Wing profile with corrugated wall surface and design method of wing profile

Abstract

The invention relates to a corrugated wall surface airfoil profile and a design method thereof, which are applied to an unmanned aerial vehicle, and are characterized in that a corrugated wall surface is arranged in a chordwise region of the upper surface of the airfoil profile, and the corrugated wall surface is used for inducing a boundary layer of the upper surface of the airfoil profile to transition in advance and inhibiting generation of laminar flow separation bubbles; the corrugated wall surface is of a sine function corrugated structure, and the sine curve of the corrugated wall surface meets the following formula. According to the invention, the sine wave pattern-shaped wall surface structure with specific geometric parameters is arranged in the chordwise middle rear area of the upper surface of the wing profile, so that local pressure distribution of the surface of the wing profile is changed, a boundary layer is induced to transit in advance, generation of laminar separation bubbles is inhibited, wall surface friction resistance and differential pressure resistance are reduced, and the stability of the wing profile is improved. The problem that the low-altitude low-speed unmanned aerial vehicle wing type drag reduction effect is limited is solved.

Description

Technical Field

[0001] This invention relates to the fields of aviation drag reduction technology and passive flow control, and in particular to a corrugated wall airfoil and its design method. Background Technology

[0002] With the widespread application of drones in military reconnaissance, surveying and monitoring, and logistics transportation, higher requirements are being placed on their range, endurance, and flight efficiency. Under low-altitude and low-speed flight conditions, the aerodynamic drag on the surface of the drone's wing becomes a significant factor affecting flight performance. Therefore, improving the wing airfoil structure to reduce aerodynamic drag has become an important research direction in current drone design.

[0003] Currently, common drag reduction technologies mainly include active flow control and passive flow control. Active flow control typically achieves drag reduction by applying external energy to the wing surface, such as blowing, sucking, or plasma control, to alter the boundary layer flow state. However, this type of technology usually suffers from problems such as complex structure, high energy consumption, and high system reliability requirements, making it difficult to promote in application scenarios such as small unmanned aerial vehicles.

[0004] In contrast, passive flow control technology requires no additional energy input and can regulate airflow by changing the geometry of the wing surface. It offers advantages such as simple structure, high reliability, and low maintenance costs. Common passive flow control structures include transition zones, pit arrays, groove structures, and serrated trailing edges. However, most of these structures are designed for high Reynolds number aircraft, and their drag reduction effect remains limited under the operating conditions of low-altitude, low-speed unmanned aerial vehicles (UAVs).

[0005] Corrugated wall structures were initially used in heat exchangers to enhance heat transfer, and have since been introduced into aerospace drag reduction research. By forming a periodic corrugated structure on the wall, local vortex structures can be induced in the boundary layer, creating low-velocity flow regions in the troughs. This reduces wall shear stress and, to some extent, alters the local pressure distribution, helping to suppress undesirable flow separation phenomena. However, the drag reduction effect of corrugated structures is highly sensitive to parameters such as corrugation wavelength, amplitude, and placement. If these parameters are not designed properly, they may actually increase aerodynamic drag. Summary of the Invention

[0006] The purpose of this invention is to provide a corrugated wall airfoil and its design method, which can solve or at least alleviate one or more of the above-mentioned problems and other problems existing in the prior art.

[0007] To achieve the aforementioned objectives, a first aspect of the present invention provides a corrugated wall airfoil for use in an unmanned aerial vehicle (UAV). A corrugated wall is provided in the chordal region of the upper surface of the airfoil. The corrugated wall induces early boundary layer transition on the upper surface of the airfoil and suppresses the generation of laminar separation bubbles. The corrugated wall is a sinusoidal corrugated structure, and the sine curve of the corrugated wall satisfies: in, For amplitude, The ripple wavelength, For chord coordinates.

[0008] In the corrugated wall airfoil as described above, optionally, the corrugated wall is arranged in the chordal 50% to 80% region of the upper surface of the airfoil.

[0009] In the corrugated wall airfoil described above, optionally, the airfoil is the NACA4412 airfoil, with an airfoil chord length c of 100 mm and a wave amplitude of [missing information]. mm, wavelength mm.

[0010] In the corrugated wall airfoil described above, optionally, the corrugated structure is a recessed sinusoidal corrugated structure, the crest of which is tangent to the upper surface of the airfoil.

[0011] In the corrugated wall airfoil as described above, the corrugated wall may optionally be formed by laser processing or precision milling.

