JP2007090994A - Evaluating method and designing method for blade airfoil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluating method for evaluating performance of an airfoil over entire region of relative velocity of a blade in relation to the atmosphere and a designing method based on the evaluation. <P>SOLUTION: An elevation angle α<SB>n</SB>or a lift coefficient C<SB>Ln</SB>in which a resistance coefficient C<SB>D</SB>becomes a set value or more is determined by a static CFD analysis, and is used as an index for evaluating the performance of the blade. The set value is 0.03, for instance. The index is obtainable over the entire region of the relative velocity estimated when the blade is practically used. The airfoil can be evaluated by one index over the entire region of the relative velocity. The index can be used as a threshold value for deciding whether or not dynamic stall is generated. A suitable design of the airfoil is made possible by incorporating the evaluation using the index into an automatic optimum design. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for evaluating blade airfoils and a method for designing airfoils.

  FIG. 3 is a view for explaining the present invention. However, with reference to FIG. 3, the blade of the helicopter moves forward in the flight direction B while rotating in the direction of the arrow A. . Therefore, when the helicopter is moving forward, the blades have different relative velocities with respect to the atmosphere depending on the angular position of the blades. The relative velocity of the blade to the atmosphere is different at the blade root and tip. Further, FIG. 4 is a diagram for explaining the present invention. Referring to FIG. 4, in order to balance the lift force between the forward side and the backward side during forward movement, one rotation is performed. It is necessary to change the angle of attack α, also called the pitch angle of the blade. Therefore, the blade is moving under an environment in which the angle of attack and the relative speed are constantly changing.

FIG. 11 is a graph showing indices used for performance evaluation of a conventional airfoil. FIG. 11 shows the maximum lift coefficient C _Lmax and the resistance divergence Mach number M _DD . In FIG. 11, each line 1-4 shows the maximum lift coefficient _CLmax , and each line 5-7 shows resistance divergence Mach number _MDD . Lines 1 and 5 have the same airfoil characteristics, Lines 2 and 6 have the same airfoil characteristics, and Lines 3 and 6 have the same airfoil characteristics. .

The blade airfoil is designed by an automatic optimum design calculation that evaluates the performance of the airfoil while correcting the parameters that define the airfoil and obtains the optimum airfoil. An evaluation index is used to evaluate the performance of the airfoil when designing the airfoil. Evaluation index, the relative speed is low low-speed range, the maximum lift coefficient C _Lmax is used as an index, the relative speed is higher the high-speed range, the resistance diverges mach number M _DD or buffet generating lift coefficient C _Lbuffet is used. Such an evaluation index is obtained, for example, by numerical fluid analysis (abbreviated as CFD) as shown in Non-Patent Document 1.

When the relative speed is in the low speed range, increasing the angle of attack of the blade increases the lift, but reaches a maximum value at a certain angle of attack. The lift coefficient when the lift is maximum is the maximum lift coefficient C _Lmax . When the relative speed is in the high speed range, there is no clear maximum lift. Further, when the relative speed is high, the angle of attack increases and the lift tends to increase. However, a buffet that is aerodynamic vibration occurs at a certain angle of attack. The lift coefficient at the point where the _buffet is generated is the _buffet- generated lift coefficient C _Lbuffet . The resistance divergence Mach number _MDD is a Mach number representing a relative speed at which the resistance rapidly increases when the angle of attack is changed to increase the relative speed while keeping the lift coefficient constant.

The configuration using the maximum lift coefficient C _Lmax , the resistance divergence Mach number M _DD , and the _buffet- generated lift coefficient C _Lbuffet as described above has several problems as follows. The lift coefficient at the point where the solution starts to vibrate in the CFD calculation is the calculated _buffet- generated lift coefficient C _Lbuffet , which originally means a condition for starting the vibration of the physical fluid force. Whether or not a numerical solution becomes a vibration solution also depends on the time integration method, which is a purely numerical algorithm, and there is a question of equating it with physical fluid vibration. FIG. 11 shows only the resistance divergence Mach number M _DD, but the resistance divergence Mach number M _DD and the _buffet- generated lift coefficient C _Lbuffet used as an index in the high-speed range show different limit values. I cannot judge whether to give priority to. As shown in FIG. 11, the resistance divergence Mach number _MDD is less than 0.8. However, in the actual machine, when the relative velocity of the atmosphere with respect to the blade is expressed by the Mach number, M> 0.8 is used. Therefore, it can not be said that the resistance divergence Mach number _MDD is an index that correctly expresses the limit regarding the characteristics in the high speed range.

Further, as apparent from FIG. 11, the maximum lift coefficient C _Lmax and the resistance divergence Mach number M _DD are discontinuous, and it cannot be determined which index should be used in the vicinity of the boundary. FIG. 11 shows only the relationship between the maximum lift coefficient C _Lmax and the resistance divergence Mach number M _DD , but the maximum lift coefficient C _Lmax and the _buffet- generated lift coefficient C _Lbuffet are also discontinuous, and the same problem occurs _. Have. In FIG. 11, each of the lines 1 to 4 indicating the maximum lift coefficient C _Lmax extends over a wide range of the Mach number M representing the relative speed. However, as described above, a clear maximum lift may not appear in the high speed range. Therefore, the maximum lift coefficient C _Lmax cannot be used over the entire area. Thus, with the conventional configuration, the performance of the airfoil cannot be evaluated over the entire range of the relative speed. The maximum lift coefficient C _Lmax , the resistance divergence Mach number M _DD, and the _buffet- generated lift coefficient C _Lbuffet , which are static characteristics of the airfoil, have been used as evaluation indices for the helicopter blade airfoil. Considering the wide usage range of blades, it is not optimal. Also, it does not take into account the dynamic changes in speed fluctuation and angle of attack fluctuation to which the airfoil blade is exposed.

