CN112380648A - Tidal current energy water turbine analysis method containing winglet blades - Google Patents

Tidal current energy water turbine analysis method containing winglet blades Download PDF

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CN112380648A
CN112380648A CN202011252836.2A CN202011252836A CN112380648A CN 112380648 A CN112380648 A CN 112380648A CN 202011252836 A CN202011252836 A CN 202011252836A CN 112380648 A CN112380648 A CN 112380648A
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winglet
blade
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任毅如
金其多
刘秉文
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Hunan University
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    • G06F30/00—Computer-aided design [CAD]
    • G06F30/10—Geometric CAD
    • G06F30/17—Mechanical parametric or variational design
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03B—MACHINES OR ENGINES FOR LIQUIDS
    • F03B3/00—Machines or engines of reaction type; Parts or details peculiar thereto
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Abstract

The invention provides a tidal energy water turbine analysis method containing winglet blades, wherein the tidal energy water turbine comprises a main shaft and a plurality of blades, the blades comprise winglets, and the analysis method comprises the following steps: establishing a structural model of a single blade according to the geometric data of the blade; establishing a flow field CFD calculation model; carrying out uncertainty analysis and verification, carrying out grid convergence index analysis by adopting three grids of a sparse grid, a medium grid and a fine grid, and realizing discrete error analysis by calculating power factors of the three grids; performing hydrodynamic characteristic analysis, comparing power coefficients and thrust coefficients of the tidal current energy water turbine containing the winglet blades with those of a traditional water turbine, and analyzing the influence of winglets on the performance of the tidal current energy water turbine; and selecting design variables, and establishing a design variable and hydrodynamic characteristic database, wherein the design variables comprise the bending direction of the winglet, the length of the upper chord and the inclination angle. The analysis method provided by the invention has high accuracy.

Description

Tidal current energy water turbine analysis method containing winglet blades
Technical Field
The invention relates to the technical field of tidal current energy power generation, in particular to a tidal current energy water turbine analysis method containing winglet blades.
Background
Tidal current energy is taken as a renewable clean energy source, has great development potential and is paid attention from various countries. However, the power generation efficiency of tidal current energy is still at a low level, and has become the biggest obstacle limiting the commercialization thereof. The tidal current energy water turbine is a tidal current energy power generation device with great potential. The water flow drives the blades to rotate, so that kinetic energy of the water flow can be converted into mechanical energy and then into electric energy. In the design of a water turbine, a blade is one of the most critical components, the fluid dynamic performance of the blade is good and bad, and the capture efficiency and the power generation efficiency of the water turbine on tidal current energy are determined.
Therefore, there is a need for a new method for analyzing a tidal current energy water turbine including winglet blades, which provides data support for the design of high energy conversion efficiency water turbine blades.
Disclosure of Invention
The invention aims to overcome the technical problems and provide a tidal current energy water turbine analysis method containing winglet blades.
In order to achieve the above object, the present invention provides a tidal current energy water turbine analysis method including winglet blades, the tidal current energy water turbine including a main shaft and a plurality of blades mounted on the main shaft, the blades including an arc-shaped blade body and winglets disposed at the tips of the arc-shaped blade body, the analysis method including the steps of:
s1: establishing a structural model of a single blade according to the geometric data of the blade;
s2: establishing a flow field CFD calculation model according to the structural model of the blade;
s3: carrying out uncertainty analysis and verification, carrying out grid convergence index analysis by adopting three grids with different densities, namely a sparse grid, a medium grid and a fine grid, and realizing discrete error analysis by calculating power factors of the three grids;
s4: performing hydrodynamic characteristic analysis, comparing power coefficients and thrust coefficients of the tidal current energy water turbine with the winglet blades and a traditional water turbine, and analyzing the influence of the winglet on the performance of the tidal current energy water turbine;
s5: selecting design variables, and establishing a database of the design variables and hydrodynamic characteristics, wherein the design variables include a bend direction of the winglet, a winglet length, an upper chord length, and a cant angle.
Preferably, the arc blade body with main shaft fixed connection, the winglet includes the suction side winglet, the suction side winglet set up in the apex position of arc blade body, the suction side winglet with arc blade body integrated into one piece and smooth transition, the suction side winglet orientation the suction side of arc blade body is crooked, and with the trailing edge of arc blade body is tangent, just the central line of suction side winglet with the center of arc blade body apex is tangent.
Preferably, the cross-sectional area of the suction surface winglet decreases from the root along the extension direction, the thickness of the suction surface winglet decreases from the root along the extension direction, the length of the suction surface winglet is 1/30-1/15 of the diameter of the arc-shaped blade body, the chord length of the tip section of the suction surface winglet is 1/5-1/10 of the length of the suction surface winglet, and the inclination angle is 50-90 degrees.
