Duct parameter design method based on twin-propeller structure

Abstract

The invention belongs to the technical field of aerodynamic design of aircrafts, and particularly relates to a duct parameter design method based on a twin-propeller structure. Comprising the following steps: S1, according to a selected duct section airfoil, the chord length C of the airfoil is parallel to a rotating shaft of a twin-propeller, and the chord length C is not smaller than the distance L between an upper propeller and a lower propeller; s2, a vertical line of the chord length is made by passing through a 1 / 4 point of the chord length C of the airfoil, the vertical line intersects with the lower surface of the airfoil, and the intersection point is recorded as p1; s3, a horizontal line is drawn through the rotation center p2 of the upper rotor, the length of the horizontal line is the radius R of the propeller, and the end point of the horizontal line is recorded as p3; s4, point-to-point translation is conducted on the airfoil profile, and the p1 point and the p3 point coincide; s5, a straight line parallel to the rotating shaft of the propeller is made through the p3 point, the straight line intersects with the rotating radius of the lower propeller, and the intersection point is p4; recording the trailing edge point of the airfoil as p5; and S6, according to p3, p4, p5 and a point p6 of an extension line of the linear segment p3p4, control over the gap between the duct and the propeller and control over the divergence angle of the duct are achieved correspondingly.

Description

Technical Field

[0001] The invention belongs to the technical field of aircraft aerodynamic design, and in particular relates to a duct parameter design method based on a twin-propeller structure. Background Art

[0002] Ducted aircraft can take off and land vertically and hover, and have good maneuverability and controllability. They play an increasingly important role in modern warfare and have been valued by researchers from various countries. Compared with ducted single-rotor aircraft, ducted dual-rotor aircraft have unique advantages. First, the torque of the front and rear dual rotors is balanced with each other, and there is no need to consume additional power to offset the anti-torque. Second, it can produce greater thrust and has broad application prospects in the military. However, the development of ducted dual-rotor aircraft started relatively late in China, and the current research is still in the stage of technology accumulation and exploration and verification. Compared with foreign countries, the relevant key technologies are not mature, and there is a certain gap in the performance of the developed products, which requires continuous in-depth research. Therefore, it is of great significance to carry out parameter influence analysis of ducted dual rotors and master the aerodynamic coupling mechanism of ducted dual rotors. Summary of the invention

[0003] In order to explore the parameter influence rules of ducted twin-rotor aircraft, the present invention proposes a parametric design method for ducted shape.

[0004] In order to achieve the above object, the present invention adopts the following technical solution to achieve it.

[0005] A duct parameter design method based on a twin-propeller structure, the method comprising:

[0006] S1, according to the selected duct section airfoil, the airfoil chord length C is parallel to the rotation axis of the twin propellers, and the chord length C is not less than the upper and lower propeller blade spacing L;

[0007] S2, through the 1 / 4 point of the airfoil chord length C, draw a perpendicular line of the chord length, intersecting with the lower surface of the airfoil, and the intersection point is recorded as p1;

[0008] S3, draw a horizontal line through the upper rotor rotation center p2, the length of the horizontal line is the propeller radius R, and the endpoint of the horizontal line is recorded as p3;

[0009] S4, translate the airfoil from point to point so that point p1 and point p3 coincide;

[0010] S5, draw a straight line through point p3 parallel to the propeller rotation axis, the straight line intersects with the lower propeller rotation radius, and the intersection point is p4;

[0011] The trailing edge point of the airfoil is denoted as p5;

[0012] S6, based on p3, p4, p5, and point p6 which is the extension line of straight line segment p3p4, respectively realize the control of the gap between the duct and the propeller and the control of the duct expansion angle.

[0013] Furthermore,

[0014] In S6, the clearance between the duct and the propeller is controlled as follows:

[0015] Replace the original airfoil curve part with straight line segments p3p4 and p4p5;

[0016] The distance between the upper and lower propeller tips and the straight line segment p3p4 of the airfoil is g. By changing the size of g, the gap between the duct and the propeller can be controlled.

