Method for generating thin arc rotor wing type suitable for low Reynolds number flow field

Abstract

The invention belongs to the technical field of aircraft rotors, and particularly relates to a generation method of a thin arc-shaped rotor wing type suitable for a low Reynolds number flow field, and the thin arc-shaped rotor wing type comprises an upper arc line and a lower arc line; the upper arc line comprises an upper arc line front edge section, an upper arc line arc section, an upper arc line transition section and an upper arc line rear edge section; the lower arc line comprises a lower arc line front edge section, a lower arc line arc section and a lower arc line rear edge section; the generation method comprises the steps of 1, drawing a reference arc to obtain an upper main body arc and a lower main body arc; 2, drawing a trailing edge section of a lower arc line of the airfoil profile; 3, drawing an upper arc trailing edge section of the airfoil; and 4, obtaining an upper arc leading edge section and a lower arc leading edge section of the airfoil profile. The problem that an existing low-Reynolds-number thin-arc airfoil profile is not smooth in appearance is solved, the requirements for high lift and good stall characteristics of a rotor wing profile can be met, and the lift coefficient and the lift-drag ratio in the low-Reynolds-number environment are remarkably increased.

Description

Technical Field

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

[0002] In recent years, micro and small rotorcraft have been more and more widely used in both civilian and military fields. Due to their small size and low flight speed, the flight Reynolds number of micro and small rotorcraft is usually in the order of 10 4 -10 5 magnitude, belonging to low Reynolds number aircraft. In the low Reynolds number flow field, due to the more significant viscous effect of air, the flow field structure presents characteristics different from those of conventional Reynolds numbers, including laminar separation, separation-induced transition, etc. The low Reynolds number effect will have many adverse effects on the aerodynamic characteristics, mainly manifested as a decrease in the lift-to-drag ratio, a reduction in aerodynamic efficiency, and a deterioration in stability.

[0003] The airfoil is a very important design parameter affecting the aerodynamic characteristics of the rotor. Considering the characteristics of the low Reynolds number flow field in airfoil design can effectively improve the aerodynamic performance of the rotor. At present, when designing such rotors, little consideration is given to the working characteristics of the airfoil in a low Reynolds number environment, and existing low Reynolds number thin circular arc type airfoils still have problems such as unclear definition and unsmooth shape. Summary of the Invention

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

[0005] The technical solution adopted in this application is as follows: A generation method of a thin circular arc type rotor airfoil applicable to a low Reynolds number flow field, the thin circular arc type rotor airfoil includes: an upper arc line, a lower arc line; the upper arc line includes an upper arc line leading edge section, an upper arc line circular arc section, an upper arc line transition section, and an upper arc line trailing edge section; the lower arc line includes a lower arc line leading edge section, a lower arc line circular arc section, and a lower arc line trailing edge section; The upper arc line leading edge section and the lower arc line leading edge section are tangent to each other at the airfoil leading edge point to form the airfoil leading edge; the upper arc line trailing edge section and the lower arc line trailing edge section intersect at the airfoil trailing edge point; a reference circular arc is formed between the airfoil leading edge point and the airfoil trailing edge point, and the distance from the farthest point of the reference circular arc to the airfoil chord line is d; the distance between the farthest point of the upper arc line circular arc section of the airfoil from the airfoil chord line and the farthest point of the lower arc line circular arc section of the airfoil from the airfoil chord line is t; except that the upper arc line trailing edge section and the lower arc line trailing edge section intersect at the airfoil trailing edge point, the rest of the sections of the airfoil are tangent to each other; 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 the maximum distance from the arc to the chord line of the airfoil being d through the leading edge point and trailing edge point of the airfoil as the reference arc. Translate the reference arc upward and downward by a distance of 0.5t respectively to obtain the upper main arc and the lower main arc; Step 2: Draw a straight line passing through the trailing edge point of the airfoil and tangent to the lower main 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 of the airfoil; Step 3: Draw a straight line perpendicular to the chord line of the airfoil through the first tangent point, intersecting the upper main arc at a point. Connect this point and the trailing edge point to obtain a straight line segment. Draw a transition arc with a radius of c and tangent to both the upper main arc and this straight line segment. The transition arc is tangent to the upper main arc at the second tangent point and tangent to the straight line segment at the third tangent point. The arc segment between the second tangent point and the third tangent point is the transition segment of the upper arc of the airfoil, and the straight line segment between the third tangent point and the trailing edge point of the airfoil is the trailing edge segment of the upper arc of the airfoil; Step 4: Draw two ellipses with their centers on the chord line of the airfoil and tangent to the leading edge point. One ellipse is also 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 at a distance of 1.8t 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 arc 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 at a distance of t 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 arc of the airfoil; The arc segment between the fourth tangent point and the second tangent point is the upper arc segment, and the upper arc segment is on the upper main arc; The arc segment between the first tangent point and the fifth tangent point is the lower arc segment, and the lower arc segment is on the lower main arc; Thus, a thin arc - type rotary wing airfoil with a relative camber of d / c and a relative thickness of t / c is generated.