Preferably, the winglet further comprises a pressure surface winglet, the pressure surface winglet is arranged at the tip position of the arc-shaped blade body, the pressure surface winglet is integrally formed with the arc-shaped blade body and is in smooth transition, the pressure surface winglet faces to the pressure surface bending of the arc-shaped blade body and is tangent to the rear edge of the arc-shaped blade body, and the central line of the pressure surface winglet is tangent to the center of the tip of the arc-shaped blade body.
Preferably, the cross-sectional area of the pressure-surface winglet decreases from the root along the extension direction, the thickness of the pressure-surface winglet decreases from the root along the extension direction, the length of the pressure-surface winglet is 1/30-1/15 of the diameter of the arc-shaped blade body, the chord length of the tip cross-section of the pressure-surface winglet is 1/5-1/10 of the length of the pressure-surface winglet, and the inclination angle is 50-90 degrees.
Preferably, the step S1 includes the following steps:
s11: acquiring two-dimensional coordinates of the airfoil at any section of the blade through an airfoil database;
s12: with airfoil aerodynamic centre (x)p,yp) Solving the two-dimensional coordinate (x) of the airfoil under the new coordinate system by taking the connecting line of the front edge and the rear edge of the airfoil as the original point and the x axis1,y1) By a translation transformation (x)1,y1)＝(x0,y0)-(xp,yp)；
S13: according to the chord length and the torsion angle data of each section of the blade, obtaining three-dimensional space coordinates (x, y, z) of each discrete voxel point of the blade through scaling transformation and rotation transformation respectively, wherein the scaling transformation process comprises the following steps: (x)2,y2)＝c(x1,y1) (ii) a The process of the rotation transformation is as follows:
Figure BDA0002772149050000031
c is the chord length of the blade section, alpha is the torsion angle of the blade section, and r is the position of the section;
s14: and introducing the obtained three-dimensional space coordinates (x, y, z) of the discrete points of the leaf elements into modeling to establish each section of the blade, and obtaining a three-dimensional model of the blade through a sweeping function.
Preferably, the step S2 includes the following steps:
s21: establishing a basic control equation, carrying out turbulence numerical simulation by adopting a Reynolds time-mean method, converting an instantaneous value of a physical quantity in the basic control equation into the sum of a time-mean value and a pulsation value, and then respectively obtaining a continuity equation and a momentum equation:
Figure BDA0002772149050000032
Figure BDA0002772149050000033
where i is 1,2,3, u is the water velocity, μ is the dynamic viscosity, ρ is the water density, S is the source term,
Figure BDA0002772149050000034
the Reynolds stress term is added to satisfy equation closure and is controlled and established by a turbulence model;
s22: establishing a turbulence model to meet the closure of a momentum equation, wherein the expression of the turbulence viscosity in the turbulence model is as follows:
Figure BDA0002772149050000035
where S is the absolute value of vorticity, k is the turbulent kinetic energy, ω is the dissipation ratio, a1Is a constant coefficient;
s23: establishing a rotation model, and performing numerical simulation on the rotation of the blade by adopting a multi-reference coordinate system;
the rotational domain continuity equation is as follows:
Figure BDA0002772149050000036
and the form to the left of the equal sign of the momentum equation in the rotating coordinate system is as follows:
Figure BDA0002772149050000037
wherein
Figure BDA0002772149050000041
In order to be the absolute speed of the movement,
Figure BDA0002772149050000042
in order to be the relative speed of the movement,
Figure BDA0002772149050000043
is the angular velocity of the rotating coordinate system;
s24: setting boundary conditions, dividing grids, solving a discrete equation, and completing the establishment of a CFD calculation model of the flow field.
Preferably, the turbulence model is a k- ω shear stress transport turbulence model, and in step S22, expressions of a turbulence kinetic energy transport equation and a dissipation ratio equation are as follows:
Figure BDA0002772149050000044
the constant coefficient is calculated by the following formula:
φ＝φ1F1+φ2(1-F1)
wherein phi1Is a constant coefficient in the k-epsilon turbulence model formula, phi2Is a constant coefficient in a k-omega turbulence model formula; the sealing coefficient and the auxiliary relationship in the above formula are shown as the following formula:
Figure BDA0002772149050000045
Figure BDA0002772149050000046
Figure BDA0002772149050000047
Figure BDA0002772149050000048
in the above formula, L is the distance to the next curved surface, PkFor rate of generation of kinetic energy of turbulence, σk1,σk2,σω1,σω2,μt,μl,β*Are all constant.
