CN114781270A - Multi-working-condition self-adaptive variable-pitch propeller design optimization method - Google Patents
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Abstract
The invention discloses a multi-working-condition self-adaptive variable-pitch propeller design optimization method, and belongs to the field of aircraft design. According to the method, firstly, according to task requirements, a positive-camber high-lift wing type is obtained through optimization; then, optimizing and determining the chord length and the torsion angle distribution of the propeller by adopting a reverse design method based on a strip theory, and expressing aerodynamic force and inertial force borne by the blades as functions of design parameters by taking 1/4 chord line control parameters and rotating shaft position parameters of the blades as design variables; and finally, constructing an optimal design method of the key parameters of the self-adaptive variable pitch propeller by using a strip theory and a multi-objective genetic algorithm. The design result of the invention balances the aerodynamic moment, can be adaptive to the performance requirements of various working conditions, and the designed propeller can keep high-efficiency operation within a wide application range.
Description
Technical Field
The invention relates to the field of aircraft design, in particular to a multi-working-condition self-adaptive variable-pitch propeller design optimization method.
Background
In the emerging development era of various low-speed propeller aircrafts, due to different types of aircrafts, the realized functions are different, and the working conditions to be faced in the task execution process tend to be complex, so that certain requirements are provided for the propellers to keep higher efficiency under various working conditions in a multi-mode working environment.
For small vertical take-off and landing aircrafts and low-speed propeller aircrafts such as solar unmanned aerial vehicles with generally lighter structural mass, the propeller active pitch-changing device is adopted, so that the challenges are undoubtedly increased in design complexity, manufacturing cost and manipulation difficulty, and finally, the loss caused by the extra weight part added to the whole aircraft cannot be necessarily made up by the efficiency improved by the pitch-changing propeller.
Foreign scholars firstly put forward a PVPP (Passive variable PitchPropeller) concept and make experiments to verify the feasibility of the concept, Eppler325 reverse-bending wing type is adopted in the experimental design, the purpose is to balance the head raising moment of a focusing point and the lift force of the reverse-bending wing type to the head lowering moment of a rotating shaft, a pneumatic pitch moment balancing state is achieved, the propeller can self-adaptively balance a pitch angle under different forward ratios, and the range of the applicable forward ratio of the propeller is greatly increased.
At present, in addition to the propeller technology for actively controlling variable pitch, some self-adaptive variable pitch propeller mechanisms are also provided at home and abroad. An automatic variable-pitch propeller device is provided by Chenjun-Yin and the like (Chenjun-Yin, Xunxin, Zhengenhui, and the like; CN208897310U [ P ].2019.), and a measuring module is utilized to determine the working condition of the propeller in real time, automatically optimize the working condition to obtain the optimal pitch angle and implement variable-pitch operation; the invention discloses a self-adaptive variable pitch propeller (Baotong, Van jin hong, Liu Shuang, and the like) and an airplane, wherein the self-adaptive variable pitch propeller and the airplane are CN205499338U [ P ] 2016), and the self-adaptive variable pitch propeller can change the spring deformation quantity arranged on the propeller by the pulling force generated along with the change of the flying speed, thereby adaptively changing the pitch of the propeller.
Zhou et al propose a design method of a pneumatic variable pitch canard layout propeller (Zhou, Fangzhong, a design method of a self-adaptive pneumatic variable pitch propeller, CN109693807A [ P ].2019.), and balance of pitching moment is realized by taking moment on a rotating shaft by front blades and rear blades in canard layout, so that self-adaptive variable pitch is achieved.
If one wants to achieve adaptive pitch, the emphasis is on the balancing of the pitching moment and the elimination of two unbalanced moments during the design process: the static unbalance moment generated by the gravity center of the blade on the pitching rotating shaft and the dynamic unbalance moment generated by the change of the angular momentum on the pitching rotating shaft are respectively.
Disclosure of Invention
In conclusion, the invention provides a self-adaptive variable-pitch multi-working-condition propeller design optimization method, so that the propeller can perform variable pitch on a preset pitching rotating shaft in a self-adaptive manner according to different inflow angles under each advancing ratio, and the efficiency is always maintained at a higher value.
The invention relates to a multi-working-condition self-adaptive variable-pitch propeller design optimization method, which comprises the following specific steps of:
step 1: selecting low forward ratio working condition to design and determining incoming flow speed V∞And a target tension requirement T.