[0012] According to a second aspect of the present invention, a method for designing a corrugated wall airfoil is also provided, comprising the following steps: S1: Obtain the geometric coordinate data of the airfoil and establish the geometric model of the airfoil; S2: In the chordal region of the upper surface of the airfoil to A corrugation function region is established within the original airfoil, and this region is called the corrugation region. This region is defined on the baseline of the original airfoil's upper surface. A sinusoidal perturbation function is superimposed to form a corrugated wall structure, the coordinates of which satisfy: in, For the corrugated surface coordinates, The coordinates of the original airfoil's upper surface are: For amplitude, For wavelength, This is the starting position of the ripples. This is the end position of the ripples. For chord coordinates; S3: Smooth the corrugated surface in step S2 to achieve a smooth transition between the corrugated area and the original smooth surface of the airfoil. S4: Evaluate the aerodynamic performance of the smoothed corrugated airfoil to obtain aerodynamic performance parameters; S5: Optimize the corrugated structure parameters: Among them, the corrugated structure parameters include the corrugation initiation position. ,Wave termination position ,amplitude and wavelength The value of ; change the starting position of the ripple ,Wave termination position ,amplitude and wavelength The values ​​of are determined, and steps S2 to S4 are repeated to obtain the aerodynamic performance parameters corresponding to different parameter combinations. And set the parameter constraints as follows: Under the premise of meeting the constraints, determine the corrugated structure parameters that meet the target aerodynamic performance requirements.

[0013] As described above in the design method for corrugated wall airfoils, optionally, in step S3, the corrugated area is locally smoothed using a cubic B-spline to smooth the ends of the corrugations. and The first and second derivatives at point A are continuous.

[0014] As described above, in the design method of the corrugated wall airfoil, the aerodynamic performance evaluation in step S4 can optionally be performed by numerical simulation. During the numerical simulation, the flow field around the airfoil is meshed, and the mesh is locally refined along the chord direction in the corrugated region so that the number of nodes arranged in a single corrugation cycle is greater than 10.

[0015] As described above in the design method for corrugated wall airfoils, optionally, in the numerical simulation, the height of the first layer of mesh near the airfoil surface is set to... .

[0016] As described above, the design method for corrugated wall airfoils can optionally employ a k-kl-ω three-equation transition model to perform numerical simulations of the flow around the airfoil.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention arranges a sinusoidal corrugated wall structure with specific geometric parameters in the mid-rear region of the chordal direction on the upper surface of an airfoil. By combining parametric modeling and numerical analysis, the starting position, ending position, amplitude, and wavelength of the corrugated structure are optimized. This changes the local pressure distribution on the airfoil surface, induces the boundary layer to transition earlier, suppresses the generation of laminar separation bubbles, and reduces wall friction drag and pressure drag. This solves the problem of limited drag reduction effect of airfoils for low-altitude, low-speed UAVs. It achieves the technical effect of significantly reducing airfoil aerodynamic drag without increasing additional energy input or changing the original airfoil structure strength and control surface layout. This improves the UAV's range, flight time, and payload capacity, and will significantly increase the UAV's mission radius. Attached Figure Description

[0018] Figure 1 This is the original airfoil diagram of the NACA4412 airfoil in this invention; Figure 2 This is an airfoil diagram of the corrugated wall wing airfoil in this invention; Figure 3 for Figure 2 Enlarged view of the wavy area; Figure 4 This is a schematic diagram of the UAV with a corrugated wall wing airfoil according to the present invention; Figure 5 This is a partial enlarged view of the mesh of the corrugated wall airfoil in this invention; Figure 6 This is a velocity field contour map of the NACA4412 airfoil at an angle of attack of 2° in this invention. Figure 7 This is a near-wall streamline diagram of the NACA4412 airfoil with an angle of attack of 2° in this invention; Figure 8 This is a velocity field cloud diagram of the corrugated wall airfoil in this invention with an angle of attack of 2°. Figure 9 This is a near-wall streamline diagram of the corrugated wall airfoil in this invention with an angle of attack of 2°. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that in the description of this invention, the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. The terms "first," "second," and similar words used in the description of this invention do not indicate any order, quantity, or importance, but are only used to distinguish different components, and therefore should not be construed as limiting this invention.

[0021] Furthermore, it should be understood that, for ease of description, the dimensions of the various components shown in the accompanying drawings are not drawn to actual scale; for example, the thickness or width of some layers may be exaggerated relative to other layers.

