A duct parameter design method based on double propeller structure

Abstract

The application belongs to the technical field of aircraft aerodynamic design, and particularly relates to a duct parameter design method based on a double-screw propeller structure. The method comprises the following steps: S1, according to the selected duct profile airfoil, the airfoil chord length C is parallel to the double-screw propeller rotation axis, and the chord length C is not less than the upper and lower propeller blade spacing L; S2, a vertical line of the chord length is drawn through the 1 / 4 point of the airfoil chord length C, and the vertical line intersects the airfoil lower surface, and the intersection point is recorded as p1; S3, a horizontal line is drawn through the upper rotor rotation center p2, and the horizontal line length is the propeller radius R, and the horizontal line end point is recorded as p3; S4, the airfoil is point-to-point translated, so that the p1 point and the p3 point are coincided; S5, a straight line parallel to the propeller rotation axis is drawn through the p3 point, the straight line intersects the lower propeller rotation radius, and the intersection point is p4; the airfoil trailing edge point is recorded as p5; S6, according to the p3, p4 and p5, and the point p6 of the straight line segment p3p4 extension line, the gap control between the duct and the propeller and the control of the duct expansion angle size are respectively realized.

Description

Technical Field

[0001] The present 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, capable of vertical takeoff and landing and hovering, while also possessing excellent maneuverability and controllability, are playing an increasingly important role in modern warfare and have attracted the attention of researchers worldwide. Compared to ducted single-rotor aircraft, ducted dual-rotor aircraft offer unique advantages. First, the torques of the front and rear rotors are balanced, eliminating the need to consume additional power to offset the counter-torque. Second, they can generate greater thrust, offering broad military applications. However, the development of ducted dual-rotor aircraft in China began relatively late, and current research is still in the stage of technological accumulation and exploratory verification. Compared with international research, the relevant key technologies are not yet mature, and the performance of developed products lags behind, necessitating continued in-depth research. Therefore, conducting parameter impact analysis on ducted dual-rotor aircraft and understanding their aerodynamic coupling mechanisms are of great significance. 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-mentioned purpose, the present invention adopts the following technical solutions 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 cross-section airfoil, the airfoil chord length C is parallel to the twin propeller rotation axis, 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 to 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 parallel to the propeller rotation axis through point p3, and the straight line intersects with the lower propeller rotation radius at point p4;

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

[0012] S6, according to p3, p4, p5, and the point p6 of the extension line of the straight line segment p3p4, respectively, the control of the gap between the duct and the propeller and the control of the size of the duct expansion angle are realized.

[0013] Further,

[0014] In S6, the control of the gap between the duct and the propeller is realized, specifically:

[0015] The straight line segment p3p4 and the straight line segment p4p5 replace the original airfoil curve part;

[0016] The distance between the upper and lower propeller tips and the straight line segment p3p4 of the airfoil is g, and by changing the size of g, the control of the gap between the duct and the propeller is realized.

[0017] Further,

[0018] In S6, the control of the size of the duct expansion angle is realized, specifically:

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

[0020] Further,

[0021] The method further comprises: S7, control of the duct lip radius.

[0022] Further,

[0023] S7 specifically is:

[0024] The control of the position of the airfoil leading edge point is unchanged, a circle is made inside the leading edge tangent to the leading edge point, and by controlling the size of the tangent circle radius, the control of the duct lip radius is realized.

[0025] Further,

[0026] On the tangent circle for controlling the size of the lip radius, take points p12 and p11 of 0.85S and 0.15S respectively with the airfoil leading edge point p7 as the vertex, where S is the circumference of the tangent circle, connect p11p9 and p12p10 with spline lines respectively, and the two ends of the spline lines are tangent to the airfoil line and the tangent circle.

[0027] Further,

[0028] After S7, the method further comprises:

[0029] S8, a circle is made tangent to the inside of the airfoil trailing edge, and the tangent point is the airfoil trailing edge point p5, and the airfoil trailing edge is completed.

[0030] Further,

[0031] After S8, the method further comprises:

[0032] S9, after the trailing edge of the airfoil is modified, the airfoil is rotated 360° around the propeller rotation axis to obtain the final duct profile.

[0033] The technical scheme of the present application realizes the parametric design of the duct lip radius, the duct expansion angle and the duct gap by changing the coordinates of the parameter points on the duct profile airfoil, and under the condition that other parameters remain unchanged, the size specification of a single parameter can be quickly and effectively adjusted, thereby providing a modeling method for the design and optimization of the duct BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 A duct profile airfoil parameterization schematic diagram is provided for the embodiment of the present application.

[0035] Figure 2 An original airfoil schematic diagram is provided for the embodiment of the present application.

[0036] Figure 3 An endpoint establishment schematic diagram is provided for the embodiment of the present application.