Step 2: an appropriate propeller diameter D is determined from the rotor disk load limits, and the design state of the propeller speed n is determined taking into account the influence of the propeller tip noise and the shock resistance.
And 3, step 3: the propeller blades adopt positive camber high lift coefficient wing profiles, low-speed common high lift wing profiles CLARKY are used as reference wing profiles for optimization, and the optimization targets are high wing profile lift coefficients and lift-drag ratios.
And 4, step 4: obtaining a positive camber high-lift coefficient airfoil profile from the step 3, determining the thickness distribution of the airfoil profile from a root to a tip, radially dividing the propeller into 17 strips, and regarding the radius of the propeller as a propeller hub area within the range of 0.15R; the thickness of the airfoil profile at each characteristic section is different, and airfoil response surface models with different Reynolds numbers and different attack angle ranges are established for the airfoil profiles with different thicknesses.
And 5: and (3) adopting a reverse design method based on a strip theory to design chord lengths and torsion angles.
And 6: after the chord length and the torsion angle distribution are obtained, the lift force, the resistance force, the pitching moment to 1/4 chord points and the attack angle of each propeller strip are obtained according to strip theory calculation, and therefore the situation of the pitching moment borne by the propeller strips is determined.
And 7: representing a chord line of the propeller 1/4 by using a 5-order CST curve, and calculating to obtain a pitching moment function of the blades to the rotating shaft; by introducing a weighting coefficient omega for considering the rotation speed and the gradient C of the characteristic profile lifting linelαThe longitudinal static stability of the whole propeller can be judged through chord length and dynamic pressure.
And step 8: the statically unstable pitching moment of the center of gravity to the rotating shaft is expressed by a function.
CST curve fitting is carried out on the wing profile upper and lower curves of each characteristic section, the gravity center of each section is solved by using a method of dispersing into points and then integrating the wing profile closed curve, and a function G (x, y, z) ═ F (A) of the total gravity center is obtained after weighting0,A1,...,A6,yaxis)；A0～A6Parameters in a function expression for the total center of gravity; y isaxisIs the position of the rotating shaft.
And step 9: eliminating the dynamic unbalance moment generated by the change of angular momentum on the rotating shaft, wherein the eliminating moment is satisfied
①IX'Y'＝0
②IX'X'＝IY'Y'；
Wherein, IX'Y'Is the product of inertia, I, of the entire blade with respect to the local coordinate system X 'Y' ZX'X'And IY'Y'The moments of inertia of the entire blade about the X 'and Y' axes, respectively; thus, eliminating the imbalance moment can be translated into solving the moment of inertia and the product of inertia described above.
The discrete method in step 8 can obtain:
IX'X'＝H1(A0,A1,...,A6,yaxis)
IX'Y'＝H2(A0,A1,...,A6,yaxis)
IY'Y'＝H3(A0,A1,...,A6,yaxis)
for an arbitrarily distributed 1/4 chord line, the total distortion function for each characteristic profile with respect to the initial distribution can be obtained: x ═ X
Wherein, A0～A6Is a parameter in the expression; y isaxisIs the position of the rotating shaft.
Step 10: optimizing by using a multi-target genetic algorithm, wherein the optimization target is as follows:
wherein M is the total pitching moment; gxX-coordinate, G, of the centre of gravity of the bladeyY-coordinate, H, of the blade centre of gravity1，H2，H3Are respectively IX'X'，IX'Y'，IY'Y'Is expressed as a function of the total deformation quantity.
The constraint conditions are as follows:
and (5) until convergence obtains an optimization result meeting the optimization target and the constraint condition, if the optimization result is not met, changing 1/4 chord coefficient and the limited variation range of the position of the rotating shaft, and re-optimizing.
Step 11: measuring and verifying the gravity center, the inertia product and the inertia moment of the finally designed propeller, and performing CFD simulation verification to completely balance the pitching moment of the rotating shaft; and calculating corresponding different trim angles and propeller efficiencies under different forward ratios, and comparing the trim angles and the propeller efficiencies with an efficiency-forward ratio curve of each fixed pitch.
The invention has the advantages that:
1. the multi-working-condition self-adaptive variable-pitch propeller design optimization method can realize self-adaptive pneumatic variable pitch without adopting an additional variable-pitch mechanism, and the blades have the longitudinal static stability characteristic.
