Airfoil profile structure for improving large-attack-angle NACA0012 airfoil profile performance through suction surface traveling wave type oscillation

Abstract

According to the airfoil structure for improving the performance of the large-attack-angle NACA0012 airfoil through suction surface traveling wave type oscillation, when the included angle between the airfoil and incoming flow is larger than or equal to 15 degrees, the suction surface of the airfoil is a traveling wave type suction surface, and by arranging alternate wave crests and wave troughs on the suction surface, an air boundary layer is changed into turbulent flow from laminar flow in advance, so that the performance of the large-attack-angle NACA0012 airfoil is improved, and the performance of the large-attack-angle NACA0012 airfoil is improved. Therefore, separation of a fluid boundary layer is delayed, and the aerodynamic performance of the airfoil is improved. And the amplitude of the traveling wave type suction surface is firstly increased and then decreased in the direction from the front edge of the airfoil profile to the tail edge of the airfoil profile. Continuous energy is provided for the boundary layer through traveling wave type oscillation, and separation of the boundary layer at the large attack angle is effectively restrained.

Description

Technical Field

[0001] This invention relates to the field of airfoil or aircraft technology, specifically to an airfoil structure that improves the performance of the NACA0012 airfoil by suction surface traveling wave oscillation. Background Technology

[0002] As the angle of attack of the NACA0012 airfoil gradually increases, lift and drag also gradually increase. However, when the angle of attack exceeds the critical angle of attack, lift begins to decrease sharply and drag begins to increase sharply, leading to airfoil stall. This is because at smaller angles of attack, the boundary layer of the airfoil's suction surface does not separate, or if it does, it is only temporary. However, at large angles of attack, due to the adverse pressure gradient, the boundary layer of the airfoil's suction surface separates near the leading edge, forming a large separation zone covering most of the upper surface of the airfoil, filled with low-speed or even swirling flow. The lift of the airfoil mainly relies on the pressure difference between the suction and pressure surfaces. At large angles of attack, the separation zone of the airfoil is filled with separation vortices, which significantly reduces the kinetic energy and increases the pressure dramatically. Although the force on the pressure surface increases, the pressure difference between the suction and pressure surfaces decreases, resulting in a sharp drop in airfoil lift. Drag primarily originates from pressure drag and friction drag. At high angles of attack, airfoils experience increased pressure drag due to boundary layer separation, and the friction drag in the larger separation zone also increases. Both pressure drag and friction drag increase, resulting in increased drag on the airfoil. The decrease in lift and increase in drag lead to a decline in airfoil performance; therefore, a better method is needed to improve the aerodynamic performance of the NACA0012 airfoil at higher angles of attack.

[0003] Currently, methods for improving airfoil performance at higher angles of attack can be broadly categorized into two types: passive methods and active control methods. Passive control methods do not require external energy input, but their effectiveness is limited. Active control methods, on the other hand, require external energy input, such as jet technology or blow-in-draw methods, which actively provide energy to the boundary layer airflow, suppressing boundary layer separation and thus improving airfoil aerodynamic performance. In addition to standalone active and passive methods, there are also combined active and passive methods.

[0004] In recent years, an active control method has been proposed to apply sinusoidal oscillations to the suction surface of an airfoil to provide external energy to improve its aerodynamic performance. However, this method has limited impact on the aerodynamic performance of the NACA0012 airfoil with a large angle of attack. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an airfoil structure that enhances the performance of the NACA0012 airfoil at high angles of attack by using a traveling wave oscillation on the suction surface. By setting alternating crests and troughs on the suction surface, the air boundary layer transitions from laminar to turbulent flow earlier, thereby delaying the separation of the fluid boundary layer and improving the aerodynamic performance of the airfoil.

[0006] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0007] An airfoil structure for improving the performance of the NACA0012 airfoil at high angle of attack by using a traveling wave oscillation on the suction surface, wherein when the angle between the airfoil and the incoming flow is greater than or equal to 15°, the suction surface of the airfoil is a traveling wave suction surface. By setting alternating crests and troughs on the suction surface, the air boundary layer is made to change from laminar flow to turbulent flow in advance, thereby delaying the separation of the fluid boundary layer and improving the aerodynamic performance of the airfoil.

[0008] Furthermore, the traveling wave position of the suction surface is located at the leading edge of the airfoil to 2 / 3 of the chord length.

[0009] Furthermore, the amplitude of the traveling wave varies at different chord lengths of the suction surface.

[0010] Furthermore, the amplitude of the traveling wave suction surface first increases and then decreases along the direction from the leading edge of the airfoil to the trailing edge.