[0037] Figure 4 An airfoil translation schematic diagram is provided for the embodiment of the present application.

[0038] Figure 5 An intersection P4 establishment schematic diagram is provided for the embodiment of the present application.

[0039] Figure 6 A straight line segment instead of an airfoil lower surface curve schematic diagram is provided for the embodiment of the present application.

[0040] Figure 7 A gap size control schematic diagram is provided for the embodiment of the present application.

[0041] Figure 8 An expansion angle size control schematic diagram is provided for the embodiment of the present application.

[0042] Figure 9 An intersection determination schematic diagram is provided for the embodiment of the present application.

[0043] Figure 10 A control lip radius circle schematic diagram is provided for the embodiment of the present application.

[0044] Figure 11 A circle and airfoil line connection schematic diagram is provided for the embodiment of the present application.

[0045] Figure 12 A trailing edge chamfer schematic diagram is provided for the embodiment of the present application.

[0046] Figure 13 A duct profile schematic diagram is provided for the embodiment of the present application. DETAILED DESCRIPTION

[0047] The technical scheme of the present application is described in detail below with reference to the accompanying drawings.

[0048] The technical scheme of the present application realizes the geometric parameterization control of the duct by extracting design variables on the duct profile airfoil, including the following steps:

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

[0050] 2) A vertical line of chord length is made through the 1 / 4 point of the chord length C, and intersects with the lower surface of the airfoil, and the intersection point is denoted as p1;

[0051] 3) A horizontal line is made through the upper rotor rotation center p2, and the length of the horizontal line is the propeller radius R, and the end point of the horizontal line is denoted as p3;

[0052] 4) The airfoil is translated point to point to make the p1 point and the p3 point coincide;

[0053] 5) A straight line parallel to the propeller rotation axis is made through the p3 point, and the straight line intersects with the lower propeller rotation radius, and the intersection point is p4;

[0054] 6) The point of the rear edge of the airfoil is denoted as p5, and the straight line segment p3p4 and the straight line segment p4p5 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, and the gap between the duct and the propeller is controlled by changing the size of g;

[0056] 8) A point p6 is taken on the extension line of p3p4, and p6p5 is connected, and the position of the p6 point on the extension line is changed to control the size of the duct expansion angle;

[0057] 9) The position of the leading edge point of the airfoil is unchanged, a circle tangent to the leading edge point is made inside the leading edge, and the radius of the tangent circle is controlled to control the lip radius of the duct;

[0058] 10) On the basis of the modified airfoil, a circle tangent to the inside 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 profile airfoil selects an asymmetric airfoil, and the chord length is C (C>D).

[0061] The duct profile parameterization airfoil is as shown in Figure 1The coordinate origin O is the center of rotation of the lower rotor, the horizontal direction is the H-axis, and the vertical direction is the V-axis. The specific parameterization control of a single variable is described as follows:

[0062] (I) Parameter control

[0063] 1. Gap control

[0064] Step one:

[0065] A vertical line of chord length is drawn through the 1 / 4 point of the airfoil chord C, intersecting the lower surface of the airfoil at point p1; as shown in Figure 2 .

[0066] Step two:

[0067] A horizontal line is drawn through the upper rotor center of rotation p2, with a length equal to the propeller radius R. The end point of the horizontal line is denoted as p3; as shown in Figure 3 .

[0068] Step three:

[0069] The airfoil is translated point-to-point so that the p1 point and the p3 point coincide; as shown in Figure 4 .

[0070] Step four:

[0071] A straight line parallel to the V-axis is drawn through the p3 point, intersecting the lower propeller rotation radius at point p4. The coordinates of points p3 and p4 are (R, D) and (R, 0), respectively; as shown in Figure 5 .

[0072] Step five:

[0073] The point p5 on the trailing edge of the airfoil is noted, and the original airfoil curve portion is replaced by the straight line segment p3p4 and the straight line segment p4p5, as shown in Figure 6 .

[0074] Step six:

[0075] The longitudinal coordinates of points p3 and p4 are kept unchanged, and the modified airfoil is moved horizontally along the H-axis. This method can control the size of the gap between the duct inner wall and the propeller tip. As shown in Figure 7 .

[0076] 2. Expansion angle control

[0077] Step one:

[0078] Repeat steps one to five in the gap control.

[0079] Step two:

[0080] A point p6 is taken on the extension of the straight line segment p3p4, and p5p6 is connected. The angle between the line segment p5p6 and the extension of the line segment p3p4 is defined as the expansion angle. The coordinate of the point p6 is (H6, V6). H6 is kept unchanged, and the size of the expansion angle is controlled by increasing or decreasing V6. As shown in Figure 8 .

[0081] 3. Lip radius control

[0082] Step one:

[0083] Steps one to five in the repeat gap control are repeated.

