Floating fan multi-domain coupling simulation method based on computational fluid mechanics

Abstract

The invention discloses a floating type fan multi-domain coupling simulation method based on computational fluid mechanics, and belongs to the technical field of computational fluid mechanics multi-phase flow simulation. In the multi-domain coupling simulation method for the floating type fan, a computational domain is divided into a rotor domain and a floating type fan platform domain, and mutual influence between aerodynamic characteristics of a rotor and hydrodynamic characteristics of a floating type fan platform is achieved through coupling between thrust of the rotor and motion response of the floating type fan platform. The rotor domain and the platform domain of the method are complete example models respectively, calculation can be completed independently, and coupling calculation among multiple calculation domains can be achieved through the method. Compared with a traditional integral coupling method and calculation results of other studies, the simulation result of the method has good consistency. Under the condition of the same precision, compared with a traditional floating type draught fan coupling simulation method, the method has the advantage that the calculation efficiency is obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of floating wind power, and relates to a simulation method for multi-domain coupling of a floating wind turbine based on computational fluid dynamics. Background Art

[0002] In recent years, my country's offshore wind power industry has developed rapidly, and the application of offshore floating wind turbines has gradually moved towards the deep sea. Compared with traditional onshore wind power, offshore wind power has greater development potential and obvious advantages. As an innovative form of offshore wind energy, floating offshore wind turbines have received widespread attention and have been gradually applied in recent years. Unlike traditional fixed offshore wind turbines, floating offshore wind turbines can be deployed in deeper waters, utilizing richer and more stable wind resources, and have greater development potential. However, floating offshore wind turbines face more complex environmental load challenges. The variability and uncertainty of offshore conditions, such as waves, wind speeds, and currents, will affect the stability of floating offshore wind turbines, leading to complex changes in platform motion response, mooring cable loads, aerodynamic thrust, wake effects, and other aspects.

[0003] Many scholars have carried out overall coupled simulation calculations of floating wind power systems based on computational fluid dynamics methods to study motion response, aerodynamic thrust, output power, anchor chain tension, and wind turbine wake. Although computational fluid dynamics methods can more comprehensively simulate the wave field and wake of floating wind turbines and intuitively reflect the impact of flow fields on wind power systems, computational efficiency has always been a key factor restricting the application of computational fluid dynamics methods in floating wind power systems. Summary of the invention

[0004] The present invention proposes an efficient simulation method for multi-domain coupling of floating wind turbines based on computational fluid dynamics. Based on the floating wind turbine coupling simulation method proposed in the invention, efficient simulation of the aerodynamic-hydrodynamic-mooring coupling model of floating wind turbines under the combined action of wind, wave and flow loads can be achieved, and the aerodynamic, hydrodynamic and mooring dynamics analysis of the wind turbine can be completed.

[0005] A simulation method for multi-domain coupling of a floating wind turbine based on computational fluid dynamics includes the following steps:

[0006] S1. Create the geometry file required to generate the mesh according to the shape of the floating wind turbine platform being simulated;

[0007] S2. Define the computational domain and rotor computational domain sizes of the floating wind turbine platform for simulation in OpenFOAM, create a specific computational grid in the computational domain of the floating wind turbine platform using the geometry file in step S1, and create a refined grid in the rotor computational domain according to computational requirements;

[0008] S3, merge the computational domain of the floating wind turbine platform and the computational domain of the rotor, define the multiphase flow calculation phase fraction and wave field file in the computational domain of the floating wind turbine platform, and define the wind turbine area cellZone in the computational domain of the rotor;

[0009] S4. Based on the velocity-pressure coupling algorithm, multi-domain coupling simulation of floating wind turbines based on computational fluid dynamics is carried out. The overall calculation steps include:

[0010] S41. Calculate the aerodynamic load of the floating wind turbine under platform motion in the rotor domain. According to the blade parameter information and platform motion information, calculate the lift and drag on the blade using the following formula:

[0011] (1)

[0012] (2)

[0013] in: represents the air density, c represents the chord length, dr represents the length of the airfoil unit on the blade, is the relative speed of the blade under the influence of platform motion and rotor rotation, and are the lift coefficient and drag coefficient of the corresponding airfoil respectively;

