High-efficiency low-noise bionic propeller for unmanned aerial vehicle

Abstract

The utility model belongs to the propeller manufacturing field for unmanned aerial vehicle, the utility model is composed of hub, left propeller blade and right propeller blade, left propeller blade is composed of blade I and tip wing tip bionic structure II, tip wing tip bionic structure II is composed of 1, 2, 3 three small wings, right propeller blade is same with left propeller blade structure, blade I airfoil curve is obtained by long owl wing airfoil curve fitting, can produce greater lift-drag ratio, improve the efficiency of blade, tip wing tip bionic structure II imitates the wing tip structure of long owl gliding, three small wings length and upturned height increase gradually, effectively reduce the induced drag of propeller blade rotation flight, the large eddy current of wing tip in flow field is weakened to small eddy current, inhibit the aerodynamic noise of vortex flow separation, further improve the flight efficiency and reduce noise.

Description

Technical Field

[0001] This invention belongs to the field of drone propeller manufacturing, specifically relating to a high-efficiency, low-noise biomimetic propeller. Background Technology

[0002] In recent decades, with the gradual maturation of drone research and development technology and the significant reduction in manufacturing costs, drones have been widely used in many fields. However, the high aerodynamic noise and short flight time of drones remain major problems that urgently need to be solved, severely limiting their application in both civilian and military fields. In the civilian sector, drones do not yet meet the noise standards for mixed residential and commercial areas, causing serious disturbance to residents during operation; in the military sector, high noise significantly reduces their stealth performance and weakens their battlefield survivability. The drone propeller is a key component affecting its aerodynamic noise and flight time. Reducing its aerodynamic noise during rotation and improving its aerodynamic performance are important ways to enhance the acoustic performance and flight time of drones.

[0003] The long-eared owl possesses excellent flight capabilities. Its wings ensure sufficient lift and suppress flow separation during gliding; even at high speeds, its noise level is low enough to go unnoticed by prey. Research has found that this is closely related to its wing structure. The long-eared owl's wing airfoil is a low-drag airfoil with a smooth surface and relatively large wingspan, resulting in a high lift-to-drag ratio. Furthermore, the long-eared owl's wingtips exhibit a backward-upward curve, a wingtip structure that reduces vortex losses at the wingtips, lowers induced drag, and further improves flight efficiency and reduces noise.

[0004] In summary, based on the wing characteristics of the long-eared owl, this invention proposes a high-efficiency, low-noise biomimetic propeller for UAVs, which effectively solves the problems of high noise and low efficiency during UAV flight. Summary of the Invention

[0005] The purpose of this invention is to provide a high-efficiency, low-noise biomimetic propeller for unmanned aerial vehicles based on the wing features of a long-eared owl. The propeller uses the long-eared owl's biomimetic airfoil as the blade airfoil curve, and at the same time, it designs an upward-curving wingtip biomimetic structure based on the wingtip structure features of the long-eared owl, thereby improving the propeller's efficiency and noise reduction performance.

[0006] The invention consists of a hub (A), a left propeller blade (B), and a right propeller blade (C). The left propeller blade (B) is composed of blade I and a blade tip wingtip biomimetic structure II. The blade tip wingtip biomimetic structure II is composed of three small winglets, 1, 2, and 3. The right propeller blade (C) has the same structure as the left propeller blade (B).

[0007] The airfoil curve of blade I is obtained by fitting the airfoil curve of the long-eared owl. The airfoil section is evenly arranged at 5 locations along the span of blade I. The airfoil width distribution and deflection angle at different locations are arranged according to the classic distribution of propeller blades.

[0008] The aforementioned blade tip wingtip biomimetic structure II is modeled after the wingtip structure of the long-eared owl during gliding. It has three small wing structures, whose length increases sequentially along the direction of the incoming flow, and whose upward tilt increases sequentially along the direction perpendicular to the plane of blade rotation. The shape of each small wing structure is controlled by four guide lines: front, rear, top, and bottom.

[0009] The beneficial effects of this invention are as follows:

[0010] 1. Using the airfoil of a long-eared owl as the vertical section of the propeller blade effectively improves the propeller's efficiency.

[0011] 2. A biomimetic wingtip structure with upturned tips was designed, inspired by the wingtip structure of the long-eared owl, to further improve propeller efficiency and reduce aerodynamic noise. Attached Figure Description

[0012] Figure 1 Axonometric view of a drone propeller

[0013] Figure 2 Schematic diagram of airfoil section parameters

[0014] Figure 3 Front view of the biomimetic structure of the tip and wingtip of a drone propeller.