[0022] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined or described in one figure, it will not need to be discussed or described in detail in the description of the subsequent figures.

[0023] like Figure 1-3 As shown, according to one aspect of the present invention, a corrugated wall airfoil is provided, wherein a corrugated wall is provided in the chordal region of the upper surface of the airfoil, the corrugated wall having a sinusoidal corrugated structure, and the sinusoidal curve of the corrugated wall satisfying: in, For amplitude, The ripple wavelength, For chord coordinates.

[0024] The corrugated wall surface on the upper surface of the airfoil alters the local pressure distribution on the airfoil surface and induces the boundary layer to transition earlier, inhibiting the generation of laminar separation bubbles and reducing wall friction drag and pressure drag.

[0025] In this embodiment, as Figure 1 As shown, the airfoil adopts the NACA4412 airfoil, with an airfoil chord length c of 100 mm. Figure 2-3 As shown, the corrugated wall is arranged in the chordal region of the upper surface of the airfoil from 50% to 80%, that is, within the range of 50 mm to 80 mm from the leading edge. The corrugated wall is a sinusoidal corrugated structure with 40 cycles and a corrugation depth of 0.3 mm. The corrugated structure adopts a concave corrugated design, so that the corrugation crests are tangent to the original airfoil surface, thereby ensuring the geometric continuity between the corrugated structure and the original airfoil surface and avoiding the generation of additional step drag. That is, when the airfoil chord length is 100 mm, the wavelength mm. The ripple depth is 0.3 mm, which corresponds to the ripple amplitude. mm.

[0026] In addition, the corrugated structure is only set on the upper surface of the wing airfoil, while the lower surface remains the original smooth airfoil surface to ensure the structural strength of the wing and the stiffness of the control surfaces.

[0027] Furthermore, the corrugated structure can be formed using laser processing or precision milling; alternatively, it can be formed from aerospace-grade aluminum alloy through precision five-axis milling and then surface polished to achieve the required surface roughness. .

[0028] Therefore, it can be seen that the corrugated wall only requires a certain degree of processing on the upper surface of the airfoil, without the need for additional energy input, and has strong robustness. Moreover, the corrugated structure transitions smoothly with the original airfoil, without affecting the original control surface layout and structural strength, and has high engineering applicability.

[0029] like Figure 4 As shown, according to a second aspect of the present invention, a fixed-wing unmanned aerial vehicle (UAV) is provided. The UAV includes a fuselage, a straight wing, and a V-tail. The straight wing has a span of 2000 mm and an angle of attack of 2°, i.e., the airfoil has an angle of attack of 2°. The straight wing airfoil is a corrugated wall wing airfoil as described above. Figure 4 The enlarged view at point A shows the area with the corrugated structure, the enlarged view at point B shows the front end area of ​​the corrugated structure, and the enlarged view at point C shows the rear end area of ​​the corrugated structure.

[0030] like Figure 5-9 As shown, according to a third aspect of the present invention, a method for designing a corrugated wall airfoil is provided, comprising the following steps: Step 101: Obtain the geometric coordinate data of the airfoil and establish the geometric model of the airfoil.

[0031] Specifically, coordinate data of the upper and lower surfaces of the airfoil can be obtained from an airfoil database, and the original airfoil geometric model can be constructed using this coordinate data to provide a reference profile for the subsequent construction of the corrugated structure. The original airfoil can be selected according to the flight mission requirements of the target UAV.

[0032] Step 102: In the chordal region of the original airfoil's upper surface to A corrugation function region is established within the original airfoil, and this region is called the corrugation region. This region is defined on the baseline of the original airfoil's upper surface. A sinusoidal perturbation function is superimposed to form a corrugated wall structure, the coordinates of which satisfy: in, For the corrugated surface coordinates, The coordinates of the original airfoil's upper surface are: For amplitude, For wavelength, This is the starting position of the ripples. This is the end position of the ripples. For chord coordinates.

[0033] The negative sign in the above formula indicates that the constructed corrugations are concave corrugations, making the wave crests tangent to the original airfoil's upper surface, thus ensuring the geometric continuity between the corrugated structure and the original airfoil surface. Outside the specified interval, the airfoil surface retains its original smooth profile.

[0034] Among them, the starting position of the ripples ,Wave termination position ,amplitude and wavelength All parameters are adjustable and can be set according to the airfoil drag reduction requirements.

