A spanwise oscillating wall drag reduction structure utilizing body vibration energy

Abstract

The application discloses a spanwise oscillation wall surface drag reduction structure using body vibration energy, which comprises a movable wall surface arranged on the surface of an aircraft wing, wherein the movable wall surface is in the form of a whole piece or multiple pieces spliced together, the movable wall surface is parallel to the surface of the wing, and the movable wall surface is connected with the surface of the wing through multiple elastic structure rib strips; the length direction of the rib strip is along the heading direction of the wing, and the thickness direction of the rib strip is inclined to the movable wall surface and the surface of the wing. The vibration energy which is difficult to eliminate by the aircraft body is converted into the spanwise oscillation energy of the movable wall surface block through the design of the movable wall surface, so that the effect of reducing the frictional resistance is achieved; meanwhile, the strength of the near-wall vortex system of the boundary layer is weakened, and the effect of reducing the noise is also achieved; according to the numerical calculation result, the spanwise oscillation of the movable wall surface can achieve the effect of reducing the frictional resistance by more than 30%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aviation and aerodynamics, and particularly relates to a spanwise oscillation wall surface drag reduction structure utilizing body vibration energy. BACKGROUND

[0002] For transport category aircraft, the frictional drag can account for more than 50% of the total drag. For example, for the commonly used A320 civil aircraft, if the drag increases by 1%, 3 tons of fuel will be consumed for each flight, which means that the flight range will be shortened by 120 kilometers under the condition of the same take-off weight. If the lift-drag ratio increases by 1%, 14 passengers can be added. If the aircraft is larger in size, the economic effect will be more significant. The frictional drag of a long-endurance unmanned aerial vehicle with a large aspect ratio and a flying wing layout aircraft accounts for a higher proportion of the total drag, and the performance improvement of reducing the frictional drag will be more prominent. The U.S. Air Force launched the ESMC program (the Engineered Surfaces, Materials and Coatings program) in 2014, aiming to reduce the frictional drag by about 6%, which will reduce the annual fuel cost by 400 million U.S. dollars. For underwater vehicles with good streamline, the frictional drag can account for more than 80% of the total drag, and reducing the frictional drag can significantly improve the navigation performance indicators. For wind turbines, foreign technicians use surface groove structures to not only reduce the aerodynamic drag, but also delay the stall of the wind turbine blades and mitigate the load fluctuation of the wind turbine. In addition, the surface grooves on the blades can increase the power generation by 5%. If the wind turbine power generation in China in 2019 is 405.7 billion kWh, the wind turbine applying the groove drag reduction technology can increase the power generation by 202.85 billion kWh per year. For high-speed trains, if the drag is reduced by 2%, and 100 trains run for 10 hours per day, 2 million kWh of electricity can be saved per day. Therefore, drag reduction has great value for most carriers.

[0003] So far, domestic and foreign researchers have carried out research work for many years, and have been committed to the exploration of drag reduction methods. Many methods for reducing frictional resistance have been disclosed. The method for reducing frictional resistance has active and passive methods. The active method often needs additional energy input, and the driving measure is complex, and is rarely applied to actual engineering. Passive methods have gained more favor due to low cost and simple implementation, such as the above-mentioned micro-groove wall drag reduction. However, the passive drag reduction method often has limited drag reduction effect, such as micro-groove drag reduction, which can only reduce the frictional resistance by 10% (which cannot be achieved in actual engineering application), and the active technology often achieves greater drag reduction effect. According to the existing research results, it is shown that the wall surface can be oscillated in the spanwise direction with a certain parameter to reduce the frictional resistance by 40%, which is much higher than the groove drag reduction method. However, the method of oscillating the wall surface in the spanwise direction is often regarded as a method existing only in the academic research level, because it is impossible to oscillate the whole wall surface in the spanwise direction in actual engineering, and additional driving power is required. SUMMARY

[0004] The purpose of the present application is to provide a spanwise oscillation wall surface drag reduction structure using body vibration energy, which converts the body vibration energy that cannot be eliminated in engineering into the spanwise oscillation expected by the wall surface drag reduction, so as to achieve the purpose of drag reduction.