2. The design optimization method of the multi-working-condition self-adaptive variable-pitch propeller uses the optimized positive camber high lift coefficient airfoil profile, and solves the defect that the commonly used negative camber airfoil profile lift coefficient of the pneumatic variable-pitch propeller is insufficient and cannot meet the condition of large pulling force.
3. The design optimization method of the multi-working-condition self-adaptive variable-pitch propeller disclosed by the invention is used for balancing the head raising moment caused by the positive camber airfoil profile by a method of parametrizing the control propeller 1/4 chord line.
4. The invention relates to a multi-working condition self-adaptive variable pitch propeller design optimization method, which adopts a discretized mathematical method to express various inertia moments by using 1/4 chord line parameters and eliminates the inertia moments by using a multi-target genetic algorithm, thereby needing no additional mass balancing and inertia balancing mechanisms.
Drawings
FIG. 1 is a design flow chart of the optimization method for the design of the multi-operating-condition adaptive variable-pitch propeller of the present invention;
FIG. 2 is a graph comparing airfoil optimization results with a reference airfoil ClarkY;
FIG. 3 is a schematic illustration of torque extraction from a rotating shaft;
FIG. 4 is a schematic representation of an inertial frame and a local frame of the blade;
FIG. 5 is a schematic view of a discretized airfoil profile;
FIG. 6 is a graph of efficiency versus forward ratio for an adaptive variable pitch propeller and for each fixed pitch.
Detailed Description
The design methods illustrated in the present invention are described in more detail below with reference to examples, and specific data, operations, etc. are exemplary and should not be construed as limiting the invention. Each step is not necessarily the result obtained by the operation in the example, and the entire design optimization method is not limited to be applied to the following example. Those skilled in the art may make appropriate changes, modifications, and alterations to the following embodiments within the scope and spirit of the invention without departing from the principles and spirit of the invention.
The invention discloses a multi-working-condition self-adaptive variable-pitch propeller design optimization method, which comprises the following specific steps as shown in figure 1:
step 1: and analyzing the using condition, and determining the incoming flow speed and the pulling force.
The propeller designed for preventing the working condition of large advancing ratio stalls airflow under the working condition of small advancing ratio, cannot generate effective aerodynamic force, and cannot necessarily meet the requirement of large pulling force of small advancing ratio, so that the working condition of low advancing ratio is selected from a plurality of working conditions faced by the propeller as the design state of the propeller, and the incoming flow speed V is determined∞(ii) a Determining a target tension requirement T according to the task requirement under the working condition; in this embodiment, the design of the working conditions at the vertical take-off and landing stage of the unmanned aerial vehicle is adopted, and the incoming flow velocity V is∞5 m/s. The propeller needs to provide tension in the vertical stage
Wherein, G0Is the gross weight of the aircraft, N0The number of propellers.
And 2, step: determining the diameter and the rotating speed of the propeller in a design state;
an appropriate rotor diameter D is determined from the rotor disc load limit, which is typically no more than 200N/m since an increase in rotor disc load results in a decrease in rotor effort and a decrease in control efficiency2. In this embodiment, the propeller diameter is determined by the rotor disc load
Wherein Q is the paddle load.
Considering the spiral shellDetermining the propeller rotating speed n in a design state under the influence of the propeller tip noise and the shock wave resistance of the propeller; in the present embodiment, the Mach number Ma of the blade tip is takentipIs 0.4, whereby the rotational speed can be obtained
And step 3: and optimizing to obtain the positive-camber high-lift airfoil profile for the blade.
The earliest aerodynamic pitch-variable propeller adopts a reverse-curved airfoil Eppler325 airfoil family, so that the lift force can be used for balancing the low-head moment caused by the moment of taking the shaft by utilizing the self-carrying head-raising moment, but the balancing lift force coefficient of the reverse-curved airfoil is too low to meet the requirement of the example on high tension force under low advancing ratio. Because the pulling force demand T is great, therefore the propeller blade adopts positive camber high lift coefficient wing section.
Therefore, the existing low-speed common airfoil ClarkY is selected as a reference airfoil for optimization, the optimization targets are that the airfoil lift coefficient and the lift-drag ratio are as high as possible, the airfoil with the positive camber and the high lift coefficient is finally obtained and used as a blade airfoil, and the optimized airfoil and the reference airfoil pair are shown in figure 2.