[0035] Step 103: Smooth the corrugated surface to achieve a smooth transition between the corrugated area and the original smooth surface of the airfoil.

[0036] Specifically, cubic B-splines can be used to locally smooth the corrugated area, making the ends of the corrugations smooth. and The first and second derivatives are continuous at the point, thereby reducing or eliminating geometric steps and curvature abrupt changes, and avoiding additional resistance caused by local abrupt changes.

[0037] Step 104: Evaluate the aerodynamic performance of the smoothed corrugated airfoil. The aerodynamic performance evaluation is conducted through numerical simulation to obtain the aerodynamic performance parameters of the airfoil. In this embodiment, the aerodynamic performance parameter is the drag coefficient. .

[0038] Specifically, the smoothed corrugated airfoil geometric model is discretized using the finite element method (FEM) for the airfoil's flow region, generating an O-shaped topological structured mesh. 401 nodes are arranged on the upper surface, 201 nodes on the lower surface, and approximately 10 nodes on the trailing edge. Local mesh refinement is applied along the chord direction in the corrugated region to ensure the accuracy of the corrugated geometry. At least 10 nodes are arranged within a single wave period to maintain the sinusoidal shape. A boundary layer mesh is then placed near the airfoil surface, with the first layer set to a height of [missing information]. ， To ensure the wall If the y+ value is too large, the mesh nodes will fall in the buffer layer or the turbulent core region, leading to significant deviations in the calculation of transition locations and frictional resistance. Defined as: , The wall friction speed is... ; The distance from the wall to the center of the first layer of grid, For the fluid kinematic viscosity coefficient, For wall shear stress, The fluid density is given.

[0039] In the numerical calculations, a k-kl-ω three-equation transition model capable of capturing the boundary layer transition process is employed, and a second-order precision discretization scheme is used for the calculations. The corrugated structure can induce the laminar boundary layer to transition to a turbulent boundary layer earlier, while also changing the local pressure distribution on the airfoil surface, thereby reducing wall friction drag and pressure drag.

[0040] Step 105: Optimize the corrugated structure parameters.

[0041] Specifically, changing the corrugated structure parameters , , , Change the starting position of the ripples. ,Wave termination position ,amplitude and wavelength By taking the values ​​of , repeat steps 102 to 104 to obtain the airfoil drag coefficients corresponding to different parameter combinations. Feedback and optimization design are then performed.

[0042] Among them, the drag coefficient It is a key dimensionless indicator for measuring the aerodynamic drag of airfoils and UAVs, and its definition is as follows: Among them, C D ρ is the drag coefficient; ∞ V is the free flow density; ∞ denoted as free-flow velocity; S as wing reference area; and D as aerodynamic drag.

[0043] Furthermore, with drag coefficient To minimize the optimization objective, the objective function is established as follows: And set the parameter constraints as follows: Under the premise of satisfying the constraints, the response surface methodology or genetic algorithm is used to optimize the parameter space in order to obtain the best combination of corrugated structure parameters for drag reduction.

[0044] Specifically, the original airfoil is the NACA4412 type, with an angle of attack of 2°, a chord length of c=100mm, and a corrugated structure arranged on the upper surface of the airfoil at 50% of the chord length. 80%c region, i.e. Forty periodic sinusoidal wave structures are arranged within this area. The wavelength is... Amplitude Under atmospheric pressure conditions at sea level, with a Mach number of 0.1 and in level flight, the static pressure is 101325 Pa, the static temperature is 288.15 K, and the air density is 1.225 kg / m³. The changes in air parameters satisfy the ideal gas equation and Sutherland's law. The k-kl-ω transition model is used for calculation.

[0045] Numerical simulations of flow around an airfoil were performed using ANSYS Fluent 2023 R1 software. The drag coefficient of the original NACA4412 airfoil was... After adopting a corrugated wall design: During the computer simulation, the velocity field contour plot and near-wall streamline plot of the NACA4412 airfoil are shown in [the image / data]. Figure 6 and Figure 7 Velocity field cloud diagram and near-wall streamline diagram of the corrugated wall airfoil are shown in [reference needed]. Figure 8 and Figure 9 The result of a drag coefficient reduction of approximately 25% indicates that corrugated structures can effectively promote boundary layer transition and reduce airfoil aerodynamic drag, thereby improving the range and flight efficiency of UAVs.

