Numerical prediction method for operation characteristics of one-way turbine wave energy power generation system

Abstract

The application discloses a numerical prediction method for operation characteristics of a one-way turbine wave energy power generation system, and belongs to the field of wave energy development and utilization. The numerical prediction method for operation characteristics of the one-way turbine wave energy power generation system comprises the following steps: establishing a three-dimensional geometric model of an air chamber integrated with a one-way valve and a one-way air turbine and a numerical wave pool; setting a calculation domain and dividing the grid of the three-dimensional geometric model and the numerical wave pool; setting boundary conditions; setting a turbulence model, a wave making type, a pressure-velocity coupling solution algorithm and air density; setting a momentum source term of the one-way valve area; setting the one-way air turbine area as a rigid body rotating around a fixed shaft and setting corresponding physical parameter monitoring; and solving energy conversion efficiency and operation stability indexes of the system. The method completely reproduces a complex energy chain transmission process from wave energy to mechanical energy, and ensures physical authenticity of the prediction result.

Description

Technical Field

[0001] This invention relates to the field of wave energy development and utilization, and more specifically, to a numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system. Background Technology

[0002] As one of the most commercially viable wave energy capture technologies currently available, the core of the oscillating water column wave energy conversion device lies in the efficient and reliable conversion of the kinetic energy of the oscillating airflow within the air chamber into mechanical energy. In this stage, the performance of the air turbine directly determines the energy recovery efficiency and operational stability of the entire system.

[0003] A search revealed that Chinese patent CN114297949B discloses a CFD-based model of the entire process of an air chamber and its efficiency prediction method. This method can accurately incorporate the damping effect of the air turbine into the air chamber, fully consider the dynamic coupling effect between the air turbine and the air chamber, and can truly reflect the working state of the oscillating water column, making a reasonable prediction of the efficiency of the entire process.

[0004] The above simulation method is only applicable to the simulation and prediction of bidirectional turbines and cannot be used for the simulation and prediction of unidirectional turbines. In view of this, we propose a numerical prediction method for the operating characteristics of unidirectional turbine wave energy power generation systems. Summary of the Invention

[0005] 1. Technical problems to be solved The purpose of this invention is to provide a numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system, so as to solve the problems mentioned in the background art.

[0006] 2. Technical Solution This invention is achieved through the following technical solution: A numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system is applied to such a system, which includes a numerical wave pool and an air chamber at one end of the pool. The air chamber is connected to the outside via a one-way valve and an air flow channel. A unidirectional air turbine is installed within the air flow channel. The method includes the following steps: S1. Establish a three-dimensional geometric model of the air chamber integrating a one-way valve and a one-way air turbine, and a numerical wave pool. S2. Set up the computational domain and mesh the three-dimensional geometric model and the numerical wave pool; S3. Set boundary conditions; S4. Set the turbulence model, wave type, pressure-velocity coupled solution algorithm, and air density; S5. Set the momentum source term for the one-way valve region as follows: ; in, The coefficient of viscosity resistance. The inertial drag coefficient, It is the apparent velocity vector; The viscous resistance coefficient and the inertial resistance coefficient are dynamically adjusted according to the instantaneous pressure difference between the inside and outside of the gas chamber, and are used to simulate the opening and closing state of the one-way valve. S6. Set the unidirectional air turbine region as a rigid body rotating about a fixed axis, and calculate the angular acceleration of the unidirectional air turbine using the following formula: ; ; Let be the aerodynamic torque acting on the unidirectional air turbine blade at the Tth time step; Aerodynamic forces on a unidirectional air turbine blade micro-element; It is a position vector; The generator load torque is negative. Torque coefficient, I R The moment of inertia of a unidirectional air turbine rotor; The angular acceleration of the unidirectional air turbine rotor; S7. Set the corresponding physical parameter monitoring, and set the calculation time step and calculation time. Start the calculation. After the calculation is completed, obtain the time series of the corresponding parameters. S8. Based on the time series of the corresponding parameters, solve for the energy conversion efficiency and operational stability index of the system.

[0007] In this scheme, a dynamic parameter porous medium model is used to replace the one-way valve. Without the need for dynamic mesh, the opening and closing process of the one-way valve and its regulation effect on airflow are represented with high fidelity. This can simulate the operating state of the one-way air turbine and ensure the physical authenticity of the prediction results.

[0008] As a preferred embodiment of this application, when the pressure difference between the inside and outside of the gas chamber is greater than a first threshold, the values ​​of the viscous drag coefficient and the inertial drag coefficient are

[10] . 4 ~ 10 6 When the pressure difference between the inside and outside of the air chamber is less than the second threshold, the values ​​of the viscous drag coefficient and the inertial drag coefficient are

[10] . -5 ~ 10 -3 When the pressure difference between the inside and outside of the air chamber is between the first threshold and the second threshold, the values ​​of the viscous drag coefficient and the inertial drag coefficient are determined by linear interpolation.

