A design method for high-efficiency and low-noise counter-rotating propeller fans

Abstract

A design method for a high-efficiency and low-noise counter-rotating propeller fan includes the following steps: Step 1: Calculate the three-dimensional flow field under the cruise and take-off design conditions based on the original configuration; Step 2: Based on the three-dimensional flow field, select the airfoil at the radial position where the cruise shock wave is strong and the take-off leading edge separation bubble is large on the propeller fan as the design object, and under the design conditions, with the goal of reducing the cruise and take-off resistance of the airfoil and the constraint that the maximum thickness of the airfoil does not decrease, carry out the airfoil optimization design to obtain the optimized airfoil; Step 3: Assemble the optimized airfoil to the front and rear propellers of the counter-rotating propeller fan, and shear the rear propeller according to the front propeller tip vortex to obtain a new three-dimensional counter-rotating propeller fan shape; then use the three-dimensional counter-rotating propeller fan as the original shape to carry out the aerodynamic and noise coupling optimization design of the counter-rotating propeller fan blades to obtain the optimized counter-rotating propeller fan blades. The present invention can effectively reduce the number of design variables and can achieve aerodynamic and acoustic multi-objective and multi-disciplinary optimization for the counter-rotating propeller fan.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft design, and in particular to a design method for a high-efficiency and low-noise counter-rotating propeller fan. Background Art

[0002] As the main thrust source of the open rotor engine, the performance of the counter-rotating propeller fan has a decisive influence on the fuel consumption rate, propulsion efficiency and noise of the whole machine. However, there is complex aerodynamic interference between the front and rear propellers of the counter-rotating propeller fan. During the design process, multiple working conditions such as take-off, cruising, and landing must be considered, and aerodynamic and noise performance must be taken into account. This is a typical multi-objective and multi-disciplinary optimization problem, so its aerodynamic shape design is difficult. The high-efficiency and low-noise design of the counter-rotating propeller fan is a key technology that must be overcome in the development of open rotor engines.

[0003] At present, there is no dedicated design method for high-efficiency and low-noise counter-rotating propellers. When designing the three-dimensional configuration of traditional wings, there are two main approaches to aircraft optimization design methods: one is to use an optimization framework based on a proxy model to solve the problem of long CFD calculation time, and the other is to use an adjoint method to deal with the high-dimensional design variable problem caused by refined design. However, when these two existing processing methods are applied to the design of counter-rotating propellers, the following problems are encountered: the configuration of the counter-rotating propeller is complex. If the optimization design of parameters such as airfoil, chord length, torsion angle, and sweep angle is directly carried out on the three-dimensional configuration, the design variables usually reach hundreds of dimensions. When using evolutionary algorithm optimization, as the number of design variables increases, the call of the objective function increases quadratically, which is unbearable for engineering. Even if a proxy model is used, it still requires a large number of sample points to establish a high-precision proxy model under transonic conditions. Although gradient methods such as the adjoint method can alleviate the dimensionality disaster caused by large-scale design variables to a certain extent, it is still difficult to cope with multi-objective and multi-disciplinary optimization problems. In addition, directly carrying out acoustic property optimization design on three-dimensional configurations also has the problem of low design efficiency because acoustic calculations are time-consuming. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention proposes a design method for high-efficiency and low-noise counter-rotating propeller fans. The CFD method based on sliding grid for unsteady calculation is used to calculate the flow field of three-dimensional counter-rotating propeller fans, which can accurately capture key flow characteristics such as cruise strong shock waves and takeoff leading edge separation bubbles, so as to accurately obtain the locations of these two flow phenomena in the three-dimensional counter-rotating propeller fan flow field, and then determine the key two-dimensional profile to ensure the design quality; the present invention adopts an optimization strategy from two-dimensional airfoils to three-dimensional blades. Compared with directly carrying out the optimization design of parameters such as airfoils, chord length, torsion angle, sweep angle, etc. on the three-dimensional configuration of counter-rotating propeller fans, the present invention can effectively reduce the number of design variables and improve the optimization efficiency; the present invention adopts the means of rear propeller shearing and constrains the front propeller wake and tip vortex intensity in the takeoff state in the optimization, so as to consider the influence of noise in aerodynamic optimization, thereby realizing multi-objective and multi-disciplinary optimization of aerodynamics and acoustics.

[0005] The present invention is achieved through the following technical solutions:

[0006] A design method for a high-efficiency and low-noise counter-rotating propeller fan includes the following steps:

[0007] Step 1: Based on the original three-dimensional model of the counter-rotating propeller fan, set the three-dimensional design conditions, including the cruise design conditions and the take-off design conditions; carry out the flow numerical simulation of the counter-rotating propeller fan under the three-dimensional design conditions to obtain the flow field simulation results under the three-dimensional design conditions; obtain the key flow characteristics of the counter-rotating propeller fan based on the flow field simulation results; the key flow characteristics include the shock wave intensity, the leading edge separation bubble size and its location;

[0008] Step 2: Based on the key flow characteristics obtained in step 1, a two-dimensional cross-sectional airfoil in the radial region where a shock wave exists under the cruise design condition and a leading edge separation bubble exists under the takeoff design condition is selected as the design object on the counter-rotating propeller blade;

