Large-scale offshore wind turbine blade tip trailing edge fusion fractal hole wing structure and wind turbine
Technical Field
The invention relates to a wind turbine blade, in particular to a large-scale offshore wind turbine blade tip trailing edge fusion fractal hole wing structure and a wind turbine.
Background
With the development of the world economy and the continuous improvement of the technological level, the energy problem becomes more serious, more and more countries in the world pay attention to the development of renewable green new energy, and in recent 10 years, intermittent renewable energy is rapidly developed and becomes one of the important energy supply forms in China. The wind energy is a renewable energy source which is green, pollution-free, abundant in reserves, wide in distribution range and relatively high in energy utilization rate, and is emphasized and developed and adopted by many countries.
Compared with a land wind turbine, the offshore wind turbine can generate motions such as yawing, pitching, surging and the like under the influence of the wind and wave combination effect, and can influence the inflow wind speed at the plane of the wind wheel, so that the pneumatic performance of the wind turbine is influenced. In addition, offshore wind energy reserves are abundant, a large wind speed exists, and the blades of the wind turbine usually run under the working condition of the large wind speed and generate flow separation on the suction surface of the blades, so that the lift force of the blades is reduced, the resistance of the blades is increased, the integral noise and vibration of the wind turbine are increased, and the wind turbine can run unstably and the service life of the wind turbine is shortened when the wind turbine runs under the working condition for a long time. In order to improve the aerodynamic performance of a wind turbine blade at high wind speeds, an effective method is needed to delay the flow separation of the suction surface of the blade.
The prior art has developed a number of methods that utilize actively or passively regulated stall. While active stall regulation can be effective in improving the flow separation phenomenon at the blade surface, it requires more cost. While the existing methods of passively adjusting stall can increase the lift coefficient, they can result in significant drag increase.
Disclosure of Invention
The invention aims to provide a large offshore wind turbine blade tip trailing edge fusion fractal hole wing structure and a wind turbine, wherein the blade tip trailing edge fusion wing section is provided with fractal holes with self-similarity, the passive regulation mode is adopted to effectively reduce the flow separation phenomenon of the suction surface of the large offshore wind turbine under the high-wind-speed operation working condition, inhibit the generation of stall, reduce the vibration and unstable operation of the blades, prolong the service life of the wind turbine and save more cost compared with the active stall regulation.
The purpose of the invention can be realized by the following technical scheme:
a large offshore wind turbine blade tip trailing edge fusion fractal hole wing structure comprises a blade main body and a fractal hole wing section, wherein the fractal hole wing section is connected to the tail end of the blade tip of the blade main body, the wing section of the fractal hole wing section is the same as the wing section of the blade tip of the blade main body, a fractal hole is formed in the trailing edge of the fractal hole wing section, and the fractal hole penetrates through the pressure surface and the suction surface of the fractal hole wing section.
The fractal hole wing segment and the blade tip part of the blade main body are in smooth transition.
The span length of the fractal hole wing panel is 1% -3% of the radius of the wind wheel of the wind turbine.
The fractal hole of the blade tip blending wing section is arranged from 0.75 chord length of the relative chord to the tail edge.
The fractal orifice is perpendicular to the grid structure of the blade chord.
The section of the fractal hole is square.
The distribution holes are arranged in a plurality and are arranged in a grid shape.
All the fractal holes comprise first fractal holes and second fractal holes, the second fractal holes surround the first fractal holes, and the size of the first fractal holes is larger than that of the second fractal holes.
The ratio of the side lengths of all the first fractal openings is 3 times that of the second fractal openings.
A wind turbine comprises the blade.
Compared with the prior art, the invention has the following beneficial effects:
1) the fractal holes with self-similarity are arranged on the blade tip trailing edge fusion wing section, the flow separation phenomenon of the suction surface of the offshore large wind turbine under the high wind speed operation working condition is effectively reduced by adopting a passive regulation mode, the generation of stall is inhibited, the vibration and the unstable operation of the blade are reduced, the service life of the wind turbine is prolonged, and the cost is saved compared with the active stall regulation.
2) The blade tip trailing edge blending wing section is smoothly connected with the blade tip part of the blade and has the same wing profile, the fractal hole wing section increases the pressure surface and the suction surface pressure difference of the blade tip, and the torque at the blade tip is improved, so that the total power of the wind turbine is increased, and the wind turbine has good pneumatic performance.
3) The fractal orifice structure is formed by derivation iteration based on a fractal theory, so that the flow resistance of the blade is reduced, the flow blending degree at the tail edge of the blade tip is improved, and the fractal orifice structure is simple in structure and easy to manufacture.