[0014] S42, integrating the lift resistance of all blade units calculated above along the blade radial direction to obtain the aerodynamic thrust of the fan rotor, and saving the thrust information in a dictionary file of the aerodynamic load;

[0015] S43. In the calculation domain of the floating wind turbine platform, calculate the total fluid load on the floating body, including the surface pressure and viscous force on the floating wind turbine platform;

[0016] S44. Calculate the mooring load on the floating wind turbine platform. Divide the mooring cable into several mass points. Each mass point is connected by a massless spring. The total mass of all mass points represents the mass of the mooring cable. The spring stiffness represents the tensile stiffness of the mooring cable. The fluid load on the mooring unit is calculated by Morrison equation.

[0017] S45, calculating the motion information of the floating wind turbine platform according to the total load on the floating wind turbine platform: velocity, displacement, acceleration, and saving the information to a dictionary file of the motion information, and using a grid solver to calculate the displacement of grid nodes;

[0018] S46. In the rotor calculation domain, read the dictionary file of motion information, update the rotor rotation center position based on the global coordinate system, and calculate the position and relative speed of each segment of the blade based on the rotor local coordinate system.

[0019] Furthermore, the pre-treatment of the floating wind turbine platform includes the following steps:

[0020] a. Define the grid motion setting file based on the floating wind turbine platform parameter information;

[0021] b. Establish the aerodynamic load constraint conditions for the fan rotor and set the aerodynamic load action points.

[0022] Furthermore, the rotor calculation domain pre-processing includes the following steps:

[0023] a. Establish the source item file for the calculation of the fan load in the rotor domain, define the local coordinate system of the fan blade, blade parameter information, number of blade segments, blade load interpolation range and blade rotation parameters;

[0024] b. Define the coupling mode between the wind turbine rotor and the floating wind turbine platform in the rotor calculation domain source item file.

[0025] Furthermore, in the multi-operating simulation of multiple platform forms and rotor forms:

[0026] Establish multiple floating wind turbine platform computational domains: platform 1, platform 2, ... platform n;

[0027] Establish multiple rotor calculation domains: rotor 1, rotor 2... rotor n;

[0028] For a specific working condition, the multiphase flow calculation phase fraction is defined in the floating wind turbine platform domain, and the wind turbine area cellZone is defined in the rotor calculation domain; the corresponding floating wind turbine platform domain and rotor calculation domain are merged to realize the multi-domain coupling calculation of a certain platform form and wind turbine form.

[0029] The beneficial effects of the present invention are as follows:

[0030] (1) The grids required for wave and wind turbine wake calculations are encrypted in the floating platform wind turbine calculation domain and the rotor calculation domain, respectively. Unnecessary grids can be easily thinned in each calculation domain to reduce the overall number of grids.

[0031] (2) The calculation of the rotor domain and the floating wind turbine platform domain is completed successively within one time step, and the calculation efficiency is improved superlinearly compared with the traditional method.

[0032] (3) In the calculation of multiple floating wind turbine platform forms and multiple rotor forms, each calculation domain can be reused, and the modeling efficiency is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solution of the present invention, the drawings required for describing the technical solution are briefly introduced below.

[0034] Figure 1It is the multi-domain coupling simulation flow chart.

[0035] Figure 2 Schematic diagram of the floating body domain and rotor domain in the multi-domain coupling simulation method.

[0036] Figure 3 Schematic diagram of domain merging in the efficient simulation process of the multi-domain coupled simulation method.

[0037] Figure 4 It is the surge response diagram calculated by the multi-domain coupling simulation method.

[0038] Figure 5 It is the heave response diagram calculated by the multi-domain coupling simulation method.

[0039] Figure 6 This is the pitch response diagram calculated by the multi-domain coupling simulation method.