  As other conventional techniques related to the performance of a blade, techniques disclosed in Patent Documents 1 to 4 are known. Patent Document 1 discloses a method for generating a wing structure analysis model in which a wing structure analysis is directly performed on the basis of three-dimensional measurement data of a real wing. Patent Document 2 discloses an analysis experiment apparatus for a flow around a blade that enables visualization of a flow field around a test blade row and simultaneous measurement of wall pressure and the like. Patent Document 3 discloses a flow separation control device that suppresses a separation phenomenon that occurs between an object surface or a channel wall surface and a fluid flow, and that can improve stall and instability phenomena. . In addition, as a conventional technique related to analysis, Patent Document 4 discloses that efficiency of assigning analysis conditions to a shape to be analyzed when computer analysis is performed by applying finite element method analysis, and greatly reduces the number of processing steps. An apparatus for setting analysis conditions for an analysis shape model is shown. Even if these configurations of Patent Documents 1 to 4 are used, the performance of the airfoil cannot be evaluated over the entire range of the relative speed.

Shima: “Analysis of CFD technology for aerodynamic design in Kawasaki Heavy Industries”, Journal of Computational Fluid Dynamics, Vol. 6, No. 2, 1998, pp. 45-57 Japanese Patent Laid-Open No. 11-281328 JP-A-6-341919 JP-A-5-16892 JP-A-4-257704

  An object of the present invention is to provide a blade airfoil evaluation method capable of evaluating the performance of the airfoil over the entire range of the relative velocity of the blade to the atmosphere, and a blade airfoil design method based on this evaluation. .

The present invention evaluates the blade attack angle at which the resistance coefficient when the blade is arranged in a uniform air flow is a predetermined value or more, or the lift coefficient at which the resistance coefficient is the set value or more, by evaluating the blade shape of the blade. As an index, an analysis process obtained by static analysis,
A blade airfoil performance evaluation method comprising: an evaluation step of evaluating the performance of the blade airfoil using the obtained evaluation index.

  According to the present invention, the angle of attack or lift coefficient at which the resistance coefficient is equal to or greater than the set value is obtained by static analysis, and the angle of attack or lift coefficient is used as an evaluation index for evaluating the performance of the blade airfoil. It is done. This evaluation index is an index obtained over the entire range of the relative speed at which the blade is assumed to be actually used. Relative speed is the relative speed of the blade to the atmosphere. Therefore, by using this evaluation index, it is possible to evaluate the airfoil with one evaluation index over the entire range of relative speeds where the blade is assumed to be actually used, and to appropriately evaluate the static characteristics of the airfoil. Can do.

  The evaluation index can also be used as a threshold for determining whether or not dynamic stall occurs based on a result obtained by dynamic analysis. Thus, the evaluation index can be used not only as an index representing the static characteristics but also for estimating the dynamic characteristics of the airfoil. Therefore, the evaluation index can be used for airfoil evaluation in consideration of dynamic changes in relative speed and angle of attack, and has high utility.

  In addition, the present invention is characterized in that the set value of the resistance coefficient is 0.02 or more and 0.1 or less.

According to the present invention, the angle of attack or the lift coefficient at which the resistance coefficient is not less than a set value set in the range of 0.02 to 0.1 is used as the evaluation index. When the angle of attack is larger than the angle of attack at which the lift coefficient is maximum and the angle of attack where the buffet is generated, the resistance value tends to increase rapidly as the angle of attack increases. Since the resistance coefficient at which the resistance value starts to increase is present within the above range, setting the set value within the above range enables evaluation in consideration of the maximum lift coefficient C _Lmax and the _buffet- generated lift coefficient C _Lbuffet. Become.

The present invention also includes an initial setting step for initial setting parameters for defining the blade shape of the blade;
An airfoil definition process for defining an airfoil according to set parameters;
A performance determination step of evaluating the performance of the defined airfoil by the performance evaluation method of the blade airfoil according to claim 1 or 2,
Based on the airfoil performance judgment result, it is determined whether or not the airfoil performance has converged to the optimal value. If it is determined that it has converged to the optimal value, that airfoil is output as the design airfoil. A judgment output step;
A blade airfoil design comprising: a repetitive process of correcting and setting the parameters and repeating from the airfoil definition process to the determination output process when it is determined that it has not converged in the determination output process Is the method.

  According to the present invention, the airfoil defined by the initially set parameters is evaluated, until the evaluation result converges to the optimum value, the parameters are corrected and the airfoil is redefined, and the airfoil evaluation is repeated. Optimal airfoils can be designed. The method of repeating the evaluation while correcting the parameters and obtaining the optimum value of the parameters is a so-called automatic optimum design method. By incorporating the evaluation of the airfoil by the above-described evaluation method into this automatic optimum design, the airfoil can be designed based on a suitable evaluation, and a suitable airfoil can be designed.

  According to the present invention, the airfoil can be evaluated with one evaluation index over the entire range of the relative speed in which the blade is assumed to be actually used, and the static characteristics of the airfoil can be suitably evaluated. The evaluation index can also be used for airfoil evaluation considering dynamic changes in relative speed and angle of attack, and has high utility.

Further, according to the present invention, it is possible to _perform an evaluation in consideration of the maximum lift coefficient C _Lmax and the _buffet- generated lift coefficient C _Lbuffet . Therefore, it is possible to evaluate a more suitable airfoil.

  Further, according to the present invention, by incorporating the evaluation of the airfoil by the aforementioned evaluation method into the automatic optimum design, the airfoil can be designed based on a suitable evaluation, and a suitable airfoil can be designed. it can.

  FIG. 1 is a flowchart showing a blade airfoil design method using a blade airfoil performance evaluation method (hereinafter simply referred to as “evaluation method”) according to an embodiment of the present invention. FIG. 2 is a block diagram showing a design apparatus 20 that executes the design method of FIG. FIG. 3 is a plan view showing the air speed distribution of the blade 11 during forward flight of the helicopter 10. FIG. 4 is a diagram showing the angle of attack distribution of the blade 3. The helicopter 10 is provided with a plurality of rotor blades (hereinafter simply referred to as “blades”) 11, but only one blade 11 is virtually shown in FIG. 3.