[0017] Furthermore,

[0018] In S6, the duct expansion angle is controlled as follows:

[0019] On the extension line of p3p4, take a point p6, connect p6p5, and by changing the position of point p6 on the extension line, the size of the duct expansion angle can be controlled.

[0020] Furthermore,

[0021] The method further includes: S7, controlling the radius of the duct lip.

[0022] Furthermore,

[0023] S7 is specifically:

[0024] The leading edge point of the airfoil is controlled to remain unchanged, and a circle tangent to the leading edge point is made on the inner side of the leading edge. The radius of the duct lip is controlled by controlling the radius of the tangent circle.

[0025] Furthermore,

[0026] On the tangent circle that controls the lip radius, take the leading edge point p7 of the airfoil as the vertex, take points p12 and p11 at 0.85S and 0.15S respectively, where S is the circumference of the tangent circle, and use splines to connect p11p9 and p12p10 respectively. The two ends of the spline are tangent to the airfoil line and the tangent circle.

[0027] Furthermore,

[0028] After S7, the method further includes:

[0029] S8, make a circle tangent to the inner side of the airfoil trailing edge, with the tangent point being the airfoil trailing edge point p5, to complete the airfoil trailing edge modification.

[0030] Furthermore,

[0031] After S8, the method further includes:

[0032] S9, after the airfoil trailing edge modification is completed, the airfoil is rotated 360° around the propeller rotation axis to obtain the final duct shape.

[0033] The technical solution of the present invention realizes the parametric design of the duct lip radius, duct expansion angle, and duct clearance by changing the coordinates of the parameter points on the duct section airfoil. Under the condition that other parameters remain unchanged, the size specification of a single parameter can be adjusted quickly and effectively, providing a modeling method for the design and optimization of the duct. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a parameterized duct section airfoil provided in an embodiment of the present invention;

[0035] Figure 2 A schematic diagram of an original airfoil provided in an embodiment of the present invention;

[0036] Figure 3 A schematic diagram of establishing an endpoint provided in an embodiment of the present invention;

[0037] Figure 4 A schematic diagram of airfoil translation provided by an embodiment of the present invention;

[0038] Figure 5 A schematic diagram of establishing intersection point P4 provided in an embodiment of the present invention;

[0039] Figure 6 A schematic diagram of a straight line segment replacing a curve on the lower surface of an airfoil provided in an embodiment of the present invention;

[0040] Figure 7 A schematic diagram of gap size control provided by an embodiment of the present invention;

[0041] Figure 8 A schematic diagram of controlling the expansion angle provided by an embodiment of the present invention;

[0042] Fig. 9 A schematic diagram of determining an intersection provided by an embodiment of the present invention;

[0043] Fig.10 A schematic diagram of a circle for controlling the lip radius provided by an embodiment of the present invention;

[0044] Fig.11 A schematic diagram of the connection between a circle and an airfoil line provided in an embodiment of the present invention;

[0045] Fig.12 A schematic diagram of a trailing edge chamfer provided in an embodiment of the present invention;

[0046] Fig.13 A schematic diagram of a duct shape provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0048] The technical solution of the present invention realizes geometric parameterized control of the duct by extracting design variables on the duct section airfoil, and comprises the following steps:

[0049] 1) According to the selected airfoil, the airfoil chord length C is parallel to the rotation axis of the twin propellers, and the chord length C is not less than the pitch L between the upper and lower propellers;

[0050] 2) Draw a perpendicular line through the 1 / 4 point of the airfoil chord length C, which intersects with the lower surface of the airfoil. The intersection point is recorded as p1;

[0051] 3) Draw a horizontal line through the upper rotor rotation center p2. The length of the horizontal line is the propeller radius R, and the endpoint of the horizontal line is recorded as p3;

[0052] 4) Translate the airfoil from point to point so that point p1 and point p3 coincide;

[0053] 5) Draw a straight line through point p3 that is parallel to the propeller rotation axis. This straight line intersects with the lower propeller rotation radius, and the intersection point is p4;

[0054] 6) The trailing edge point of the airfoil is recorded as p5, and the straight line segments p3p4 and p4p5 are used to replace the original airfoil curve part;

