A method for generating thin arc-shaped rotor airfoil suitable for low Reynolds number flow fields

Abstract

The present application belongs to the field of aircraft rotor technology, and specifically relates to a method for generating a thin arc-type rotor airfoil suitable for low Reynolds number flow fields, wherein the thin arc-type rotor airfoil comprises: an upper arc line and a lower arc line; the upper arc line comprises an upper arc line leading edge segment, an upper arc line circular segment, an upper arc line transition segment, and an upper arc line trailing edge segment; the lower arc line comprises a lower arc line leading edge segment, a lower arc line circular segment, and a lower arc line trailing edge segment; the generation method comprises the following steps: one: drawing a reference arc to obtain upper and lower main arcs; two: drawing the trailing edge segment of the lower arc line of the airfoil; three: drawing the trailing edge segment of the upper arc line of the airfoil; and four: obtaining the leading edge segment of the upper arc line and the leading edge segment of the lower arc line of the airfoil. The present application solves the problem of the existing low Reynolds number thin arc-type airfoil having an unsmooth shape, can meet the requirements of high lift and good stall characteristics of the rotor airfoil, and significantly increases the lift coefficient and lift-to-drag ratio in a low Reynolds number environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of wing shape design, and in particular relates to a low Reynolds number thin arc rotor airfoil and a generation method thereof. Background Art

[0002] In recent years, micro-rotor aircraft have been widely used in both civil and military fields. Due to their small size and low flight speed, the flight Reynolds number of micro-rotor aircraft is usually around 10 4 -10 5 This is a low-Reynolds-number aircraft. In low-Reynolds-number flow fields, the viscous effects of air are more pronounced, and the flow field structure exhibits characteristics different from those at conventional Reynolds numbers, including laminar separation and separation-induced transition. Low-Reynolds-number effects can have many adverse effects on aerodynamic characteristics, primarily manifesting as a reduced lift-to-drag ratio, lower aerodynamic efficiency, and reduced stability.

[0003] The airfoil is a crucial design parameter that influences a rotor's aerodynamic characteristics. Considering the characteristics of low-Reynolds-number flow fields during airfoil design can effectively improve aerodynamic performance. Currently, the design of these rotors rarely considers the airfoil's operating characteristics in low-Reynolds-number environments. Existing low-Reynolds-number thin arc airfoils suffer from unclear definition and a choppy appearance. Summary of the Invention

[0004] The main purpose of this application is to improve the lift coefficient and lift-to-drag ratio of the airfoil in a low Reynolds number environment, and to provide a well-defined thin arc-type rotor airfoil and a generation method suitable for a low Reynolds number environment.

[0005] The technical solution adopted in this application:

[0006] A method for generating a thin circular arc rotor airfoil suitable for a low Reynolds number flow field, the thin circular arc rotor airfoil comprising: an upper camber line and a lower camber line; the upper camber line comprising an upper camber line leading edge segment, an upper camber line circular arc segment, an upper camber line transition segment, and an upper camber line trailing edge segment; the lower camber line comprising a lower camber line leading edge segment, a lower camber line circular arc segment, and a lower camber line trailing edge segment;

[0007] The leading edge segment of the upper camber line and the leading edge segment of the lower camber line are tangent to the leading edge point of the airfoil to form the leading edge of the airfoil; the trailing edge segment of the upper camber line and the trailing edge segment of the lower camber line intersect at the trailing edge point of the airfoil; a reference arc is formed between the leading edge point and the trailing edge point of the airfoil, and the distance from the farthest end of the reference arc to the chord line of the airfoil is d; the distance between the farthest point of the upper camber line segment and the farthest point of the lower camber line segment from the chord line of the airfoil is t; except for the trailing edge segment of the upper camber line and the trailing edge segment of the lower camber line intersecting at the trailing edge point of the airfoil, the other segments of the airfoil are tangent; the chord length of the airfoil is c, the relative camber of the airfoil is d / c, and the relative thickness of the airfoil is t / c;

[0008] The generation method includes the following steps:

[0009] Step 1: Draw an arc through the leading edge point and the trailing edge point of the airfoil with a distance d from the farthest end to the airfoil chord as the reference arc. Shift the reference arc upward and downward by a distance of 0.5t to obtain the upper main arc and the lower main arc.