  For example, the airfoil of the blade 11 of the helicopter 10 which is a high-performance helicopter is designed by an automatic optimum design method, which is also called a numerical optimization method, using a numerical fluid analysis (abbreviation CFD) based on computational fluid dynamics. In this automatic optimum design method, an optimum airfoil is designed by repeating evaluation of the airfoil performance, for example, several tens to several thousand times while correcting parameters defining the airfoil. Therefore, if a suitable index used for evaluating the performance of the airfoil is obtained, an iterative loop in which parameter correction and evaluation are repeated can be executed to design an excellent airfoil. Thus, in the design of an airfoil, the evaluation of the performance of the airfoil is an important key, and the evaluation index used for the evaluation is important. The present invention is suitably implemented for the optimum design of such an airfoil.

  The blade 11 of the helicopter 10 advances in the flight direction B at the flight speed V and changes the angle of attack α, also called the pitch angle, for example, with rotation in the rotation direction A counterclockwise when viewed from above. Do a complicated exercise. When it is assumed that there is no wind, the relative speed of the blade 11 to the atmosphere (hereinafter referred to as “airspeed”) Va is the rotational speed R · Ω when the rotational angular speed of the blade is Ω and the azimuth angle is ψ. It is represented by the sum (= R · Ω + Vsinψ) with the direction component (rotation direction component) Vsinψ perpendicular to the blade of the flying speed V. “·” Is an operator representing multiplication. R is the distance from the center of rotation, and the azimuth angle ψ is the angle in the rotational direction A from the rear angular position, and represents the angular position of the blade 11. In the hovering state, the flight speed V is 0, and the airspeed Va is the rotational speed R · Ω regardless of the angular position of the blade 11.

  An example of the airspeed Va is indicated by the Mach number M. In the hovering state, for example, the airspeed Va of the blade root 12 is M = 0.2, and the airspeed Va of the blade tip 13 is M = 0. 6. When the flying speed V is M = 0.2, the airspeed Va of the blade tip 13 of the blade 11 is M = 0.8 at an angular position where the forward azimuth angle ψ is 90 ° during one rotation. Thus, M = 0.4 at the position where the backward azimuth angle ψ is 270 °. In the present embodiment, the performance of the airfoil is evaluated and the airfoil is designed using an evaluation index that can be used over the entire air speed Va in a wide range. In the present embodiment, M = 0.4 or less is a low speed region, M = 0.7 or more is a high speed region, and a middle speed region is between the low speed region and the high speed region. Hereinafter, the Mach number M may be simply referred to as the airspeed Va.

  In the present invention, the relatively high speed region means a relatively high speed region including the high speed region (M ≧ 0.7), and is not limited to the high speed region, and M = approximately 0.6. It means the above area. In the present invention, the relatively low speed region means a relatively low speed region including the low speed region (M ≦ 0.4), and is not limited to the low speed region. An area of less than 6 is meant.

  The design apparatus 20 shown in FIG. 2 includes an input unit 21, a storage unit 22, an external recording unit 23, a calculation unit 24, and an output unit 25. The design device 20 is realized using, for example, a computer. The input means 21 is a means for inputting information including parameter information defining the airfoil and command information for instructing the evaluation and design of the airfoil, such as a keyboard.

  The storage means 22 is a means for storing information in a medium provided inside the computer, such as a hard disk drive and a semiconductor memory, for example, an arithmetic program for executing the design method and evaluation method of the present invention, and an arithmetic program Data necessary for the calculation by is stored. The external recording means 23 is means for recording information on a removable recording medium such as a compact disc (abbreviated CD) and a digital versatile disc (abbreviated DVD) and reproducing the information recorded on the recording medium, for example, An arithmetic program for executing the design method and the evaluation method of the present invention, data necessary for arithmetic operations by the arithmetic program, and the like are stored. An information holding means for holding information such as a calculation program and data is configured including the storage means 22 and the external recording means 23.

  The arithmetic means 24 is realized by, for example, a central arithmetic processing unit (abbreviated as CPU), and based on command information input by the input means 21, an optimal design arithmetic program, CFD, or the like is obtained from either the storage means 22 or the external recording means 23. A calculation program and data including an analysis calculation program are read, and calculation for evaluation and design of the airfoil is executed using the parameter information input by the input means 21. The output unit 25 is a unit that outputs a calculation result by the calculation unit 24, and is, for example, a display device. The calculation result by the calculation unit 24 may be output by being recorded on a recording medium by the external recording unit 23. Therefore, a result output means for outputting the calculation result is configured including the output means 25 and the external recording means 23.

  Specifically, the design method is executed by the design device 20, specifically, by the calculation unit 24. When the information indicating the initial value of the parameter defining the airfoil is input by the input unit 21 and the command information for instructing the design of the airfoil is given to the calculation unit 24, as shown in FIG. The design is started and the process proceeds to step s1. In step s1, the computing means 24 initializes parameters that define the airfoil of the blade 11. Specifically, the parameter is set to an initial value input by the input unit 21. The parameter is a value representing the shape of the blade, and includes, for example, the blade thickness, camber, chord length, leading edge radius, and the like. This step s1 corresponds to an initial setting step.

  When the parameter initialization in step s1 ends, the process proceeds to step s2, and the calculation means 24 defines the airfoil according to the set parameters. This step s2 corresponds to an airfoil definition process. When the definition of the airfoil in step s2 ends, the process proceeds to step s3. In step s3, the calculation means 24 obtains the fluctuation characteristics of moment and the fluctuation characteristics of lift by CFD analysis when the airspeed Va is in a relatively high speed region for the defined airfoil. Here, the moment is a moment in the pitching direction with respect to the blade, and includes a torsional moment.