[0005] In order to achieve the above-mentioned task, the present application adopts the following technical solutions:

[0006] A spanwise oscillation wall surface drag reduction structure using body vibration energy, comprising an active wall surface arranged on the surface of an aircraft wing, the active wall surface being in the form of a whole piece or multiple pieces spliced together, the active wall surface being parallel to the surface of the wing, and the active wall surface and the surface of the wing being connected through a plurality of rib pieces of elastic structure; the length direction of the rib piece is along the heading of the wing, and the thickness direction of the rib piece is inclined to the active wall surface and the surface of the wing.

[0007] Further, the included angle between the rib piece and the surface of the wing and the active wall surface is 70°, and the rib piece is in the form of a long rectangular structure.

[0008] Further, the active wall surface is arranged on the upper surface of the wing, the lower surface of the wing, or both the upper and lower surfaces of the wing.

[0009] Further, the determination process of the arrangement area of the active wall surface on the surface of the wing is as follows:

[0010] determining the position of the wing entering the turbulent stage and the boundary layer thickness δ, the surface kinematic viscosity coefficient v and the surface friction velocity u of the aircraft in the cruising state, τ These parameters can be obtained through actual flight test or numerical simulation after modeling the aircraft; and the arrangement area is:

[0011] In the heading direction, the distance from the point where the wing enters the turbulent phase extends to a distance of twelve times the boundary layer thickness δ from the aileron; in the span direction, the distance from the wing root to the wingtip extends to a distance of twelve times the boundary layer thickness δ.

[0012] Furthermore, the elastic modulus of the rib material is selected according to the following requirements:

[0013] After the rib connects the wing surface and the movable wall, the maximum displacement in the spanwise direction is:

[0014] Among them, A + T is the dimensionless maximum spanwise velocity. + The dimensionless oscillation period is given by these two data points, which were determined through numerical simulation; ν is the surface kinematic viscosity coefficient, u τ denoted as σ0, represents the surface friction velocity.

[0015] Furthermore, the dimensionless maximum spanwise velocity A + =12, dimensionless oscillation period T + =100.

[0016] Furthermore, regardless of whether multiple wall panels are combined or a single movable wall panel is used, the movable wall panel should be arranged within the layout area, and its maximum shape should be the same as or smaller than the layout area.

[0017] Furthermore, when using a multi-panel composite structure, adjacent panels are not connected to each other, but are connected to the wing surface by ribs.

[0018] An aircraft, wherein the wing surface of the aircraft is provided with the aforementioned spanwise oscillating wall drag reduction structure that utilizes the vibration energy of the aircraft body.

[0019] Compared with the prior art, the present invention has the following technical features:

[0020] This invention, through the design of movable walls, transforms the vibrational energy of an aircraft body, which is difficult to eliminate, into spanwise oscillation energy of the movable wall blocks, thereby reducing frictional drag. Simultaneously, by weakening the intensity of the near-wall vortex system in the boundary layer, it also reduces noise. Numerical calculations show that spanwise oscillation of the movable walls can reduce frictional drag by more than 30%. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the movement of the movable wall surface;

[0022] Figure 2 This is a schematic diagram of the layout of the movable wall in the expansion direction;

[0023] Figure 3 This is a schematic diagram showing the layout area of ​​the movable wall surface on the upper surface of the wing;

[0024] Figure 4 These are the calculation results for a wing with a fixed wall and a wing with a movable wall added; the lines with squares represent the results for the fixed wall, and the lines with circles represent the results for the movable wall.

[0025] Figure 5 The near-wall vortex distributions are shown for a fixed wall and an airfoil with an added movable wall. (a) is the result for the fixed wall, (b) is the result for the movable wall when the drag coefficient is large, and (c) is the result for the movable wall when the drag coefficient is small. Detailed Implementation

[0026] In practical engineering, aircraft fuselages vibrate due to various factors (such as engine vibration and turbulent excitation from external fluids). Transforming the complex vibration patterns of the fuselage into spanwise oscillations of the wall surface can significantly reduce frictional drag. Furthermore, since spanwise wall vibration reduces the intensity of near-wall turbulence in the boundary layer, this solution not only reduces frictional drag but also decreases noise generated by the wall surface during high-speed flight, thereby improving the overall performance of the aircraft.