[0055] 7) The distance between the upper and lower propeller tips and the straight line segment p3p4 of the airfoil is g. By changing the value of g, the gap between the duct and the propeller can be controlled;

[0056] 8) On the extension line of p3p4, take a point p6, connect p6p5, and control the duct expansion angle by changing the position of point p6 on the extension line;

[0057] 9) Keep the leading edge point of the airfoil unchanged, draw a circle tangent to the leading edge point on the inner side of the leading edge, and control the radius of the duct lip by controlling the radius of the tangent circle;

[0058] 10) On the basis of the modified airfoil, a circle tangent to the inner side of the trailing edge of the airfoil is further made, and the tangent point is the trailing edge point p5 of the airfoil;

[0059] 11) The modified airfoil is rotated 360° around the propeller rotation axis to generate the duct shape.

[0060] Specifically, the propeller radius is R, the propeller pitch is D, the duct section airfoil selects an asymmetric airfoil, and the chord length is C (C>D).

[0061] The parametric airfoil of the duct section is as follows Figure 1The coordinate origin O is the rotation center of the lower rotor, the horizontal direction is the H axis, and the vertical direction is the V axis. The parameterized control description of a single variable is as follows:

[0062] (I) Parameter control

[0063] 1. Gap control

[0064] Step 1:

[0065] Through the 1 / 4 point of the airfoil chord length C, draw a perpendicular line to the chord length, which intersects with the lower surface of the airfoil. The intersection point is recorded as p1; Figure 2 shown.

[0066] Step 2:

[0067] Draw a horizontal line through the upper rotor rotation center p2, the length of the horizontal line is the propeller radius R, and the endpoint of the horizontal line is recorded as p3; Figure 3 shown.

[0068] Step 3:

[0069] Translate the airfoil from point to point so that point p1 and point p3 coincide; Figure 4 shown.

[0070] Step 4:

[0071] Draw a straight line parallel to the V axis through point p3. This straight line intersects with the rotation radius of the lower propeller. The intersection point is p4. The coordinates of points p3 and p4 are (R, D) and (R, 0) respectively. Figure 5 shown.

[0072] Step 5:

[0073] The trailing edge point of the airfoil is denoted as p5, and the straight line segments p3p4 and p4p5 are used to replace the original airfoil curve. Figure 6 shown.

[0074] Step 6:

[0075] Keep the ordinates of points p3 and p4 unchanged, and move the modified airfoil horizontally along the H axis. In this way, the gap between the inner wall of the duct and the tip of the coaxial propeller can be controlled. Figure 7 shown.

[0076] 2. Expansion angle control

[0077] Step 1:

[0078] Repeat steps 1 to 5 in gap control.

[0079] Step 2:

[0080] Take a point p6 on the extension line of the straight line segment p3p4, connect p5p6, and define the angle between the line segment p5p6 and the extension line of the line segment p3p4 as the expansion angle. The coordinates of point p6 are (H6, V6). Keep H6 unchanged and increase or decrease V6 to control the expansion angle. Figure 8 shown.

[0081] 3. Lip radius control

[0082] Step 1:

[0083] Repeat steps 1 to 5 in gap control.

[0084] Step 2:

[0085] Select a point p8 on the chord line of the airfoil that is 0.95±0.001 times the chord length, and draw a perpendicular line through p8 to intersect with the upper and lower surfaces of the airfoil, respectively. The intersection points are p9 and p10. Fig. 9 shown.

[0086] Step 3:

[0087] Keep the position of the leading edge point p7 unchanged, and make a circle tangent to the leading edge point on the inside of the leading edge, such as Fig.10 As shown, the radius of the lip is controlled by the radius of the tangent circle;

[0088] Step 4:

[0089] On the circle that controls the radius of the lip, take the airfoil leading edge point p7 as the vertex, and select points p12 and p11 at 0.85S and 0.15S respectively, where S is the circumference. Use splines to connect p11p9 and p12p10 respectively, and the two ends of the spline are tangent to the airfoil line and the circle, as shown in the figure below: Fig.11 shown.