[0015] Figure 4 Axonometric view of the biomimetic structure of the tip and wingtip of a drone propeller.

[0016] Where: A. Hub, B. Left propeller blade, C. Right propeller blade, I. Blade, II. Bionic structure of blade tip and wingtip, 1, 2, and 3 are all winglets; x is the chord direction, y is the direction perpendicular to the airfoil surface, c is the airfoil chord, Z (c)max For the maximum curvature, Z (t)max s1 is the maximum thickness; h1 is the length of the first winglet, h2 is the upturn height of the first winglet, s2 is the length of the second winglet, h2 is the upturn height of the second winglet, s3 is the length of the third winglet, h3 is the upturn height of the third winglet; L 1前 For the first winglet leading curve, L 1后 For the first winglet aft guide curve, L 1上 For the first guide curve on the winglet, L 1下 For the first winglet guide curve; L 2前 For the second winglet leading curve, L 2后 For the second winglet aft guide curve, L 2上For the guide curve on the second winglet, L 2下 For the second winglet guide curve; L 3前 For the third winglet leading curve, L 3后 For the third winglet aft guide curve, L 3上 For the third winglet guide curve, L 3下 This is the guide curve for the third winglet. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings:

[0018] like Figure 1 As shown, the present invention consists of a hub (A), a left propeller blade (B) and a right propeller blade (C). The left propeller blade (B) is composed of blade I and a wingtip biomimetic structure II. The wingtip biomimetic structure II is composed of three small winglets, 1, 2 and 3. The right propeller blade (C) has the same structure as the left propeller blade (B).

[0019] The airfoil curve of blade I is obtained by fitting the airfoil curve of a long-eared owl's wing. Five airfoil sections are evenly distributed along the span of blade I. The airfoil width distribution and deflection angle at different positions are arranged according to the classic propeller blade distribution. The airfoil sections are as follows... Figure 2 As shown, the steps to obtain it are as follows:

[0020] (1) Obtain point cloud data of the wings of the long-eared owl and import it into the 3D modeling software.

[0021] (2) Establish a plane perpendicular to the wing span, distributed along the span at 10% half-wing spans from the wing root to the wing tip, for a total of 11 airfoil sections. Based on the selected airfoil sections, use the point plotting method to obtain the coordinates of points at 3% chord lengths of the upper and lower arcs, and at the same time obtain the coordinates of the mid-arc line and thickness at 3% chord length of each airfoil.

[0022] (3) Figure 2 As shown, with the chord direction as the x-axis and the vertical airfoil surface as the y-axis, curve equations are fitted to the coordinates of the mid-curve point and the thickness coordinates. The fitting function used is the Birnbaum-Glauert function. The mathematical formulas for the distribution of the mid-curve and thickness along the chord direction are as follows:

[0023]

[0024]

[0025] Among them, z (c) Let z be the ordinate of the point on the middle arc. (t) Let x be the ordinate of the thickness line point, c be the chord length, η = x / c be the ratio of the chord coordinates, and S be the ordinate of the thickness line point. n and A nThese are undetermined coefficients. The undetermined coefficients for each spanwise section of the airfoil are obtained through fitting, thereby determining the thickness and mid-curve equations for each spanwise airfoil. Based on the relationship between the airfoil thickness, mid-curve, and upper and lower curvatures, the equations for the upper and lower surface curvatures are obtained. The relationship equations are as follows:

[0026] z (u) =z (c) +z (t) (3)

[0027] z (l) =z (c) -z (t) (4)

[0028] Among them, z (u) and z (l) These are the coordinates of the upper and lower arcs of the airfoil, respectively.

[0029] (4) Based on the obtained fitted airfoil shapes, considering that the airfoil tips are mostly composed of feathers and are relatively thin, they are not very meaningful for reference in the hydrodynamic analysis of airfoils. Therefore, five groups of airfoils with relatively obvious profiles with spanwise 20%, 30%, 40%, 50%, and 60% were selected for aerodynamic performance analysis. For each group of airfoils, the lift coefficient, drag coefficient, and lift-drag ratio were analyzed under different angles of attack (-6°, -3°, 0°, 3°, 6°, 9°, 12°) and different incoming flow velocities (10m / s, 25m / s, 50m / s), and the aerodynamic performance of airfoils with different spanwise directions was compared.