[0009] Based on the three-dimensional design working condition set in step 1, according to the requirement that the two-dimensional and three-dimensional flow states are similar, the two-dimensional airfoil design working condition is determined; the two-dimensional airfoil design working condition includes the Mach number, angle of attack, Reynolds number and design lift coefficient corresponding to the cruising state and the take-off state; and under the two-dimensional airfoil design working condition, with the goal of reducing the cruising resistance and take-off resistance of the two-dimensional airfoil, with the maximum thickness of the two-dimensional airfoil not being reduced relative to the original airfoil as a geometric constraint, the two-dimensional airfoil optimization design of the blade of the counter-rotating propeller fan is carried out to obtain the optimized airfoil;

[0010] Step 3: Assemble the optimized airfoil obtained in step 2 to the front and rear blades of the counter-rotating propeller three-dimensional model, and determine the interference area of ​​the front propeller tip vortex on the rear propeller according to the flow field simulation results under the three-dimensional design conditions obtained in step 1, and shear the rear propeller according to the interference area to obtain a new counter-rotating propeller three-dimensional model; then use the new counter-rotating propeller three-dimensional model as the optimized original configuration, under the three-dimensional design conditions, with the goal of reducing the power of the counter-rotating propeller, with the aerodynamic constraint that the thrust of the counter-rotating propeller is not reduced relative to the original configuration, and with the acoustic constraint that the entropy in the front propeller wake does not increase under the takeoff design conditions in the three-dimensional design conditions, carry out the aerodynamic and noise coupling optimization design of the counter-rotating propeller blades that takes into account both cruise and takeoff, and obtain the optimized counter-rotating propeller blades.

[0011] Furthermore, in step 1, the sliding grid method is used to calculate the unsteady flow field of the original three-dimensional model of the counter-rotating propeller fan to obtain the flow field simulation results under the three-dimensional design conditions.

[0012] Furthermore, in step 2, the method for determining the two-dimensional airfoil design condition is specifically as follows:

[0013] For the cruise state, the incoming flow Mach number corresponding to the cruise design condition in the three-dimensional design condition is and the rotational Mach number The superposition value determines the upper limit of the incoming flow Mach number of the two-dimensional airfoil; the upper limit of the incoming flow Mach number is multiplied by the cosine value of the local blade leading edge sweep angle to obtain the lower limit of the incoming flow Mach number of the two-dimensional airfoil; the Mach number is adjusted between the upper limit of the incoming flow Mach number and the lower limit of the incoming flow Mach number, and the two-dimensional airfoil is calculated by CFD to obtain the cruise state flow field simulation result of the two-dimensional airfoil; the cruise state flow field simulation result of the two-dimensional airfoil is compared with the cruise design condition flow field simulation result under the three-dimensional design condition obtained in step 1, and when the shock wave intensity and position in the two flow field simulation results match, the Mach number at this time is selected as the cruise state Mach number of the two-dimensional airfoil design condition ; The cruise state angle of attack is the angle of attack of the cross-section position of the two-dimensional airfoil in the three-dimensional flow field simulation result under the cruise condition obtained in step 1; the cruise state Reynolds number is determined by the cruise altitude and the cruise state Mach number; the lift coefficient of the two-dimensional airfoil under the cruise state Mach number, the cruise state angle of attack, and the cruise state Reynolds number is taken as the cruise state design lift coefficient;

[0014] For the take-off state, the take-off state Mach number of the two-dimensional airfoil design condition Determined according to the following formula:

[0015]

[0016] in, is the incoming flow Mach number corresponding to the takeoff design condition in the three-dimensional design condition, is the rotational Mach number corresponding to the takeoff design condition in the three-dimensional design condition;

[0017] The take-off angle of attack for the two-dimensional airfoil design condition is obtained by the following process:

[0018] The angle of attack of the two-dimensional airfoil in the takeoff design condition flow field simulation result under the three-dimensional design condition obtained in step 1 is taken as the initial angle of attack, and the flow fields corresponding to other angles of attack values ​​within a set range near the initial angle of attack are calculated by CFD to obtain the takeoff state flow field simulation results of the two-dimensional airfoil corresponding to each angle of attack, and the sizes of the leading edge separation bubbles in the takeoff state flow field simulation results of the two-dimensional airfoil corresponding to each angle of attack are compared with the sizes of the leading edge separation bubbles in the takeoff design condition flow field simulation results under the three-dimensional design condition obtained in step 1. When the proportion of the leading edge separation bubble to the chord length in the two flow field simulation results matches, the corresponding angle of attack at this time is selected as the takeoff state angle of attack of the two-dimensional airfoil design condition; the takeoff state Reynolds number is determined by the takeoff state Mach number; and the lift coefficient of the two-dimensional airfoil under the takeoff state Mach number, the takeoff state angle of attack, and the takeoff state Reynolds number is taken as the takeoff state design lift coefficient.

[0019] Furthermore, in step 2, the mathematical expression of the optimization model for the two-dimensional airfoil optimization design is as follows:

[0020]

[0021] in: is the drag coefficient of the two-dimensional airfoil at takeoff, is the drag coefficient of the two-dimensional airfoil in cruise state, is the maximum thickness of the two-dimensional airfoil, is the maximum thickness of the original airfoil.