And 4, step 4: and establishing response surface models of the airfoils with different thicknesses.
a. Determining the thickness distribution of the airfoil from the root to the tip;
after the blade airfoil is obtained in step 3, the bending moment on the structure is gradually reduced from the root to the tip, so that the thickness of the blade airfoil is gradually reduced from the root to the tip, and the thickness distribution of the airfoil adopted in the embodiment is as follows:
in the formula (I), the compound is shown in the specification,
is the relative thickness of the airfoil,
is a relative radial position ofThe thickness distribution can be adapted to composite propellers; b is the absolute chord length at the characteristic profile, c is the absolute thickness at the characteristic profile, and R is the absolute radius at the characteristic profile, ranging from 0.1R to R; and R is the propeller radius.
b. The propeller radius is considered to be the hub area within 0.15R, dividing the blade portion equally from 0.15R to R into 17 strips, each strip having a width of 0.05R.
c. Taking the section of the central position of each strip as a characteristic section, wherein the thickness of the airfoil profile at each characteristic section is different, and establishing airfoil profile response surface models with different Reynolds numbers and different attack angle ranges for the airfoil profiles with different thicknesses:
and taking 5 Reynolds numbers and 23 attack angles of-4-18 degrees for each characteristic profile, and constructing a response surface model of each characteristic profile airfoil according to the Reynolds numbers and the attack angles. The response surface model can interpolate lift coefficient and drag coefficient under any attack angle and Reynolds number, and is prepared for subsequent design. The Reynolds number of 5 persons mentioned above increases from inside to outside according to the resultant velocity of each section
VrAs the rotational speed, VSIn order to obtain the speed of the device,
is the square of the incoming flow velocity; a resultant velocity is estimated and a classical initial chord length distribution is given, so that a Reynolds number can be estimated, and on the basis of the Reynolds number, the chord length c0 is expanded to five Reynolds numbers of c0+0.005, c0+0.01, c0-0.005 and c 0-0.01.
And 5: and (3) designing chord lengths and torsion angles by adopting a reverse design method based on a strip theory.
Because the propeller minimum energy loss condition (Betz condition for short) uses the assumption that a light-load propeller (the axial induction speed is far less than the incoming flow speed and the annular induction speed is far less than the rotating speed of the propeller tip) is not suitable for the propeller, and the Betz condition is easy to solve a singular solution that the chord length is not in a normal value range, the method adopts a reverse design method based on the strip theory to carry out optimization design. The core of the strip theory lies in solving the interference angle beta, and then the tension and the torque of the propeller can be obtained. The chord length is derived by the strip theory and is a function of an interference angle, a characteristic section airfoil lift coefficient CL and an airfoil resistance coefficient CD, and under the condition of determining an airfoil, if the chord length and torsion angle distribution is given, the aerodynamic coefficient of the airfoil can be obtained at each characteristic section, the interference angle beta can be obtained, so that the tension, the torque and the efficiency can be obtained. Under the condition of meeting the limitation of given tension, a 4-order function shape function transformation curve (CST curve for short) is used for parameterizing chord length distribution and a 4-order polynomial curve is used for parameterizing torsion angle distribution, and then optimization is carried out in the direction with highest efficiency.
1) Parameterizing the chord length by using a 4-order CST curve:
where x is the radial relative position (along the propeller radius, e.g. 0.1R, 0.2R.) and ranges from 0 to 1, and C is the relative chord length (relative to the propeller radius, e.g. C ═ 0.01, where the actual chord length is C ═ R ═ 0.01R); a. theU(i) Is the coefficient of each curve, crootAnd ctipThe relative chord lengths (relative to radius R) at the root and tip of the blade, respectively; n is a radical of hydrogenUIs the order of the CST curve, equal to 4.
2) In order to prevent the final propeller shape from being unreasonable due to the fact that the torsion angles of different characteristic profiles have sudden changes, the torsion angles are parameterized by a 4-order polynomial curve:
wherein, BU(i) Is the coefficients of the 4 th order polynomial curve.
3) Sampling 400 points by adopting a Latin hypercube method according to 12 parameters of the torsion angle and the chord length;
4) calculating the tension, torque and efficiency of the propeller corresponding to the sample point by combining the strip theory and the response surface model built in the step 4;
5) and training the artificial neural network agent model according to the calculation result of the step 4).
