A vortex generator for reducing fuselage drag and delaying airflow separation

Abstract

The embodiment of the present invention discloses a vortex generator for reducing fuselage drag and delaying airflow separation, which relates to the technical field of rotorcraft manufacturing, and can realize the passive flow control of the flow field near the fuselage of the rotorcraft when encountering strong crosswind or sideways flight, thereby achieving the purpose of reducing drag of the rotorcraft, while reducing the implementation cost and failure rate. The present invention includes: the value of the installation angle (2) of the vortex generator is greater than or equal to 10° and less than or equal to 45°; the second corner (20) of the single-piece vortex generator is the angle between the upper surface (7) of the second section and the connection section (19) between the vortex generator and the object surface, the value of the first corner (9) of the single-piece vortex generator is less than 30°, and the value of the second corner (20) is greater than or equal to 40° and less than or equal to 60°. The present invention is suitable for the passive flow control of the flow field near the fuselage of the rotorcraft when encountering strong crosswind or sideways flight.

Description

Technical Field

[0001] The invention relates to the technical field of rotorcraft manufacturing, and in particular to a vortex generator used for reducing fuselage drag and delaying airflow separation. Background Art

[0002] In many application fields, rotorcraft is irreplaceable. As the speed of rotorcraft continues to increase, it is becoming more and more important to reduce the drag of rotorcraft. Generally speaking, the drag of the rotorcraft fuselage accounts for 25% to 30% of the total drag, so it is very necessary to carry out drag reduction work on the rotorcraft fuselage.

[0003] Among them, crosswind oncoming flow is a more difficult problem in the drag reduction design of rotorcraft. When the rotorcraft is in a crosswind oncoming flow, the fuselage is non-streamlined relative to the oncoming flow. At this time, a large area of ​​airflow separation area is prone to occur in the fuselage flow field, which greatly increases the fuselage resistance and rotor power consumption, and even causes a crash. Therefore, it is very necessary to carry out drag reduction work on the rotorcraft fuselage in crosswind oncoming flow.

[0004] At present, the industry mainly adopts the drag reduction solution, which requires the use of several active technologies to reduce the airflow separation in the rear door area of ​​the rotorcraft, thereby reducing the fuselage resistance. The required active control device is not only expensive, but also requires additional flight control program and operation process design, which increases the complexity of system design, reduces the redundancy of the system and increases the failure rate. Summary of the invention

[0005] An embodiment of the present invention provides a vortex generator for reducing fuselage drag and delaying airflow separation, which can achieve passive flow control of the flow field near the fuselage of a rotorcraft when encountering strong side winds or sideways flight, thereby achieving the purpose of reducing the drag of the rotorcraft while reducing the implementation cost and failure rate.

[0006] To achieve the above object, the embodiments of the present invention adopt the following technical solutions:

[0007] The installation angle (2) of the vortex generator is the angle between the vortex generator and the second horizontal reference line (v2), and the value of the installation angle (2) of the vortex generator is greater than or equal to 10° and less than or equal to 45°;

[0008] A first corner (9) of the monolithic vortex generator is an angle between the upper surface (5) of the first section and a connecting section (19) of the vortex generator and an object surface, wherein the object surface is a part of the fuselage surface of the aircraft;

[0009] The second corner (20) of the single-chip vortex generator is the angle between the upper surface (7) of the second section and the connecting section (19) between the vortex generator and the object surface. The value of the first corner (9) of the single-chip vortex generator is less than 30°, and the value of the second corner (20) is greater than or equal to 40° and less than or equal to 60°.

[0010] Wherein, L1 represents the horizontal length from the front end (4) of the vortex generator to the rear end (8) of the upper surface of the vortex generator, and the value of L1 is greater than or equal to 3h and less than or equal to 5h;

[0011] L2 represents the horizontal length from the front end (4) of the vortex generator to the inflection point (6) of the upper surface of the vortex generator, and the value of L2 is greater than or equal to 0.4 times L1 and less than or equal to 0.6 times L1.

[0012] The value of the thickness (H1) of the vortex generator is greater than or equal to 0.1h and less than or equal to 0.4h, and the height (H2) of the vortex generator is 1h.

[0013] The distance (3) between the two front ends of a pair of vortex generators is greater than or equal to 0.8h and less than or equal to 2h.

[0014] Compared with the drag reduction scheme using active control devices in the prior art, this embodiment provides a passive drag reduction scheme, which mainly achieves passive drag reduction by adding vortex generators outside the fuselage. Compared with the active control devices that must be used in the active drag reduction scheme, vortex generators are easy to install and have low manufacturing costs, so they can be considered to be applied to the fuselage of a blunt-body rotorcraft flying at a cruising speed, thereby achieving the purpose of drag reduction.