[0006] Further, the operating Mach number range of the airfoil is 0.0 - 0.6, and the operating Reynolds number range of the airfoil is 10 4 -10 5 。

[0007] The present application has the following beneficial effects: Before the airfoil stalls, the lift coefficient increases with the increase of the angle of attack, and is greater than 1 after the angle of attack reaches 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 high lift and good stall characteristics of the rotary wing airfoil. With the increase of the Reynolds number, the drag coefficient at the same angle of attack shows a decreasing trend. With the increase of the Reynolds number, the lift - to - drag ratio at the same angle of attack increases significantly, and the maximum lift - to - drag ratio also increases significantly. Brief Description of the Drawings

[0008] Figure 1 It is a schematic diagram of the overall structure of the low - Reynolds - number thin - arc - type rotary wing airfoil of the present invention; Figure 2 Schematic diagram of the method for generating the upper and lower main arcs of the low-Reynolds-number thin circular-arc type rotor blade airfoil of the present invention; Figure 3 Schematic diagram of the method for generating the trailing edge part of the low-Reynolds-number thin circular-arc type rotor blade airfoil of the invention; Figure 4 Schematic diagram of the method for generating the leading edge part of the low-Reynolds-number thin circular-arc type rotor blade airfoil of the present invention; Figure 5 Graph of the lift coefficient varying with the angle of attack at different Reynolds numbers when the relative camber d / c of the low-Reynolds-number thin circular-arc type rotor blade airfoil of the present invention is 6% and the relative thickness t / c is 5%; Figure 6 Graph of the drag coefficient varying with the angle of attack at different Reynolds numbers when the relative camber d / c of the low-Reynolds-number thin circular-arc type rotor blade airfoil of the present invention is 6% and the relative thickness t / c is 5%; Figure 7 Graph of the lift-to-drag ratio varying with the angle of attack at different Reynolds numbers when the relative camber d / c of the low-Reynolds-number thin circular-arc type rotor blade airfoil of the present invention is 6% and the relative thickness t / c is 5%.

[0009] In the figure: 1. Leading edge section of the upper arc, 2. Circular arc section of the upper arc, 3. Transition section of the upper arc, 4. Trailing edge section of the upper arc, 5. Leading edge section of the lower arc, 6. Circular arc section of the lower arc, 7. Trailing edge section of the lower arc, 8. Leading edge point of the airfoil, 9. Trailing edge point of the airfoil, 10. Reference circular arc, 11. Upper main arc, 12. Lower main arc, 13. First tangent point, 14. Second tangent point, 15. Third tangent point, 16. Fourth tangent point, 17. Fifth tangent point. Detailed implementation manner

[0010] The following will describe the present application in detail with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary and are not intended to limit the scope of the present application. In addition, in the following description, descriptions of structures and well-known technical common sense are omitted to avoid unnecessarily confusing the concepts of the present application.

