CN104408260B - A kind of tidal current energy water turbine vane airfoil profile method for designing - Google Patents
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Abstract
The invention discloses a kind of tidal current energy water turbine vane airfoil profile method for designing, consider the various requirement including the turbine blade design including lift coefficient, resistance coefficient, lift-drag ratio and cavitation phenomenon etc., selected object function can carry out comprehensive assessment according to different design requirements to water wheels airfoil type.Choose first edge tangent line, trailing edge tangent line and in aerofoil profile on lower curve the abscissa and ordinate at control point as design variable.Cubic spline curve is employed, with fitting precision higher.Employ FLUENT or CFX cfdrcs or XFOIL aerofoil profiles estimation software etc. to calculate hydrodynamic performance and pressure distribution of hydrofoil profile etc., fully ensure that the accuracy for calculating.Hydrofoil profile method for designing is based on genetic Optimization Algorithm, is obtained in that globally optimal solution.The present invention is not only able to improve the hydrodynamic performances of tidal current energy water turbine vane airfoil profile, moreover it is possible to reduce the maximum pressure coefficient on surface, the purpose of cavitation phenomenon is avoided so as to reach.
Description
Technical Field
The invention belongs to the field of renewable energy sources, and particularly relates to a blade airfoil design method for designing a tidal current energy water turbine.
Background
With the development of the world economy, the energy consumption is more and more. Clean renewable energy is becoming increasingly important due to the fossil energy crisis and the problems of environmental pollution and carbon emissions from traditional energy sources. Tidal current energy is a very important new energy source, has the advantages of reliability, periodicity, wide distribution, sustainability and the like, and can play an important role in future energy sources. In order to utilize tidal current energy, water turbines are employed as the primary energy capture devices. Therefore, how to improve the capability capture efficiency of the tidal current energy water turbine becomes a key factor influencing the popularization and application of tidal current energy power generation.
The hydrofoil profile, which is one of the most important factors forming the blade profile, has an important influence on the energy conversion efficiency of the tidal current energy water turbine. At present, the known airfoil profiles are basically obtained by considering design requirements of aerospace, wind turbines and the like, the special hydrofoil profiles for tidal current energy water turbines are few, and the design methods of the airfoil profiles are few.
The traditional airfoil design method applied to the aspects of aerospace and wind power mainly has two problems: firstly, hydrofoil wing profiles have certain special design requirements different from those of aerospace and wind turbines, and the wing profile design method of aerospace and wind turbines cannot be applied; secondly, most design methods are based on a single target, the actual design target of the wing profile is very complex, and a reasonable wing profile can be obtained only by considering multiple targets; thirdly, most design methods are optimization methods based on sensitivity analysis, and global optimal solutions are difficult to obtain. With the development of tidal current energy power station projects in China, a complete wing section design method must be established for developing a tidal current energy water turbine with independent intellectual property rights.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method for designing a blade airfoil of a tidal current energy water turbine.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
the method comprises the following steps: determining design variables and an objective function according to design requirements, and establishing a hydrofoil wing section optimization model;
step two: determining a calculation method of hydrodynamic performance and pressure coefficient and a fitness function of a genetic algorithm;
step three: generating an initial population and fitting a hydrofoil profile curve;
step four: generating a hydrofoil airfoil fluid region grid model, calculating and outputting hydrodynamic performance, and outputting information such as lift force, resistance, pressure and the like;
step five: and calculating a target function according to the hydrodynamic coefficient and the pressure coefficient, evaluating according to the fitness function, judging whether convergence occurs or not, finishing optimization if convergence occurs, otherwise, generating a new population, and returning to the step three.
The method comprehensively considers various requirements of the design of the water turbine blade including a lift coefficient, a drag coefficient, a lift-drag ratio, cavitation and the like, the selected objective function can comprehensively evaluate the water turbine airfoil according to different design requirements, the abscissa and the ordinate of a control point on a leading tangent line, a trailing tangent line and upper and lower curves of the airfoil are selected as design variables, a cubic spline curve is adopted, the fitting precision is high, hydrodynamic performance, pressure distribution and the like of the hydrofoil airfoil are calculated by using FLUENT or CFX computational fluid dynamics software or XFOIL airfoil estimation software and the like, the calculation accuracy is fully ensured, and the hydrofoil airfoil design method is based on a genetic optimization algorithm and can obtain a global optimal solution.