[0015] In view of the complex operating environment of the rotorcraft, when the rotorcraft encounters strong side winds or sideways flight, the fuselage is prone to large-area airflow separation, and the conventional vortex generator is usually designed to work in the cruising state of the rotorcraft, and the range of the incoming flow angle of attack in the working state is relatively small. In the face of strong sideways flow, instability may occur, thus failing to achieve the effect of reducing drag and inhibiting airflow separation. In view of this phenomenon, this embodiment proposes a new vortex generator design that can still work normally under large incoming flow angles, which is used to delay the occurrence of airflow separation, and realizes passive control of the flow field near the fuselage of the rotorcraft when it encounters strong side winds or sideways flight, thereby achieving the purpose of reducing drag of the rotorcraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 Three-view and three-dimensional diagram of the vortex generator provided by the embodiment of the present invention;

[0018] Figure 2 A schematic diagram of the dimensions of a front vortex generator provided in an embodiment of the present invention;

[0019] Figure 3 A schematic diagram of the operation of a vortex generator at a high angle of attack provided by an embodiment of the present invention;

[0020] Figure 4 A schematic diagram of the working principle of a vortex generator provided in an embodiment of the present invention;

[0021] Figure 5 A schematic structural diagram of an airflow separation system for reducing fuselage drag and delaying airflow separation provided by an embodiment of the present invention;

[0022] Figure 6 A schematic structural diagram of another airflow separation system for reducing fuselage drag and delaying airflow separation provided by an embodiment of the present invention;

[0023] Figure 7a-7d It is a schematic diagram showing the variation of lift and drag of a traditional vortex generator with the number of iteration steps;

[0024] Figure 8a-8d A schematic diagram showing the variation of the lift resistance of a vortex generator provided by an embodiment of the present invention with the number of iteration steps;

[0025] Fig. 9 It is the velocity vector diagram and pressure cloud diagram in the specific example;

[0026] Fig.10 It is the streamline diagram and velocity cloud diagram in the specific example;

[0027] Fig.11 Streamline diagrams and pressure cloud diagrams at different cross-sectional locations in a specific example;

[0028] Fig.12 It is the streamline diagram of the space body in the specific example. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention will be described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention. It can be understood by those skilled in the art that, unless specifically stated, the singular forms "one", "one", "said" and "the" used herein may also include plural forms. It should be further understood that the term "including" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups. It should be understood that when we say that an element is "connected" or "coupled" to another element, it can be directly connected or coupled to other elements, or there may also be intermediate elements. In addition, the "connection" or "coupling" used here may include wireless connection or coupling. The term "and / or" used herein includes any unit and all combinations of one or more associated listed items. It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as generally understood by those of ordinary skill in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0030] In order to solve the problem of increased resistance of the helicopter due to airflow separation when encountering strong side winds or flying sideways, the present embodiment provides a vortex generator design that can still work normally under large incoming flow angles of attack, which is used to delay the occurrence of airflow separation, thereby achieving the purpose of helicopter straightening and drag reduction.

[0031] The vortex generator designed in the solution of this embodiment is different from the traditional vortex generator in that it has a wider range of working angle of attack, that is, it can still work normally under the condition of large incoming flow velocity angle of attack. It has obvious differences in appearance from the traditional vortex generator, mainly to achieve the function of increasing the working angle of attack of the vortex generator. Figure 1 Shown are the three-view drawings and three-dimensional schematic diagram of the designed vortex generator.

[0032] Among them, the installation angle (2) of the vortex generator is the angle between the vortex generator and the second horizontal reference line (v2), and the value of the installation angle (2) of the vortex generator is greater than or equal to 10° and less than or equal to 45°, wherein v1, v2, v3, and v4 are four mutually parallel horizontal reference lines.

[0033] The first corner (9) of the monolithic vortex generator is the angle between the upper surface (5) of the first section and the connecting section (19) of the vortex generator and the object surface, wherein the object surface is part of the fuselage surface of the aircraft.

[0034] The second corner (20) of the single-chip vortex generator is the angle between the upper surface (7) of the second section and the connecting section (19) between the vortex generator and the object surface. The value of the first corner (9) of the single-chip vortex generator is less than 30°, and the value of the second corner (20) is greater than or equal to 40° and less than or equal to 60°.

[0035] In this embodiment, the shape characteristics of the vortex generator are as follows: Figure 2 As shown, Figure 2 (a) is a top view and (b) is a side view. The height of the vortex generator is H2 = 1h, which is roughly equivalent to the thickness of the local boundary layer.