  The blade 11 of the helicopter 10 is an elongated wing and has low torsional rigidity. Therefore, when a large torsional moment due to aerodynamic force is applied, torsional deformation occurs, and the expected aerodynamic characteristics may not be obtained. In addition, since the rotational surface of the rotor changes due to aerodynamic forces including lift acting on the blades 11, when the sudden change in lift occurs, the rotational surface of the rotor exhibits unexpected behavior. When the airspeed Va is in the vicinity of M = 0.8 or higher, unexpected behavior of the rotating surface is likely to occur due to a transonic phenomenon in which a shock wave is generated in the flow field around the blade 11. Suppressing moment variation and lift variation when in the relatively high speed region leading to this unexpected behavior of the rotating surface is one of the important points in airfoil design.

The moment fluctuation characteristics and lift fluctuation characteristics in a relatively high speed region are analyzed by keeping the angle of attack α constant and gradually increasing the airspeed Va from M = 0.6. The amount of change from the value when M = 0.6 of moment and lift can be represented by Mach numbers exceeding a preset threshold value, respectively. The variation characteristic of the moment is called Mach tack. In another embodiment of the present invention, instead of these characteristics, the lift coefficient C _L is kept constant, and the airspeed Va is gradually increased from M = 0.6 to perform the analysis. In addition, it is also possible to use characteristics each represented by a Mach number at which the amount of change from the value when M = 0.6 of moment and angle of attack α exceeds a preset threshold value. It can be said that these characteristics are more excellent as the numerical value is higher. In step s3, the performance of the airfoil is evaluated according to the value of these characteristics, that is, the Mach number. When the characteristic analysis in step s3 ends, the process proceeds to step s4.

In step s4, the arithmetic means 24, relative to the wing type defined is evaluated based on the drag coefficient C _D. The evaluation method for evaluating the performance of the airfoil in step s4 includes an analysis process and an evaluation process. In the analysis step, the drag coefficient C _D is the angle of attack (the "index angle of attack") alpha _n or the resistance coefficient C _D of the blade 11 becomes more than the set value predetermined in the case where a blade 11 uniformly air stream The lift coefficient (hereinafter referred to as “index lift coefficient”) C _Ln that becomes equal to or larger than the set value is obtained by static analysis as an evaluation index of the blade shape of the blade 11. In the evaluation process, the performance of the airfoil is evaluated using the evaluation index obtained in the analysis process. The resistance coefficient C _D is a coefficient representing the resistance force received by the blade 11, and the lift coefficient C _L is a coefficient representing the lift force received by the blade 11.

Served in the index angle of attack alpha _n and index the lift coefficient C _Ln letter "n" is a number representing the set value of the resistance coefficient C _D, which is 100 times the value of the set value of the resistance coefficient C _D. Thus, for example, the index coefficient of lift C _L300 is drag coefficient C _D means the lift coefficient when it is 0.03. Set value of the resistance coefficient C _D is, for example, 0.02 to 0.1. More preferably, it is 0.03 or more and 0.05 or less.

FIG. 5 is a graph showing an index lift coefficient C _L300 representing a lift coefficient when the resistance coefficient _CD is 0.03. FIG. 5 shows index lift coefficients CL ₃₀₀ of a plurality of airfoils, specifically, NACA0012, NACA23012, VR-7, VR-8, HH-02, NACA23008, SC1095, and AK100D. 37, respectively. Thus, the index lift coefficient C _L300 is an index that is continuous over the entire air speed Va in which the blade 11 is assumed to be used, that is, from the low speed range to the high speed range. In FIG. 5, since the airfoil performance evaluation is hardly affected, the airspeed Va is omitted in the speed range where M <0.2.

In step s4, for example, an index lift coefficient C _L300 representing a lift coefficient when the resistance coefficient _CD is 0.03 as shown in FIG. 5 is obtained, and the performance of the airfoil is evaluated. Specifically, in the analysis step, an index lift coefficient C _L300 is obtained. In the evaluation process, the performance of the airfoil is evaluated using the index lift coefficient C _L300 . The higher the index lift coefficient C _L300 is, the higher the performance of the airfoil is. As shown in the graph of FIG. 5, the higher the index lift coefficient C _L300 is, the higher the airfoil performance is. Therefore, in the evaluation process, depending on what value the index lift coefficient C _L300 shows over the entire air speed Va, that is, in the graph as shown in FIG. Evaluate performance.

Further, when the helicopter 10 flies at 160 kt, if the required performance of the airfoil represented by the index lift coefficient C _L300 is the performance indicated by the broken line 38 in FIG. 5, the index lift of the airfoil to be evaluated If the coefficient C _L300 exists on the upper right side of the broken line 38, the airfoil to be evaluated satisfies the required performance. In the evaluation process, whether or not the required performance is satisfied is also evaluated. The required performance related to the index lift coefficient C _L300 determined in step s5 is input by the input means 21 together with the initial value of the parameter, for example, before starting the design operation. Such step s4 corresponds to a performance determination step. When the performance judging process in step s4 is completed, the process proceeds to step s5.

  In step s5, the calculation means 24 determines whether or not the performance of the airfoil has converged to the optimum value based on the performance determination result of the airfoil in the performance determination process of step s4 and the evaluation result in step s3. To do. Specifically, it is determined whether or not the performance of the airfoil satisfies the required performance and is as high as possible. The influence of the moment variation characteristic and the lift variation characteristic on the rotor performance in a relatively high speed region varies depending on the rigidity of the blade 11 as described above. Therefore, the importance depends on the structure of the blade 11. Different. For example, if the blade 11 and the drive mechanism having extremely high rigidity and strength can be realized, it can be extremely discussed that it is not necessary to pay attention to the fluctuation characteristics of the moment and the fluctuation characteristics of the lift.

In step s5, based on the structure of the blade 11, relative weight is assigned to the evaluation regarding the variation characteristics of the moment and the variation characteristics of the lift and the evaluation using the index lift coefficient C _L300 to obtain an optimal value comprehensively. It is determined whether or not it has converged. If it is determined in this step s5 that it has not converged to the optimum value, the process proceeds to step s6, and if it is determined that it has converged to the optimum value, the process proceeds to step s7. This step s5 corresponds to a determination output step.