[0022] When solving the above optimization problem model, the FFD method is used to parameterize the airfoil. The control points at the leading and trailing edges are fixed control points, and the control points at the upper and lower surfaces are movable control points. The design variables are the longitudinal coordinates of the movable control points on the upper and lower surfaces of the airfoil. The optimization algorithm adopts a multi-objective genetic algorithm. During optimization, the aerodynamic performance of the airfoil is calculated using the open source solver CFL3D, and the turbulence model uses SST.

[0023] Furthermore, in step 3, the optimized airfoil is assembled to the front and rear blades of the counter-rotating propeller fan three-dimensional model, and the specific method of shearing to obtain a new counter-rotating propeller fan three-dimensional model is as follows: the airfoil in the area where shock waves exist under the cruise design conditions in the front and rear propeller blades of the counter-rotating propeller fan is replaced with the optimized airfoil; the part of the rear propeller blade that is affected by the tip vortex of the front propeller under the cruise design conditions is cut off, and the remaining part is retained as the new rear propeller.

[0024] Furthermore, in step 3, the optimization model for the optimal design of the counter-rotating propeller blades is:

[0025]

[0026] in: is the power coefficient of the counter-rotating propeller fan under cruise design conditions, is the power coefficient of the counter-rotating propeller fan under the take-off design condition, is the thrust coefficient of the counter-rotating propeller under cruise design conditions, is the tension coefficient of the original configuration under cruise design conditions, is the thrust coefficient of the counter-rotating propeller fan under the take-off design condition, is the pull coefficient of the original configuration under takeoff design conditions, represents the entropy increase of the airflow after passing through the front propeller of the counter-rotating propeller fan under the design takeoff condition, It represents the entropy increase of the airflow after passing through the front propeller of the original configuration under the takeoff design condition.

[0027] When solving the above optimization problem model, the FFD method is used to parameterize the three-dimensional blades, the control points at the roots of the front and rear blades are fixed control points, the control points at other sections outside the front and rear blades are moving control points, and the design variables are the sweep angle, chord length, and torsion angle of other sections outside the front and rear blades; the optimization algorithm adopts a multi-objective genetic algorithm; during optimization, the specific method for calculating the aerodynamic performance of the counter-rotating propeller fan is as follows: based on a single-channel model composed of front and rear single blades, periodic boundary conditions and multiple non-inertial systems are used for quasi-steady simulation, and the turbulence model is SST.

[0028] Beneficial Effects

[0029] The present invention provides a design method for a high-efficiency and low-noise counter-rotating propeller fan, which has the following advantages:

[0030] The present invention calculates the flow field of a three-dimensional counter-rotating propeller fan by using a CFD method that uses a sliding grid for unsteady calculations, and can accurately capture the key flow characteristics of a cruise strong shock wave and a takeoff leading edge separation bubble, so that the locations of these two flow phenomena in the three-dimensional counter-rotating propeller fan flow field can be accurately obtained, and the key two-dimensional profile can be obtained to ensure the design quality; the present invention adopts an optimization strategy from a two-dimensional airfoil to a three-dimensional blade, and compared with directly performing the optimization design of parameters such as the airfoil, chord length, torsion angle, and sweep angle on the three-dimensional configuration of the counter-rotating propeller fan, the number of design variables can be effectively reduced and the optimization efficiency can be improved; the present invention adopts the means of rear propeller shearing and in the optimization, by constraining the front propeller wake and the blade tip vortex intensity in the takeoff state, the influence of noise can be considered in the aerodynamic optimization, so that aerodynamic and acoustic multi-objective and multi-disciplinary optimization can be achieved for counter-rotating propeller fans. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a design flow chart of a counter-rotating propeller fan according to an embodiment of the present invention;

[0032] Figure 2 The geometric shape of the original configuration of the counter-rotating propeller fan of the embodiment of the present invention;

[0033] Figure 3 The front propeller pressure distribution and Mach number cloud diagram and surface streamline diagram of the original configuration of the embodiment of the present invention under the cruise and take-off design conditions;

[0034] Figure 4 The pressure distribution and Mach number cloud diagram and surface streamline diagram of the rear propeller of the original configuration of the embodiment of the present invention under the cruise and take-off design conditions;

[0035] Figure 5 Schematic diagram of the interference of the front propeller tip vortex on the rear propeller under the cruise design condition of the original configuration of the embodiment of the present invention;

[0036] Figure 6 Schematic diagram of the interference of the front propeller tip vortex on the rear propeller under the take-off design condition of the original configuration of the embodiment of the present invention;

[0037] Figure 7 A schematic diagram of FFD control points of a parameterization method for a two-dimensional airfoil according to an embodiment of the present invention;

[0038] Figure 8 A schematic diagram of FFD control points of a parameterization method for a three-dimensional blade according to an embodiment of the present invention;

[0039] Fig. 9 The figure is a comparison of the geometrical shapes of the two-dimensional airfoil of an embodiment of the present invention before and after optimization;

[0040] Fig.10 The two-dimensional airfoil of the embodiment of the present invention is optimized in a cruise state, and the lift-to-drag ratio varies with the lift coefficient before and after;

[0041] Fig.11 The lift-to-drag ratio of the two-dimensional airfoil of the embodiment of the present invention changes with the lift coefficient before and after optimization in the take-off state;

[0042] Fig.12 Comparison of pressure distribution on the front and rear surfaces of the front propeller blade of the embodiment of the present invention at the cruise design point optimization;