[0036] Specifically, L1 represents the horizontal length from the front end (4) of the vortex generator to the rear end (8) of the upper surface of the vortex generator, and the value of L1 is greater than or equal to 3h and less than or equal to 5h. L2 represents the horizontal length from the front end (4) of the vortex generator to the inflection point (6) of the upper surface of the vortex generator, and the value of L2 is greater than or equal to 0.4 times L1 and less than or equal to 0.6 times L1. That is, L2 is 0.4 to 0.6 times L1.

[0037] In this embodiment, the value of the vortex generator thickness (H1) is greater than or equal to 0.1h and less than or equal to 0.4h, the height (H2) of the vortex generator is 1h, and the value of the distance (3) between the two front ends of a pair of vortex generators is greater than or equal to 0.8h and less than or equal to 2h.

[0038] Compared with the drag reduction scheme using active control devices in the prior art, this embodiment provides a passive drag reduction scheme, which mainly achieves passive drag reduction by adding vortex generators outside the fuselage. Compared with the active control devices that must be used in the active drag reduction scheme, vortex generators are easy to install and have low manufacturing costs, so they can be considered to be applied to the fuselage of a blunt-body rotorcraft flying at a cruising speed, thereby achieving the purpose of drag reduction.

[0039] In view of the complex operating environment of the rotorcraft, when the rotorcraft encounters strong side winds or sideways flight, the fuselage is prone to large-area airflow separation, and the conventional vortex generator is usually designed to work in the cruising state of the rotorcraft, and the range of the incoming flow angle of attack in the working state is relatively small. In the face of strong sideways flow, instability may occur, thus failing to achieve the effect of reducing drag and inhibiting airflow separation. In view of this phenomenon, this embodiment proposes a new vortex generator design that can still work normally under large incoming flow angles, which is used to delay the occurrence of airflow separation, and realizes passive control of the flow field near the fuselage of the rotorcraft when it encounters strong side winds or sideways flight, thereby achieving the purpose of reducing drag of the rotorcraft.

[0040] Specific as Figure 3 The figure shows a schematic diagram of a vortex generator operating at a high angle of attack. When a helicopter flies sideways or encounters a large side wind, the vortex generator may operate in this state. Figure 3 It is a top view, in which the direction of the incoming flow velocity is indicated (1), 10 is the working angle of attack of the vortex generator, and is the angle between the vortex generator 11 and the incoming flow 1.

[0041] Further, such as Figure 4 The figure shows the working diagram of the vortex generator, with the viewing direction being Figure 3 In the W1 direction, the incoming flow direction is shown as 1. When the fluid passes through the front half 17 of the vortex generator, since 17 is a small piece with a sharp leading edge, the fluid will flow along the front half of the vortex generator and form a leading edge vortex system 16 with smaller intensity but quite stable at the inflection point 6. Then the vortex system moves backward along the vortex system axis 12. Under the action of the leading edge vortex 16, the fluid on the rear half 18 of the vortex generator will exchange and transfer energy between the mainstream fluid and the boundary layer fluid, thereby enhancing the anti-separation ability of the fluid that has been separated or is about to be separated at a large angle of attack in the rear half of the vortex generator, thereby delaying the airflow separation on the rear half of the vortex generator, and the fluid will continue to move backward to form a stronger induced vortex 15 with an induced vortex axis of 14. The induced vortex 15 is the main vortex that improves the airflow separation phenomenon on the fuselage surface.

[0042] In the best solution of this embodiment: the value of the installation angle (2) of the vortex generator is 25°. In the second best solution: the value of the installation angle (2) of the vortex generator is 20°.

[0043] In the optimal solution of this embodiment: the value of the first corner (9) is 15°, and the value of the second corner (20) is 45°. In the suboptimal solution: the value of the first corner (9) is 20°; the value of the second corner (20) is 50°.

[0044] In the optimal solution of this embodiment: the value of L1 is 4h. In the suboptimal solution: the value of L1 is 4.5h.

[0045] In the optimal solution of this embodiment: the value of L2 is 0.5L1. In the suboptimal solution: the value of L2 is 0.55L1.

[0046] The following examples show specific test data to illustrate the beneficial effects of this embodiment:

[0047] Experimental scenario: The drag reduction analysis and design were conducted on the drag characteristics of the transport helicopter under cruising and sideways flight conditions. First, based on the unstructured grid generated around the fuselage, a CFD method that can effectively simulate the drag characteristics of the helicopter was established, and the ROBI N fuselage with experimental results was used for example verification. Then, the established CFD method was used to carefully simulate the flow characteristics and fuselage drag characteristics near the fuselage under the action of the vortex generator designed in this embodiment. The example comparison shows that under cruising and sideways flight conditions, the addition of the vortex generator designed in this embodiment can effectively reduce the expansion of the separation zone at the connection between the rear door and tail cantilever of the fuselage, thereby achieving the purpose of reducing the drag of the helicopter.