[0011] Example 1: Combining the attached Figures 1-4 , the present application discloses a method for generating a thin circular-arc type rotor blade airfoil applicable to a low-Reynolds-number flow field. The thin circular-arc type rotor blade airfoil includes: an upper arc and a lower arc; the upper arc includes a leading edge section 1 of the upper arc, a circular arc section 2 of the upper arc, a transition section 3 of the upper arc, and a trailing edge section 4 of the upper arc; the lower arc includes a leading edge section 5 of the lower arc, a circular arc section 6 of the lower arc, and a trailing edge section 7 of the lower arc; The leading edge section 1 of the upper arc is tangent to the leading edge section 4 of the lower arc at the airfoil leading edge point 8 to form the airfoil leading edge; the trailing edge section 4 of the upper arc intersects the trailing edge section 7 of the lower arc 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 from the farthest end of the reference arc 10 to the airfoil chord line is d; the distance between the farthest point of the upper arc section of the airfoil from the airfoil chord line and the farthest point of the lower arc section of the airfoil from the airfoil chord line is t; except for the intersection of the trailing edge section 4 of the upper arc and the trailing edge section 7 of the lower arc at the airfoil trailing edge point, the rest of the sections are tangent to each other; 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 from the farthest end to the airfoil chord line of d through the airfoil leading edge point 8 and the airfoil trailing edge point 9 as the reference arc 10, and translate the reference arc 10 upward and downward by a distance of 0.5t respectively to obtain the upper main arc 11 and the lower main arc 12; Step 2: Draw a straight line passing through the airfoil trailing edge point 9 and tangent to the lower main 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 trailing edge section 7 of the airfoil lower arc; Step 3: Draw a straight line perpendicular to the airfoil chord line through the first tangent point 13, intersecting the upper main arc 11 at a point. Connect this point with the trailing edge point to obtain a straight line segment. Draw a transition arc with a radius of c and tangent to both the upper main arc 11 and this straight line segment at the same time. The transition arc is tangent to the upper main arc at the second tangent point 14 and tangent to the straight line segment at the third tangent point 15. The arc section between the second tangent point 14 and the third tangent point 15 is the upper arc transition section 3 of the airfoil, and the straight line segment between the third tangent point 15 and the airfoil trailing edge point 9 is the trailing edge section 4 of the airfoil upper arc; 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 at a distance of 1.8t 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 leading edge section 1 of the airfoil upper arc. 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 at a distance of t from the airfoil leading edge point 8. The elliptical arc between the airfoil leading edge point 8 and the fifth tangent point 17 is the leading edge section 5 of the airfoil lower arc; the arc section between the fourth tangent point 16 and the second tangent point 14 is the upper arc section 2, and the upper arc section 2 is on the upper main arc 11; the arc section between the first tangent point 13 and the fifth tangent point 17 is the lower arc section 6, and the lower arc section 6 is on the lower main arc 12; thus, the thin arc - type rotary wing airfoil with a relative camber of d / c and a relative thickness of t / c is generated.

[0012] Furthermore, the operating Mach number range of the airfoil is 0.0 - 0.6, and the operating Reynolds number range of the airfoil is 10 4 -10 5 .

[0013] Furthermore, when the relative camber d / c is 6% and the relative thickness t / c is 5%, the lift coefficient, drag coefficient, and lift-to-drag ratio of the thin circular arc type rotor blade airfoil vary with the angle of attack within the range of Reynolds number 0.2×10 5 -0.8×10 5 as shown in the attached Figures 5-7 . The lift coefficient curve in the attached Figure 5 shows that before the airfoil stalls, the lift coefficient increases with the increase of the angle of attack, and is greater than 1 after the angle of attack reaches 7°. There is a relatively obvious linear region in the lift curve, and the stall angle of attack is greater than 10°, meeting the requirements of high lift and good stall characteristics of the rotor blade airfoil; The drag coefficient curve in the attached Figure 6 shows that with the increase of the Reynolds number, the drag coefficient of the airfoil at the same angle of attack shows a decreasing trend; The lift-to-drag ratio curve in the attached Figure 7 shows that with the increase of the Reynolds number, the lift-to-drag ratio of the airfoil at the same angle of attack increases significantly, and the maximum lift-to-drag ratio also increases significantly.

[0014] The above embodiments merely illustrate the principles and effects of the present application, rather than limiting the present application. Any simple substitution or change within the scope of the technical ideas disclosed in the present application and based on the technical solutions of the present application shall be within the protection scope of the present application.

Claims

1. A method for generating a thin arc-shaped rotor airfoil suitable for a low Reynolds number flow field, characterized in that: 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 (1), an upper arc line circular arc segment (2), an upper arc line transition segment (3), and an upper arc line trailing edge segment (4); the lower arc line comprises a lower arc line leading edge segment (5), a lower arc line circular arc segment (6), and a lower arc line trailing edge segment (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 of the airfoil 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 to each other; the airfoil chord length is c, the airfoil relative camber is d / c, and the airfoil relative thickness is t / c; The generation method includes the following steps: 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 chord line of the airfoil 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), and the line segment from the first tangent point (13) to the airfoil trailing edge point (9) is the airfoil lower arc line trailing edge segment (7); Step 3: draw a straight line perpendicular to the chord line of the airfoil 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, draw a transition arc with a radius of c and 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), 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 leading edge point (8) of the airfoil, the elliptical arc between the leading edge point (8) of the airfoil to 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, 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 a low Reynolds number flow field 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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