[0043] Fig.13 Comparison of pressure distribution on the front and rear surfaces of the rear propeller blade for cruise design point optimization according to an embodiment of the present invention;

[0044] Fig.14 Comparison of front and rear surface streamlines for optimizing the takeoff design point of the front propeller blade of an embodiment of the present invention;

[0045] Fig.15 Comparison of front and rear surface streamlines for optimizing the takeoff design point of the rear propeller blade of an embodiment of the present invention;

[0046] Fig.16 A schematic diagram of a noise assessment model according to an embodiment of the present invention;

[0047] Fig.17 This is a comparison of the total sound pressure level directivity of the counter-rotating propellers before and after optimization under the cruise design working condition of the embodiment of the present invention;

[0048] Fig.18 The figure is a comparison of the directivity of the total sound pressure level before and after the optimization of the counter-rotating propeller fans under the take-off design conditions of the embodiment of the present invention. DETAILED DESCRIPTION

[0049] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer and more understandable, and to enable those skilled in the art to better understand the solutions of the present invention, the present invention is further described and fully described in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0050] This embodiment uses a design method for high-efficiency and low-noise counter-rotating propeller fans proposed by the present invention to carry out aerodynamic and noise optimization design of a certain type of counter-rotating propeller fan, such as Figure 1 As shown, the above method specifically includes the following steps:

[0051] Step 1: Based on the original three-dimensional model of the counter-rotating propeller fan, set the three-dimensional design conditions, including the cruise design conditions and the take-off design conditions; carry out the flow numerical simulation of the counter-rotating propeller fan under the three-dimensional design conditions to obtain the flow field simulation results under the three-dimensional design conditions; obtain the key flow characteristics of the counter-rotating propeller fan based on the flow field simulation results; the key flow characteristics include the shock wave intensity, the leading edge separation bubble size and its location;

[0052] In this embodiment, the specific original configuration of the counter-rotating propeller fan is as follows: Figure 2 As shown, the front propeller of the counter-rotating propeller fan is an 8-blade propeller and the rear propeller is a 6-blade propeller; the cruise design conditions are set as follows: the incoming flow Mach number is 0.72, the cruising altitude is 10km, the front and rear propeller speeds are 850RPM, and the incoming flow angle of attack is 0°; the take-off design conditions are as follows: the incoming flow Mach number is 0.2, the take-off altitude is 0km, the front and rear propeller speeds are 1000RPM, and the incoming flow angle of attack is 0°; the Reynolds number is determined by the incoming flow Mach number and altitude, and the determination method is a technical means known to those skilled in the art. The sliding grid method is used to calculate the unsteady flow field of the original three-dimensional model of the counter-rotating propeller fan, and the flow field simulation results under the three-dimensional design conditions are obtained; Figure 3 and Figure 4The pressure distribution of the front and rear blades under three-dimensional design conditions (including cruise design conditions and takeoff design conditions) and the Mach number cloud diagram and surface streamline diagram are given. It can be seen that under cruise design conditions, there is a shock wave outside the 60% radius of the blade, and the shock wave is located at 70%~95% of the local chord length of the airfoil; and under takeoff design conditions, there is a leading edge separation bubble, which covers a maximum of 30% of the local chord length of the airfoil. These two flow phenomena are unfavorable to the aerodynamic and noise performance of the counter-rotating propeller fan. In addition, by Figure 5 It can be seen that under the cruise design condition, the influence range of the front propeller tip vortex on the rear propeller is outside the 95.5% radius, while Figure 6 It can be seen that under the take-off design conditions, the influence range of the front propeller tip vortex on the rear propeller is between 89% and 97%, which will form a tip vortex interference noise source.

[0053] Step 2: Based on the key flow characteristics obtained in step 1, a two-dimensional cross-sectional airfoil in the radial region where a shock wave exists under the cruise design condition and a leading edge separation bubble exists under the takeoff design condition is selected as the design object on the counter-rotating propeller blade;

[0054] Based on the three-dimensional design working condition set in step 1, according to the requirement that the two-dimensional and three-dimensional flow states are similar, the two-dimensional airfoil design working condition is determined; the two-dimensional airfoil design working condition includes the Mach number, angle of attack, Reynolds number and design lift coefficient corresponding to the cruising state and the take-off state; and under the two-dimensional airfoil design working condition, with the goal of reducing the cruising resistance and take-off resistance of the two-dimensional airfoil, with the maximum thickness of the two-dimensional airfoil not being reduced relative to the original airfoil as a geometric constraint, the two-dimensional airfoil optimization design of the blade of the counter-rotating propeller fan is carried out to obtain the optimized airfoil;

[0055] In this embodiment, according to the key flow characteristics obtained in step 1, the two-dimensional cross-sectional airfoil at the 75% radius of the front propeller is selected as the design object. The cruise shock wave at this position under the three-dimensional design condition is strong, the takeoff leading edge separation bubble is more obvious, and the influence of the blade tip vortex is small, which is more in line with the two-dimensional flow hypothesis. The original airfoil geometry at this position is as follows Figure 7 As shown in , the maximum thickness of the original airfoil is 2.560%, the maximum camber thereof is 1.771%, and the trailing edge thickness is 0.447%, all of which are expressed using dimensionless quantities commonly used in the art.