Preferably, the step S3 specifically includes: calculating power factors of three grids including a sparse grid, a medium grid and a fine grid to realize discrete error analysis, wherein the estimation precision is obtained by the following formula:
Figure BDA0002772149050000049
Figure BDA00027721490500000410
Figure BDA00027721490500000411
Figure BDA0002772149050000051
rij＝ni/nj
in the formula:
Figure BDA0002772149050000052
respectively calculating power coefficients obtained by sparse grid, medium grid and fine grid, wherein subscripts i and j represent C, M and F, p is convergence order, q is analog variable, r is grid refinement rate, and n is grid number;
the mesh convergence index can be calculated from the following equation:
Figure BDA0002772149050000053
Figure BDA0002772149050000054
wherein FsTo a safety factor, eMFIs a relative error.
Preferably, the analyzing of the hydrodynamic characteristics in step S4 includes flow field analysis and power coefficient analysis, and the flow field analysis analyzes the flow field characteristics of the tidal energy turbine through a pressure cloud chart of the blade surface, a pressure cloud chart of the blade section, a flow chart of the blade section, and a tip vorticity and tip flow chart; and the power coefficient analysis compares the power coefficient and the thrust coefficient of the water turbine containing the winglet blade tidal current energy with those of the traditional water turbine by utilizing a CFD flow field calculation model.
Compared with the related art, the invention has the beneficial effects that:
1) compared with the traditional tidal energy water turbine blade structure, the tidal energy water turbine blade with the winglet has the advantages of simple structure, convenience in design and the like;
2) the blade structure of the tidal energy water turbine with the winglet can effectively reduce the strength of the tip vortex and improve the energy conversion efficiency of the water turbine;
3) the analysis method provided by the invention has higher universality and accuracy, can accurately obtain the hydrodynamic characteristics of the tidal energy water turbine blade, and ensures the calculation convergence and accuracy by adopting an uncertainty analysis method.
4) A design parameter and hydrodynamic performance database is established through design variable analysis, and appropriate design parameters can be selected according to actual design requirements.
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In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without inventive efforts, wherein:
FIG. 1 is a flow chart of an analysis method of a tidal current energy water turbine with winglet blades provided by the invention;
fig. 2 is a schematic structural view of a tidal energy turbine provided by the present invention;
FIG. 3 is a schematic illustration of the suction side winglet of FIG. 2;
FIG. 4 is a schematic illustration of the pressure side winglet of FIG. 2;
FIG. 5(a) is a diagram of blade vorticity in the first embodiment; FIG. 5(b) is a diagram showing the vorticity of the blade according to the second embodiment; FIG. 5(c) is a view showing the vorticity of the blade in the third embodiment; FIG. 5(d) is a vorticity diagram of a blade of a water turbine in the related art;
fig. 6 is a graph showing the power increase of the tidal energy turbine in the first embodiment, the second embodiment and the third embodiment and the tidal energy turbine in the related art.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1 to 6, the tidal turbine 100 includes a main shaft 10 and a plurality of blades 20 mounted on the main shaft 10, where the blades 20 include an arc-shaped blade body 21 and a winglet, the arc-shaped blade body 21 is fixedly connected to the main shaft 10, the winglet is disposed at a blade tip of the arc-shaped blade body 21, the winglet includes a suction surface winglet 22, the suction surface winglet 22 is bent toward a suction surface of the arc-shaped blade body 21 and is tangent to a rear edge of the arc-shaped blade body 21, and a center line of the suction surface winglet 22 is tangent to a center of the blade tip of the arc-shaped blade body 21. Preferably, the suction surface winglet 22 is integrally formed with the curved blade body 21 and has a smooth transition to reduce the profile drag at the junction of the curved blade body 21 and the suction surface winglet 22.
Further, the winglet may further include a pressure-side winglet 23, wherein the pressure-side winglet 23 is curved toward the pressure side of the curved blade body 21 and is tangent to the rear edge of the curved blade body 21, and the center line of the pressure-side winglet 23 is tangent to the center of the tip of the curved blade body 21. Preferably, the pressure surface winglet 23 is integrally formed with the curved blade body 21 and has a smooth transition to reduce the profile drag at the junction of the curved blade body 21 and the pressure surface winglet 23.
The suction surface winglet 22 and the pressure surface winglet 23 can improve the torque at the blade tip of the arc-shaped blade body 21, reduce the strength of the blade tip vortex, and further improve the hydrodynamic performance of the tidal turbine 100.
The cross section of the suction surface winglet 22 is triangular or trapezoidal, the cross section area of the suction surface winglet 22 decreases from the root along the extension direction, and the thickness of the suction surface winglet 22 decreases from the root along the extension direction. Further, the length of the suction surface winglet 22 is 1/30-1/15 of the diameter of the arc-shaped blade body 21, the chord length of the top section of the suction surface winglet 22 is 1/5-1/10 of the length of the suction surface winglet 22, and the inclination angle of the suction surface winglet 22 is 50-90 degrees.