[0090] (ii) Trailing edge modification

[0091] On the basis of the modified airfoil, a circle tangent to the inner side of the airfoil trailing edge is further made, and the tangent point is the airfoil trailing edge point p5, as shown in Fig.12 shown.

[0092] (III) The duct shape is rotated

[0093] The modified airfoil of the duct section is rotated 360° around the V axis to obtain the final duct shape, as shown in Fig.13 shown.

[0094] The present invention proposes a parametric design method for the duct shape. By changing the coordinates of the parameter points on the duct section airfoil, the parametric design of the duct lip radius, the duct expansion angle, and the duct clearance is realized. Under the condition that other parameters remain unchanged, the size specification of a single parameter can be adjusted quickly and effectively, providing a modeling method for the design and optimization of the duct. The parametric design of the duct can be realized quickly. Compared with the coaxial twin propeller, the total efficiency after installing the duct is increased by more than 4% under the same total pitch.

Claims

1. A duct parameter design method based on a twin-propeller structure, characterized in that: The method comprises: S1, according to the selected duct section airfoil, the airfoil chord length C is parallel to the rotation axis of the twin propellers, and the chord length C is not less than the upper and lower propeller blade spacing L; S2, through the 1 / 4 point of the airfoil chord length C, draw a perpendicular line of the chord length, intersecting with the lower surface of the airfoil, and the intersection point is recorded as p1; S3, draw a horizontal line through the upper rotor rotation center p2, the length of the horizontal line is the propeller radius R, and the endpoint of the horizontal line is recorded as p3; S4, translate the airfoil from point to point so that point p1 and point p3 coincide; S5, draw a straight line through point p3 parallel to the propeller rotation axis, the straight line intersects with the lower propeller rotation radius, and the intersection point is p4; The trailing edge point of the airfoil is denoted as p5; S6, based on p3, p4, p5, and point p6 which is the extension line of straight line segment p3p4, respectively realize the control of the gap between the duct and the propeller and the control of the duct expansion angle.

2. A duct parameter design method based on a twin-propeller structure according to claim 1, characterized in that: In S6, the clearance between the duct and the propeller is controlled as follows: Replace the original airfoil curve part with straight line segments p3p4 and p4p5; The distance between the upper and lower propeller tips and the straight line segment p3p4 of the airfoil is g. By changing the size of g, the gap between the duct and the propeller can be controlled.

3. The duct parameter design method based on a twin-propeller structure according to claim 1, characterized in that: In S6, the duct expansion angle is controlled as follows: On the extension line of p3p4, take a point p6, connect p6p5, and by changing the position of point p6 on the extension line, the size of the duct expansion angle can be controlled.

4. The duct parameter design method based on a twin-propeller structure according to claim 1, characterized in that: The method further includes: S7, controlling the radius of the duct lip.

5. A duct parameter design method based on a twin-propeller structure according to claim 4, characterized in that: S7 is specifically: The leading edge point of the airfoil is controlled to remain unchanged, and a circle tangent to the leading edge point is made on the inner side of the leading edge. The radius of the duct lip is controlled by controlling the radius of the tangent circle.

6. A duct parameter design method based on a twin-propeller structure according to claim 5, characterized in that: On the tangent circle that controls the lip radius, take the leading edge point p7 of the airfoil as the vertex, take points p12 and p11 at 0.85S and 0.15S respectively, where S is the circumference of the tangent circle, and use splines to connect p11p9 and p12p10 respectively. The two ends of the spline are tangent to the airfoil line and the tangent circle.

7. A duct parameter design method based on a twin-propeller structure according to claim 4, characterized in that: After S7, the method further includes: S8, make a circle tangent to the inner side of the airfoil trailing edge, with the tangent point being the airfoil trailing edge point p5, to complete the airfoil trailing edge modification.

8. A duct parameter design method based on a twin-propeller structure according to claim 6, characterized in that: After S8, the method further includes: S9, after the airfoil trailing edge modification is completed, the airfoil is rotated 360° around the propeller rotation axis to obtain the final duct shape.

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