[0009] Preferably, the first threshold is positive 1 / 100 of the peak value of the internal and external pressure difference; the second threshold is negative 1 / 100 of the peak value of the internal and external pressure difference.

[0010] As a preferred embodiment of this application, step S2 further includes: refining the mesh in the area near the wave free interface of the numerical wave pool, the unidirectional air turbine rotor, the stator and guide vane surfaces and the unidirectional valve area, and generating two or more prism layer meshes in the gap between the rotor blade tip and the casing of the unidirectional air turbine, for accurately simulating the blade tip leakage flow.

[0011] As a preferred embodiment of this application, in step S3, the left side of the numerical wave pool is the flow velocity inlet, the top is the pressure outlet, and the bottom, right side and sides are set as non-slip walls.

[0012] In a preferred embodiment of this application, in step S4, the Reynolds-averaged Navier-Stokes equations are used to describe the fluid motion, and the k-ωSST turbulence model is used to close the Reynolds stress term; the wave type is a second-order Stokes regular wave; the pressure-velocity coupled solution algorithm uses the SIMPLE algorithm; the air density is calculated using the following formula: ; in, P atm Where is atmospheric pressure, and R is the gas constant, with a value of 8.314 J / (mol·K).

[0013] In a preferred embodiment of this application, in step S7, the air-water free surface is captured using the fluid volume method, and the governing equation is: ; Where γ is the fluid volume fraction in the discrete grid cell, with a value ranging from 0 to 1, U is the fluid velocity, and Uc is the compression velocity at the water-air interface.

[0014] As a preferred embodiment of this application, in step S7, the physical parameters include: the pressure difference between the inside and outside of the air chamber, the volumetric flow rate through the unidirectional air turbine, the instantaneous rotational speed of the unidirectional air turbine rotor, and the aerodynamic torque of the unidirectional air turbine rotor.

[0015] As a preferred embodiment of this application, step S8 includes: calculating the wave-gas conversion efficiency using the following formula: ; in, For average aerodynamic power, The incident wave power per unit crest width; The gas turbine conversion efficiency is calculated using the following formula: ; in, This represents the average mechanical power of a unidirectional air turbine rotor. The overall conversion efficiency of the wave converter is calculated using the following formula: ; The operational stability index is calculated using the following formula: ; ω max and ω min These represent the maximum and minimum angular velocities of a unidirectional air turbine rotor within one cycle.

[0016] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are: 1) This application uses a dynamic parameter porous medium model to represent a check valve, achieving a high-fidelity equivalent of the transient opening and closing process of the check valve and its effect on airflow regulation without the need for dynamic meshing. Simultaneously, by coupling air compressibility, the VOF free surface model, and rotor dynamics, the complex energy chain transfer process from wave energy to mechanical energy is fully reproduced, ensuring the physical accuracy of the prediction results.

[0017] 2) This application can simultaneously output a complete set of data from macroscopic performance, such as multi-stage efficiency and average power, as well as microscopic dynamics, such as pressure fluctuations, flow rate changes, and speed pulsations; which enables researchers to gain in-depth insights into the working mechanism of the system. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of a unidirectional turbine wave energy generation system; Figure 2 This is a schematic diagram of the air chamber structure of a unidirectional turbine wave energy generation system. Figure 3 This is a schematic diagram of a unidirectional air turbine, which is a unidirectional turbine wave energy power generation system. Figure 4 It is a graph showing the air pressure difference between the inside and outside of the chamber; Figure 5 It is a volumetric flow rate curve obtained through a one-way air turbine; Figure 6 It is a graph of the instantaneous rotational speed of a unidirectional air turbine rotor; Figure 7 It is the aerodynamic torque of a unidirectional air turbine rotor; Figure 8 It is a graph of aerodynamic power; Figure 9 It is a graph of the mechanical power of a unidirectional air turbine rotor; Figure 10 It is a graph showing the efficiency of a one-way air turbine; In the diagram: 1. Numerical wave pool; 2. Air chamber; 3. One-way valve; 4. Air flow channel; 5. One-way air turbine. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0020] like Figure 1 and Figure 2 In this design, the diameter of air chamber 2 is b = 8 m, the height is c = 10 m, and the draft below the still water surface is d = 7 m; Figure 3 As shown in the figure, a is the rotor of the unidirectional air turbine 5, b is the stator of the unidirectional air turbine 5, and c is the guide vane of the unidirectional air turbine 5. The rotor of the unidirectional air turbine 5 has a diameter of 0.8 m and is equipped with 30 rotor blades and 26 stationary guide vanes.