The invention has the advantages that:
1) compared with the traditional water turbine design method, the invention comprehensively considers various aspects of the water turbine hydrofoil profile design and can obtain the optimal hydrofoil profile curve according to different water areas and ocean environment requirements.
2) The design variable selection and curve fitting method in the proposed design method can accurately describe the real hydrofoil airfoil curve, can expand the design space as much as possible,
3) compared with the traditional optimization method, the genetic algorithm adopted by the invention has the advantages of feasible solution representation universality, group searching property, random searching property, global property and the like, and can obtain the global optimal solution.
Drawings
FIG. 1 is a flow chart of a method for designing an airfoil profile of a tidal current energy water turbine in the invention;
FIG. 2 is a hydrofoil airfoil and its design variables in the present invention;
FIG. 3 is a plot of the target lift coefficient in the present invention;
FIG. 4 is a view showing cavitation of a hydrofoil airfoil of the water turbine according to the present invention;
FIG. 5 is a comparison of different design hydrofoil airfoil designs in an embodiment of the present invention;
FIG. 6 is a comparison of pressure distributions for different design objective functions in the embodiment of the present invention;
FIG. 7 is a comparison of lift coefficients for different design objective functions in the embodiments of the present invention;
FIG. 8 is a comparison of drag coefficients for different design objective functions in the embodiments of the present invention;
FIG. 9 is a comparison of lift-to-drag ratios for different design objective functions in the embodiment of the present invention;
in the figure:
1. a hydrofoil; 2. An airfoil profile; 3. An airfoil centerline; 4. A leading edge;
5. a trailing edge; 6. A control point; 7. A control point design domain; 8. Conventional lift coefficient curves;
9. target lift coefficient curve
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and examples.
As shown in fig. 1, the method for designing the airfoil profile of the tidal current energy water turbine hydrofoil 1 provided by the invention comprises an optimization module, an objective function module and a performance calculation module.
The optimization module mainly generates an initial design scheme, evaluates the hydrodynamic performance of the new hydrofoil 1 airfoil scheme, and generates new airfoil design parameters on the basis of the original design scheme.
The objective function module mainly has the functions of generating a new geometric configuration according to the airfoil parameters of the hydrofoil 1, extracting an analysis result from a computational fluid dynamics analysis result, and obtaining an objective function according to the computation result.
The performance calculation module has the main functions of generating discrete grid data according to the geometric configuration, calculating the lift coefficient, the drag coefficient, the pressure distribution and the like of the airfoil of the hydrofoil 1 by adopting FLUENT software, CFX software or XFOIL software, and providing a calculation basis for the objective function module.
According to the three modules, the tidal current energy water turbine hydrofoil 1 wing profile is optimally designed by adopting a genetic algorithm, and the calculation of the hydrofoil 1 wing profile optimization method is carried out according to the following steps.
Firstly, determining design variables and an objective function according to design requirements, and establishing a hydrofoil 1 airfoil optimization model.
Design variables are directly related to the hydrofoil 1 airfoil profile, so how to address the sampling point method and the curve fitting method is particularly important. The selection of the target function is directly related to the performance of the designed hydrofoil 1 airfoil profile and needs to be flexibly set according to design requirements.
As shown in fig. 2, a typical hydrofoil 1 is provided, an airfoil centerline 3 is connected between a leading edge 4 and a trailing edge 5, at least four control points 6 are selected on an airfoil curve 2 of the hydrofoil 1 according to an initial design scheme, the control points 6 are points on the airfoil curve 2, and the positions of the control points 6 can be moved by changing the abscissa or the ordinate of the control points 6, so as to change the shape of the airfoil curve 2, thereby achieving the purpose of improving the hydrodynamic performance of the hydrofoil 1.
x＝(x00,x11,y11,x12,y12,...,x1m,y1m,x21,x21,x22,y22,...,x2n,y2n,x01)
Wherein x00And x01The sizes of the tangents of the leading edge and the trailing edge of the hydrofoil 1 airfoil respectively (x)1m,y1m) And (x)2n,y2n) Respectively, the coordinates, x, of the control point 6 on the hydrofoil upper and lower airfoil curves 22nAnd x1mIs the abscissa of the control point 6 of the hydrofoil upper and lower airfoil curves 2, and y1mAnd y2nIs the ordinate of the control point 6 of the upper and lower airfoil profiles 2 of the hydrofoil.