[0056] In this embodiment, the method for determining the two-dimensional airfoil design working condition is as follows:

[0057] For the cruise state, the incoming flow Mach number corresponding to the cruise design condition in the three-dimensional design condition is and the rotational Mach number The superposition value of determines the upper limit of the incoming flow Mach number of the two-dimensional airfoil; considering the sweep effect, multiplying the upper limit of the incoming flow Mach number by the cosine value of the local blade leading edge sweep angle to obtain the lower limit of the incoming flow Mach number of the two-dimensional airfoil; adjusting the Mach number between the upper limit of the incoming flow Mach number and the lower limit of the incoming flow Mach number, and performing CFD calculation on the two-dimensional airfoil to obtain a cruise state flow field simulation result of the two-dimensional airfoil; comparing the cruise state flow field simulation result of the two-dimensional airfoil with the cruise design condition flow field simulation result under the three-dimensional design condition obtained in step 1, when the shock wave intensity and position in the two flow field simulation results match, selecting the Mach number at this time as the cruise state Mach number of the two-dimensional airfoil design condition ; The cruise state angle of attack is the angle of attack of the cross-section position of the two-dimensional airfoil in the three-dimensional flow field simulation result under the cruise condition obtained in step 1; the cruise state Reynolds number is determined by the cruise altitude and the cruise state Mach number; the lift coefficient of the two-dimensional airfoil under the cruise state Mach number, the cruise state angle of attack, and the cruise state Reynolds number is taken as the cruise state design lift coefficient;

[0058] For the take-off state, the take-off state Mach number of the two-dimensional airfoil design condition Determined according to the following formula:

[0059]

[0060] in, is the incoming flow Mach number corresponding to the takeoff design condition in the three-dimensional design condition, is the rotational Mach number corresponding to the takeoff design condition in the three-dimensional design condition;

[0061] The take-off angle of attack for the two-dimensional airfoil design condition is obtained by the following process:

[0062] The angle of attack of the two-dimensional airfoil in the takeoff design condition flow field simulation result under the three-dimensional design condition obtained in step 1 is taken as the initial angle of attack. However, since the size of the leading edge separation bubble is sensitive to the change of the angle of attack, the flow field corresponding to the angle of attack near the initial angle of attack of the two-dimensional airfoil is further CFD calculated to obtain the takeoff state flow field simulation results of the two-dimensional airfoil corresponding to each angle of attack. The takeoff state flow field simulation results of the two-dimensional airfoil corresponding to each angle of attack are compared with the size of the leading edge separation bubble in the takeoff design condition flow field simulation result under the three-dimensional design condition obtained in step 1. When the proportion of the leading edge separation bubble to the chord length in the two flow field simulation results matches, the corresponding angle of attack at this time is selected as the takeoff state angle of attack of the two-dimensional airfoil design condition. Here, the matching refers to that the proportion of the leading edge separation bubble to the chord length is consistent, and the difference is not greater than the set requirement. The takeoff state Reynolds number is determined by the takeoff state Mach number. The lift coefficient of the two-dimensional airfoil under the takeoff state Mach number, the takeoff state angle of attack, and the takeoff state Reynolds number is taken as the takeoff state design lift coefficient.

[0063] In this embodiment, the two-dimensional airfoil at the 75% radius of the selected front propeller is specifically determined as follows:

[0064] Cruise condition: ;

[0065] Take-off conditions: .

[0066] In this embodiment, the optimization model of the two-dimensional airfoil optimization design is: with the goal of reducing the cruise resistance and takeoff resistance of the two-dimensional airfoil, and with the maximum thickness of the two-dimensional airfoil not being reduced relative to the original airfoil as a geometric constraint, the mathematical expression is as follows:

[0067]

[0068] in: is the drag coefficient of the two-dimensional airfoil at takeoff, is the drag coefficient of the two-dimensional airfoil in cruise state, is the maximum thickness of the two-dimensional airfoil, is the maximum thickness of the original airfoil;

[0069] When solving the above optimization problem model, the FFD method is used to parameterize the two-dimensional airfoil, such as Figure 7 As shown in the figure, the control points at the leading and trailing edges of the two-dimensional airfoil are fixed control points, and the control points at the upper and lower surfaces of the two-dimensional airfoil are movable control points; the design variables are the ordinates of the movable control points on the upper and lower surfaces of the two-dimensional airfoil, of which there are 11 control points on the upper surface and 11 control points on the lower surface, for a total of 22 design variables; the optimization method uses a multi-objective genetic algorithm with a crossover rate of 0.9, a mutation rate of 0.1, a population size of 80, and an optimization generation of 50. The aerodynamic performance of the two-dimensional airfoil is calculated using the open source solver CFL3D, and the turbulence model uses SST.