[0048] 1. Comparison of forces on vortex generators.

[0049] Numerical simulations were performed on the conventional vortex generator and the vortex generator designed in this embodiment, and the drag and lift of the single-chip vortex generator in the simulation results were extracted for comparative analysis to ensure that the two have the same grid size, length, height, thickness of the vortex generator, and the same calculation state and calculation method. The following table shows the designed calculation state. Under the same incoming flow Mach number, the angle of attack of the incoming flow is changed to simulate gusts in various directions.

[0050]

[0051] Figure 7a-7d The figure shows the variation of lift resistance of the traditional vortex generator with the number of iteration steps, where the interval of the Y axis is 0.005N.

[0052] Figure 8a-8d The figure shows the variation of the lift resistance of the vortex generator provided in this embodiment with the number of iteration steps. Figure 8a-8d It can be seen that when the incoming flow angle increases, periodic oscillation force appears behind the traditional vortex generator. At this time, the traditional vortex generator stalls and cannot play a role in exchanging the boundary layer fluid and the mainstream fluid energy. The vortex generator in this embodiment can still keep the fluid in a good adhesion state at a large angle of attack and has a large working angle of attack. Therefore, it can be applied to situations where the working incoming flow angle of the vortex generator is large, such as when a helicopter is flying sideways. .

[0053] 2. Comparative analysis of flow field cloud maps.

[0054] The flow fields of the conventional vortex generator and the vortex generator designed in this embodiment are compared and analyzed. Fig. 9 The velocity vector diagram and pressure cloud diagram shown in Fig.10 The streamline diagram and velocity cloud diagram shown are the velocity vector diagram and pressure cloud diagram and the streamline diagram and velocity cloud diagram at the same cross section when the incoming flow Mach number is 0.18 and the incoming flow angle of attack is 0°. It can be seen that even at a small incoming flow angle of attack, the vortex generator designed in this embodiment can still make the fluid near the fuselage adhere better.

[0055] Furthermore, when the incoming flow Mach number is 0.18 and the incoming flow angle of attack is 60°, Fig.11 The streamline diagram and pressure cloud diagram at different cross-sectional positions shown in Fig.12 The spatial body streamline diagram shown. It can be seen that the airflow separation phenomenon of the traditional vortex generator is significant under the condition of large incoming flow angle, and as the fluid moves away from the wall (Y increases), the separation phenomenon becomes more and more serious, and shedding vortices appear far away from the wall or even at the rear, which is also an important reason for the lift and resistance of the vortex generator to become blocked and unstable in this state. However, the vortex generator designed in this embodiment has no shedding vortices at all positions, and the flow field is in a stable state, so the effectiveness of the vortex generator under large incoming flow angle can be guaranteed. It can be seen from the body streamline diagram that there is an obvious shedding vortex in the flow field of the traditional vortex generator. In addition, a large airflow separation phenomenon also occurs on one side of the expansion section of the vortex generator, while the vortex generator of this embodiment does not have the above problems.

[0056] It can be seen that the effects of vortex generators and conventional vortex generators at the same incoming flow speed and different incoming flow angles are compared and analyzed, and the drag characteristics of a certain type of transport rotorcraft under cruise flight conditions are numerically simulated and drag reduction analysis is carried out. The calculation results show that adding vortex generators can effectively reduce the expansion of the separation zone at the connection between the rear door and the tail cantilever of the fuselage, thereby achieving the purpose of reducing the drag of the rotorcraft. However, conventional vortex generators will become unstable when the incoming flow angle is large, and the vortex generator cannot work normally. The vortex generator designed in this paper can still work normally at a large incoming flow angle, and the additional drag caused by the vortex generator is much smaller than that of conventional vortex generators.

[0057] Therefore, the vortex generator provided in this embodiment is designed to address the phenomenon of large-area airflow separation when the rotorcraft fuselage operates in various gust environments (for example, the transition section of the rotorcraft). A new vortex generator with a wide range of working angles of attack is designed to delay the airflow separation phenomenon that occurs when the rotorcraft operates in a harsh flight environment, thereby achieving the purpose of reducing drag when the rotorcraft operates in harsh environments.

[0058] This embodiment also provides an airflow separation system for reducing fuselage drag and delaying airflow separation, and the airflow separation system is composed of at least two vortex generators provided in this embodiment.