[0010] Step 2: Draw a straight line through the trailing edge point of the airfoil that is tangent to the lower main body arc at the first tangent point. The line segment from the first tangent point to the trailing edge point of the airfoil is the trailing edge segment of the lower arc line of the airfoil;

[0011] Step 3: Draw a straight line perpendicular to the airfoil chord through the first tangent point, intersecting the upper main arc at a point, connecting the point with the trailing edge point to obtain a straight line segment, and draw a transition arc with a radius of c that is tangent to both the upper main arc and the straight line segment. The transition arc is tangent to the upper main arc at the second tangent point, and the transition arc is tangent to the straight line segment at the third tangent point. The arc segment between the second and third tangent points is the upper camber transition segment of the airfoil, and the straight line segment between the third tangent point and the trailing edge point of the airfoil is the upper camber trailing edge segment of the airfoil;

[0012] Step 4: Draw two ellipses with their centers on the airfoil chord line and tangent to the leading edge point, one of the ellipses is tangent to the upper main arc at the fourth tangent point, the projection of the fourth tangent point on the reference arc in step 1 is 1.8t away from the leading edge point of the airfoil, the elliptical arc between the leading edge point of the airfoil and the fourth tangent point is the leading edge segment of the upper camber line of the airfoil, the other ellipse is tangent to the lower main arc at the fifth tangent point, the projection of the fifth tangent point on the reference arc in step 1 is t away from the leading edge point of the airfoil, the elliptical arc between the leading edge point of the airfoil and the fifth tangent point is the leading edge segment of the lower camber line of the airfoil; the upper camber line segment is between the fourth tangent point and the second tangent point, and the upper camber line segment is on the upper main arc; the lower camber line segment is between the first tangent point and the fifth tangent point, and the lower camber line segment is on the lower main arc; at this point, a thin arc-type rotor airfoil with a relative curvature of d / c and a relative thickness of t / c is generated.

[0013] Furthermore, the working Mach number range of the airfoil is 0.0-0.6, and the working Reynolds number range of the airfoil is 10 4 -10 5 .

[0014] This application has the following beneficial effects:

[0015] Before the airfoil stalls, the lift coefficient increases with increasing angle of attack and remains above 1 above 7°. The lift line exhibits a distinct linear region, and the stall angle of attack is greater than 10°, meeting the requirements for high lift and good stall characteristics for the rotor airfoil. As the Reynolds number increases, the drag coefficient decreases at the same angle of attack. As the Reynolds number increases, the lift-to-drag ratio increases significantly at the same angle of attack, and the maximum lift-to-drag ratio also increases significantly. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the overall structure of the low Reynolds number thin arc rotor airfoil of the present invention;

[0017] Figure 2 Schematic diagram of the method for generating the upper and lower main body arcs of the low Reynolds number thin arc rotor airfoil of the present invention;

[0018] Figure 3 A schematic diagram of the method for generating the trailing edge portion of a low Reynolds number thin arc-shaped rotor airfoil of the invention;

[0019] Figure 4 Schematic diagram of the method for generating the leading edge portion of a low Reynolds number thin arc-shaped rotor airfoil of the present invention;

[0020] Figure 5 This is a curve diagram showing the lift coefficient changing with angle of attack at different Reynolds numbers when the relative camber d / c of ​​the low Reynolds number thin arc rotor airfoil of the present invention is 6% and the relative thickness t / c is 5%;

[0021] Figure 6 This is a graph showing how the drag coefficient changes with the angle of attack at different Reynolds numbers when the relative camber d / c of ​​the low-Reynolds-number thin arc rotor airfoil of the present invention is 6% and the relative thickness t / c is 5%;

[0022] Figure 7 The figure is a curve diagram showing the lift-to-drag ratio variation with angle of attack at different Reynolds numbers when the relative camber d / c of ​​the low-Reynolds-number thin arc rotor airfoil of the present invention is 6% and the relative thickness t / c is 5%.

[0023] In the figure: 1. upper arc leading edge segment, 2. upper arc arc segment, 3. upper arc transition segment, 4. upper arc trailing edge segment, 5. lower arc leading edge segment, 6. lower arc arc segment, 7. lower arc trailing edge segment, 8. airfoil leading edge point, 9. airfoil trailing edge point, 10. reference arc, 11. upper main body arc, 12. lower main body arc, 13. first tangent point, 14. second tangent point, 15. third tangent point, 16. fourth tangent point, 17. fifth tangent point. DETAILED DESCRIPTION

[0024] The present application will be described in detail below with reference to the accompanying drawings, but it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present application. In addition, in the following description, descriptions of common structural and technical knowledge are omitted to avoid unnecessary confusion of the concepts of the present application.