[0021] S1. Establish a three-dimensional geometric model of the air chamber 2 integrating the one-way valve 3 and the one-way air turbine 5, and a numerical wave pool 1. S2. Set up the computational domain and mesh the three-dimensional geometric model and numerical wave pool 1; The computational domain size of numerical wave pool 1 is set to be 120 m long and 20 m high, with the air domain and water domain occupying 10 m, to ensure the full development and attenuation of the wave free surface. Discretization was performed using a cut volume mesh, and local refinement was applied to the following key areas: A. The region near the free surface of the wave, to ensure the accuracy of the VOF method in capturing the interface; B. Unidirectional air turbine 5 rotor, stator and guide vane surfaces to accurately analyze the complex flow around the blades; C. Check valve, zone 3, to accurately calculate its pressure drop characteristics; Furthermore, two or more prismatic mesh layers are generated at the gap between the rotor blade tip and the casing of the unidirectional air turbine 5 to accurately simulate the blade tip leakage flow.

[0022] S3. Set boundary conditions; the left side of the numerical wave pool 1 is the velocity inlet, the top is the pressure outlet, and the bottom, right side and sides are set as non-slip walls; S4. Set the turbulence model, wave type, pressure-velocity coupled solution algorithm, and air density; The k-ωSST model was selected for the turbulence model because it is more accurate in predicting flow separation under adverse pressure gradients. The wave type is a second-order Stokes regular wave, with a wave height of 1.0 m and a period of T of 4.5 s. The pressure-velocity coupling uses the SIMPLE algorithm; the time discretization uses a second-order implicit scheme for transient calculation.

[0023] The air density is set to be calculated using the ideal gas law to account for compressibility effects.

[0024] S5. Configure the momentum source term for zone 3 of the check valve: When the pressure difference between the inside and outside of chamber 2 is greater than 1 / 100 of the peak pressure difference, the values ​​of the viscous drag coefficient and the inertial drag coefficient are both 10. 5 When the pressure difference between the inside and outside of chamber 2 is less than -1 / 100 of the peak pressure difference, the values ​​of the viscous drag coefficient and the inertial drag coefficient are both 10. -3 When the pressure difference between the inside and outside of chamber 2 is between positive 1 / 100 and negative 1 / 100 of the peak value of the pressure difference, the values ​​of the viscous drag coefficient and the inertial drag coefficient are determined by linear interpolation.

[0025] S6. Set the relevant parameters for zone 5 of the one-way air turbine; Set generator load torque coefficient = 2 N·m·s / rad, and perform transient simulations for several wave cycles until the flow field and rotor speed reach a periodic steady state; Set the moment of inertia I of the unidirectional air turbine rotor. R =20kg·m 2 ; S7. Set the physical parameter monitoring to the pressure difference inside and outside the air chamber 2, the volumetric flow rate through the one-way air turbine 5, the instantaneous speed of the rotor of the one-way air turbine 5, and the aerodynamic torque of the rotor of the one-way air turbine 5. The time step was set to 1 / 1500 of the period T; the calculation time was set to 10T. S8. Monitoring results are as follows Figures 4 to 7 As shown; according to Figure 4 and Figure 5 The monitoring results of the given air pressure difference and volumetric flow rate show that only significant positive air pressure difference values ​​occur in air chamber 2. The one-way air turbine 5 mainly only undergoes the process of exhausting air outwards, while the negative air pressure difference values ​​and the volumetric flow rate of air drawn inwards through the one-way air turbine 5 are very small, basically fluctuating around 0, thus achieving a successful simulation of the one-way valve 3. Figure 6 and Figure 7 The instantaneous rotational speed and torque shown simulate the actual motion state of the air turbine 5 under the action of the one-way valve 3.

[0026] Calculate aerodynamic power based on monitoring results, such as Figure 8 As shown; the mechanical power of the unidirectional air turbine 5-plane rotor is as follows: Figure 9 As shown, this can be used as a design guide for a unidirectional air turbine.