The blades of the water turbine have different design requirements at different positions in the spanwise direction, and the blades are close to the outer side of the blade, so that the airfoil profile is required to have a large lift coefficient, a large lift-drag ratio and a small drag coefficient, and the specified hydrodynamic load can be achieved by adopting a small chord length. The lift-to-drag ratio of the tip region is the most important parameter from a hydrodynamic design perspective. Because the load that the hydraulic turbine received is great, in order to satisfy the requirement of structural design, generally adopt thicker wing section. Due to the extreme loads near the root, the airfoil thickness must be particularly demanding for structural layout requirements, but at the expense of greater hydrodynamic performance. In order to optimize the hydrodynamic performance of the turbine, different airfoils are therefore arranged in the spanwise direction, and it is necessary to design specific airfoils according to different design requirements. Therefore, the design target is divided into two types, one type is basic hydrodynamic performance, including a lift coefficient, a resistance coefficient and a lift-drag ratio, and is directly related to the energy conversion efficiency of the water turbine; the second type is a pressure coefficient, which is directly related to cavitation phenomenon and may affect the service life and reliability of the water turbine.
First for hydrodynamic performance. For airfoils in the field of wind turbines, the wind turbine blades may be in the stall region and aerodynamic efficiency may drop dramatically after the angle of attack reaches the stall point. As shown in fig. 3, which is a comparison between a conventional lift coefficient curve 8 and a target lift coefficient curve 9, the conventional airfoil profile may cause a sharp drop of the lift coefficient near the stall point, which may affect the energy utilization efficiency of the tidal current energy turbine, and thus is not suitable as the airfoil profile of the turbine hydrofoil 1. For tidal current energy turbines, it is more desirable in the design that the hydrodynamic performance not vary too strongly with angle of attack, especially in the stall region. Therefore, the invention proposes that the separation point is required to slowly move towards the trailing edge along with the increase of the attack angle in the specific airfoil design, and the specific expression is that the lift coefficient of the target lift coefficient curve 9 is slowly changed along with the increase of the attack angle, so that the performance of the water turbine is fully ensured. In addition, the coefficient of drag, lift-drag ratio, etc. also have a significant impact on the hydrodynamic performance of the turbine hydrofoil 1. In order to design the hydrofoil 1 airfoil with the best performance, the objective function is required to consider hydrodynamic properties such as lift coefficient, drag coefficient, lift-drag ratio and pressure coefficient under multiple working conditions, and comprehensive optimization design is developed.
Second for the pressure coefficient problem. Bubbles form when the pressure in a certain fluid region is less than the cavitation pressure value. Cavitation is due to the rapid collapse of an air bubble in water, creating a shock wave. Cavitation of the pass-through type typically occurs in mechanical structures such as pumps, propellers and impellers. From a fluid design point of view, cavitation problems due to turbine blade pressure should be considered in turbine blade airfoil design, as the shock wave generated by the collapse of the inertial cavitation can cause significant damage to the turbine structure. As shown in fig. 4, which shows the generating condition of the cavitation phenomenon on the hydrofoil 1, the pressure coefficient distribution has a maximum value along with the chord-wise position distribution, when the pressure coefficient C on the hydrofoil 1pGreater than cavitation coefficient sigmacCavitation occurs at that time.
The cavitation coefficient is defined as follows:
the pressure coefficient is defined as follows:
wherein p isvIs the cavitation pressure, pLThe airfoil surface pressure of the hydrofoil 1 mainly depends on the temperature of water. p is a radical of0The local pressure, q the dynamic pressure, V the water flow velocity.
The cavitation phenomenon is a specific problem in the design of a water turbine, and the cavitation phenomenon occurring in the running process of the tidal current energy water turbine can directly damage the structure of the water turbine, so that the service life and the reliability of the water turbine are influenced. Therefore, the possibility of cavitation of the tidal current energy water turbine is reduced as much as possible. In order to avoid the occurrence of cavitation, it is necessary to reduce the maximum pressure coefficient of the upper part of the hydrofoil 1, which is therefore required when designing the hydrofoil 1. However, the pressure coefficient has a direct relationship with hydrodynamic performance such as lift coefficient and lift-drag ratio, and the lift coefficient can be obtained by numerically integrating the pressure coefficient along the airfoil curve 2. Therefore, the purpose of avoiding cavitation and not losing hydrodynamic performance can be achieved through two aspects in the optimization model. On the one hand, the maximum pressure coefficient is reduced as much as possible, and on the other hand, the pressure coefficient is distributed as uniformly as possible along the airfoil curve 2. In order to avoid the cavitation phenomenon, the invention proposes the pressure coefficient as one of the design objective functions.