6) The artificial neural network agent model is optimized, the optimization algorithm is set as a genetic algorithm, the optimization target is that the efficiency of the propeller is as high as possible, and the constraint condition is that T is 40N. The optimization target converges after about 100 generations, at which time parameter AU(i)、BU(i)、croot、ctipI.e. the distribution of the propeller chord length and the twist angle is determined.
Step 6: analyzing the pitching moment condition borne by the propeller strips;
and (5) after the chord length and the torsion angle distribution are obtained through the step (5), the lift force and the resistance of each propeller strip, the pitching moment to the 1/4 chord point and the attack angle are obtained through theoretical calculation of the strips, and the situation of the pitching moment borne by the propeller strips is analyzed.
For the propeller blades, they are subjected to lift dL, drag dD, and pitching moment dM at chord point 1/40And the incoming flow attack angle alpha are all obtained through the strip theory (dM)0After the attack angle is obtained, the pitch moment coefficient cm of 1/4 chord points is calculated separately for each characteristic section,
rho is the areal density; c is the chord length of each profile airfoil), each profile taking a moment to the pitch axis as shown in fig. 3.
Wherein:
dMx＝(dL·cosα+dD·sinα)·xac+dM0
xacdistance, dM, from chord point of each strip 1/4 to pitch pivotxA resultant pitching moment of the shaft for each strip; v in FIG. 3sIs the resultant velocity of the air flow.
And 7: and (3) parameterizing a chord line of the propeller 1/4 by using a 5-order CST curve, and calculating to obtain a total pitching moment function and a longitudinal static stability function of the blades to the rotating shaft.
Parameterizing a chord line of the propeller 1/4 by using a 5-order CST curve, and determining the plane shape of the propeller at the moment; and (3) rotating each propeller strip around the pitch rotating shaft by the torsion angle obtained in the step 5 to determine the shape of the propeller.
X in step 6acDepending on the position of the chord of the strip 1/4 and the pitch pivot, the strip-to-pivot pitch moment dMxDepending on 1/4 chord position and spindle position yaxisThe total pitch moment M of the propeller to the shaft is 1/4 chord coefficient and yaxisFunction of (c): m is M1(A0,A1,...,A6,yaxis)，A0～A6The parameters in the curve expression after chord line of the propeller 1/4 are represented by the CST curve.
Introducing a weighting factor ω (c) taking into account the rotational speed
Resultant velocity VSObtained by strip theory, combined with characteristic profile lifting line slope ClαChord length ch ord, dynamic pressure
And distance x from chord point of each section 1/4 to the axis of rotationacThe longitudinal static stability of the whole propeller can be judged:
if M isα<0, the blade has longitudinal static stability. If not, the algorithm will continue to seek the optimum.
And step 8: the statically unstable pitching moment of the center of gravity to the rotating shaft is expressed by a function.
CST curve fitting is carried out on the wing profile upper and lower curves of each characteristic section, the gravity center of each section is solved by using a method of dispersing into points and then integrating the wing profile closed curve, and a function G (x, y, z) ═ F (A) of the total gravity center is obtained after weighting0,A1,...,A6,yaxis)。
For ease of understanding, an inertial frame XYZ is established at the centre of the propeller and a local frame X ' Y ' Z ' at the centre of gravity of the blades, as shown in figure 4.
The condition of eliminating the static unstable moment caused by the gravity center is that the gravity center falls on the pitching rotating shaft, and a function expression of the gravity center position is required to be solved for the purpose. The method for achieving the target in the example is to parameterize the upper and lower curves of each section airfoil, and disperse the upper and lower curves into enough m sections of microelements (m is more than or equal to 1000) in the direction from the front edge to the rear edge, as shown in FIG. 5.
If each section airfoil leading edge point is at the origin of the XY plane, its center of gravity can be represented as:
wherein x isgAnd ygRespectively an x coordinate and a y coordinate of the gravity center of each small section of infinitesimal element, and dS is the area of each infinitesimal element;
since the chord position of each airfoil 1/4 is determined by the 1/4 chord line and shaft position, the center of gravity of each eigensection and the weighted blade's overall center of gravity are also determined by the 1/4 chord line coefficients and the shaft position.