[0046] In conjunction with the above embodiments of the present invention, a sinusoidal corrugated wall structure with specific geometric parameters is arranged in the chord-direction rear region of the upper surface of the airfoil. By combining parametric modeling and numerical analysis, the parameters such as the starting position, ending position, amplitude, and wavelength of the corrugated structure are optimized, thereby changing the local pressure distribution on the airfoil surface, inducing the boundary layer to transition earlier, suppressing the generation of laminar separation bubbles, and reducing wall friction drag and pressure drag. This solves the problem of limited drag reduction effect of airfoils for low-altitude, low-speed UAVs. It achieves the technical effect of significantly reducing airfoil aerodynamic drag without increasing additional energy input or changing the original airfoil structure strength and control surface layout, thus improving the UAV's range, flight time, and payload capacity, and significantly increasing the UAV's mission radius.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A design method for a corrugated wall airfoil, characterized in that, Includes the following steps: S1: Obtain the geometric coordinate data of the airfoil and establish the geometric model of the airfoil; S2: In the chordal region of the upper surface of the airfoil to A corrugation function region is established within the original airfoil, and this region is called the corrugation region. This region is defined on the baseline of the original airfoil's upper surface. A sinusoidal perturbation function is superimposed to form a corrugated wall structure, the coordinates of which satisfy: in, For the corrugated surface coordinates, The coordinates of the original airfoil's upper surface are: For amplitude, For wavelength, This is the starting position of the ripples. This is the end position of the ripples. For chord coordinates; S3: Smooth the corrugated surface in step S2 to achieve a smooth transition between the corrugated area and the original smooth surface of the airfoil. S4: Evaluate the aerodynamic performance of the smoothed corrugated airfoil to obtain aerodynamic performance parameters; S5: Optimize the corrugated structure parameters: Among them, the corrugated structure parameters include the corrugation initiation position. ,Wave termination position ,amplitude and wavelength The value of ; change the starting position of the ripple ,Wave termination position ,amplitude and wavelength The values ​​of the parameters are determined by repeating steps S2 to S4 to obtain the aerodynamic performance parameters corresponding to different parameter combinations. And set the parameter constraints as follows: Under the premise of meeting the constraints, determine the corrugated structure parameters that meet the target aerodynamic performance requirements.

2. The design method for the corrugated wall airfoil as described in claim 1, characterized in that, In step S3, the corrugated area is locally smoothed using a cubic B-spline to smooth the ends of the corrugations. and The first and second derivatives at point A are continuous.

3. The design method for the corrugated wall airfoil as described in claim 1, characterized in that, The aerodynamic performance evaluation in step S4 is carried out through numerical simulation. During the numerical simulation, the flow field around the airfoil is divided into grids, and the grids are locally refined along the chord direction in the corrugated region so that the number of nodes arranged in a single corrugation cycle is greater than 10.

4. The design method for the corrugated wall airfoil as described in claim 3, characterized in that, In the numerical simulation, the height of the first mesh layer near the airfoil surface is set to... .

5. The design method for the corrugated wall airfoil as described in claim 3, characterized in that, The numerical simulation uses a k-kl-ω three-equation transition model to perform the flow simulation around the airfoil.

6. A corrugated wall wing airfoil for use in unmanned aerial vehicles (UAVs), characterized in that: The corrugated wall airfoil designed by the design method of any one of claims 1-5 has a corrugated wall in the chordal region of the upper surface of the airfoil. The corrugated wall is used to induce early boundary layer transition on the upper surface of the airfoil and suppress the generation of laminar separation bubbles. The corrugated wall is a sinusoidal corrugated structure, and the sine curve of the corrugated wall satisfies: in, For amplitude, The ripple wavelength, For chord coordinates.

7. The corrugated wall airfoil as described in claim 6, characterized in that, The corrugated wall is arranged in the chordal region of the upper surface of the airfoil, from 50% to 80%.

8. The corrugated wall airfoil as described in claim 7, characterized in that, The airfoil is NACA4412, with an airfoil chord length c of 100 mm and a wave amplitude of [missing information]. mm, wavelength mm.

9. The corrugated wall airfoil as described in claim 8, characterized in that, The corrugated structure is a recessed sinusoidal corrugated structure, and the peak of its sinusoidal wave is tangent to the upper surface of the airfoil.

10. The corrugated wall airfoil as described in claim 6, characterized in that, The corrugated wall surface is formed by laser processing or precision milling.

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