Finally, in order to obtain an airfoil curve 2 of the hydrofoil 1 with optimal performance, an objective function comprehensively considers a lift coefficient, a drag coefficient, a lift-drag ratio and a pressure coefficient, and combines design variables to establish an airfoil optimization model as follows:
an objective function:
f(x)＝f(CL,CL/CD,CD,Cpmax)
constraint conditions are as follows:
wherein C isL、CL/CD、CDAnd CpThe lift coefficient, lift-drag ratio, drag coefficient and maximum pressure coefficient under any attack angle are all functions of a design variable x.Andrespectively is the lower boundary of the front edge, the tail edge, the abscissa of the control point of the upper surface of the wing profile, the ordinate of the control point of the upper surface of the wing profile, the abscissa of the control point of the lower surface of the wing profile and the ordinate of the control point of the lower surface of the wing profile,andthe control point abscissa of the upper surface of the wing profile, the ordinate of the control point ordinate of the upper surface of the wing profile, the abscissa of the control point abscissa of the lower surface of the wing profile and the upper bound of the ordinate of the control point ordinate of the lower surface of the wing profile are respectively the leading edge, the trailing edge, the abscissa of the control point of the upper surface of the wing profile, the ordinate. And m and n are the number of control points of the upper and lower airfoil profiles of the hydrofoil respectively. The control point design domain 7 of the control point 6 on the airfoil curve 2 of the hydrofoil 1 is the abscissa interval of the control point 6 on the upper surface of the airfoilAnd the ordinate intervalOr the horizontal coordinate interval of the control point 6 on the lower surface of the airfoilAnd the ordinate intervalThe enclosed rectangular range within which the control point 6 varies and the optimum is solved.
The objective function f (x) can be any combination of hydrodynamic performance and pressure coefficient, and can be flexibly selected according to requirements in actual wing profile design. The following types of objective functions can be selected:
1)f(x)＝w1CL+w2CL/CD+w3CD+w4Cpmax
wherein wi(i 1.. 4) are weights of a lift coefficient, a lift-drag ratio, a drag coefficient, and a maximum pressure coefficient, respectively, and satisfyAnd 0. ltoreq. wi1 (1, 2,3,4) is equaled or less, can select according to the design needs in the actual airfoil section design in a flexible way.
2)f(x)＝(w1CL+w2CL/CD+w3CD)Cpmax
The objective function is the product of the hydrodynamic performance and the pressure coefficient of the airfoil, where wi(i 1.. 3) are weights of a lift coefficient, a lift-drag ratio, and a drag coefficient, respectively, and satisfyAnd 0. ltoreq. wiLess than or equal to 1, and can be flexibly selected according to the design requirement in the actual wing profile design.
The specific objective function is not limited to the three types, and can be flexibly selected according to the requirements of the actual sea area. The lift coefficient, drag coefficient, lift-drag ratio and pressure coefficient may be a single arbitrary angle of attack situation, or may be a combined function g (x) of each hydrodynamic coefficient and pressure coefficient function at a plurality of angles of attack as shown in the following formula.
Wherein, αuThe size of the attack angle of the hydrofoil is the same,has an attack angle of αuThe hydrodynamic performance objective function under the condition v is the selected number of attack angles in the objective function, and the combination function g (x) can comprehensively consider the hydrodynamic performance parameters under any attack angle, can adopt any type of combination mode, and preferably can adopt a weighted summation method shown in the following formula.
Wherein ω isuIs a weight coefficient and satisfies
And secondly, determining a calculation method of the hydrodynamic coefficient and the pressure coefficient and a fitness function of the genetic algorithm.