  In step s6, the computing means 24 corrects and sets the parameters again, for example, using a genetic algorithm, and proceeds to step s2. As described above, when it is determined that the convergence has not been achieved in the determination output process of step s5, the parameter is corrected and set again, and the process from the airfoil definition process of step s2 to the determination output process of step s5 is repeated. The process of repeating steps s2 to s5 in this way corresponds to the repetition process.

  When it is determined that the airfoil design process by the automatic optimum design using the static analysis is configured including the processes from step s1 to step s6, and it is determined in step s5 that the blade has converged to the optimum value, the blade The result is output as a design airfoil in the airfoil design process by automatic optimal design using static analysis, that is, a design airfoil based on the evaluation of static performance. Such processes of steps s1 to s6 are procedures of a so-called automatic optimum design method. In other words, the present embodiment defines the airfoil by setting parameters, repeats the evaluation of the airfoil while correcting the parameters, and derives the optimum airfoil by automatically reconfiguring the airfoil. As a mold evaluation method, performance evaluation using an evaluation index as in step s4 is newly adopted. Thereby, an airfoil can be designed based on a suitable evaluation, and a suitable airfoil can be designed.

  In step s7, the calculation means 24 is determined to converge to the optimum value in step s5, performs dynamic CFD analysis on the obtained design airfoil, obtains the dynamic performance of the airfoil, and proceeds to step s8. . In step s8, the computing means 24 determines whether or not the dynamic performance obtained in step s7 is good, specifically, whether or not the required performance is satisfied. The required performance related to the dynamic performance determined in step s8 is input by the input unit 21 together with the initial value of the parameter, for example, before starting the design operation. If it is determined in step s8 that the dynamic performance is good, the process proceeds to step s9. If it is determined that the dynamic performance is not good, the process proceeds to step s1.

  In step s9, the computing means 24 defines a three-dimensional rotor using the defined airfoil, and proceeds to step s10. In step s10, the computing means 24 performs a three-dimensional CFD analysis on the rotor defined in step s9, obtains the three-dimensional performance of the rotor, and proceeds to step s11. In step s11, the calculation means 24 determines whether or not the three-dimensional performance obtained in step s10 is good, specifically, whether or not the required performance is satisfied. The required performance related to the three-dimensional performance determined in step s11 is input by the input means 21 together with the initial value of the parameter, for example, before starting the design operation. If it is determined in step s11 that the three-dimensional performance is good, the process proceeds to step s12. If the design operation is terminated and it is determined that the three-dimensional performance is not good, the process proceeds to step s1.

  When the process proceeds from step s8 or step s11 to step s1, the parameter initialization in step s1 may be the same initialization as when the design operation is started and the parameters are initialized first, or from step s8. When shifting, the initial value may be newly calculated based on the result of step s7. When shifting from step s11, the initial value is newly calculated based on the result of step s10. You may do it.

  As described above, in this embodiment, in addition to the static CFD analysis, the performance is confirmed by the dynamic CFD analysis and the three-dimensional CFD analysis in steps s7 to s11. Therefore, a more suitable airfoil can be designed. it can. The process of steps s7 to s11 is not an essential configuration, and may be a configuration without steps s7 to s11 as another embodiment of the present invention.

FIG. 6 is a graph showing the three component force characteristics in the low speed region. FIG. 7 is a graph showing the three component force characteristics in the high speed region. The three component force characteristics are a lift coefficient C _L , a resistance coefficient _CD and a moment coefficient C _M. The moment coefficient C _M is a coefficient representing the moment that the blade receives. FIG. 6 shows the three-component force characteristics when the airspeed Va is M = 0.35, and FIG. 7 shows the three-component force characteristics when the airspeed Va is M = 0.75. Indicates. FIGS. 6 (1) and 7 (1) show the three component force characteristics when the airfoil is NACA0012, and FIGS. 6 (2) and 7 (2) show that the airfoil is VR-7. The three component force characteristics are shown. 6 and 7, each line 40 to 47 represents a lift coefficient C _L , each line 50 to 57 represents a resistance coefficient C _D , each line 60 to 67 represents a moment coefficient C _M, and a broken line 70 represents resistance coefficient C _D in the graph indicates a position which is 0.03.

As is clear from the three-component force characteristic illustrated in FIG. 6, in the low speed range, the lift increases monotonously as the angle of attack α increases until the angle of attack α reaches a certain angle of attack. Shows the maximum lift. This is called the maximum lift, and the lift coefficient C _D there is called the maximum lift coefficient, and is represented by the symbol C _Lmax . Further attack angle α is equal to or greater than around angle of attack α which indicates the maximum lift coefficient C _Lmax, with increasing α angle of attack, the resistance coefficient C _D is rapidly increased, since the moment coefficient C _M suddenly changes, lift Not only does it not increase any more, but in general it is not possible to use a wing with a higher angle of attack α.

As the Mach number M representing the airspeed Va increases, the maximum lift coefficient C _Lmax gradually decreases. As is clear from the three-component force characteristics illustrated in FIG. 7, the tendency varies somewhat depending on the airfoil, but in the relatively high speed region where M = about 0.6 or more with respect to the maximum lift coefficient C _Lmax , the low speed region The maximum lift is not shown at a certain angle of attack, and the lift may once decrease.However, when the angle of attack exceeds a certain angle, the lift gradually increases as the angle of attack increases. resistance rapidly, i.e. resistance coefficient C _D it can be seen that the surge.