[0040] Figure 7 It is a schematic diagram of the wake field and wave field calculated by the multi-domain coupling simulation method. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] 1. The simulation steps of a single wind turbine coupling model are as follows:

[0044] a. Create the geometry file required to generate the mesh according to the shape of the floating wind turbine platform being simulated;

[0045] b. Define the computational domain and rotor computational domain size of the floating wind turbine platform used for simulation in OpenFOAM, create a specific computational grid in the computational domain of the floating platform using the geometry file in claim 1a, and create a specific refined grid in the computational domain of the rotor according to computational requirements;

[0046] c. The pre-treatment of the floating platform includes the following steps;

[0047] c1. Define the grid motion setting file based on the floating platform parameter information to ensure that the calculation of a single floating platform can be completed within the floating platform calculation domain;

[0048] c2. Establish the aerodynamic load constraint conditions of the fan rotor and set the aerodynamic load action point;

[0049] d. The rotor calculation domain pre-processing includes the following steps;

[0050] d1. Establish the source item file for the rotor domain fan load calculation, define the fan blade local coordinate system, blade parameter information, blade segment number, blade load interpolation range and blade rotation parameters, and ensure that the fixed fan rotor simulation calculation can be performed;

[0051] d2. Define the coupling mode between the wind turbine rotor and the floating platform in the rotor calculation domain source item file;

[0052] e. Combine the grids of the floating platform domain and the rotor calculation domain, define the multiphase flow calculation phase fraction and wave field file in the floating platform domain, and define the wind turbine area cellZone in the rotor calculation domain;

[0053] f. Based on the velocity-pressure coupling algorithm, a multi-domain coupling simulation of floating wind turbines based on computational fluid dynamics is carried out. The overall calculation steps include:

[0054] f1. Calculate the aerodynamic load of the floating wind turbine under platform motion in the rotor domain, which is characterized by calculating the lift and drag on the blades according to the blade parameter information and platform motion information through the following formula

[0055] (1)

[0056] (2)

[0057] in represents the air density, c represents the chord length, dr represents the length of the airfoil unit on the blade, is the relative speed of the blade under the influence of platform motion and rotor rotation, and are the lift and drag coefficients of the corresponding airfoil, respectively;

[0058] f2. Integrate the lift resistance of all blade units calculated in step f1 along the blade radial direction to obtain the aerodynamic thrust of the fan rotor, and save the thrust information to the dictionary file corresponding to the aerodynamic load;

[0059] f3. In the floating platform domain, calculate the total fluid load on the floating body, including the surface pressure and viscous force on the floating platform;

[0060] f4. Calculate the mooring load on the floating platform, characterized in that the mooring cable is divided into a number of mass points, each mass point is connected by a massless spring, wherein the total mass of all mass points represents the mass of the mooring cable, the spring stiffness represents the tensile stiffness of the mooring cable, and the fluid load on the mooring unit is calculated by Morrison equation;

[0061] f5. Calculate the motion information of the floating wind turbine platform based on the total load on the floating platform, and use the mesh solver to calculate the mesh node displacement based on the velocity, displacement, acceleration and other motion information and save it in the corresponding dictionary file of the motion information;

[0062] f6. In the rotor calculation domain, read the motion information dictionary file, update the rotor rotation center position based on the global coordinate system, and calculate the position and relative speed of each segment of the blade based on the rotor local coordinate system;

[0063] 2. In the multi-operating simulation of multiple platform forms and rotor forms, efficient modeling and simulation include the following steps;

[0064] g. For multi-platform and rotor multi-condition simulations, use step c1 to establish multiple floating platform calculation domains: platform 1, platform 2 ... platform n;

[0065] h. For multi-platform and multi-rotor simulations, use step d1 to establish multiple rotor calculation domains: rotor 1, rotor 2, ... rotor n;

[0066] i. For multi-operating condition simulations of multiple platform forms and rotor forms, a specific operating condition uses the right e step to merge the corresponding floating platform domain rotor calculation domain to achieve multi-domain coupling calculation of a certain platform form and wind turbine form.

[0067] The following is a detailed introduction to the specific implementation process of a specific case:

[0068] Build as Figure 2 The floating platform domain and rotor domain of the NREL5MW semi-submersible wind turbine are shown, and the domains are merged;

[0069] The calculation conditions used in the embodiment are wind speed of 11.4 m / s, wave height of 7.58 m, and wave period of 12.1 s.

[0070] The calculated results of surge, heave and pitch are as follows: Figure 4 , 5 As shown in Figure 6, the multi-domain coupling method proposed in the present invention is consistent with the calculation results of the traditional overall coupling method. The calculated wake field and wave field results are shown in Figure 6. Figure 7 shown.

