right in the crosswind direction.

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