The cross section of the pressure surface winglet 23 is triangular or trapezoidal, the cross section area of the pressure surface winglet 23 is reduced from the root along the extension direction, and the thickness of the pressure surface winglet 23 is reduced from the root along the extension direction. Further, the length of the pressure surface winglet 23 is 1/30-1/15 of the diameter of the arc-shaped blade body 21, the chord length of the section at the top end of the pressure surface winglet 23 is 1/5-1/10 of the length of the pressure surface winglet 23, and the inclination angle of the pressure surface winglet 23 is 50-90 degrees.
The method for analyzing the tidal current energy water turbine containing the winglet blades comprises the following steps:
s1: and establishing a structural model of the single blade according to the geometric data of the blade.
According to the blade geometric data of the tidal current energy water turbine, a three-dimensional model of the blade can be established by using modeling software, and the step S1 is specifically as follows:
s11: obtaining two-dimensional coordinates (x) of the airfoil at any section of the blade through an airfoil database0,y0)；
S12: with airfoil aerodynamic centre (x)p,yp) Solving the two-dimensional coordinate (x) of the airfoil under the new coordinate system by taking the connecting line of the front edge and the rear edge of the airfoil as the original point and the x axis1,y1) By a translation transformation (x)1,y1)＝(x0,y0)-(xp,yp)；
S13: according to the cross-section of the bladeAnd the chord length and the torsion angle data are subjected to scaling transformation and rotation transformation respectively to obtain three-dimensional space coordinates (x, y, z) of each leaf element discrete point of the blade, wherein the scaling transformation process comprises the following steps: (x)2,y2)＝c(x1,y1) (ii) a The process of the rotation transformation is as follows:
Figure BDA0002772149050000081
c is the chord length of the blade section, alpha is the torsion angle of the blade section, and r is the position of the section.
The scaling transformation and the rotation transformation processes can be realized through programming, batch operation is easy to realize, and the time cost of calculation is reduced.
S14: and introducing the obtained three-dimensional space coordinates (x, y, z) of the discrete points of the leaf elements into modeling to establish each section of the blade, and obtaining a three-dimensional model of the blade through a sweeping function.
S2: and establishing a flow field CFD calculation model according to the structural model of the blade.
The step S2 includes the following steps:
s21: and establishing a basic control equation.
Establishing a basic control equation, carrying out turbulence numerical simulation by adopting a Reynolds time-mean method, converting an instantaneous value of a physical quantity in the basic control equation into the sum of a time-mean value and a pulsation value, and then respectively obtaining a continuity equation and a momentum equation:
Figure BDA0002772149050000082
Figure BDA0002772149050000083
where i is 1,2,3, u is the water velocity, μ is the dynamic viscosity, ρ is the water density, S is the source term,
Figure BDA0002772149050000084
the reynolds stress term, which is added to satisfy the equation closure, is established by the turbulence model control.
S22: establishing a turbulence model to meet the closure of a momentum equation, wherein the expression of the turbulence viscosity in the turbulence model is as follows:
Figure BDA0002772149050000085
where S is the absolute value of vorticity, k is the turbulent kinetic energy, ω is the dissipation ratio, a1Is a constant coefficient.
In order to meet the closure of the momentum equation, a Reynolds stress term controlled by a turbulence model is added into the partial differential equation. A k-omega Shear Stress Transport (SST) turbulence model is adopted for simulating the tidal energy water turbine, and the model can capture the influence of factors such as free flow turbulence, pressure gradient and the like on transition, so that the calculation precision is high.
The expressions of the turbulent kinetic energy transport equation (k-equation) and the dissipation ratio equation (ω -equation) are as follows:
Figure BDA0002772149050000091
the constant coefficient is calculated by the following formula:
φ＝φ1F1+φ2(1-F1) Wherein phi1Is a constant coefficient in the k-epsilon turbulence model formula, phi2Is a constant coefficient in the k-omega turbulence model formula.
The blocking coefficient and the auxiliary relationship in the above equation are shown below:
Figure BDA0002772149050000092
Figure BDA0002772149050000093
Figure BDA0002772149050000094
Figure BDA0002772149050000095
in the above formula, L is the distance to the next curved surface, PkFor rate of generation of kinetic energy of turbulence, σk1，σk2,σω1,σω2,μt,μl,β*Are all constant.
S23: and establishing a rotation model, and performing numerical simulation on the rotation of the blade by adopting a multi-reference coordinate system.
The rotation of the blades was numerically simulated using a multi-reference coordinate system (MRF). The MRF model uses a steady state approximation method, assuming different speeds or rotational speeds in each sub-domain, and solving the mesh flow for each sub-domain using the motion reference system equations. At the interface of each computation domain, the flow variables in the sub-domain are computed using the local reference frame and then translated into adjacent sub-domains. The fluid of the rotating domain adopts a rotating reference system, and the control equation of the static domain can be simplified into a static form.