After the optimization model is established, the optimization design is adopted for the established model. To accurately evaluate the hydrodynamic performance of the hydrofoil 1, lift coefficients, drag coefficients, lift-to-drag ratios and pressure distributions are calculated using a FLUENT or CFX or XFOIL numerical simulation program. The specific numerical calculation method can be flexibly selected according to the design requirement. In order to obtain the airfoil curve 2 of the hydrofoil 1 with the best performance, a genetic algorithm with global search capability is adopted, and in the process of carrying out the genetic algorithm, the evaluation of the fitness function of each design scheme has important influence on the optimization result and the calculation process.
The fitness function is a key factor for evaluating the hydrodynamics of the hydrofoil 1 wing profile, and relates to an optimization process, wherein a solution with high fitness is reserved according to the fitness function in the optimization process, and a solution with poor fitness is eliminated. The present invention employs a fitness function as shown in the following formula.
Wherein h(s) is the fitness of the s-th design scheme, ss is the number of design schemes in the population, and f (x)s) Is the objective function of the s-th design.
And thirdly, generating an initial population and fitting an airfoil curve 2 of the hydrofoil 1.
And according to the design variables and the upper and lower bounds thereof, randomly selecting ss initial design schemes (ss is greater than or equal to 10), wherein the initial design schemes in the set are initial population groups. This set of initial design solutions is generated to fit to the hydrofoil 1 airfoil curve 2. In order to accurately describe the airfoil profile and not sacrifice geometric information too much, the selection of the fitting curve is crucial, and the number of design variables can be obviously reduced by the polynomial spline curve. The invention mainly adopts a cubic spline curve, which is different from a common cubic spline curve fitting method, and the invention provides that the cubic spline curve is fitted by the abscissa and ordinate of the control point 6 and the tangent lines of the leading edge and the trailing edge, thereby achieving the purpose of controlling the sizes of the tangent lines of the leading edge and the trailing edge and keeping the favorable hydrodynamic performance of the airfoil profile. However, the form of the curve fitting is not limited in the specific implementation, and any other curve fitting method may be used. In order to enlarge the search space as much as possible, control points 6 are selected on the airfoil curve 2 as possible, the airfoil curve 2 is fitted by points on the airfoil curve 2 and tangents to the leading and trailing edges, using the abscissa and the ordinate of each point as design variables. Thereby generating the airfoil curve 2 of the hydrofoil 1.
And fourthly, generating a hydrofoil 1 airfoil fluid region grid model, calculating and outputting hydrodynamic performance, and outputting information such as lift force, resistance, pressure and the like.
And processing the generated airfoil curve 2 of the hydrofoil 1 in geometric processing software such as AUTOCAD or CATIA to generate a geometric model. And (3) introducing the generated geometric model into grid generation software such as ICEMCFD (integrated computer computing device), GRIDGEN (grid identification gen) or GAMBIT (gamma-gamma ray imaging device), and establishing a grid model of the airfoil fluid region of the hydrofoil 1 in the software. And importing the generated mesh file into hydrodynamic software such as FLUENT or CFX, calculating corresponding lift force, resistance and pressure, and outputting the lift force, the resistance and the pressure as a basis for calculating an objective function. In order to improve the calculation efficiency, XFOIL software can be adopted, and the software only needs geometric curve information and does not need to carry out complicated geometric CAD information and a grid process, so the calculation efficiency can be greatly improved.
And fifthly, calculating a target function according to the hydrodynamic coefficient and the pressure coefficient, evaluating according to the fitness function, judging whether convergence occurs or not, finishing optimization if convergence occurs, otherwise, generating a new population, and returning to the third step.
Extracting a calculation result, calculating target functions of different design schemes in the population, evaluating the fitness of ss different design schemes according to the fitness function, sequencing the design schemes according to the fitness, and judging whether convergence occurs according to the fitness and iteration times of the design schemes in the population. And if the water wing 1 is converged, finishing the calculation, and taking the design scheme with the highest fitness in the population as the optimal solution of the airfoil curve 2 of the water wing 1. If not, a new population needs to be regenerated as follows.