[0071] In this case, the overall coupling method calculates about 2.7 million grids, and the calculation time for each time step is 12 seconds. The multi-domain coupling method calculates about 1.9 million grids, and the calculation time for each time step is 7 seconds. Compared with the traditional overall coupling method, the multi-domain coupling method reduces the number of grids and the calculation time at the same calculation accuracy, and the calculation efficiency is nearly doubled.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A simulation method for multi-domain coupling of floating wind turbines based on computational fluid dynamics, characterized in that: The following steps are involved: S1. Create the geometry file required to generate the mesh according to the shape of the floating wind turbine platform being simulated; S2. Define the computational domain and rotor computational domain sizes of the floating wind turbine platform for simulation in OpenFOAM, create a specific computational grid in the computational domain of the floating wind turbine platform using the geometry file in step S1, and create a refined grid in the rotor computational domain according to computational requirements; S3, merge the computational domain of the floating wind turbine platform and the computational domain of the rotor, define the multiphase flow calculation phase fraction and wave field file in the computational domain of the floating wind turbine platform, and define the wind turbine area cellZone in the computational domain of the rotor; S4. Based on the velocity-pressure coupling algorithm, multi-domain coupling simulation of floating wind turbines based on computational fluid dynamics is carried out. The overall calculation steps include: S41. Calculate the aerodynamic load of the floating wind turbine under platform motion in the rotor domain. According to the blade parameter information and platform motion information, calculate the lift and drag on the blade using the following formula: （1）； （2）； in: represents the air density, c represents the chord length, dr represents the length of the airfoil unit on the blade, is the relative speed of the blade under the influence of platform motion and rotor rotation, and are the lift coefficient and drag coefficient of the corresponding airfoil respectively; S42, integrating the lift resistance of all blade units calculated above along the blade radial direction to obtain the aerodynamic thrust of the fan rotor, and saving the thrust information in a dictionary file of the aerodynamic load; S43. In the calculation domain of the floating wind turbine platform, calculate the total fluid load on the floating body, including the surface pressure and viscous force on the floating wind turbine platform; S44. Calculate the mooring load on the floating wind turbine platform. Divide the mooring cable into several mass points. Each mass point is connected by a massless spring. The total mass of all mass points represents the mass of the mooring cable. The spring stiffness represents the tensile stiffness of the mooring cable. The fluid load on the mooring unit is calculated by Morrison equation. S45, calculating the motion information of the floating wind turbine platform according to the total load on the floating wind turbine platform: velocity, displacement, acceleration, and saving the information to a dictionary file of the motion information, and using a grid solver to calculate the displacement of grid nodes; S46. In the rotor calculation domain, read the dictionary file of motion information, update the rotor rotation center position based on the global coordinate system, and calculate the position and relative speed of each segment of the blade based on the rotor local coordinate system.

2. The method for simulating multi-domain coupling of floating wind turbines based on computational fluid dynamics according to claim 1, characterized in that: The pre-treatment of floating wind turbine platform includes the following steps: a. Define the grid motion setting file based on the floating wind turbine platform parameter information; b. Establish the aerodynamic load constraint conditions for the fan rotor and set the aerodynamic load action points.

3. The method for simulating multi-domain coupling of floating wind turbines based on computational fluid dynamics according to claim 2, characterized in that: The rotor calculation domain pre-processing includes the following steps: a. Establish the source item file for the calculation of the fan load in the rotor domain, define the local coordinate system of the fan blade, blade parameter information, number of blade segments, blade load interpolation range and blade rotation parameters; b. Define the coupling mode between the wind turbine rotor and the floating wind turbine platform in the rotor calculation domain source item file.

4. The method for simulating multi-domain coupling of floating wind turbines based on computational fluid dynamics according to claim 3, characterized in that: In the multi-operating simulation of multiple platform forms and rotor forms: Establish multiple floating wind turbine platform computational domains: platform 1, platform 2, ... platform n; Establish multiple rotor calculation domains: rotor 1, rotor 2... rotor n; For a specific working condition, the multiphase flow calculation phase fraction is defined in the floating wind turbine platform domain, and the wind turbine area cellZone is defined in the rotor calculation domain; the corresponding floating wind turbine platform domain and rotor calculation domain are merged to realize the multi-domain coupling calculation of a certain platform form and wind turbine form.

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