The continuity equation in the rotational domain is as follows:
Figure BDA0002772149050000096
and the form to the left of the equal sign of the momentum equation in the rotating coordinate system is as follows:
Figure BDA0002772149050000097
the above equation is established in terms of absolute velocity in the momentum equation, where
Figure BDA0002772149050000098
Absolute motion velocity (which is the velocity observed in the stationary reference frame),
Figure BDA0002772149050000099
as a relative speed of movement (observed in a rotating system)Speed) of the vehicle,
Figure BDA00027721490500000910
is the angular velocity of the rotating coordinate system. The governing equations for each subfield are based on the reference frame for the subfield, while the speed is stored in the absolute reference frame.
S24: setting boundary conditions, dividing grids, solving a discrete equation, and completing the establishment of a CFD calculation model of the flow field.
Due to the periodicity of the turbine blades, periodic rotation boundary conditions are set on both sides of the calculation domain. In order to ensure that the other outer boundaries are not affected by the external pressure, symmetrical boundary conditions are set on these boundaries. Since the rotation region between the blade and the surrounding region is relatively stationary, the condition of no sliding wall surface is provided on the blade surface. For adjacent sub-regions, boundary conditions are set at the interface and simple linear interpolation of the boundaries is performed to convey fluid information.
S3: and carrying out uncertainty analysis and verification, carrying out grid convergence index analysis by adopting three grids with different densities, namely a sparse grid, a medium grid and a fine grid, and realizing discrete error analysis by calculating power factors of the three grids.
The uncertainty analysis verification process includes two processes, verification and validation. Validation is the process of evaluating numerical uncertainty, i.e., whether the computational equations are solved correctly. Instead, validation is the process of evaluating model uncertainty, i.e., whether the mathematical model was built correctly.
Discrete error analysis is realized by calculating the power factors of the three grids. The estimation accuracy is given by the following formula:
Figure BDA0002772149050000101
Figure BDA0002772149050000102
Figure BDA0002772149050000103
Figure BDA0002772149050000104
rij＝ni/nj
in the formula:
Figure BDA0002772149050000105
the power coefficients obtained by calculation of the sparse grid, the medium grid and the fine grid are respectively, subscripts represent C, M and F, are convergence orders, are analog variables, are grid refinement rates and are grid quantity.
The mesh convergence index can be calculated from the following equation:
Figure BDA0002772149050000106
Figure BDA0002772149050000111
wherein FsTo a safety factor, eMFIs a relative error. Further, confirmation of the CFD calculation results was obtained by comparison with experimental data.
S4: and analyzing the hydrodynamic characteristics, comparing the power coefficient and the thrust coefficient of the tidal current energy water turbine containing the winglet blades with those of the traditional water turbine, and analyzing the influence of the winglet on the performance of the tidal current energy water turbine.
The hydrodynamic characteristic analysis comprises two parts of energy conversion efficiency analysis and flow field analysis. The energy conversion efficiency analysis comprises two parts of power coefficient analysis and thrust coefficient analysis.
The flow field analysis process comprises the following steps:
the pressure cloud chart of the blade surface, the pressure cloud chart and the flow chart of the blade section and the blade tip vorticity and the flow chart can be researchedThe flow field characteristics of the traditional horizontal-axis tidal current energy water turbine are researched. When the pressure is reduced to a certain limit, the internal volume of the liquid is destroyed, creating cavitation. Cavitation develops with increasing flow rate and decreasing water pressure. From no cavitation streaming to super cavitation streaming, cavitation goes through several stages of non-cavitation streaming, primary cavitation streaming, limited cavitation streaming and super cavitation streaming. The main parameters determining the different states are the water pressure and the flow rate. If infinite incoming flow pressure P∞And the pressure at the lowest pressure point of the airfoil surface is higher than the initial cavitation pressure Pc of water, so that no cavitation occurs. With P∞Is continuously reduced or the incoming flow velocity V∞Initial cavitation, limiting cavitation and supercavitation began to occur.
According to bernoulli's principle, and neglecting hydraulic losses, one can obtain:
Figure BDA0002772149050000112
where P and v represent the pressure and flow velocity at any point on the airfoil. For cavitation flow, cavitation length, cavitation thickness, cavitation development and cavitation critical pressure have very important influence on the flow field around the airfoil. Thus, the cavitation coefficient λ is introduced, which can be expressed as:
Figure BDA0002772149050000113
where ρ is the density of water, PcIs the cavitation pressure value of the incoming water.
The pressure coefficient of the blade surface is:
Figure BDA0002772149050000121
wherein, P' is the pressure value of any point on the surface of the circumfluence object.