According to the fitness of ss different design schemes in a population, eliminating the design schemes with low fitness according to a certain proportion (5% -20%), then coding each design scheme in the population by adopting binary numbers, coding all 2m +2n +2 design variables in a certain design scheme into a binary number, and arranging according to the sequence of a leading edge tangent line, an airfoil upper surface curve abscissa and ordinate, an airfoil lower surface curve abscissa and ordinate and a trailing edge tangent line. The better design scheme is kept to carry out variation and hybridization operation according to a certain proportion (5% -20%) to obtain a new solution, thereby ensuring that the population quantity ss is not changed. The binary number encoded for each design is shown as:
p ═ m abscissa and ordinate airfoil upper surface and n abscissa and ordinate trailing edge tangents of airfoil upper surface
The tangent of the front edge, the abscissa and the ordinate of the curve of the upper surface of the airfoil, the abscissa and the ordinate of the curve of the lower surface of the airfoil and the tangent of the rear edge are respectively represented by a binary number. The specific expression is as follows, the first row represents the binary number after conversion, the second row represents the number of the design variables in the coded binary number, there are 2m +2n +2 design variables in total, the 1 st is the leading edge tangent line x002 nd to 2m +1 th are the abscissa and ordinate of the upper surface curve of the airfoil profile and are in accordance with (x)11,y11)(x12,y12)...(x1m,y1m) In the order of (1), the 2m +2 to 2m +2n +1 are the abscissa and the ordinate of the lower surface curve of the airfoil profile and are in accordance with (x)21,y21)(x22,y22)...(x2m,y2m) In a sequence of which the last one is a trailing edge tangent x01。
Decoding the design plan in the new population from binary coding to decimal number, returning to the third step and neglecting the step of generating the new population.
Example 1:
in order to verify the design method provided by the invention, hydrofoil airfoil curves under different design conditions are optimally designed. For tidal current energy water turbines, different positions of blades in the spanwise direction have different design requirements, a thin airfoil with a high lift-to-drag ratio is a better choice near the wingtip, and in a wide range of attack angles, a high lift coefficient and a high lift-to-drag ratio are required, and the drag coefficient should be as small as possible. Since the root portion is subjected to a large load, the root airfoil is required to have a large thickness in order to ensure sufficient structural rigidity and strength of the blade. Furthermore, to avoid cavitation, it may result in the need to select thicker airfoils. In order to avoid the occurrence of cavitation, the maximum pressure coefficient should be minimized. Therefore, in order to comprehensively evaluate the design method of the tidal current energy water turbine airfoil, the Reynold number is 1e6, and the objective function is the lift coefficient, the drag coefficient, the lift-drag ratio and the pressure coefficient under the condition that the attack angle is 3 degrees. Three control points are respectively taken on the upper wing-shaped curve and the lower wing-shaped curve, six control points are totally taken, each control point has two design variables of a horizontal coordinate and a vertical coordinate, the tangent lines of the leading edge and the trailing edge have eight design variables totally, and 10 initial population numbers are selected.
Based on the optimization model and the solution method provided by the invention, the airfoil curves of several different design requirements under various conditions are finally obtained as shown in fig. 5. As can be seen from the figure, when the drag coefficient is minimized and the lift coefficient is maximized, the airfoil curve is relatively close, the maximum thickness is located 35% away from the leading edge of the airfoil when the lift-drag ratio is maximized, and the maximum thickness is 8.8% of the chord length; under the condition of minimizing the drag coefficient, the maximum thickness is 35 percent away from the front edge, and the maximum thickness is 8.3 percent of the chord length. For the water turbine, the larger lifting force part is the thrust force perpendicular to the plane of the water turbine, and the specific gravity of the axial rotating force converted into the water turbine is smaller. Unlike the lift coefficient, the reduction of the drag coefficient can significantly improve hydrodynamic performance, and thus the drag coefficient plays a more important role in turbine design. In contrast to the first two airfoils, the airfoils obtained by maximizing the lift coefficient and minimizing the minimum pressure coefficient are significantly different. Under the condition of maximizing the lift coefficient, the front part of the airfoil profile is thicker, the thickness of the airfoil profile is reduced to the trailing edge, the maximum thickness is positioned 39% away from the leading edge of the airfoil profile, and the maximum thickness is 11.4% of the chord length; while for minimizing the minimum negative pressure coefficient, the maximum thickness is located 52% from the airfoil leading edge, with the maximum thickness being 8.8% of the chord length.