The total center of gravity is a function G (x, y, z) ═ F (A)0,A1,...,A6,yaxis) The requirement of the blade total barycenter coordinate obtained after integrating the barycenter of each section airfoil is converted into a chord line coefficient A of 1/40～ANAnd yaxisAnd (4) optimizing the target.
And step 9: the dynamic unbalance moment generated on the rotating shaft by the change of the angular momentum is eliminated.
To eliminate the dynamic unbalance moment caused by the angular momentum change during the rotation process, the following two conditions need to be satisfied:
①IX'Y'＝∫X'Y'dm＝0
②IX'X'＝IY'Y'
wherein, IX'X'＝∫(Y'2+Z'2)dm，IY'Y'＝∫(X'2+Z'2)dm。
dm is ρ times dS, i.e. the mass per infinitesimal, IX'Y'Is the product of inertia, I, of the entire blade with respect to the local coordinate system X 'Y' ZX'X'And IY'Y'Respectively, of the entire blade pair X'The moments of inertia of the axis and the Y' axis;
thus, eliminating the imbalance moment can be translated into solving the moment of inertia and the product of inertia described above. For each section ixx ═ j ^ (y)2+z2)ρdS，iyy＝∫(x2+z2) rhodS, the section inertia moments ixx and iyy can be obtained by adopting the discrete rectangular integral in the step 8, and the I of the gravity center of the blade pair is obtained by integrating along the radial direction of the propellerX'X'＝∫ixxdSSection plane，dSSection planeIs the blade cross-sectional area, IY'Y'＝∫iyydSSection plane,IX'Y'＝∫ixydSSection planeAnd are all A0,A1,...,A6,yaxisAs follows:
IX'X'＝H1(A0,A1,...,A6,yaxis)
IX'Y'＝H2(A0,A1,...,A6,yaxis)
IY'Y'＝H3(A0,A1,...,A6,yaxis)
for an arbitrarily distributed 1/4 chord line, the total distortion function for each characteristic profile with respect to the initial distribution can be obtained: x ═ X ═
Ready for the subsequent optimization process.
Step 10: optimizing by using a multi-target genetic algorithm, wherein the optimization parameters are 1/4 chord line coefficients and a rotating shaft position, and the optimization targets obtained by the steps 7, 8 and 9 are as follows:
in the formula, GxAs x-coordinate of the centre of gravity of the blade, GyY-coordinate, H, of the blade centre of gravity1，H2，H3Are respectively IX'X'，IX'Y'，IY'Y'Is expressed as a function of the total deformation quantity.
Constraint conditionsComprises the following steps:
and (5) until convergence obtains an optimization result meeting the optimization target and the constraint condition, if the optimization result does not meet the optimization target and the constraint condition, changing 1/4 the limit change range of the chord coefficient and the position of the rotating shaft, and re-optimizing.
Step 11: after the multi-round iterative optimization is finished, the gravity center and inertia attributes (inertia product and inertia moment) of the design result are verified, and whether the pitching moment of the rotating shaft is balanced or not is verified by CFD simulation. And calculating corresponding different trim angles and propeller efficiencies under different forward ratios, and comparing the trim angles and the propeller efficiencies with an efficiency-forward ratio curve of each fixed pitch.
For each forward ratio, the propeller is pitched and rotated by a corresponding angle delta beta due to the fact that the shape of the propeller is determined, the delta beta for enabling M to be 0 is obtained through iterative solution, namely the pitching angle for balancing the propeller is obtained, and the efficiency of the propeller at the moment can be calculated through a strip theory. As shown in fig. 6, the center of gravity and inertia properties of the efficiency-forward ratio curve verification design result can be obtained by solving a plurality of forward ratios, and CFD simulation verification is used, and if the pitching moment trim angle of the rotating shaft and the Δ β error obtained by the calculation are within 10%, the error is an acceptable range.
Through the design optimization of the specific steps, the multi-working-condition propeller can be obtained, the pitch angle can be adaptively increased or decreased according to the pneumatic pitch moment, so that the balance at a certain trim angle is achieved, and the efficiency is always at the peak value of each numerical value fixed pitch propeller.