[0011] Furthermore, let the origin O of the coordinate system be fixed at the leading edge of the airfoil, the x-axis point along the chord to the trailing edge, and the y-axis be perpendicular to the x-axis. Let the amplitude of the traveling wave suction surface change along the y-axis. :

[0012] ,

[0013] In the formula:

[0014] A indicates the set amplitude;

[0015] Represents the dimensionless x-coordinate;

[0016] Indicates angular velocity;

[0017] t represents time;

[0018] c represents the airfoil chord length;

[0019] Used to simulate wave propagation, the phase changes linearly along the chord direction.

[0020] Furthermore, the dimensionless x-coordinate The formula for expressing this is as follows:

[0021] ,

[0022] In the formula, The chord length position is set to ensure uniform oscillation distribution. =0.2c.

[0023] further, The expression is as follows:

[0024] ,

[0025] In the formula: Indicates wavelength.

[0026] An aircraft equipped with an airfoil structure that enhances the performance of the NACA0012 airfoil at high angles of attack by oscillating suction surface.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. The airfoil structure of the present invention, which improves the performance of the NACA0012 airfoil at high angles of attack by using traveling-wave oscillation on the suction surface, causes the air boundary layer to transition from laminar to turbulent flow earlier by setting alternating crests and troughs on the suction surface, thereby delaying the separation of the fluid boundary layer and improving the aerodynamic performance of the airfoil. The traveling-wave oscillation provides continuous energy to the boundary layer, effectively suppressing boundary layer separation at high angles of attack.

[0029] 2. The airfoil structure of the present invention, which improves the performance of the NACA0012 airfoil at large angles of attack by suction surface traveling wave oscillation, can significantly improve the lift coefficient and lift-to-drag ratio at angles of attack of 15° and 20°; moreover, the structure is simple and easy to implement in flow control systems. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are some embodiments of the present invention. For those skilled in the art, it is obvious that other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a comparison diagram of the airfoil structure described in this invention and the airfoil structure in the prior art.

[0032] Figure 2 This is a schematic diagram illustrating the deformation law of the suction surface described in this invention.

[0033] Figure 3 This is a comparison chart of the pressure coefficients of existing airfoils and traveling wave oscillating airfoils when the NACA0012 airfoil has an angle of attack of 15°.

[0034] Figure 4 This is a comparison chart of the pressure coefficients of existing airfoils and traveling wave oscillating airfoils when the NACA0012 airfoil has an angle of attack of 20°.

[0035] Figure 5The image shows a comparison of velocity cloud diagrams of the existing airfoil and the traveling wave oscillating airfoil when the angle of attack of the NACA0012 airfoil is 15°. In the image, a is the existing airfoil and b is the traveling wave oscillating airfoil.

[0036] Figure 6 The image shows a comparison of velocity cloud diagrams of the existing airfoil and the traveling wave oscillating airfoil when the angle of attack of the NACA0012 airfoil is 20°. In the image, a is the existing airfoil and b is the traveling wave oscillating airfoil.

[0037] In the picture:

[0038] 1-Original airfoil suction surface; 2-Pressure surface; 3-Traveling wave oscillating suction surface. Detailed Implementation

[0039] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0040] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "axial," "radial," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the 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, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0041] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] The existing NACA0012 airfoil, such as Figure 1As shown in the figure, the existing NACA0012 airfoil includes a suction surface and a pressure surface 2. To distinguish the existing airfoil's suction surface, it is represented by the original airfoil suction surface 1. The original airfoil suction surface 1 is streamlined. At high angles of attack (the angle between the airfoil and the incoming flow is greater than or equal to 15°), the airflow is prone to boundary layer separation at the leading edge of the suction surface due to the adverse pressure gradient, forming a large area of ​​low-speed separation zone, resulting in a sharp drop in lift and a surge in drag, i.e., stall phenomenon. To suppress separation, existing active control methods such as constant-frequency jet, blow-in-draw, or local sinusoidal oscillation can inject energy into the boundary layer, but their effective range is limited, the energy distribution is uneven or lacks continuity, and it is difficult to effectively control the large-scale separation vortex structure at high angles of attack. Therefore, the improvement effect on aerodynamic performance is limited.

[0043] Therefore, as Figure 1 As shown, the airfoil structure of the present invention, which improves the performance of the NACA0012 airfoil by traveling wave oscillation of suction surface, when the angle between the airfoil and the incoming flow is greater than or equal to 15°, is a traveling wave oscillating suction surface 3 on the suction surface. By setting alternating peaks and troughs on the suction surface, the air boundary layer is made to change from laminar flow to turbulent flow in advance, thereby delaying the separation of the fluid boundary layer and improving the aerodynamic performance of the airfoil.