[0070] The optimized airfoil geometry is as follows: Fig. 9 As shown, the geometric coordinates of the upper and lower surfaces of the optimized airfoil are expressed as follows:

[0071]

[0072] in, Represents the horizontal coordinates of the upper and lower surfaces of the airfoil, Represents the ordinate corresponding to the upper and lower surfaces of the airfoil, Represents the step at the root of the airfoil coordinate, Represents the fitting coefficients of the upper and lower surfaces of the airfoil;

[0073] The fitting coefficient of the optimized airfoil upper surface is:

[0074]

[0075] The fitting coefficient of the optimized airfoil lower surface is:

[0076]

[0077] The maximum thickness of the optimized airfoil is 2.596%, the maximum camber is 1.463%, and the trailing edge thickness is 0.447%, all of which are expressed in dimensionless quantities commonly used in this field. The lift coefficient, drag coefficient, and maximum thickness of the optimized airfoil at the design points of takeoff and cruise conditions are shown in Table 1. It can be seen that the lift-to-drag ratio of the optimized airfoil at the design points of cruise and takeoff conditions is increased by 44.3% and 78.4%, respectively.

[0078] Table 1 Comparison of lift, drag coefficient and maximum thickness of airfoil before and after optimization

[0079]

[0080] in is the lift coefficient in cruise state, is the drag coefficient in cruising state, is the angle of attack in cruise state, is the lift coefficient at takeoff, is the drag coefficient at takeoff, is the angle of attack at takeoff, is the maximum thickness.

[0081] The aerodynamic performance of the optimized airfoil near the design point of cruise and takeoff conditions was calculated by CFD. The comparison of the calculation results is as follows: Fig.10 and Fig.11 As shown in the figure, the lift coefficient corresponding to its maximum lift-to-drag ratio is just near the design lift coefficient. At the same time, the good aerodynamic performance near the design point shows that the optimization result of the two-dimensional airfoil has good robustness.

[0082] Step 3: Assemble the optimized airfoil obtained in step 2 to the front and rear blades of the counter-rotating propeller three-dimensional model, and determine the interference area of ​​the front propeller tip vortex on the rear propeller according to the flow field simulation results under the three-dimensional design conditions obtained in step 1, and shear the rear propeller according to the interference area to obtain a new counter-rotating propeller three-dimensional model; then use the new counter-rotating propeller three-dimensional model as the optimized original configuration, under the three-dimensional design conditions, with the goal of reducing the power of the counter-rotating propeller, with the aerodynamic constraint that the thrust of the counter-rotating propeller is not reduced relative to the original configuration, and with the acoustic constraint that the entropy in the front propeller wake does not increase under the takeoff design conditions in the three-dimensional design conditions, carry out the aerodynamic and noise coupling optimization design of the counter-rotating propeller blades that takes into account both cruise and takeoff, and obtain the optimized counter-rotating propeller blades.

[0083] In this embodiment, the optimized airfoil is assembled to the front and rear blades of the counter-rotating propeller fan three-dimensional model, and the specific method of shearing to obtain a new counter-rotating propeller fan three-dimensional model is: replace the airfoil outside the 60% radius of the front and rear propeller blades of the counter-rotating propeller fan (i.e., the airfoil of the blade with shock waves under the cruise design condition shown by the flow field simulation results in step 1) with the optimized airfoil obtained in step 2, and cut off the part outside the 95.5% radius of the rear propeller blade, and only keep the part within the 95.5% radius as the new rear propeller. The reason for obtaining the rear propeller by shearing operation is that, according to the CFD calculation results, Figure 5 and Figure 6 As shown, it can be seen that under the cruise design condition, the influence range of the front propeller tip vortex on the rear propeller is outside the 95.5% radius, while under the take-off design condition, the influence range of the front propeller tip vortex on the rear propeller is between 89% and 97%. Cutting off the part outside the 95.5% radius of the rear propeller blade can reduce the noise caused by the tip vortex interference. The influence range of the front propeller tip vortex on the rear propeller under the take-off design condition is not used as a reference in order to avoid excessive loss of aerodynamic efficiency.

[0084] In this embodiment, the optimization model for the optimal design of the contra-rotating propeller blades is: with the goal of reducing the power of the contra-rotating propeller, the thrust of the contra-rotating propeller relative to the original configuration is not reduced as an aerodynamic constraint, the takeoff design condition in the three-dimensional design condition, the entropy in the front propeller wake is not increased as an acoustic constraint, and the front propeller wake strength is restricted. The mathematical expression of the optimization model is as follows:

[0085]

[0086] in: is the power coefficient of the counter-rotating propeller fan under cruise design conditions, is the power coefficient of the counter-rotating propeller fan under the take-off design condition, is the thrust coefficient of the counter-rotating propeller under cruise design conditions, is the tension coefficient of the original configuration under cruise design conditions, is the thrust coefficient of the counter-rotating propeller fan under the take-off design condition, is the pull coefficient of the original configuration under takeoff design conditions, represents the entropy increase of the airflow after passing through the front propeller of the counter-rotating propeller fan under the design takeoff condition, It represents the entropy increase of the airflow after passing through the front propeller of the original configuration under the takeoff design condition.

[0087] When solving the above optimization problem model, the FFD method is used to parameterize the three-dimensional blade, such as Figure 8As shown in the figure, the control points at the roots of the front and rear propeller blades are fixed control points, and the control points at the four sections at equal intervals on the outside of the front and rear propeller blades are moving control points; the design variables are the sweep angle, chord length and torsion angle of the four sections on the outside of the front and rear propeller blades, with a total of 24 design variables; the optimization algorithm adopts a multi-objective genetic algorithm with a crossover rate of 0.9, a mutation rate of 0.1, a population size of 80, and an optimization algebra of 80; during the optimization, the specific method for calculating the aerodynamic performance of the counter-rotating propeller fan is as follows: based on the single-channel model composed of the front and rear single blades, the periodic boundary conditions and multiple non-inertial systems are used for quasi-steady simulation, and the turbulence model is SST.