Drawings
FIG. 1 is a schematic structural view of a wind turbine blade with a tip trailing edge fused with a fractal hole wing section according to the present invention;
FIG. 2 is an enlarged structural schematic view of a blade tip trailing edge fused fractal orifice wing section;
FIG. 3 is a cloud chart comparing pressure differences of pressure surfaces of an original blade and a fractal hole blade;
FIG. 4 is a cloud chart comparing pressure differences of suction surfaces of an original blade and a fractal hole blade;
FIG. 5 is a graph of power versus time for a raw blade and a fractal orifice blade;
FIG. 6 is a vector diagram of the velocity of the flow field around the original blade tip position cross section;
FIG. 7 is a vector diagram of flow field velocity around the cross section of the blade tip position of a fractal hole blade;
wherein: 1. the blade comprises a blade body, 2 parts of fractal hole wing sections and 3 parts of fractal holes.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
A large-scale offshore wind turbine blade tip trailing edge fusion fractal hole 3 wing structure is applied to a wind turbine and comprises a blade main body 1 and a fractal hole 3 wing section 2, wherein the fractal hole 3 wing section 2 is connected to the tail end of the blade tip of the blade main body 1, the wing section of the fractal hole 3 wing section 2 is the same as the wing section of the blade tip of the blade main body 1, a fractal hole 3 is formed in the trailing edge of the wing section 2 of the fractal hole 3, and the fractal hole 3 penetrates through a pressure surface and a suction surface of the wing section 2 of the fractal hole 3.
Generally, the wing section 2 of the fractal hole 3 and the blade tip part of the blade main body 1 are in smooth transition, and the span length of the wing section 2 of the fractal hole 3 is 1-3% of the radius of a wind wheel of a wind turbine.
Fig. 2 shows an enlarged structure schematic diagram of a blade tip trailing edge fusion fractal orifice 3 and a wing section 2, and the fractal orifice 33 structure is formed by derivation iteration of any geometric figure based on the fractal theory and has self-similarity, scale invariance and self-affine property. The square hole is adopted in the embodiment, and the one-time iteration width of the fractal hole 3 is 10% -15% of the span-wise length of the wing section 2 of the fractal hole 3. In order to meet the requirement that a fractal hole 3 for secondary iteration is generated on a fused blade tip wing section, the local part of the fractal hole is similar to the whole part in a certain sense, and the iteration width ratio of the secondary iteration hole to the primary iteration hole is always kept as 1: 3.
specifically, as shown in fig. 2, the fractal holes include a first fractal hole and a second fractal hole, the second fractal hole surrounds the first fractal hole, the size of the first fractal hole is larger than that of the second fractal hole, and the side length ratio of all the first fractal holes is 3 times that of the second fractal hole.
Referring to fig. 2, fractal holes 33 are arranged from 0.75 chord length of relative chord of the blade tip to the trailing edge, and form a grid structure which penetrates through the pressure surface and the suction surface of the blade tip blending wing section and is perpendicular to the blade chord, and is also aligned with the incoming flow velocity direction, so that the incoming flow can penetrate through the upper surface and the lower surface of the wing section. Compared with a linearly arranged hole structure, the fractal hole 3 structure improves the flow mixing degree by utilizing the self-similarity, improves the flow field of the blade tip tail edge, reduces the flow resistance of the blade, and further improves the pneumatic performance.
Computational fluid dynamics calculation simulation analysis is carried out on the blades of the wind turbine with or without the blade tip and tail edge fused fractal hole 3 wing sections 2 under the working conditions of surging, pitching and yawing motion generated by the joint action of wind and waves at the rated operating wind speed of 11.4m/s, and as shown in figures 3 and 4, a pressure surface pressure difference comparison cloud picture and a suction surface pressure difference comparison cloud picture of the original blade and the fractal hole 3 are respectively shown. It can be observed that the pressure distribution of the two types of blades is basically the same on the pressure surface of the blade, the negative pressure of the blade tip tail edge fusion fractal hole 3 and the wing section 2 is larger on the suction surface of the blade, the larger negative pressure area is positioned near the fractal hole 3, the larger pressure difference improves the work capacity of the blade tip, and therefore the output power of the blade is increased. As shown in fig. 5, which is a graph of the power of the original blade and the fractal hole 3 blade changing with time, it can be seen that when the wind wheel of the wind turbine rotates for 4 turns, i.e. about 20s, the power of the wind turbine is substantially stable, the output power of the fractal hole 3 blade is 5.16MW, the output power of the original blade is 5.03MW, and the output power of the fractal hole 3 blade is increased by about 2.6% compared with the output power of the original blade.
In addition, the large offshore wind turbine often operates under a high-wind-speed working condition, and the flow separation phenomenon can occur on the upper surface of the wing profile under the influence of the self-rotation of the blades of the wind turbine and high-speed incoming wind. Further adopting computational fluid dynamics calculation, setting blade simulation of the wing section 2 of the blade tip and tail edge fusion fractal hole 3 under the high wind speed operation working condition, and as shown in figures 6 and 7, intercepting flow field velocity vector diagrams around the blade tip position section of the original blade tip and the fractal hole 3 when the wind speed of the inlet incoming flow is 25 m/s. The analysis of the flow field behind the blade tip shows that under the action of high-speed incoming wind, the flow separation phenomenon appears in the flow field behind the suction surface of the original blade, and stall clusters appear near the suction surface, however, under the same wind speed working condition, the flow field behind the suction surface of the fractal orifice 3 blade does not observe the obvious flow separation phenomenon, because the small-scale turbulence is generated at the trailing edge of the blade due to the existence of the fractal orifice 3, the flow field forming the stall cluster area is disturbed, and the stall separation is inhibited.