The process of power coefficient analysis is as follows:
by comparing the power coefficient and the thrust coefficient of the triangular winglet-suction-surface winglet hydraulic turbine and the traditional hydraulic turbine through the CFD method, the influence of the designed winglet-suction-surface winglet on the hydrodynamic performance of the horizontal-axis tidal current energy hydraulic turbine is analyzed, and the reason for changing the hydrodynamic performance of the hydraulic turbine by the winglet-suction-surface winglet can be explored.
S5: selecting design variables, and establishing a database of the design variables and hydrodynamic characteristics, wherein the design variables include a bend direction of the winglet, a winglet length, an upper chord length, and a cant angle.
The design goals of winglets on the suction side of the tip are to minimize induced drag and to increase profile drag. However, blade drag is determined by many factors, such as the wet surface of the blade, airfoil cross-sectional shape, angle of attack, etc., and is therefore difficult to predict. There is a need to study the effect of suction surface winglet design variables on its hydrodynamic performance. By researching the influence law of the suction surface winglet bending direction, the suction surface winglet length, the upper chord length and the inclination angle on the hydrodynamic performance of the horizontal axis water turbine, a database of design variables and power coefficients can be established, a basis is provided for the follow-up tidal energy water-cooled machine blade selection, and appropriate blade design parameters can be selected according to actual requirements.
Example one
In this embodiment, only the suction surface winglet is provided, the suction surface winglet is a triangular winglet, the cross section of the tip end of the winglet is an ellipse with a length-to-axis ratio of 18:1, the inclination angle of the first suction surface winglet 22 is 90 °, the chord length of the cross section of the tip end of the winglet is 2mm, and the height of the winglet is 22 mm.
Example two
In this embodiment, only the suction side winglets are provided, and are trapezoidal winglets with a cross-section of the airfoil NACA63-418, a cant angle of 90 for the suction side winglets, and a chord length in the tip section and a height of the suction side winglets of 10mm and 22mm, respectively.
EXAMPLE III
In this embodiment, suction side winglets and pressure side winglets are provided and are each NACA63-418 in cross-section. The chord length, the inclination angle and the height of the tip section of the suction surface winglet are respectively 10mm, 75 mm and 22mm, and the chord length, the inclination angle and the height of the tip section of the pressure surface winglet 23 are respectively 8mm, 85 mm and 16 mm.
The tidal energy water turbine in the three embodiments and the related technology is analyzed by adopting the analysis method provided by the invention, the fluid is set to be liquid water, and the density is 1024kg/m3In order to simulate the rotating motion of the water turbine, the above-mentioned CFD model of the flow field is set in the rotating field, and the angular velocity of the rotating field is set to 270 rpm.
Referring to fig. 5(a) -5 (d), in order to investigate the influence of winglets on the tip vortex of blades of a tidal turbine, vortex quantity graphs of the tip vortex under the condition that the tip speed ratio is TSR-5 are respectively given. In the figure, the first tip vortex is located in the plane of the rear tip of the blade at a distance of 0.066R from the blade tip, and the spacing of each plane is 0.017R.
The strength of the tip vortex formed behind the blade tip of the tidal energy water turbine in the related art is obviously maximum. The tidal energy turbine in the first embodiment, the second embodiment and the third embodiment can reduce the strength of the wing tip vortex.
In all turbines, the tip vortex of the triangular suction surface winglet turbine closest to the blade tip has the smallest strength in all tidal energy turbines, and the tip vortex strength in each plane behind the blade tip is very close and gradually weakens in the process of dissipating downstream. Reducing the tip vorticity can improve the energy conversion efficiency of the tidal energy turbine.
The tip vortex of the trapezoidal suction surface winglet hydraulic turbine consists of two connected vortexes, one vortex is arranged behind the top end of the suction surface winglet, and the other vortex is arranged near the root of the suction surface winglet. The tip vortex strength near the suction surface winglet is greater than that at the root part of the suction surface winglet, and the two kinds of vortex strength are both less than that of a single-blade tip vortex of a traditional water turbine. As the two tip vortices dissipate downstream, the tip vortex near the root of the winglet on the tip suction side gradually disappears.
A strong tip vortex can also be observed in the first tip plane of a bidirectional trapezoidal wingtip suction surface winglet hydraulic turbine (comprising a trapezoidal suction surface winglet and a trapezoidal pressure surface winglet), but the dissipation speed of the blade tip vortex is much higher than that of a traditional tidal energy hydraulic turbine.
Referring to fig. 6, the bar I, the bar II and the bar III are the power increase of the tidal energy turbine of the first embodiment, the second embodiment and the third embodiment, respectively, compared with the tidal energy turbine of the related art. As can be seen from the figure, the tidal energy water turbine in the first embodiment, the second embodiment and the third embodiment has improved power compared with the conventional water turbine, the winglet can improve the energy conversion efficiency of the water turbine under most tip speed ratios, and the tidal energy water turbine of the three embodiments can reach the maximum power factor under the condition that the TSR is 5.