[0044] like Figure 1 As shown, the amplitude of the traveling wave at different chord length positions of the suction surface is different. The amplitude of the traveling wave suction surface first increases and then decreases along the direction from the leading edge to the trailing edge of the airfoil. The traveling wave position of the suction surface is from the leading edge of the airfoil to 2 / 3 of the chord length.

[0045] Assume the origin O of the coordinate system is fixed at the leading edge of the airfoil, the x-axis points along the chord to the trailing edge, and the y-axis is perpendicular to the x-axis. The amplitude of the traveling wave suction surface varies along the y-axis. :

[0046] ,

[0047] In the formula:

[0048] A indicates the set amplitude;

[0049] Represents the dimensionless x-coordinate;

[0050] Indicates angular velocity;

[0051] t represents time;

[0052] c represents the airfoil chord length;

[0053] Used to simulate wave propagation, the phase changes linearly along the chord direction.

[0054] dimensionless x-coordinate The formula for expressing this is as follows:

[0055] ,

[0056] In the formula, The chord length position is set to ensure uniform oscillation distribution. =0.2c.

[0057] The expression is as follows:

[0058] ,

[0059] In the formula: Indicates wavelength.

[0060] like Figure 1 and Figure 2 As shown, the deformation function of the suction surface of the NACA0012 airfoil uses a traveling wave function, which represents a sinusoidal wave propagating along the chord length. The wave propagates at a velocity v = ƒλ, and the direction of propagation depends on the sign of the phase term. Here, we use a negative sign to indicate that the wave propagates in the positive x-direction, i.e., from the leading edge to the trailing edge. Considering that airfoils typically have a thickness distribution, a phase shift function is introduced during propagation. This ensures that the wave changes uniformly along the airfoil's suction surface. When the flow begins, the suction surface of the NACA0012 airfoil begins to deform in a traveling wave pattern. With time and along the chord of the airfoil, the peak value and position of the wave attached to the suction surface continuously change simultaneously, providing continuous external energy to the boundary layer fluid at the suction surface to effectively suppress boundary layer separation. 1-Original airfoil suction surface; 2-Pressure surface; 3-Traveling wave oscillating suction surface.

[0061] Numerical simulations were performed on a traveling wave oscillating airfoil with a traveling suction surface to verify the effectiveness of the proposed method. The calculation results of the original airfoil suction surface 1 and the traveling wave oscillating suction surface 3 of this invention were compared at different angles. In the numerical simulation, the Re of the incoming gas was 30000, and the airfoil chord length was c = 0.15 m. The deformation position of the traveling wave oscillating airfoil suction surface was from the beginning of the airfoil leading edge to the position corresponding to 2c / 3 of the chord length. The oscillation function had ω = 94.25 rad / s and λ = c / 15. =0.2c. For example... Figure 2 As shown, the function changes when the amplitude of deformation A = 0.004c.

[0062] This invention verifies the oscillation of the NACA0012 airfoil at angles of attack of 15° and 20° when the amplitude A = 0.004c. The numerical simulation results were used to calculate 30 convergence periods, followed by the calculation of the average lift and drag coefficients and the average lift-to-drag ratio. Table 1 shows the average lift coefficient C when the airfoil's angle of attack is 15° and 20°. L The table shows a comparison, revealing that the traveling wave oscillating airfoil exhibits a significant increase in lift coefficient compared to the original airfoil, despite a decrease in the average drag coefficient C. D There has also been an increase, but the average lift-to-drag ratio C in the chart... L / C D The comparison chart shows a significant improvement in lift-to-drag ratio. Therefore, the numerical simulation results demonstrate that this method can effectively improve the aerodynamic performance of the NACA0012 airfoil at angles of attack of 15° and 20°.

[0063] In addition, Table 1 also compares sinusoidal suction surface airfoils with constant amplitude. As shown in Table 1, when the angle of attack of the airfoil is 15°, the sinusoidal oscillation of the suction surface of the airfoil will reduce the average lift coefficient and lift-drag ratio of the airfoil, and has limited effect on improving the aerodynamic performance of the airfoil.