The propeller finally designed by the method has the capability of realizing variable pitch by virtue of pure pneumatic pitching moment without an active pitch-changing device in a wide range of advancing ratio. The design results in a trim condition at low forward ratios, and as the forward ratio increases the inflow angle increases, the angle of attack of each section decreases, and the blade, due to its longitudinal static stability, produces a downward lift increase at the focal point, resulting in a head-up moment on the radially disposed shaft. The moment can increase the pitch, the incidence angle of each section is close to the original optimal incidence angle, and the overall efficiency of the propeller is improved.
The efficiency is always maintained at a high value compared to a fixed pitch propeller, where the efficiency reaches a high level only at a small forward ratio. In addition, in the design process, the static unstable moment of the gravity center on the rotating shaft and the dynamic unstable moment caused by the change of the angular momentum are balanced, so that the complexity and the calculated amount are greatly reduced when the blade balancing angle is solved by simulating different working conditions in the follow-up process.
Claims (3)
1. A multi-working-condition self-adaptive variable-pitch propeller design optimization method is characterized by comprising the following steps of: the method comprises the following steps:
step 1: selecting low forward ratio working condition to design and determining incoming flow speed V∞And a target tension requirement T;
and 2, step: determining a proper propeller diameter D by the load limit of a propeller disc, and determining the propeller rotating speed n in a design state by considering the influence of the tip noise and the shock wave resistance of the propeller;
and step 3: the propeller blades adopt positive-camber high-lift coefficient airfoils, and are optimized by taking low-speed common high-lift airfoils CLARKY as reference airfoils, and the optimization targets are high airfoil lift coefficients and lift-drag ratios;
and 4, step 4: obtaining a positive camber high-lift coefficient airfoil profile in the step 3, determining the thickness distribution of the airfoil profile from a blade root to a blade tip, radially dividing the propeller into 17 strips, and regarding the radius of the propeller as a propeller hub area within the range of 0.15R; the thickness of the airfoil profile at each characteristic section is different, and airfoil response surface models with different Reynolds numbers and different attack angle ranges are established for the airfoil profiles with different thicknesses;
and 5: designing chord lengths and torsion angles by adopting a reverse design method based on a strip theory;
step 6: after the chord length and the torsion angle distribution are obtained, the lift force, the resistance force, the pitching moment to 1/4 chord points and the attack angle of each propeller strip are obtained according to strip theory calculation, and therefore the situation of the pitching moment borne by the propeller strips is determined;
and 7: the chord line of the propeller 1/4 is represented by a 5-order CST curve, and the blade pair is obtained through calculationA pitch moment function of the shaft; by introducing a weighting coefficient omega for considering the rotation speed and the gradient C of the characteristic profile lifting linelαThe longitudinal static stability of the whole propeller can be judged according to the chord length and the dynamic pressure;
and step 8: expressing the static and unstable pitching moment of the gravity center to the rotating shaft by a function;
CST curve fitting is carried out on the wing profile upper and lower curves of each characteristic section, the gravity center of each section is solved by using a method of dispersing into points and then integrating the wing profile closed curve, and a function G (x, y, z) ═ F (A) of the total gravity center is obtained after weighting0,A1,...,A6,yaxis)；A0～A6Parameters in a function expression of the total gravity center; y isaxisIs the position of the rotating shaft;
and step 9: eliminating the dynamic unbalance moment generated by the change of angular momentum on the rotating shaft, wherein the eliminating moment is satisfied
①IX'Y'＝0
②IX'X'＝IY'Y'；
Wherein, IX'Y'Is the product of inertia, I, of the entire blade with respect to the local coordinate system X 'Y' ZX'X'And IY'Y'The moments of inertia of the entire blade about the X 'axis and the Y' axis, respectively; thus, eliminating the unbalanced moment can be translated into solving the moment of inertia and the product of inertia;
the discrete method in step 8 can obtain:
IX'X'＝H1(A0,A1,...,A6,yaxis)
IX'Y'＝H2(A0,A1,...,A6,yaxis)
IY'Y'＝H3(A0,A1,...,A6,yaxis)
the total deformation function of each characteristic section relative to the initial distribution can be obtained for any distribution of 1/4 chord lines:
wherein A is0～A6Is a parameter in the expression; y isaxisIs the position of the rotating shaft;
step 10: optimizing by using a multi-target genetic algorithm, wherein the optimization target is as follows:
wherein M is the total pitching moment; gxAs x-coordinate of the centre of gravity of the blade, GyY-coordinate, H, of the blade centre of gravity1，H2，H3Are respectively IX'X'，IX'Y'，IY'Y'X is a total deformation function;
the constraint conditions are as follows:
until convergence obtains an optimization result meeting the optimization target and the constraint conditions, if the optimization result does not meet the requirements, changing 1/4 chord line coefficients and the limited variation range of the position of the rotating shaft, and re-optimizing;
step 11: measuring and verifying the gravity center, the inertia product and the inertia moment of the finally designed propeller, and performing CFD simulation verification to completely balance the pitching moment of the rotating shaft; and calculating corresponding different trim angles and propeller efficiencies under different forward ratios, and comparing the trim angles and the propeller efficiencies with an efficiency-forward ratio curve of each fixed pitch.