The surface pressure coefficients of four different airfoils under the condition of an attack angle of 3 degrees are shown in fig. 6, and it can be known from the graph that the pressure distribution is most uniform when the pressure coefficient is minimized, the minimum value is about-0.5, and it can be seen that the minimized pressure coefficient can greatly improve the pressure distribution on the airfoil surface, and can avoid the cavitation phenomenon as much as possible. The minimum pressure coefficient of the airfoil under the conditions of the minimum resistance coefficient and the maximum lift-drag ratio is about-1.1, and the minimum pressure coefficient and the maximum lift-drag ratio are relatively close. The minimum pressure coefficient peak value under the condition of maximizing the lift coefficient is the minimum and reaches about-1.5, and the cavitation problem is most likely to be generated more easily.
Lift coefficient, drag coefficient and lift-drag ratio for different design objective function cases are shown in fig. 7-9. Similar to the airfoil data results, both airfoils resulting from minimizing drag coefficient and maximizing lift-to-drag ratio have very close hydrodynamic performance. Under the condition that the negative pressure coefficient is taken as the target function, the lift coefficient is greatly smaller than that under the other three conditions, and the resistance coefficient is close to that under the condition of minimizing the resistance coefficient. The maximum lift coefficient has a larger lift coefficient but the drag coefficient is significantly larger than the other airfoils, and the airfoil has the largest lift coefficient at an angle of attack of 3 deg., but the airfoil at which the lift-to-drag ratio is maximized and the drag coefficient is minimized has a larger lift coefficient as the angle of attack increases. Therefore, when designing the wing profile, only the hydrodynamic performance at one attack angle cannot be considered, and comprehensive design is needed.
The embodiment can obtain that the design method of the hydrofoil wing section of the water turbine provided by the invention not only can obviously improve the lift coefficient, the resistance coefficient and the lift-drag ratio, but also can reduce the maximum pressure coefficient, thereby achieving the purposes of improving the hydrodynamic performance and avoiding the cavitation phenomenon.
The foregoing examples are set forth to illustrate the present invention more clearly and are not to be construed as limiting the scope of the invention, which is defined in the appended claims to which the invention pertains, as will be apparent to those skilled in the art, after reading the present invention.
Claims (9)
1. A method for designing a blade airfoil of a tidal current energy water turbine is characterized by comprising the following steps:
the method comprises the following steps: determining design variables and an objective function according to design requirements, and establishing a hydrofoil wing section optimization model;
wherein,
an objective function:
f(x)＝f(CL,CL/CD,CD,Cpmax)
designing variables:
x＝(x00,x11,y11,x12,y12,...,x1m,y1m,x21,x21,x22,y22,...,x2n,y2n,x01)
constraint conditions are as follows:
wherein, CL、CL/CD、CDAnd CpmaxRespectively is a lift coefficient, a lift-drag ratio, a resistance coefficient and a maximum pressure coefficient under any attack angle condition, and are functions of a design variable x;
andrespectively including the front edge, the tail edge, the abscissa of the control point on the upper surface of the wing profile, the ordinate of the control point on the upper surface of the wing profile, the abscissa of the control point on the lower surface of the wing profile and the lower surface of the wing profileThe lower bound of the surface control point ordinate, andthe control points are respectively the upper boundaries of the front edge, the tail edge, the abscissa of the control point on the upper surface of the wing profile, the ordinate of the control point on the upper surface of the wing profile, the abscissa of the control point on the lower surface of the wing profile and the ordinate of the control point on the lower surface of the wing profile;
m and n are the number of curve control points of the upper and lower wing profiles of the hydrofoil respectively;
x00and x01Are respectively tangent lines of the front edge and the rear edge of the hydrofoil airfoil (x)1m,y1m) And (x)2n,y2n) Respectively as the coordinates of control points, x, on the upper and lower airfoil profiles of the hydrofoil2nAnd x1mIs the abscissa of the control point of the upper and lower airfoil profiles of the hydrofoil, and y1mAnd y2nThe longitudinal coordinates of the curve control points of the upper and lower wing profiles of the hydrofoil are shown;
step two: determining a calculation method of hydrodynamic performance and pressure coefficient and a fitness function of a genetic algorithm;
step three: generating an initial population and fitting a hydrofoil profile curve;
step four: generating a hydrofoil airfoil fluid region grid model, calculating and outputting hydrodynamic performance, and outputting lift force, resistance and pressure information;
step five: and calculating a target function according to the hydrodynamic coefficient and the pressure coefficient, evaluating according to the fitness function, judging whether convergence occurs or not, finishing optimization if convergence occurs, otherwise, generating a new population, and returning to the step three.