[0064] Table 1

[0065] case <![CDATA[Average lift coefficient C L > <![CDATA[Average drag coefficient C D > <![CDATA[Average lift-to-drag ratio C L / C D > 15° sinusoidal airfoil (constant amplitude) 0.82896 0.27755 2.98674 15° traveling wave oscillating airfoil 0.96658 0.30452 3.17409 15° original airfoil 0.83974 0.28039 2.99494 20° traveling wave oscillating airfoil 1.12236 0.47467 2.36453 20° original airfoil 0.84526 0.36783 2.29795

[0066] Figure 3 This shows a comparison of the pressure coefficients of the original airfoil and the traveling wave oscillating airfoil when the angle of attack of the NACA0012 airfoil is 15°. Compared with the original airfoil, the pressure on the pressure surface of the traveling wave oscillating airfoil is significantly increased, and the force on the suction surface is much smaller in most parts than on the suction surface of the original airfoil. Therefore, the lift of the traveling wave oscillating airfoil is significantly increased compared with the original airfoil. Figure 4 This chart compares the pressure coefficients of the original airfoil and the traveling-wave oscillating airfoil when the NACA0012 airfoil has an angle of attack of 20°. The chart shows that the pressure coefficients of both airfoils are essentially the same at the pressure surface corresponding to the chord length of 0.4c from the leading edge. However, the pressure coefficients decrease at other locations on the pressure surface. Looking at the suction surface, the traveling-wave oscillating airfoil experiences less force in most areas compared to the original airfoil. Although, as mentioned above, the pressure decreases at the pressure surface corresponding to the chord length from 0.4c to the trailing edge, the decrease in force on the corresponding suction surface is even greater. Therefore, overall, the traveling-wave oscillating airfoil provides a significant increase in lift compared to the original airfoil.

[0067] Figure 5The velocity cloud diagrams of the NACA0012 airfoil at an angle of attack of 15° are shown in comparison. As can be seen from the diagrams, compared with airfoils of existing structures, the vortex variation of the traveling wave oscillating suction surface 3 of this invention is significant. The variation of the vortex leads to an increase in the kinetic energy of the fluid near the wall of the suction surface and a decrease in pressure, while at the same time, it increases the pressure on the pressure surface. Figure 6 The velocity cloud diagrams are compared at an angle of attack of 20°. Similar to the case at 15°, the number, shape, structure, and size of the three vortices in the traveling wave oscillation suction surface change at 20°.

[0068] This invention achieves the goal of improving the aerodynamic performance of the NACA0012 airfoil at a large angle of attack by applying reasonable traveling wave oscillations to the upper surface (suction surface) of the NACA0012 airfoil.

[0069] An aircraft equipped with an airfoil structure that enhances the performance of the NACA0012 airfoil at high angles of attack by oscillating suction surface.

[0070] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0071] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A wing profile structure for improving the performance of a high angle of attack NACA0012 airfoil by a suction surface traveling wave oscillation, characterized by, When the angle between the airfoil and the incoming flow is greater than or equal to 15°, the suction surface of the airfoil is a traveling wave oscillating suction surface. By setting alternating peaks and troughs on the suction surface, the air boundary layer changes from laminar flow to turbulent flow in advance, thereby delaying the separation of the fluid boundary layer and improving the aerodynamic performance of the airfoil.

2. The airfoil structure for high angle of attack NACA0012 airfoil performance improvement of the suction surface traveling wave oscillation lift according to claim 1, characterized by, The traveling wave position of the suction surface is located from the leading edge of the airfoil to 2 / 3 of the chord length.

3. The airfoil structure for high angle of attack NACA0012 airfoil performance improvement of the suction surface traveling wave oscillation lift according to claim 1, characterized by, The amplitude of the traveling wave varies at different chord lengths of the suction surface.

4. The airfoil structure for high angle of attack NACA0012 airfoil performance improvement of the suction surface traveling wave oscillation lift according to claim 3, characterized by, The amplitude of the traveling wave oscillating suction surface first increases and then decreases along the direction from the leading edge of the airfoil to the trailing edge.

5. The airfoil structure for improving the performance of the NACA0012 airfoil at high angles of attack through suction-surface traveling-wave oscillation as described in claim 4, characterized in that, The origin O of the coordinate system is fixed at the leading edge of the airfoil, the x-axis points to the trailing edge along the chord, and the y-axis is perpendicular to the x-axis : ， In the formula: A indicates the set amplitude; dimensionless x coordinate; denotes the angular velocity; t represents time; c represents the airfoil chord length; Used to simulate wave propagation, the phase changes linearly along the chord direction.

6. The airfoil structure for improving the performance of the NACA0012 airfoil at high angles of attack through suction-surface traveling-wave oscillation as described in claim 5, characterized in that, dimensionless x-coordinate The formula for expressing this is as follows: ， In the formula, The chord length position is set to ensure uniform oscillation distribution. =0.2c.

7. The airfoil structure for improving the performance of the NACA0012 airfoil at high angles of attack by suction-surface traveling-wave oscillation as described in claim 5, characterized in that, The expression is as follows: ， In the formula: Indicates wavelength.

8. An aircraft, characterized in that, The aircraft is equipped with an airfoil structure according to any one of claims 1-7, which uses a suction surface traveling wave oscillation to enhance the performance of the NACA0012 airfoil at high angles of attack.

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