[0088] In order to verify the reliability of the design method of the present invention, the unsteady numerical simulation method based on sliding grid is used to perform CFD calculation on the flow field and aerodynamic performance of the counter-rotating propeller fan full-channel configuration before and after optimization under three-dimensional design conditions. The comparison of the aerodynamic performance of the counter-rotating propeller fan before and after optimization is shown in Table 2. Under the premise of ensuring that the thrust is not reduced, the cruise efficiency of the optimized configuration is 86.40%, which is 2.65% higher than that of the original configuration, and the take-off efficiency is 65.84%, which is 1.53% higher than that of the original configuration.

[0089] Table 2 Comparison of aerodynamic performance of three-dimensional configuration before and after optimization

[0090]

[0091] Fig.12 and Fig.13 The pressure cloud diagrams of the front and rear propeller blades and the cross-sectional pressure distribution at 0.5 times the radius and 0.9 times the radius are given under the cruise design conditions before and after optimization. It can be seen that the shock waves in the outer sections of the front and rear propeller blades are significantly weakened. Fig.14 and Fig.15 In order to optimize the front and rear takeoff design conditions, the surface streamlines of the front and rear propeller blades are compared, and the separation bubble at the leading edge of the optimized front propeller basically disappears.

[0092] In order to further verify the reliability of the design method of the present invention, especially the design effect achieved in terms of noise reduction, the noise level of the full-channel configuration of the counter-rotating propeller fan before and after optimization under the three-dimensional design condition is calculated by combining the Morhring acoustic analogy and the finite element method. The calculation model is as follows: Fig.16 As shown in the figure, the red intersection of the rotating domain of the front and rear propellers and the external stationary domain is the surface sound source area, the green cylindrical area is the volume sound source area, which includes the main wake area of ​​the propeller fan, and the blue cylindrical area is the sound propagation area, and its outer boundary is the acoustic infinite element boundary, which is used to simulate the non-reflection boundary condition; the monitoring point is located on a semicircle with a radius of 10 times the blade radius. Fig.17 and Fig.18The directivity of the total sound pressure level is given. The total sound pressure level in the optimized configuration is reduced by 1.31 dB in cruise state and 3.5 dB in takeoff state.

[0093] In summary, the aerodynamic and noise characteristics of the counter-rotating propeller fan designed by the method of the present invention are better than those of the original configuration.

[0094] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A design method for a high-efficiency and low-noise counter-rotating propeller fan, characterized by: The steps include: Step 1: Based on the original three-dimensional model of the counter-rotating propeller fan, set the three-dimensional design conditions, including the cruise design conditions and the take-off design conditions; carry out the flow numerical simulation of the counter-rotating propeller fan under the three-dimensional design conditions to obtain the flow field simulation results under the three-dimensional design conditions; Based on the flow field simulation results, key flow characteristics of the counter-rotating propeller fan are obtained; the key flow characteristics include shock wave intensity, leading edge separation bubble size and its location; Step 2: Based on the key flow characteristics obtained in step 1, a two-dimensional cross-sectional airfoil in the radial region where a shock wave exists under the cruise design condition and a leading edge separation bubble exists under the takeoff design condition is selected as the design object on the counter-rotating propeller blade; Based on the three-dimensional design working condition set in step 1, according to the requirement of similarity between the two-dimensional and three-dimensional flow states, determine the two-dimensional airfoil design working condition; the two-dimensional airfoil design working condition includes the Mach number, angle of attack, Reynolds number and design lift coefficient corresponding to the cruise state and the take-off state respectively; and under the two-dimensional airfoil design working condition, with the goal of reducing the cruise resistance and take-off resistance of the two-dimensional airfoil, with the maximum thickness of the two-dimensional airfoil not being reduced relative to the original airfoil as a geometric constraint, carry out the two-dimensional airfoil optimization design of the blade of the counter-rotating propeller fan to obtain the optimized airfoil; Step 3: Assemble the optimized airfoil obtained in step 2 to the front and rear blades of the counter-rotating propeller fan three-dimensional model, and determine the interference area of ​​the front propeller tip vortex on the rear propeller according to the flow field simulation results under the three-dimensional design conditions obtained in step 1, and shear the rear propeller according to the interference area to obtain a new counter-rotating propeller fan three-dimensional model; Then, taking the new counter-rotating propeller three-dimensional model as the optimized original configuration, under the three-dimensional design conditions, with the goal of reducing the power of the counter-rotating propeller, with the aerodynamic constraint that the thrust of the counter-rotating propeller does not decrease relative to the original configuration, and with the acoustic constraint that the entropy in the front propeller wake does not increase under the takeoff design conditions in the three-dimensional design conditions, an aerodynamic and noise coupling optimization design of the counter-rotating propeller blades that takes into account both cruise and takeoff is carried out to obtain the optimized counter-rotating propeller blades.

2. According to claim 1, a design method for a high-efficiency and low-noise counter-rotating propeller fan is characterized by: In step 1, the sliding grid method is used to calculate the unsteady flow field of the original three-dimensional model of the counter-rotating propeller fan to obtain the flow field simulation results under the three-dimensional design conditions.