As a fluid phenomenon, it is known that the shock wave becomes stronger, the accompanying shock stall occurs, the flow becomes unstable, and the aerodynamic force starts to vibrate (Buffet on set). Is referred to as a _buffet- generated lift coefficient C _Lbuffet, and is used as an indicator of the critical performance of a blade in a high speed region as described in the prior art. The _buffet- generated lift coefficient C _Lbuffet is also a lift coefficient at which the aerodynamic force becomes unsteady at a transonic speed (M> about 0.7). Even in the calculation result by CFD, at a high angle of attack, it does not converge to a steady solution and starts to vibrate, and the angle of attack and lift at this time may be used instead of the maximum lift coefficient C _Lmax . 6 and 7, the lines 41, 43, 45, 47, 51, 53, 55, 57, 61, 63, 65, and 67 are regions showing vibrational properties. Average values are shown.

FIG. 8 is a graph showing the resistance divergence Mach number _MDD . FIG 8 (1), shows the drag divergence Mach number M _DD when airfoil is NACA0012, 8 (2) is a drag divergence Mach number M _DD when airfoil is VR-7 Show. 8, each line 71 and 72, shows the drag coefficient C _D when the lift coefficient C _L is -0.2, each line 73 and 74, the resistance coefficient when the lift coefficient C _L is 0.0 C _D is shown, and the lines 75 and 76 show the resistance coefficient C _D when the lift coefficient C _L is 0.2. In FIG. 8, a dotted line 77 indicates the resistance divergence Mach number M _DD when the lift coefficient C _L is −0.2, and each dotted line 78 and 79 indicates a case where the lift coefficient C _L is 0.0. shows the drag divergence Mach number M _DD, the dotted line 80 and 81 show the drag divergence Mach number M _DD when the lift coefficient C _L is 0.2. The dashed line 83 shows the position drag coefficient C _D in the graph is 0.03.

The performance limit of the airfoil from the low speed region to the medium speed region generally appears in the high angle-of-attack characteristics as described above, but in the high-speed region, particularly in the region exceeding M = 0.75, the angle of attack α increasing characteristic change due to the Mach number M, rapid increase in drag coefficient C _D is significant, typically. Therefore, the characteristics when the Mach number M is gradually changed under the condition that the lift is constant (that is, the angle of attack is changed in order to adjust the lift to the set value), and the Mach number M increases when the Mach number M is increased. the Mach number M resistance begins increasing rapidly with an increase in the number M, say drag divergence Mach number _{(Drag divergence Mach number) M DD} , is used as an index of high speed performance of the airfoil. Drag divergence Mach number M _DD, to the resistance coefficient C _D in M = 0.6, 0.002 Mach number which increases drag coefficient C _D.

As described in the section of the prior art, there are some problems in the method of using the maximum lift coefficient C _Lmax , the _buffet- generated lift coefficient C _Lbuffet and the resistance divergence Mach number M _DD as evaluation indexes. Therefore, a performance index that solves these problems and can express performance limits under a wider range of conditions is considered. Looking at the three component force characteristics of each airfoil and Mach number M, when the angle of attack α exceeds the maximum lift coefficient C _Lmax and the _buffet- generated lift coefficient C _Lbuffet , the resistance increases rapidly as the angle of attack α increases. You can see that Furthermore, the resistance coefficient C _{D in the} case of showing the maximum lift coefficient C _Lmax and the _buffet- generated lift coefficient C _Lbuffet for any airfoil and any Mach number is in the range of 0.02 to 0.1, particularly 0.03 The present inventors have confirmed that the concentration is within the range of 0.05 or less. In the example of FIGS. 6 to 8, the maximum lift coefficient C _Lmax, the drag coefficient C _D when indicating the buffet generating lift coefficient C _Lbuffet, about 0.03.

Therefore, the set value of the resistance coefficient C _D is set in the range of 0.02 to 0.1, preferably 0.03 to 0.05, and the blade 11 receives the resistance coefficient _{CD that} is equal to or higher than the set value. the corner at which the index angle of attack alpha _n or the resistance coefficient C _D is the set value or more becomes lift coefficient a is index lift coefficient C _Ln, by an evaluation index of the airfoil of the blade 11, the aerofoil performance It can be suitably evaluated. Because of the rapid increase in resistance, higher high-speed and high attack angles deviate from the practical range. Therefore, the index attack angle α _n and the index index lift coefficient C _Ln are simply substitutes for the maximum lift coefficient C _Lmax and the _buffet- generated lift coefficient C _Lbuffet . Not only that, it also has a practical meaning. The state of a decrease in lift and an increase in resistance at an angle of attack greater than the angle of attack that indicates the maximum lift is commonly referred to as “stall”, but it indicates that the speed is lost due to the increase in resistance.

The resistance coefficient C _D when the maximum lift coefficient C _Lmax and the _buffet- generated lift coefficient C _Lbuffet are shown varies depending on the airfoil, but is 0.02 or more and 0.1 or less for most of the airfoils by the present inventors. It has been confirmed that it exists in the range. Therefore, by setting the resistance coefficient to a value in the range of 0.02 or more and 0.1 or less, it becomes an index that can be used for the evaluation of the airfoil. In particular, the maximum lift coefficient C _Lmax, the drag coefficient C _D when indicating the buffet generating lift coefficient C _Lbuffet is, to focus on 0.03 to 0.05, has been confirmed by the present inventors, the resistance coefficient C _A more preferable index can be obtained by setting the set value of _{D to} a value in the range of 0.03 to 0.05.

Also in the high speed range, the set value of the drag coefficient C _D is, when in the range of 0.02 to 0.1, the Mach number M and the resistance coefficient C _D is the set value, the number of diverging resistance Mach M _DD Can be used instead. Therefore, the index attack angle α _n and the index index lift coefficient C _Ln can be suitably used in both the low speed range and the high speed range. Moreover, since the same index can be used from the low speed region to the high speed region, the airfoil performance can be expressed by one continuous curve for each airfoil.

FIG. 9 is a graph showing the result of static CFD analysis and the result of dynamic CFD analysis. In FIG. 9, when the airfoil is NACA0012, the index lift coefficient C _L300 by static CFD analysis is shown by a line 85, the lift coefficient C _L by dynamic CFD analysis is shown by a solid line 86, and the resistance by dynamic CFD analysis is shown. It shows the coefficient C _D by the dashed line 87.