[0027] See appendix Figures 1 to 3 The present invention provides a spanwise oscillating wall drag reduction structure utilizing the vibration energy of the aircraft body, comprising a movable wall disposed on the surface of an aircraft wing. The movable wall is in the form of a single piece or multiple pieces assembled together. The movable wall is parallel to the wing surface and is connected to the wing surface by multiple elastic ribs. The length direction of the ribs is along the heading of the wing, and the thickness direction of the ribs is inclined to the movable wall and the wing surface. The wing surface is the upper surface and / or the lower surface of the wing.

[0028] like Figure 1 As shown, Figure 1 The diagram shows the thickness cross-section of the rib strip. The thickness direction of the rib strip is inclined to the wing surface and the moving wall, with an angle of approximately 70° between it and the wing surface and the moving wall, in order to convert the normal vibration of the fuselage into the spanwise vibration of the moving wall. Because the length of the rib strip along the flight direction is much greater than its thickness, the rib strip has greater stiffness along the flight direction and is not easily deformed; while the thickness component in the spanwise direction is smaller, resulting in lower stiffness in the spanwise direction and easier deformation. This allows the vertical vibration of the fuselage to be converted into the spanwise oscillation of the fluid surface. The rib strip can be made of elastic metal sheets, and the rib strips are parallel to each other; for example, each of the rib strips can be a long rectangular structure.

[0029] The movable wall surface in the scheme can be arranged on the upper surface of the wing, the lower surface of the wing, or both the upper and lower surfaces of the wing. On the upper surface or the lower surface of the wing, the movable wall surface can be an integral wall surface or a plurality of wall surfaces spliced together. When the plurality of wall surfaces are spliced together, the adjacent wall surfaces are not connected and are connected to the surface of the wing through rib pieces.

[0030] The arrangement area of the movable wall surface on the upper surface or the lower surface of the wing has special requirements, and the process of specifically determining the arrangement area is as follows:

[0031] The position of the wing entering the turbulent stage of the aircraft in the cruising state, and the boundary layer thickness δ, the surface kinematic viscosity coefficient v and the surface friction velocity u τ For the aircraft to be drag-reduced, the position of the wing entering the turbulent stage and the related fluid mechanics parameters at this time can be obtained through actual navigation tests or numerical simulation after modeling the aircraft.

[0032] The arrangement area is:

[0033] Starting from the position of the wing entering the turbulent stage in the heading direction to the position 12 times the boundary layer thickness δ away from the aircraft aileron, and starting from the position 12 times the boundary layer thickness δ away from the wing root in the spanwise direction to the position 12 times the boundary layer thickness δ away from the wing tip, the influence of spanwise oscillation on the flow field of the control surface position and the flow at the wing tip can be ignored, and the maximum drag reduction effect can be obtained.

[0034] Regardless of the movable wall surface spliced together or the integral structure, the movable wall surface should be arranged in the arrangement area, and the maximum profile should be the same as or slightly smaller than the arrangement area.

[0035] In order to change the shape of the aircraft as little as possible, the total thickness of the movable wall surface + rib piece structure in the scheme is controlled in the order of millimeters, as shown in the accompanying Figure 2 The specific material selection of the rib piece should focus on its elastic modulus, and the elastic modulus of the rib piece material should be selected according to the following requirements:

[0036] After the rib piece connects the surface of the wing and the movable wall surface, the maximum displacement in the spanwise direction is

[0037] Wherein, A + is the dimensionless maximum spanwise velocity, and T + is the dimensionless oscillation period, and the two data are determined by numerical simulation scheme, and specifically:

[0038] The wing surface is modeled by ICEM, for the simplified model, the wing is assumed to be a flat wing, the wing surface boundary condition is set to be the spanwise oscillation boundary condition; during simulation, the wing surface is assumed to be in a fully turbulent flow state, the active wall surface heading length is dimensionless length L + = 150, the dimensionless maximum spanwise oscillation velocity A + = 12, the dimensionless oscillation period is in the range of T + = 50-200. The simulation result under the condition shows that the maximum drag reduction effect can be obtained when the dimensionless oscillation period is T + = 100. Therefore, in the present scheme, the dimensionless maximum spanwise velocity A + = 12, and the dimensionless oscillation period T + = 100.

[0039] According to the selection requirement of the elastic modulus, the rib strip satisfying the requirement is selected through experiment. The rib strip under the parameter will convert the vibration energy transmitted by the body to the active wall surface into oscillation of a certain amplitude and frequency of the fluid surface, and the frictional resistance can be reduced by 30% at most.