The power factor of the tidal turbine in the first embodiment is improved under the full-blade tip speed ratio, namely the hydrodynamic performance of the triangular tip suction surface winglet is the best, and the power factor of the tidal turbine is changed from 4.37% to 0.89% compared with that of the traditional tidal turbine from TSR (total suspended weight) 4 to TSR (total suspended weight) 7.4. However, the power factor of the turbine increases from 0.89% to 14.11% compared to the conventional turbine from TSR 7.4 to TSR 10. The power factor of the tidal turbine in the first embodiment is improved by 4.34% under the optimal tip speed ratio.
It can be concluded that the analysis method of the present invention is effective for analyzing the hydrodynamic characteristics of the tidal turbine, and the tidal turbine 100 provided by the present invention can greatly improve the hydrodynamic characteristics.
Compared with the related art, the invention has the beneficial effects that:
1) compared with the traditional tidal energy water turbine blade structure, the tidal energy water turbine blade with the winglet has the advantages of simple structure, convenience in design and the like;
2) the blade structure of the tidal energy water turbine with the winglet can effectively reduce the strength of the tip vortex and improve the energy conversion efficiency of the water turbine;
3) the analysis method provided by the invention has higher universality and accuracy, can accurately obtain the hydrodynamic characteristics of the tidal energy water turbine blade, and ensures the calculation convergence and accuracy by adopting an uncertainty analysis method.
4) A design parameter and hydrodynamic performance database is established through design variable analysis, and appropriate design parameters can be selected according to actual design requirements.
While the foregoing is directed to embodiments of the present invention, it will be understood by those skilled in the art that various changes may be made without departing from the spirit and scope of the invention.

Claims (10)

1. A tidal energy water turbine analysis method comprising winglet blades is characterized in that the analysis method comprises the following steps:
s1: establishing a structural model of a single blade according to the geometric data of the blade;
s2: establishing a flow field CFD calculation model according to the structural model of the blade;
s3: carrying out uncertainty analysis and verification, carrying out grid convergence index analysis by adopting three grids with different densities, namely a sparse grid, a medium grid and a fine grid, and realizing discrete error analysis by calculating power factors of the three grids;
s4: performing hydrodynamic characteristic analysis, comparing power coefficients and thrust coefficients of the tidal current energy water turbine with the winglet blades and a traditional water turbine, and analyzing the influence of the winglet on the performance of the tidal current energy water turbine;
s5: selecting design variables, and establishing a database of the design variables and hydrodynamic characteristics, wherein the design variables include a bend direction of the winglet, a winglet length, an upper chord length, and a cant angle.
2. The analysis method of claim 1, wherein the cambered blade body is fixedly connected with the main shaft, the winglet comprises a suction surface winglet, the suction surface winglet is arranged at the tip position of the cambered blade body, the suction surface winglet is integrally formed with the cambered blade body and is in smooth transition, the suction surface winglet is bent towards the suction surface of the cambered blade body and is tangent to the rear edge of the cambered blade body, and the central line of the suction surface winglet is tangent to the center of the tip of the cambered blade body.
3. The analysis method of claim 2, wherein the cross-sectional area of the suction surface winglet decreases from the root in the direction of the elongation, the thickness of the suction surface winglet decreases from the root in the direction of the elongation, the length of the suction surface winglet is 1/30-1/15 of the diameter of the curved blade body, the chord length of the tip cross-section of the suction surface winglet is 1/5-1/10 of the length of the suction surface winglet, and the cant angle of the suction surface winglet is 50 ° -90 °.
4. The analysis method of claim 2, wherein the winglet further comprises a pressure-side winglet, the pressure-side winglet being disposed at a tip of the curved blade body, the pressure-side winglet being integrally formed with and smoothly transitioning from the curved blade body, the pressure-side winglet curving toward the pressure side of the curved blade body and being tangential to a trailing edge of the curved blade body, and a centerline of the pressure-side winglet being tangential to a center of the tip of the curved blade body.
5. The method of claim 4, wherein the pressure face winglet has a cross-sectional area that decreases from the root in the direction of the extended length, a thickness that decreases from the root in the direction of the extended length, a length that is 1/30-1/15 of the diameter of the curved blade body, a chord length at the tip of the pressure face winglet that is 1/5-1/10 of the length of the pressure face winglet, and a cant angle that is 50-90 ° of the pressure face winglet.
