Research on the characteristic parameters and rotor layout principle of dual-rotor horizontal axis wind turbine
Introduction
In order to exploit and make use of wind energy more effective, the large-scale and generalization of wind turbine has become an inevitable trend. In 2014, the single power of the large wind turbine has reached 5 MW, and the blade length is 126 m [1]; GE’s latest 12 MW offshore wind turbine is 220 m in diameter [2]. According to the feasibility report of Upwind wind energy project in Europe, “by 2020, the power of a single wind turbine can reach 20 MW, and the blade length will be more than 200 m” [3]. In accordance with the wind turbine structure existing, blades which possess hundreds of meters in length pose greater challenges to manufacturing, transportation and installation, as well as the unbalanced load and torque on the nacelle, especially the gearbox. These affect the service life of gearbox and wind turbine components directly, thus the cost of maintenance downtime can’t be ignored.
In recent years, dual-rotor wind turbine has been developed. The blades are made into two sections installed on two rotors respectively, then the two rotors are combined to form a dual-rotor wind turbine, which can not only reduce the manufacturing cost of blades, but also offset part of the unbalanced load of the gearbox.
In order to systematically exploring the relative position of double rotor in DRWT, this paper defines three dimensionless characteristic parameters as evaluation criteria.
The research ideas of this paper are as follows: it is assumed that the power of the whole turbine is constant as P, and distributed to the double rotor according to different power ratio φ. Three characteristic parameters are defined according to the geometric parameters of the double rotor. Through simulation of upwind rotor (UR) flow field, the wind speed distribution within the downwind rotor (DR) swept area can be obtained. In combination with the given position of DR blade root in geometric parameters, the values of three characteristic parameters can be computed. Meanwhile, from the idea of calculus, we can get the calculation method of wind energy in DR swept area, then the sensitivity analysis of characteristic parameters to geometric parameters is conducted. Finally, the different requirements in the actual design and manufacture are reflected in the values of the three characteristic parameters, and the proper geometric parameters are determined according to the relationship between the characteristic parameters and the geometric parameters, so as to arrange the double rotor. The roadmap of this paper is as Fig. 1.
The specific research content of this paper is as follows: the second part is the literature review of dual-rotor wind turbine. The third part is the characterization of double rotor structure and parameters. The forth part is the upwind rotor similarity model and the finite element analysis. This part gives the cloud of wind speed distribution after UR swept area, and studied the symmetry of wind speed distribution on DR swept area. The fifth part calculates the wind energy of DR swept area and three characteristic parameters under different power ratios; The sixth part discusses the relationship between the power ratio of UR and DR, the geometric parameters and the characteristic parameters of the double rotor, besides, the sensitivity of characteristic parameters to geometric parameters is analyzed, then indicated on drawing. The seventh part summarizes the principle of the double rotor layout in four aspects. Fig. 3 is a brief sketch of the research model in this paper.
Section snippets
Related work
A 30 kW wind turbine consisting of main rotor (counter-clockwise, downwind direction) and auxiliary rotor (clockwise, upwind direction) rotating in reverse is established (as shown in Fig. 2) by Sung Nam Jung et al. [4]. Researchers from Iowa State University [5] studied the aerodynamic and wake characteristics of a two-rotor wind turbine when it rotates in the same direction and in the opposite direction with wind tunnel experiments, double rotors of equal diameter, spacing D/4. They found
Structure of double rotor
The structure of double rotor is shown in Fig. 3, downwind-rotor (DR) is in the downwind of upwind-rotor (UR). After the incoming wind passes through UR, part of the wind energy will be absorbed. Low wind speed zone will appear directly behind the swept area of UR. When arranging DR, we should avoid this zone as far as possible. Therefore, DR blade is arranged in the torus outside the UR blade tip, which can effectively reduce the influence of UR wake, as shown in Fig. 4.
Similarity model and finite element analysis
In practice, the method of combining theoretical computing and model test is widely used. Model test is an important tool to study fluid machinery.
It is very difficult and inconvenient to directly study the aerodynamic characteristics and performance of the rotor of large-scale wind turbine. Therefore, researchers use model prototypes to simulate original rotors based on the similarity characteristics of wind turbines. Without losing generality, this paper also calculates the model rotor
Calculation of wind energy on rotation plane of DR blade
Because of the symmetry of the wind speed distribution in Fig. 14, the wind energy of the entire torus can be calculated by only 1/3 of the wind speed of the torus. For the sake of convenience, the wind speed on part AB area shown in Fig. 15 on the torus are uniformly used.
The wind energy calculation formula (7) is proportional to the cube of wind speed. The wind speed derived from simulation results is the values of numerous uniformly distributed discrete points in part AB of the torus. The
Influence of geometric parameters on characteristic parameters of double rotor
In this part, two kinds of variation diagrams were drawn for the three characteristic parameters respectively: (1) At the same power ratio, the variation diagrams among the three characteristic parameters and the geometric parameters of DR is shown; (2) At different power ratios, the same characteristic parameter varies with the geometric parameters of the double rotor.
Since the variation of characteristic parameters at nine power ratios is similar, only the relation graph of three
Layout principle of double rotor
This part discusses the layout principle of the double rotor according to the different design requirements in practice.
Conclusion
In this paper, on the basis of the double rotor structure in wind turbine, with the help of CFD and fluid analysis tools, combining the finite element and calculus method, we provide an idea for calculating the wind energy in the swept area of the downwind rotor. Three characteristic parameters were characterized and their values were calculated. The influence relationship between the power ratio and geometric parameters on the characteristic parameters can be obtained. In addition, the
References (25)
- et al.
Aerodynamic performance prediction of a 30 kw counter-rotating wind turbine system
Renew Energy
(2005) - et al.
An experimental study on the aeromechanics and wake characteristics of a novel twin-rotor wind turbine in a turbulent boundary layer flow
Exp Fluid
(2016) - et al.
A novel folding blade of wind turbine rotor for effective power control
Energy Convers Manag
(2015) - et al.
An experimental study on the aerodynamic performances and wake characteristics of an innovative dual-rotor wind turbine
Energy
(2018) - et al.
Cross axis wind turbine: pushing the limit of wind turbine technology with complementary design
Appl Energy
(2017) - et al.
Measurements of the wake characteristics of co-and counter-rotating twin h-rotor vertical axis wind turbines
Energy
(2017) - et al.
Development and experimental verification of counter-rotating dual rotor/dual generator wind turbine: generating, yawing and furling
Renew Energy
(2017) - et al.
Experimental and fluid structure interaction analysis of a morphing wind turbine rotor
Energy
(2015) - et al.
Advanced methodology for feasibility studies on building-mounted wind turbines installation in urban environment: applying cfd analysis
Energy
(2019) - et al.
Concept of flexible vertical-axis wind turbine with numerical simulation and shape optimization
Energy
(2019)
Investigation of wake characteristics of a yawed hawt and its impacts on the inline downstream wind turbine using unsteady cfd
J Wind Eng Ind Aerodyn
Fluid-structure coupled computations of the nrel 5 mw wind turbine by means of cfd
Renew Energy
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