As shown in FIG. 9, the dynamic lift can momentarily exceed the static maximum lift, but if the state continues for a while, a large separation occurs immediately after that, causing a sudden increase in resistance and a sudden change in moment. I can see that. The trend is generally the same for other airfoils, and dynamic and large performance due to delamination as long as the lift coefficient by dynamic analysis is less than the index lift coefficient C _L300 indicating the performance limit of static airfoils. It is confirmed by the present invention that there is no decrease and that the static limit lift can be exceeded in a dynamic state for a short time.

In a static state, when sufficient time has elapsed, the boundary layer grows in response to the reverse pressure gradient on the blade upper surface, and the lift decreases. This is probably because the layer is kept thin. Thus, the index lift coefficient C _L300 not only shows a static performance limit, but is also effective as a criterion for determining whether or not dynamic stall occurs. Specifically, when the dynamic lift coefficient exceeds the index lift coefficient C _L300 , stall can occur, and when it does not exceed, it can be determined that no stall occurs. In the above-described determination in step s8, it may be determined whether or not the dynamic performance is good by such determination.

FIG. 10 is a graph showing the relationship between the index lift coefficient C _L300 and the required performance. FIG. 10 shows the index lift coefficient C _L300 by static CFD analysis when the airfoil is NACA23012 as a line 90, which is required for the airfoil when the helicopter 10 flies at 140 kt (259.28 km / h). The necessary performance required for the airfoil when the helicopter 10 flies at 160 kt (296.32 km / h) is indicated by an alternate long and short dash line 92, and resistance by dynamic CFD analysis by dynamic analysis is indicated by a broken line 91. It shows the coefficient C _D by a two-dot chain line 93.

The design method of the prior art has been limited to the design of an airfoil that can be used in a state where the forward speed V of the helicopter 10 is 250 km / h. The present invention can also be used for the purpose of developing a medium-sized civil helicopter that flies at a forward speed V = 300 km / h. That is, the performance required when flying at a forward speed V = 300 km / h is compared with the index lift coefficient _{CL 300} of the airfoil, and an airfoil that satisfies the required performance may be designed.

  In order to investigate the performance required for the airfoil of the blade 11 that does not show a noticeable performance degradation when the helicopter 10 is flying horizontally at a forward speed of 300 km / h, the blade airfoil is exposed in flight. It is necessary to change the Mach number, lift or angle of attack. However, in actual flight conditions, the blades are elastically deformed and have different aerodynamics from the rigid body. In addition, the blades undergo extremely complex motions due to their aerodynamic force, driving force, centrifugal force, etc. difficult. Therefore, the required performance is obtained using the output of the analysis program based on the approximation theory (linear blade element theory) for helicopter rotor blades as a reference value.

The required performance at 140 kt and 160 kt shown in FIG. 10 is, for example, a wing cross section at a 96% span position of 140 kt and 160 kt forward flight of a commercial name Kawasaki BK-117C1 which is a medium-sized civil helicopter currently on the market. shows the calculated values of the Mach number M and the lift coefficient C _L. However, since the same model is not actually configured to fly at 160 kt, it is an approximation result obtained by extrapolating the engine output and the like from the current state. The homogeneous, because airfoil is used refurbishment version of the blade 11 of NACA23012, an indication lift coefficient C _L300 if airfoil is NACA23012.

If the required performance falls within a region having a value smaller than the index lift coefficient C _L300 , that is, the lower left region, the airfoil satisfies the required performance, and the required performance is a region having a value greater than the index lift C _L300 . In other words, if the airfoil protrudes to the upper right region, the airfoil does not satisfy the required performance. In the example shown in FIG. 10, the required performance when flying at 140 kt is in the lower left region of the index lift coefficient C _L300 of the airfoil NACA 23012 and is within the performance limit range, but it flies at 160 kt. The required performance at that time protrudes into the region on the upper right side of the index lift coefficient C _L300 of the airfoil NACA 23012 and exceeds the performance limit. In this way, it can be determined whether the required performance is satisfied.

FIG. 5 shows the required performance when flying at 160 kt together with the index lift coefficient C _L300 of eight types of airfoils, but the required performance when flying at 160 kt is shown for each airfoil illustrated in FIG. not filled. However, when M = about 0.45 or more, the index lift coefficient C _L300 of any airfoil exceeds the required performance when flying at 160 kt, so an airfoil that satisfies the required performance is created by appropriate design. It is considered possible. That is, with the design method of the present embodiment, an airfoil that satisfies the necessary performance when flying at 160 kt (about 300 km / h) while evaluating the airfoil using the index lift coefficient C _L300 , 160 kt ( It is possible to design a high-performance airfoil having a performance as close as possible to that required when flying at about 300 km / h). If dynamic characteristics are taken into consideration at this time, a higher-performance airfoil can be designed.

As described above, the index lift coefficient C _Ln can uniformly express the performance limit of the airfoil for a wide Mach number (speed range) of the airspeed Va in which the blade 11 is used. In addition, dynamic airfoil performance within the range where dynamic stall does not occur can be almost predicted from static CFD analysis at the same Mach number and angle of attack. The index lift coefficient C _Ln can be used to determine whether or not dynamic stall occurs. When dynamic stall occurs, resistance sudden increase and moment sudden change occur. Therefore, the first design goal is to design the index lift coefficient C _{Ln to} be high so that the required performance does not exceed that in the operating range. By doing so, it is possible to design an airfoil that has high performance and meets the needs.

According to the present embodiment, the index lift coefficient C _Ln that is the lift coefficient at which the resistance coefficient _CD is equal to or greater than the set value is obtained by static analysis, and the index lift coefficient C _Ln is calculated based on the performance of the blade 11 airfoil. Used as an evaluation index for evaluation. This index lift coefficient C _Ln is an index obtained over the entire range of the relative speed Va where the blade 11 is assumed to be actually used. Therefore, by using this index lift coefficient C _Ln , the airfoil can be evaluated with one evaluation index over the entire range of the relative speed Va where the blade 11 is assumed to be actually used. It can be suitably evaluated.