[0059] There are at least two ways to form a gas flow separation system. One of them is: Figure 5 Shown:

[0060] Every two vortex generators form a group, and the vortex generators in each group are symmetrically distributed along the central axis, which is the central axis of the top view of the vortex generators in each group. The vortex generators in each group are symmetrically distributed in an eight-shaped shape along the central axis.

[0061] Second, if Figure 6 As shown, all vortex generators are divided into two groups, namely, a first group and a second group. The vortex generators in each group are parallel to each other. The number of vortex generators in the first group and the second group is the same, and the first group and the second group are symmetrically distributed along the central axis, which is the central axis of the top view of the first group and the second group.

[0062] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The above is only a specific implementation method of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A vortex generator for reducing fuselage drag and delaying airflow separation, characterized in that: include: The installation angle (2) of the vortex generator is the angle between the vortex generator and the second horizontal reference line (v2); A first corner (9) of the monolithic vortex generator is an angle between the upper surface (5) of the first section and a connecting section (19) of the vortex generator and an object surface, wherein the object surface is a part of the fuselage surface of the aircraft; The second corner (20) of the single-piece vortex generator is the angle between the upper surface (7) of the second section and the connecting section (19) of the vortex generator and the object surface; L1 represents the horizontal length from the front end (4) of the vortex generator to the rear end (8) of the upper surface of the vortex generator; L2 represents the horizontal length from the front end (4) of the vortex generator to the inflection point (6) on the upper surface of the vortex generator; The value of the thickness (H1) of the vortex generator is greater than or equal to 0.1h and less than or equal to 0.4h, and the height (H2) of the vortex generator is 1h; The distance (3) between the two front ends of a pair of vortex generators is greater than or equal to 0.8h and less than or equal to 2h; The value of the installation angle (2) of the vortex generator is 25°; Alternatively, the value of the installation angle (2) of the vortex generator is 20°; The value of the first corner (9) is 15°; or, the value of the first corner (9) is 20°; The value of the second corner (20) is 45°; or, the value of the second corner (20) is 50°; The value of L1 is 4h, where h represents the boundary layer thickness at the installation position of the vortex generator; or the value of L1 is 4.5h; the value of L2 is 0.5L1; or the value of L2 is 0.55L1.

2. An airflow separation system for reducing fuselage drag and delaying airflow separation, characterized in that: The airflow separation system is composed of at least two vortex generators for reducing fuselage drag and delaying airflow separation; In the vortex generator, the installation angle (2) is the angle between the vortex generator and a second horizontal reference line (v2), wherein v1, v2, and v3 are three mutually parallel horizontal reference lines; the first corner (9) of the single-piece vortex generator is the angle between the upper surface (5) of the first section and the connecting section (19) of the vortex generator and the object surface, wherein the object surface is part of the fuselage surface of the aircraft; the second corner (20) of the single-piece vortex generator is the angle between the upper surface (7) of the second section and the connecting section (19) of the vortex generator and the object surface; L1 represents the horizontal length from the front end (4) of the vortex generator to the rear end (8) of the upper surface of the vortex generator; L2 represents the horizontal length from the front end (4) of the vortex generator to the inflection point (6) on the upper surface of the vortex generator; The value of the thickness (H1) of the vortex generator is greater than or equal to 0.1h and less than or equal to 0.4h, and the height (H2) of the vortex generator is 1h; The distance (3) between the two front ends of a pair of vortex generators is greater than or equal to 0.8h and less than or equal to 2h; The value of the installation angle (2) of the vortex generator is 25°; Alternatively, the value of the installation angle (2) of the vortex generator is 20°; The value of the first corner (9) is 15°; or, the value of the first corner (9) is 20°; The value of the second corner (20) is 45°; or, the value of the second corner (20) is 50°; The value of L1 is 4h, where h represents the boundary layer thickness at the installation position of the vortex generator; or the value of L1 is 4.5h; the value of L2 is 0.5L1; or the value of L2 is 0.55L1.

3. The air flow separation system according to claim 2, characterized in that: Every two vortex generators are grouped together, and the vortex generators in each group are symmetrically distributed along a central axis, and the central axis is the central axis of a top view of the vortex generators in each group; The vortex generators in each group are symmetrically distributed in an eight-shaped shape along the central axis.

4. The air flow separation system according to claim 3, characterized in that: All vortex generators are divided into 2 groups: Group 1 and Group 2; The vortex generators in each group are parallel to each other; The number of vortex generators in the first group is the same as that in the second group, and the first group and the second group are symmetrically distributed along a central axis, and the central axis is the central axis of the top view of the first group and the second group.

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