6. The analysis method according to claim 1, wherein the step S1 includes the steps of:
s11: acquiring two-dimensional coordinates of the airfoil at any section of the blade through an airfoil database;
s12: with airfoil aerodynamic centre (x)p,yp) Solving the two-dimensional coordinate (x) of the airfoil under the new coordinate system by taking the connecting line of the front edge and the rear edge of the airfoil as the original point and the x axis1,y1) By a translation transformation (x)1,y1)＝(x0,y0)-(xp,yp)；
S13: according to the chord length and the torsion angle data of each section of the blade, obtaining three-dimensional space coordinates (x, y, z) of each discrete voxel point of the blade through scaling transformation and rotation transformation respectively, wherein the scaling transformation process comprises the following steps: (x)2,y2)＝c(x1,y1) (ii) a The process of the rotation transformation is as follows:
Figure FDA0002772149040000021
c is the chord length of the blade section, alpha is the torsion angle of the blade section, and r is the position of the section;
s14: and introducing the obtained three-dimensional space coordinates (x, y, z) of the discrete points of the leaf elements into modeling to establish each section of the blade, and obtaining a three-dimensional model of the blade through a sweeping function.
7. The analysis method according to claim 1, wherein the step S2 includes the steps of:
s21: establishing a basic control equation, carrying out turbulence numerical simulation by adopting a Reynolds time-mean method, converting an instantaneous value of a physical quantity in the basic control equation into the sum of a time-mean value and a pulsation value, and then respectively obtaining a continuity equation and a momentum equation:
Figure FDA0002772149040000031
Figure FDA0002772149040000032
where i is 1,2,3, u is the water velocity, μ is the dynamic viscosity, ρ is the water density, S is the source term,
Figure FDA0002772149040000033
the Reynolds stress term is added to satisfy equation closure and is controlled and established by a turbulence model;
s22: establishing a turbulence model to meet the closure of a momentum equation, wherein the expression of the turbulence viscosity in the turbulence model is as follows:
Figure FDA0002772149040000034
where S is the absolute value of vorticity, k is the turbulent kinetic energy, ω is the dissipation ratio, a1Is a constant coefficient;
s23: establishing a rotation model, and performing numerical simulation on the rotation of the blade by adopting a multi-reference coordinate system;
the rotational domain continuity equation is as follows:
Figure FDA0002772149040000035
and the form to the left of the equal sign of the momentum equation in the rotating coordinate system is as follows:
Figure FDA0002772149040000036
wherein
Figure FDA0002772149040000037
In order to be the absolute speed of the movement,
Figure FDA0002772149040000038
in order to be the relative speed of the movement,
Figure FDA0002772149040000039
is the angular velocity of the rotating coordinate system;
s24: setting boundary conditions, dividing grids, solving a discrete equation, and completing the establishment of a CFD calculation model of the flow field.
8. The analytical method of claim 7, wherein the turbulence model is a k- ω shear stress transport turbulence model, and the expressions of the turbulence kinetic energy transport equation and the dissipation ratio equation in step S22 are as follows:
Figure FDA00027721490400000310
Figure FDA00027721490400000311
the constant coefficient is calculated by the following formula:
φ＝φ1F1+φ2(1-F1)
wherein phi1Is a constant coefficient in the k-epsilon turbulence model formula, phi2Is a constant coefficient in a k-omega turbulence model formula; the sealing coefficient and the auxiliary relationship in the above formula are shown as the following formula:
Figure FDA0002772149040000041
Figure FDA0002772149040000042
Figure FDA0002772149040000043
Figure FDA0002772149040000044
in the above formula, L is the distance to the next curved surface, PkFor rate of generation of kinetic energy of turbulence, σk1,σk2,σω1,σω2,μt,μl,β*Are all constant.
9. The analysis method according to claim 8, wherein the step S3 is specifically: calculating power factors of three grids including a sparse grid, a medium grid and a fine grid to realize discrete error analysis, wherein the estimation precision is obtained by the following formula:
Figure FDA0002772149040000045
Figure FDA0002772149040000046
Figure FDA0002772149040000047
Figure FDA0002772149040000048
rij＝ni/nj
in the formula:
Figure FDA0002772149040000049
respectively calculating power coefficients obtained by sparse grid, medium grid and fine grid, wherein subscripts i and j represent C, M and F, p is convergence order, q is analog variable, r is grid refinement rate, and n is grid number;
the mesh convergence index can be calculated from the following equation:
Figure FDA00027721490400000410
Figure FDA00027721490400000411
wherein FsTo a safety factor, eMFIs a relative error.
10. The analysis method according to claim 1, wherein the hydrodynamic characteristics analysis in the step S4 includes a flow field analysis and a power coefficient analysis, and the flow field analysis analyzes the flow field characteristics of the tidal turbine through a pressure cloud chart of the blade surface, a pressure cloud chart of the blade section, a flow chart of the blade section, and a tip vorticity and tip flow chart; and the power coefficient analysis compares the power coefficient and the thrust coefficient of the water turbine containing the winglet blade tidal current energy with those of the traditional water turbine by utilizing a CFD flow field calculation model.
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