The index lift coefficient C _Ln can also be used as a threshold for determining whether or not dynamic stall occurs based on the result obtained by dynamic analysis. As a result, the index lift coefficient C _Ln can be used not only as an index representing the static characteristics but also for estimating the dynamic characteristics of the airfoil. Therefore, the index lift coefficient C _Ln can be used for airfoil evaluation in consideration of dynamic changes in the relative speed Va and the angle of attack α, and has high utility.

Specifically, as the index lift coefficient C _Ln , a lift coefficient at which the resistance coefficient C _D is equal to or greater than a set value set in a range of 0.02 to 0.1 is used. When the angle of attack becomes higher than the angle of attack at which the lift coefficient is maximum and the angle of attack where the buffet is generated, the resistance value tends to increase rapidly as the angle of attack increases. The resistance coefficient C _{D at} which the resistance value starts to increase rapidly exists in the range of 0.02 to 0.1. Therefore, the maximum value can be obtained by setting the set value in the range of 0.02 to 0.1. It is possible to evaluate in consideration of the lift coefficient C _Lmax and the _buffet- generated lift coefficient C _Lbuffet .

Further resistance coefficient C _D which surge begins the resistance value of the range of the 0.02 to 0.1, are concentrated in particular 0.03 to 0.05 within the range. Therefore, by setting the set value within the range of 0.03 or more and 0.05 or less, it becomes a more suitable index, and highly reliable evaluation becomes possible.

Since the evaluation using the index lift coefficient C _Ln is clear and easy, it can be incorporated into the automatic optimum design method and the airfoil can be designed based on a suitable evaluation. Can be designed. High-performance airfoil designs that were not possible with conventional technology are also possible. Moreover, since the evaluation method using the index lift coefficient C _Ln is general-purpose, it can be used for improving all purposes of the airfoil, but it can exert a great effect particularly in improving high-speed performance and hovering performance.

  For moment changes that are important in the high-speed range, the dynamic characteristics and static characteristics agree well, so it is better to evaluate using static analysis results and select an airfoil with as little moment change as possible. Mold design is possible.

The above-described embodiment is merely an example of the present invention, and the configuration can be changed. In the above-described embodiment, the lift coefficient C _L300 when the resistance coefficient C _D is 0.03 is used as the index lift coefficient C _Ln , but the resistance coefficient C _D is another set value, for example, 0.04. , 0.05 or a lift coefficient such as 0.05 may be used. When the resistance coefficient C _D is in the range of 0.03 or more and 0.05 or less, similarly highly reliable evaluation is possible. Set value of the resistance coefficient C _D is outside the range of 0.03 to 0.05, may be set within a range of 0.02 to 0.1, 0.02 and less than 0. A value exceeding 1 may be set.

Further, instead of the index lift coefficient C _Ln , an index attack angle α _n that is an angle of attack at which the resistance coefficient _CD is equal to or greater than a set value may be used as the evaluation index. Index angle of attack alpha _n may be used in the same manner as the index lift coefficient C _Ln, it is possible to achieve the same effect as the case of using an index lift coefficient C _Ln. Resistance coefficient C _D is the set value of the index angle of attack alpha _n, it is possible to use a set value of the same range as for the set value when the indicator lift coefficient C _Ln. For example, it is possible to use an angle of attack (index angle of attack) α _{500 at} which the resistance coefficient _CD is 0.05 or more, and the same effect can be obtained.

  Further, the airfoil to be evaluated and designed is not limited to the helicopter rotor blade airfoil, but includes other blade (wing) airfoil and propeller airfoil (cross-sectional shape). A propeller is also included in the blade.

It is a flowchart which shows the design method of the blade airfoil using the performance evaluation method of the blade airfoil of one Embodiment of this invention. It is a block diagram which shows the design apparatus 20 which performs the design method of FIG. 2 is a plan view showing an airspeed distribution of a blade 11 during forward flight of the helicopter 10. FIG. It is a figure which shows the angle of attack distribution of the blade. It is a graph which shows index lift coefficient _CL300 showing the lift coefficient in case resistance coefficient _CD is 0.03. It is a graph which shows the three component force characteristic in a low speed area. It is a graph which shows the three component force characteristic in a high speed region. It is a graph which shows resistance divergence Mach number _MDD . It is a graph which shows the result of a static CFD analysis, and the result of a dynamic CFD analysis. It is a graph which shows the relationship between index lift coefficient _CL300 and required performance. It is a graph which shows the parameter | index used for the performance evaluation of the airfoil of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Helicopter 11 Blade 20 Design apparatus 21 Input means 22 Storage means 23 External recording means 24 Calculation means 25 Output means

Claims (3)

The blade attack angle at which the resistance coefficient when the blade is placed in a uniform airflow is greater than or equal to a preset value or the lift coefficient at which the resistance coefficient is greater than or equal to the set value is used as an evaluation index for the blade airfoil. Analysis process required by dynamic analysis,
A blade airfoil performance evaluation method comprising: an evaluation step of evaluating the performance of the blade airfoil using the obtained evaluation index.   The blade airfoil performance evaluation method according to claim 1, wherein the set value of the resistance coefficient is 0.02 or more and 0.1 or less. An initial setting step for initial setting of parameters defining the blade shape;
An airfoil definition process for defining an airfoil according to set parameters;
A performance determination step of evaluating the performance of the defined airfoil by the performance evaluation method of the blade airfoil according to claim 1 or 2,
Based on the airfoil performance judgment result, it is determined whether or not the airfoil performance has converged to the optimal value. If it is determined that it has converged to the optimal value, that airfoil is output as the design airfoil. A judgment output step;
A blade airfoil design comprising: a repetitive process of correcting and setting the parameters and repeating from the airfoil definition process to the determination output process when it is determined that it has not converged in the determination output process Method.

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