Claims

1. A numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system, applied to a unidirectional turbine wave energy power generation system, the system comprising a numerical wave pool (1) and an air chamber (2) at one end of the numerical wave pool (1), the air chamber (2) being connected to the outside via a one-way valve (3) and an air flow channel (4), the air flow channel (4) being equipped with a unidirectional air turbine (5), characterized in that: Includes the following steps: S1. Establish a three-dimensional geometric model of the air chamber (2) of the integrated one-way valve (3) and one-way air turbine (5) and a numerical wave pool (1). S2. Set up the computational domain and mesh the three-dimensional geometric model and the numerical wave pool (1); S3. Set boundary conditions; S4. Set the turbulence model, wave type, pressure-velocity coupled solution algorithm, and air density; S5. Set the momentum source term of the one-way valve (3) region as follows: ； in, The coefficient of viscosity resistance. The inertial drag coefficient, It is the apparent velocity vector; The viscous resistance coefficient and the inertial resistance coefficient are dynamically adjusted according to the instantaneous pressure difference between the inside and outside of the gas chamber, and are used to simulate the opening and closing state of the one-way valve. S6. Set the unidirectional air turbine (5) region as a rigid body rotating about a fixed axis, and calculate the angular acceleration of the unidirectional air turbine (5) using the following formula: ； ； The aerodynamic torque acting on the blade of the unidirectional air turbine (5) at the Tth time step; Aerodynamic forces on the blade micro-element of a unidirectional air turbine (5); It is a position vector; The generator load torque is negative. Torque coefficient, I R The moment of inertia of the rotor of the unidirectional air turbine (5); The angular acceleration of the rotor of the unidirectional air turbine (5); S7. Set the corresponding physical parameter monitoring, and set the calculation time step and calculation time. Start the calculation. After the calculation is completed, obtain the time series of the corresponding parameters. S8. Based on the time series of the corresponding parameters, solve for the energy conversion efficiency and operational stability index of the system.

2. The numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system according to claim 1, characterized in that: When the pressure difference between the inside and outside of the gas chamber (2) is greater than the first threshold, the values ​​of the viscous drag coefficient and the inertial drag coefficient are [10]. 4 ~ 10 6 When the pressure difference between the inside and outside of the gas chamber (2) is less than the second threshold, the values ​​of the viscous drag coefficient and the inertial drag coefficient are [10]. -5 ~ 10 -3 When the pressure difference between the inside and outside of the gas chamber (2) is between the first threshold and the second threshold, the values ​​of the viscous drag coefficient and the inertial drag coefficient are determined by linear interpolation.

3. The numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system according to claim 2, characterized in that: The first threshold is positive 1 / 100 of the peak value of the internal and external pressure difference; the second threshold is negative 1 / 100 of the peak value of the internal and external pressure difference.

4. The numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system according to claim 1, characterized in that: Step S2 further includes: refining the mesh in the area near the wave free interface of the numerical wave pool (1), the rotor of the one-way air turbine (5), the surface of the stator and guide vanes and the area of ​​the one-way valve (3), and generating two or more prism layer meshes in the gap between the rotor blade tip and the casing of the one-way air turbine (5).

5. The numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system according to claim 1, characterized in that: In step S3, the left side of the numerical wave pool (1) is the flow velocity inlet, the top is the pressure outlet, and the bottom, right side and sides are set as non-slip walls.

6. The numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system according to claim 1, characterized in that: In step S4, the Reynolds-averaged Navier-Stokes equations are used to describe the fluid motion, and the k-ωSST turbulence model is used to close the Reynolds stress term. The wave type is a second-order Stokes regular wave, and the pressure-velocity coupled solution algorithm uses the SIMPLE algorithm. The air density is calculated using the following formula: ； in, P atm Where is atmospheric pressure, and R is the gas constant, with a value of 8.314 J / (mol·K).

7. The numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system according to claim 1, characterized in that: In step S7, the free liquid surface of air and water is captured using the fluid volume method, and the governing equation is: ； Where γ is the fluid volume fraction in the discrete grid cell, with a value ranging from 0 to 1, U is the fluid velocity, and Uc is the compression velocity at the water-air interface.

8. The numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system according to claim 1, characterized in that: In step S7, the physical parameters include: the pressure difference inside and outside the air chamber (2), the volumetric flow rate through the one-way air turbine (5), the instantaneous rotational speed of the rotor of the one-way air turbine (5), and the aerodynamic torque of the rotor of the one-way air turbine (5).

9. The numerical prediction method for the operating characteristics of a unidirectional turbine wave energy power generation system according to claim 1, characterized in that: Step S8 includes: calculating the wave-gas conversion efficiency using the following formula: ； in, The average aerodynamic power, The incident wave power per unit crest width; The gas turbine conversion efficiency is calculated using the following formula: ； in, The average unidirectional air turbine rotor mechanical power; The overall conversion efficiency of the wave converter is calculated using the following formula: ； The operational stability index is calculated using the following formula: ； ω max and ω min The maximum and minimum angular velocities of the rotor in one cycle of a unidirectional air turbine (5).

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