[0025] Example 1: Combining Figure 1-4The present application discloses a method for generating a thin circular arc rotor airfoil suitable for a low Reynolds number flow field, wherein the thin circular arc rotor airfoil comprises: an upper camber line and a lower camber line; the upper camber line comprises an upper camber line leading edge segment 1, an upper camber line circular arc segment 2, an upper camber line transition segment 3, and an upper camber line trailing edge segment 4; the lower camber line comprises a lower camber line leading edge segment 5, a lower camber line circular arc segment 6, and a lower camber line trailing edge segment 7;

[0026] The upper camber leading edge segment 1 and the lower camber leading edge segment 4 are tangent to the airfoil leading edge point 8 to form the airfoil leading edge; the upper camber trailing edge segment 4 and the lower camber trailing edge segment 7 intersect at the airfoil trailing edge point 9; a reference arc 10 is formed between the airfoil leading edge point 8 and the airfoil trailing edge point 9, and the distance between the farthest end of the reference arc 10 and the airfoil chord is d; the distance between the farthest point of the upper camber arc segment from the airfoil chord and the farthest point of the lower camber arc segment from the airfoil chord is t; except for the upper camber trailing edge segment 4 and the lower camber trailing edge segment 7 intersecting at the airfoil trailing edge point, the other segments of the airfoil are tangent; the airfoil chord length is c, the relative camber of the airfoil is d / c, and the relative thickness of the airfoil is t / c;

[0027] The generation method includes the following steps:

[0028] Step 1: Draw an arc through the leading edge point 8 and the trailing edge point 9 of the airfoil with a distance d from the farthest end to the airfoil chord as a reference arc 10. Shift the reference arc 10 upward and downward by a distance of 0.5t to obtain the upper main arc 11 and the lower main arc 12.

[0029] Step 2: Draw a straight line through the airfoil trailing edge point 9 that is tangent to the lower main body arc 12 at the first tangent point 13. The line segment from the first tangent point 13 to the airfoil trailing edge point 9 is the airfoil lower arc trailing edge segment 7.

[0030] Step 3: Draw a straight line perpendicular to the airfoil chord through the first tangent point 13, intersecting the upper main arc 11 at a point, connecting the point with the trailing edge point to obtain a straight line segment, and draw a transition arc with a radius of c that is tangent to the upper main arc 11 and the straight line segment at the same time. The transition arc is tangent to the upper main arc at the second tangent point 14, and the transition arc is tangent to the straight line segment at the third tangent point 15. The arc segment between the second tangent point 14 and the third tangent point 15 is the upper camber transition segment 3 of the airfoil, and the straight line segment between the third tangent point 15 and the trailing edge point 9 is the upper camber trailing edge segment 4 of the airfoil;

[0031] Step 4: Draw two ellipses with their centers on the airfoil chord and tangent to the leading edge point. One of the ellipses is tangent to the upper main arc at the fourth tangent point 16. The projection of the fourth tangent point 16 on the reference arc in step 1 is 1.8t away from the leading edge point 8 of the airfoil. The elliptical arc between the leading edge point 8 of the airfoil and the fourth tangent point 16 is the leading edge segment 1 of the upper arc line of the airfoil. The other ellipse is tangent to the lower main arc at the fifth tangent point 17. The projection of the fifth tangent point 17 on the reference arc in step 1 is 1.8t away from the leading edge point 8 of the airfoil. The distance between the leading edge point 8 of the airfoil is t, and the elliptical arc between the leading edge point 8 and the fifth tangent point 17 is the lower arc leading edge segment 5 of the airfoil; the upper arc segment 2 is between the fourth tangent point 16 and the second tangent point 14, and the upper arc segment 2 is on the upper main body arc 11; the lower arc segment 6 is between the first tangent point 13 and the fifth tangent point 17, and the lower arc segment 6 is on the lower main body arc 12; at this point, the thin arc-type rotor airfoil with a relative curvature of d / c and a relative thickness of t / c is generated.

[0032] Furthermore, the working Mach number range of the airfoil is 0.0-0.6, and the working Reynolds number range of the airfoil is 10 4 -10 5 .

[0033] Furthermore, when the relative camber d / c is 6% and the relative thickness t / c is 5%, the thin arc rotor airfoil has a Reynolds number of 0.2×10 5 -0.8×10 5 The curves of lift coefficient, drag coefficient and lift-to-drag ratio changing with angle of attack within the range are shown in the attached figure. Figure 5-7 As shown;

[0034] Attachment Figure 5 The mid-lift coefficient curve shows that before the airfoil stalls, the lift coefficient increases with increasing angle of attack and is greater than 1 after an angle of attack of 7°. There is a relatively obvious linear region in the lift line, and the stall angle of attack is greater than 10°, meeting the requirements of the rotor airfoil for high lift and good stall characteristics.