[0030] Based on the analysis results, the airfoil with the optimal aerodynamic performance (here, the airfoil at 60% spanwise section) was selected as the base airfoil for the design of blade I. The blade radius R is 200mm, and a 60% airfoil curve is set every 40mm. The blade is scaled according to the typical width distribution c / R (the ratio of airfoil chord length to propeller blade radius), with c / R ratios of 0.14, 0.16, 0.15, 0.12, and 0.17. The blade is deflected according to the typical blade angle distribution (the angle between the airfoil chord line and the propeller blade rotation plane), with angles of 30°, 21°, 16°, 12°, and 10°. The propeller blade is formed by multi-section curved surfaces, completing the main body design. Compared to ordinary blades, the biomimetic blades designed based on the 60% spanwise section airfoil of the long-eared owl have a greater camber, resulting in a greater difference in flow velocity and pressure between the upper and lower surfaces. This leads to increased lift and a higher lift-to-drag ratio, achieving the goal of drag reduction and efficiency improvement.

[0031] (5) Figure 3As shown, the biomimetic structure II of the blade tip has three winglets, whose lengths increase sequentially along the direction of the incoming flow, and whose upward tilt increases sequentially along the direction perpendicular to the blade's plane of rotation. The shape of each winglet is controlled by four guide lines: front, rear, upper, and lower. Taking the airfoil section at 200mm as the yoz plane, the leading edge endpoint of the airfoil as the origin, and the xoz plane passing through the origin and perpendicular to this plane, the positive X direction is along the radial direction, the positive Y direction is along the direction of the incoming flow, and the positive Z direction is along the direction perpendicular to the xoy plane and forming an acute angle with the upper arc of the airfoil. The lengths of the three winglets are determined as s1, s2, and s3, and the upward tilts are determined as h1, h2, and h3 (the winglet length is the difference in X coordinates between the intersection of the four guide lines and the origin o; in this example, the values ​​are 14mm, 17mm, and 20mm respectively; the upward tilt is the difference in Z coordinates between the intersection of the four guide lines and the origin o; in this example, the values ​​are 2mm, 4mm, and 6mm respectively). Figure 4 As shown, the leading curves of the three winglets (forward, backward, upward, and downward) are fitted, and their expressions are as follows:

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044] The fitted guide line function is imported into the modeling software. Rounding is applied to the intersection points of the guide lines, with the rounded radius not exceeding half the length of the small wing. The final result is as follows: Figure 1The biomimetic propeller shown is based on the wingtip biomimetic structure of a long-eared owl. The different lengths and upward tilts ensure that the winglets are staggered, guiding the airflow segmentation at the wingtip and reducing aerodynamic noise. At the same time, the upward tilting design of the wingtip biomimetic structure can increase the overall lift-to-drag ratio of the propeller, reduce induced drag, reduce the influence of wingtip vortices, and further improve the efficiency of the propeller.

[0045] Aerodynamic analysis revealed that, compared to conventional airfoils, the biomimetic airfoil proposed in this patent has a 3% higher lift-to-drag ratio and a 2.5-3.5 dB lower noise level, effectively improving both the aerodynamic and acoustic performance of the propeller.

Claims

1. A high efficiency low noise bionic propeller for drones, consisting of a hub (A), a left propeller blade (B) and a right propeller blade (C), characterized in that The left propeller blade (B) consists of a blade (I) and a tip wingtip biomimetic structure (II). The tip wingtip biomimetic structure (II) consists of three small wings (1, 2, 3). The right propeller blade (C) has the same structure as the left propeller blade (B). The small wings (1, 2, 3) are formed by stretching the initial stretch section along four guide lines (front, rear, top, and bottom). The upper and lower arcs of the initial stretch section completely coincide with the airfoil section of the blade (I), and the overall outline is approximately elliptical.

2. The high-efficiency, low-noise biomimetic propeller for UAVs according to claim 1, characterized in that... The airfoil curve of the blade (I) is obtained by fitting the airfoil curve of the long-eared owl. The airfoil section is evenly arranged at 5 locations along the span of the blade (I). The airfoil width distribution and deflection angle at different locations are arranged according to the classic distribution of propeller blades.

3. The high-efficiency, low-noise biomimetic propeller for UAVs according to claim 1, characterized in that... The aforementioned blade tip wingtip biomimetic structure (II) is modeled after the wingtip structure of the long-eared owl during gliding. It has three small wings (1, 2, 3), whose length increases sequentially along the direction of the incoming flow, and whose height increases sequentially along the direction perpendicular to the plane of rotation of the blade (I).

Images