2. The method for optimizing the design of the multi-working-condition self-adaptive variable-pitch propeller as claimed in claim 1, wherein the method comprises the following steps: the specific method of the step 5 comprises the following steps:
1) parameterizing the chord length by using a 4-order CST curve:
wherein x is a radial relative position ranging from 0 to 1, and C is a relative chord length; a. theU(i) Is the coefficient of each curve, crootAnd ctipThe relative chord lengths of the oar root and the oar tip are respectively; n is a radical ofUIs the order of the CST curve, equal to 4;
2) in order to prevent the final propeller shape from being unreasonable due to the fact that the torsion angles of different characteristic profiles have sudden changes, the torsion angles are parameterized by a 4-order polynomial curve:
wherein, BU(i) Is each item coefficient of a 4-order polynomial curve;
3) sampling 400 points by adopting a Latin hypercube method according to 12 parameters of the torsion angle and the chord length;
4) calculating the tension, torque and efficiency of the propeller corresponding to the sample point by combining the strip theory with the response surface model established in the step 4;
5) training an artificial neural network agent model according to the calculation result of the step 4);
6) optimizing the artificial neural network proxy model, setting the optimization algorithm as a genetic algorithm, wherein the optimization target is that the propeller efficiency is as high as possible, and the constraint condition is that T is 40N; the optimization target converges after about 100 generations, at which time parameter AU(i)、BU(i)、croot、ctipI.e. the distribution of the propeller chord length and the twist angle is determined.
3. The method for optimizing the design of the multi-working-condition self-adaptive variable-pitch propeller as claimed in claim 1, wherein the method comprises the following steps: the specific method of the step 7 comprises the following steps:
parameterizing a chord line of the propeller 1/4 by using a 5-order CST curve, and determining the plane shape of the propeller; rotating each propeller blade around the pitch rotating shaft by the torsion angle obtained in the step 5 to determine the shape of the propeller;
strip-to-counter-shaft pitching moment dMxDepending on 1/4 chord position and rotation shaft position yaxisThe total pitch moment M of the propeller to the shaft is 1/4 chord coefficient and yaxisFunction of (c): m is M1(A0,A1,...,A6,yaxis)，A0～A6The parameters in the curve expression after the chord line of the propeller 1/4 are expressed by a CST curve;
introducing a weighting factor omega considering the rotation speed and combining the slope C of the lifting line of the characteristic sectionlαChord length ch ord, dynamic pressure and distance x from chord point of each section 1/4 to rotating shaftacThe longitudinal static stability of the whole propeller can be judged:
wherein rho is the areal density; x is the number ofacDistance from the chord point of each strip 1/4 to the pitch pivot;
is the square of the incoming flow velocity; r is the radius of the characteristic profile;
if M isα<0, the blade has longitudinal static stability; if not, continuing to optimize.
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| CN107609243A (en) * | 2017-09-04 | 2018-01-19 | 西北工业大学 | A kind of design method of propeller blade |
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| US20200331602A1 (en) * | 2018-12-07 | 2020-10-22 | Joby Aero, Inc. | Rotary airfoil and design method therefor |
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| CN113987687A (en) * | 2021-11-09 | 2022-01-28 | 北京航空航天大学 | Design method of ducted propeller |
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| CN107609243A (en) * | 2017-09-04 | 2018-01-19 | 西北工业大学 | A kind of design method of propeller blade |
| US20200331602A1 (en) * | 2018-12-07 | 2020-10-22 | Joby Aero, Inc. | Rotary airfoil and design method therefor |
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