[0084] Step two:

[0085] A point p8 is taken on the airfoil chord line at 0.95±0.001 times the chord length. A perpendicular to the chord line is drawn through the point p8, and intersects the upper and lower surfaces of the airfoil at points p9 and p10, respectively. As shown in Figure 9 .

[0086] Step three:

[0087] The position of the leading edge point p7 of the airfoil is kept unchanged, and a circle is drawn inside the leading edge and tangent to the leading edge point. As shown in Figure 10 , the size of the lip radius is controlled by the radius of the tangent circle;

[0088] Step four:

[0089] On the circle for controlling the size of the lip radius, points p12 and p11 are taken at 0.85S and 0.15S of the airfoil leading edge point p7, respectively, where S is the circumference of the circle. Spline lines are connected between p11p9 and p12p10, respectively, and the ends of the spline lines are tangent to the airfoil line and the circle. As shown in Figure 11 .

[0090] (II) Trailing edge modification

[0091] On the basis of the modified airfoil, a circle is further drawn tangent to the inside of the trailing edge of the airfoil, and the tangent point is the trailing edge point p5. As shown in Figure 12 .

[0092] (III) Duct shape spinning

[0093] The modified airfoil of the duct profile is spun around the V-axis by 360° to obtain the final duct shape. As shown in Figure 13 .

[0094] The application provides a parameterized design method of a ducted configuration, which realizes parameterized design of a duct lip radius, a duct expansion angle and a duct gap by changing coordinates of a parameter point on a duct profile airfoil, and can quickly and effectively adjust the size specification of a single parameter under the condition that other parameters are unchanged, thereby providing a modeling method for design and optimization of the duct. The parameterized design of the duct can be quickly realized, and the total efficiency of the duct after being installed is improved by more than 4% compared to a coaxial double propeller under the same total pitch.

Claims

1. A ducted fan parameter design method based on a double propeller structure, characterized in that, The method comprises: S1, according to the selected duct profile airfoil, the airfoil chord length C is parallel to the double propeller rotating shaft, and the chord length C is not less than the upper and lower propeller blade spacing L; S2, a vertical line of the chord length is made through the 1 / 4 point of the airfoil chord length C, and the vertical line intersects the airfoil lower surface, and the intersection point is recorded as p1; S3, a horizontal line is made through the upper rotor rotating center p2, and the horizontal line length is the propeller radius R, and the horizontal line end point is recorded as p3; S4, the airfoil is point-to-point translated, so that the p1 point and the p3 point are coincided; S5, a straight line parallel to the propeller rotating shaft is made through the p3 point, and the straight line intersects the lower propeller rotating radius, and the intersection point is p4; The airfoil trailing edge point is recorded as p5; S6, according to the p3, the p4, the p5 and the point p6 of the straight line segment p3p4 extension line, the gap control between the duct and the propeller and the duct expansion angle size control are respectively realized; In S6, the gap control between the duct and the propeller is realized, and specifically, the original airfoil curve part is replaced by the straight line segment p3p4 and the straight line segment p4p5; The distance between the upper and lower propeller blade tips and the airfoil straight line segment p3p4 is g, and the gap control between the duct and the propeller is realized by changing the size of g; In S6, the duct expansion angle size control is realized, and specifically, a point p6 is taken on the extension line of p3p4, and p6p5 is connected, and the duct expansion angle size control is realized by changing the position of the p6 point on the extension line.

2. The duct parameter design method based on the double propeller structure according to claim 1, wherein the method further comprises: S7, the duct lip radius control. S7 is specifically: The airfoil leading edge point position is controlled to be unchanged, a tangent circle is made inside the leading edge and tangent to the leading edge point, and the duct lip radius control is realized by controlling the size of the tangent circle radius.

4. The duct parameter design method based on the double propeller structure according to claim 3, wherein on the tangent circle for controlling the size of the lip radius, the airfoil leading edge point p7 is taken as the vertex, and the points p12 and p11 of 0.85S and 0.15S are respectively taken, wherein S is the tangent circle circumference, and the spline lines of p11p9 and p12p10 are respectively connected, and the two ends of the spline lines are tangent to the airfoil line and the tangent circle.

3. The ducted parameter design method based on double propeller structure according to claim 2, characterized in that, After S7, the method further comprises: S8, a circle tangent to the airfoil trailing edge inside is made, the tangent point is the airfoil trailing edge point p5, and the airfoil trailing edge modification is completed. After S8, the method further comprises: S9, after the airfoil trailing edge modification is completed, the airfoil is rotated 360° around the propeller rotating shaft, and the final duct shape is obtained.

5. The ducted parameter design method based on double propeller structure according to claim 2, characterized in that, ​ ​ 6. The ducted parameter design method based on double propeller structure according to claim 5, characterized in that, ​ ​

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