3. According to claim 1, a design method for a high-efficiency and low-noise counter-rotating propeller fan is characterized by: In step 2, the method for determining the two-dimensional airfoil design condition is specifically as follows: For the cruise state, the incoming flow Mach number corresponding to the cruise design condition in the three-dimensional design condition is and the rotational Mach number The superposition value determines the upper limit of the incoming flow Mach number of the two-dimensional airfoil; the upper limit of the incoming flow Mach number is multiplied by the cosine value of the local blade leading edge sweep angle to obtain the lower limit of the incoming flow Mach number of the two-dimensional airfoil; the Mach number is adjusted between the upper limit of the incoming flow Mach number and the lower limit of the incoming flow Mach number, and the two-dimensional airfoil is calculated by CFD to obtain the cruise state flow field simulation result of the two-dimensional airfoil; the cruise state flow field simulation result of the two-dimensional airfoil is compared with the cruise design condition flow field simulation result under the three-dimensional design condition obtained in step 1, and when the shock wave intensity and position in the two flow field simulation results match, the Mach number at this time is selected as the cruise state Mach number of the two-dimensional airfoil design condition ; The cruise state angle of attack is the angle of attack of the cross-section position of the two-dimensional airfoil in the three-dimensional flow field simulation result under the cruise condition obtained in step 1; the cruise state Reynolds number is determined by the cruise altitude and the cruise state Mach number; the lift coefficient of the two-dimensional airfoil under the cruise state Mach number, the cruise state angle of attack, and the cruise state Reynolds number is taken as the cruise state design lift coefficient; For the take-off state, the take-off state Mach number of the two-dimensional airfoil design condition Determined according to the following formula: in, is the incoming flow Mach number corresponding to the takeoff design condition in the three-dimensional design condition, is the rotational Mach number corresponding to the takeoff design condition in the three-dimensional design condition; is the cruise Mach number of the two-dimensional airfoil design condition, is the incoming flow Mach number corresponding to the cruise design condition in the three-dimensional design condition, is the rotational Mach number corresponding to the cruise design condition in the three-dimensional design condition; The take-off angle of attack for the two-dimensional airfoil design condition is obtained by the following process: The angle of attack of the two-dimensional airfoil in the takeoff design condition flow field simulation result under the three-dimensional design condition obtained in step 1 is taken as the initial angle of attack, and the flow fields corresponding to other angles of attack values ​​within a set range near the initial angle of attack are calculated by CFD to obtain the takeoff state flow field simulation results of the two-dimensional airfoil corresponding to each angle of attack, and the sizes of the leading edge separation bubbles in the takeoff state flow field simulation results of the two-dimensional airfoil corresponding to each angle of attack are compared with the sizes of the leading edge separation bubbles in the takeoff design condition flow field simulation results under the three-dimensional design condition obtained in step 1. When the proportion of the leading edge separation bubble to the chord length in the two flow field simulation results matches, the corresponding angle of attack at this time is selected as the takeoff state angle of attack of the two-dimensional airfoil design condition; the takeoff state Reynolds number is determined by the takeoff state Mach number; and the lift coefficient of the two-dimensional airfoil under the takeoff state Mach number, the takeoff state angle of attack, and the takeoff state Reynolds number is taken as the takeoff state design lift coefficient.

4. According to claim 1, a design method for a high-efficiency and low-noise counter-rotating propeller fan is characterized by: In step 2, the optimization model for the two-dimensional airfoil optimization design is: min ( c d-cruise , c d-takeoff ) stthick max ≥ thick max-initial in: c d-takeoff is the drag coefficient of the two-dimensional airfoil at takeoff, c d-cruise is the drag coefficient of the two-dimensional airfoil in cruise state, thick max is the maximum thickness of the two-dimensional airfoil, thick max-initial is the maximum thickness of the original airfoil.

5. According to claim 1, a design method for a high-efficiency and low-noise counter-rotating propeller fan is characterized by: In step 3, the optimized airfoil is assembled to the front and rear blades of the counter-rotating propeller fan three-dimensional model, and the specific method of shearing to obtain a new counter-rotating propeller fan three-dimensional model is as follows: the airfoil in the area where shock waves exist under the cruise design conditions in the front and rear propeller blades of the counter-rotating propeller fan is replaced with the optimized airfoil; the part of the rear propeller blade that is affected by the tip vortex of the front propeller under the cruise design conditions is cut off, and the remaining part is retained as the new rear propeller.

6. According to claim 1, a design method for a high-efficiency and low-noise counter-rotating propeller fan is characterized by: In step 3, the optimization model for the optimal design of the counter-rotating propeller blades is: in: is the power coefficient of the counter-rotating propeller fan under cruise design conditions, is the power coefficient of the counter-rotating propeller fan under the take-off design condition, is the thrust coefficient of the counter-rotating propeller under cruise design conditions, is the tension coefficient of the original configuration under cruise design conditions, is the thrust coefficient of the counter-rotating propeller fan under the take-off design condition, is the pull coefficient of the original configuration under takeoff design conditions, represents the entropy increase of the airflow after passing through the front propeller of the counter-rotating propeller fan under the design takeoff condition, It represents the entropy increase of the airflow after passing through the front propeller of the original configuration under the takeoff design condition.

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