[0040] Based on the above structural design of the present application, when the aircraft is in the cruising stage, the wing will oscillate in the normal direction due to the aeroelasticity, at this time, the active wall surface of the wing surface can convert the normal oscillation into spanwise oscillation by using the elastic rib strip, and the energy of the normal oscillation of the wing itself is used for drag reduction.

[0041] Embodiment:

[0042] The mature numerical calculation method is used to carry out numerical simulation on the drag reduction structure of the present application. In order to simulate the flow details in the boundary layer, the direct numerical simulation method based on Navier-Stokes equation is used to calculate the local boundary layer flow, in order to reduce the calculation amount, the common channel flow model mode at home and abroad is used, which aims to ensure the fine simulation of the flow in the boundary layer. During simulation, the Mach number is 0.2, the Reynolds number based on the channel height is 3180; the atmospheric density, temperature and viscosity coefficient are calculated based on the sea level parameters.

[0043] Figure 4 is the calculation process result of the wing fixed wall (i.e. the original skin of the wing) and the wing added with the active wall surface; Figure 5 is the near-wall flow field vortex distribution of the fixed wall and the wing added with the active wall surface. It can be seen that compared with the frictional resistance of the fixed wall boundary layer, the average drag reduction efficiency of the active wall surface with spanwise oscillation is increased by more than 30%, and the near-wall boundary layer flow field structure presents the characteristics that the vortex is far away from the wall.

[0044] The above examples are only used to illustrate the technical solutions of the present application, but not limit the same; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalent ones; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A span-wise oscillating wall surface drag reduction structure utilizing body vibration energy, characterized in that, The active wall surface is arranged on the surface of the wing of the aircraft, and the active wall surface is in the form of a whole piece or multiple pieces, the active wall surface is parallel to the surface of the wing, and the active wall surface is connected to the surface of the wing through multiple elastic rib strips. The determination of the arrangement region of the active wall surface on the surface of the wing is as follows: determining the position of the wing of the aircraft in the turbulent phase in the cruising state, and the boundary layer thickness δ, the surface kinematic viscosity coefficient ν and the surface friction velocity u τ , which can be obtained by actual navigation test or numerical simulation after modeling the aircraft; and the layout area is: The position from which the wing enters the turbulent stage in the heading direction to the position at a distance of 12 times the boundary layer thickness δ of the aircraft aileron from the wing root in the span direction to the position at a distance of 12 times the boundary layer thickness δ of the aircraft aileron from the wing tip; The elastic modulus of the rib strip material is selected according to the following requirements: The maximum displacement in the spanwise direction after the riblets connect the wing surface and the moving wall surface is ; where, A + is the dimensionless maximum tangential velocity, T + is the dimensionless oscillation period, both data being determined by numerical simulation schemes; ν is the surface kinematic viscosity coefficient, u τ is the surface friction velocity.

2. The span-wise oscillating wall drag reduction structure utilizing body vibration energy according to claim 1, characterized in that, The angle between the rib strip and the surface of the wing and the active wall surface is 70°, and the rib strip is in the form of a long rectangular structure.

3. The span-wise oscillating wall drag reduction structure utilizing body vibration energy according to claim 1, characterized in that, The active wall surface is arranged on the upper surface of the wing, the lower surface of the wing, or both the upper and lower surfaces of the wing.

4. The span-wise oscillating wall drag reduction structure utilizing body vibration energy according to claim 1, wherein Dimensionless maximum spanwise velocity A + = 12, dimensionless oscillation period T + = 100.

5. The spanwise oscillating wall drag reduction structure utilizing body vibration energy according to claim 1, wherein Whether the active wall surface is in the form of multiple pieces or a whole piece, the active wall surface should be arranged in the arrangement region, and the maximum shape of the active wall surface should be the same as or smaller than the arrangement region.

6. The spanwise oscillating wall drag reduction structure utilizing body vibration energy according to claim 1, wherein When the active wall surface is in the form of multiple pieces, the adjacent wall surfaces are not connected, and each wall surface is connected to the surface of the wing through the rib strip. 7.An aircraft, wherein the surface of the wing of the aircraft is provided with the spanwise oscillating wall surface drag reduction structure utilizing the vibration energy of the aircraft body according to any one of claims 1-6.

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