2. The method for designing the blade airfoil of the tidal current energy turbine as set forth in claim 1, wherein the objective function f (x) takes the form of:
f(x)＝w1CL+w2CL/CD+w3CD+w4Cpmax
wherein wiI is the weight of the lift coefficient, lift-drag ratio, drag coefficient and maximum pressure coefficient, respectively, and satisfiesAnd 0. ltoreq. wi≤1。
3. The method for designing the blade airfoil of the tidal current energy turbine as set forth in claim 1, wherein the objective function f (x) takes the form of:
f(x)＝(w1CL+w2CL/CD+w3CD)Cpmax
the objective function is the product of the hydrodynamic performance and the pressure coefficient of the airfoil, where wiI is the weight of the lift coefficient, lift-drag ratio and drag coefficient, 2,3 are respectively, and satisfyAnd 0. ltoreq. wi≤1。
4. The method for designing the blade airfoil profile of the tidal current energy turbine as set forth in claim 1, wherein the objective function is a combined function g (x) of each hydrodynamic coefficient and pressure coefficient function at a plurality of attack angles as shown in the following formula,
wherein, αuThe size of the attack angle of the hydrofoil is the same,(u ═ 1, 2.., v.) an angle of attack size of αuTarget function of hydrodynamic performance under conditions, v being selected angle of attack in the target functionThe number and the combination function g (x) can comprehensively consider the hydrodynamic performance parameters under any attack angle condition, and can adopt any type of combination mode.
5. The method for designing the blade airfoil of the tidal current energy turbine as set forth in claim 1, wherein a lift coefficient, a drag coefficient, a lift-drag ratio and a pressure distribution are calculated by using a FLUENT or CFX or XFOIL numerical simulation program.
6. The method for designing the blade airfoil profile of the tidal current energy water turbine as set forth in claim 1, wherein the fitness function in the second step is in the form of:
wherein h(s) is the fitness of the s-th design scheme, ss is the number of design schemes in the population, and f (x)s) Is the objective function of the s-th design.
7. The method for designing the blade airfoil of the tidal current energy turbine as set forth in claim 1, wherein the abscissa and the ordinate of the control point on the airfoil curve of the hydrofoil, and the tangents of the leading edge and the trailing edge of the airfoil are used to fit the airfoil curve of the hydrofoil in the third step.
8. The method for designing the blade airfoil profile of the tidal current energy water turbine as claimed in claim 1, wherein the method for generating the new population in the fifth step is as follows:
according to the adaptability of ss different design schemes in a population, eliminating the design schemes with low adaptability according to the proportion of 5% -20%, then coding each design scheme in the population by adopting binary numbers, coding all 2m +2n +2 design variables in a certain design scheme into a binary number, and coding the binary number according to a leading edge tangent line, a horizontal coordinate and a vertical coordinate of an upper surface curve of the wing profile, a trailing edge tangent line and a lower surface of the wing profileThe horizontal coordinates and the vertical coordinates of the surface curve are arranged in sequence; the front edge tangent line, the abscissa and the ordinate of the airfoil upper surface curve, the abscissa and the ordinate of the airfoil lower surface curve and the rear edge tangent line are respectively represented by a binary number, the specific expression is as follows, the first row represents the converted binary number, the second row represents the number of the design variable in the coded binary number, the number is 2m +2n +2 design variables, and the 1 st is the front edge tangent line x002 nd to 2m +1 th are the abscissa and ordinate of the upper surface curve of the airfoil profile and are in accordance with (x)11,y11)(x12,y12)...(x1m,y1m) In the order of (1), the 2m +2 to 2m +2n +1 are the abscissa and the ordinate of the lower surface curve of the airfoil profile and are in accordance with (x)21,y21)(x22,y22)...(x2m,y2m) In a sequence of which the last one is a trailing edge tangent x01Numbered 2m +2n +2 in binary numbers,
the better design scheme is kept, and mutation and hybridization operations are carried out according to the proportion of 5% -20% to obtain a new solution, so that the population quantity ss is ensured to be unchanged.
9. The method for designing the blade airfoil profile of the tidal current energy turbine as set forth in claim 4, wherein the combination function g (x) adopts a weighted summation method as shown in the following formula:
wherein ω isuIs a weight coefficient and satisfies
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