[0035] Attachment Figure 6 The middle drag coefficient curve shows that with the increase of Reynolds number, the drag coefficient of the airfoil at the same angle of attack shows a decreasing trend;

[0036] Attachment Figure 7 The medium lift-to-drag ratio curve shows that with the increase of Reynolds number, the lift-to-drag ratio of the airfoil increases significantly at the same angle of attack, and the maximum lift-to-drag ratio also increases significantly.

[0037] The above embodiments are merely illustrative of the principles and effects of the present application and are not intended to limit the present application. Any changes or substitutions within the technical concepts disclosed in the present application and any changes or substitutions based on the technical solutions of the present application shall fall within the scope of protection of the present application.

Claims

1. A method for generating a thin arc-shaped rotor airfoil suitable for low Reynolds number flow fields, characterized by: The thin arc type rotor airfoil comprises: an upper arc line and a lower arc line; the upper arc line comprises an upper arc line leading edge section (1), an upper arc line circular arc section (2), an upper arc line transition section (3), and an upper arc line trailing edge section (4); the lower arc line comprises a lower arc line leading edge section (5), a lower arc line circular arc section (6), and a lower arc line trailing edge section (7); The upper camber leading edge section (1) and the lower camber leading edge section (4) are tangent to the airfoil leading edge point (8) to form the airfoil leading edge; the upper camber trailing edge section (4) and the lower camber trailing edge section (7) intersect at the airfoil trailing edge point (9); a reference arc (10) is formed between the airfoil leading edge point (8) and the airfoil trailing edge point (9), and the distance between the farthest end of the reference arc (10) and the airfoil chord line is d; the distance between the farthest point of the upper camber arc section and the farthest point of the lower camber arc section from the airfoil chord line is t; except for the upper camber trailing edge section (4) and the lower camber trailing edge section (7) intersecting at the airfoil trailing edge point, the other sections of the airfoil are tangent; the airfoil chord length is c, the relative camber of the airfoil is d / c, and the relative thickness of the airfoil is t / c; The generation method includes the following steps: Step 1: Draw an arc with a distance d from the farthest end to the airfoil chord line through the airfoil leading edge point (8) and the airfoil trailing edge point (9) as a reference arc (10), and translate the reference arc (10) upward and downward by a distance of 0.5t respectively to obtain an upper main arc (11) and a lower main arc (12); Step 2: Draw a straight line through the airfoil trailing edge point (9) that is tangent to the lower main body arc (12) at the first tangent point (13). The line segment from the first tangent point (13) to the airfoil trailing edge point (9) is the airfoil lower arc trailing edge segment (7); Step 3: Draw a straight line perpendicular to the airfoil chord through the first tangent point (13), intersecting the upper main arc (11) at a point, connecting the point with the trailing edge point to obtain a straight line segment, and draw a transition arc with a radius of c that is tangent to the upper main arc (11) and the straight line segment at the same time. The transition arc is tangent to the upper main arc at the second tangent point (14), and the transition arc is tangent to the straight line segment at the third tangent point (15). The arc segment between the second tangent point (14) and the third tangent point (15) is the upper arc transition segment (3) of the airfoil, and the straight line segment between the third tangent point (15) and the trailing edge point of the airfoil (9) is the upper arc trailing edge segment (4) of the airfoil. Step 4: Draw two ellipses with their centers on the airfoil chord line and tangent to the leading edge point. One of the ellipses is tangent to the upper main arc at the fourth tangent point (16). The projection of the fourth tangent point (16) on the reference arc in step 1 is 1.8t away from the airfoil leading edge point (8). The elliptical arc between the airfoil leading edge point (8) and the fourth tangent point (16) is the airfoil upper arc leading edge segment (1). The other ellipse is tangent to the lower main arc at the fifth tangent point (17). The projection of the fifth tangent point (17) on the reference arc in step 1 is 1.8t away from the airfoil leading edge point (8). 8) The distance is t, and the elliptical arc between the leading edge point (8) of the airfoil and the fifth tangent point (17) is the lower arc leading edge segment (5) of the airfoil; between the fourth tangent point (16) and the second tangent point (14) is the upper arc segment (2), and the upper arc segment (2) is on the upper main body arc (11); between the first tangent point (13) and the fifth tangent point (17) is the lower arc segment (6), and the lower arc segment (6) is on the lower main body arc (12). At this point, the thin arc-type rotor airfoil with a relative curvature of d / c and a relative thickness of t / c is generated.

2. The method for generating a thin arc-shaped rotor airfoil suitable for low Reynolds number flow fields according to claim 1, characterized in that: The working Mach number range of the airfoil is 0.0-0.6, and the working Reynolds number range of the airfoil is 10 4 -10 5 .

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