A method of drag reduction for segmented skin spanwise vibrations of an aerospace vehicle

Abstract

The application discloses a drag reduction method for spanwise vibration of sectional skin of an aerial vehicle, and comprises the following steps: determining fluid mechanics parameters of the aerial vehicle in a turbulent stage in a cruising state; determining a preset region for arranging active skin on a wing of the aerial vehicle, segmenting the wing in the preset region according to a preset length in a heading direction of the aerial vehicle, and then arranging the active skin outside the wing, wherein the length of the active skin in the heading direction is the preset length; the active skin is in a strip structure, a driving mechanism is arranged between each section of the active skin and a fuselage, the driving mechanism is used for driving the section of the active skin to perform spanwise oscillation on the surface of the wing, and the spanwise oscillation directions of adjacent active skins are opposite; determining spanwise oscillation parameters of the active skin at an initial moment when the aerial vehicle enters the cruising stage; and driving the active skin on the wing to perform spanwise oscillation by using the driving mechanism according to the determined spanwise oscillation parameters at the initial moment when the aerial vehicle enters the cruising stage.

Description

Technical Field

[0001] This invention relates to the fields of aviation and aerodynamics, and specifically to a method for reducing spanwise vibration of segmented skin of an aircraft. Background Technology

[0002] For transport aircraft, frictional drag can account for more than 50% of total drag. For example, with the commonly used A320 commercial airliner, every 1% increase in drag consumes an additional 3 tons of fuel per flight, meaning a 120-kilometer reduction in range for the same takeoff weight. A 1% increase in lift-to-drag ratio can accommodate 14 more passengers; the economic benefits are even more significant for larger aircraft. The proportion of frictional drag in the total drag is even higher for long-endurance UAVs with very high aspect ratios and flying-wing aircraft, making the performance improvement from reducing frictional drag even more pronounced. Since 2014, the U.S. Air Force has launched the ESMC (Engineered Surfaces, Materials, and Coatings) program, aiming to reduce frictional drag by about 6%, which would reduce annual fuel costs by $400 million. For streamlined underwater vehicles, frictional drag can even account for more than 80% of total drag, and reducing frictional drag can significantly improve flight performance. For wind turbines, foreign researchers have used surface groove structures to not only reduce aerodynamic drag but also delay blade stall and mitigate load fluctuations. Furthermore, adding surface grooves to the blades can increase power generation by 5%. Based on China's 2019 wind turbine power generation of 405.7 billion kilowatt-hours, wind turbines using groove drag reduction technology could generate an additional 20.285 billion kilowatt-hours annually. For high-speed rail, a 2% reduction in drag, assuming 100 trains operate for 10 hours a day, could save two million kilowatt-hours of electricity daily. Therefore, drag reduction is of immense value for most transport aircraft.

[0003] To date, researchers both domestically and internationally have conducted research for many years, dedicated to exploring drag reduction methods, and have published numerous methods for reducing frictional resistance. There are two main types of methods for reducing frictional resistance: active and passive. Active methods often require additional energy input and have complex driving mechanisms, and are currently rarely applied in practical engineering. Passive methods have gained more favor due to their low cost and ease of implementation, such as the aforementioned microgroove skin drag reduction. However, passive drag reduction methods often have limited effects; for example, microgroove drag reduction can only reduce frictional resistance by a maximum of 10% (this target is not achieved in practical engineering applications), while active technologies can often achieve greater drag reduction effects. Existing research results indicate that inducing a small spanwise vibration of the skin with certain parameters can reduce frictional resistance by 40%, far exceeding the effect of the groove drag reduction method. However, currently, the method of spanwise vibration of the skin is often considered to exist only at the academic research level because in practical engineering, it is impossible to induce spanwise vibration of the entire skin, and additional driving power is required. Summary of the Invention

[0004] The purpose of this invention is to provide a drag reduction method for spanwise vibration of segmented skin of an aircraft. The method involves arranging a spanwise oscillating movable skin on the surface of the aircraft wing, and having each segment perform spanwise oscillations in opposite directions to offset excess torque, thereby achieving an active drag reduction mechanism for spanwise oscillation.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for reducing spanwise vibration of segmented skin of an aircraft includes:

[0007] Determine the hydrodynamic parameters of an aircraft as it enters the turbulent phase during cruise.

[0008] Based on the aforementioned fluid dynamics parameters, a preset area for arranging movable skin on the aircraft wing is determined, and the wing within the preset area is segmented along the aircraft's heading according to a preset length.

[0009] A movable skin is arranged on the outside of the wing within the preset area. The yaw length of the movable skin is the preset length. The movable skin is a strip structure. A drive mechanism is arranged between each segment of the movable skin and the fuselage to drive the segment of the movable skin to oscillate in the spanwise direction on the wing surface. The spanwise oscillation directions of adjacent movable skins are opposite.

[0010] Determine the spanwise oscillation parameters of the active skin at the initial moment when the aircraft enters the cruise phase;

[0011] During actual flight, when an aircraft enters the cruise phase, at the initial moment, it uses a drive mechanism to drive the movable skin on the wing to oscillate in the spanwise direction according to the determined spanwise oscillation parameters.

[0012] Furthermore, the method also includes:

[0013] The hydrodynamic parameters of the wing under the current cruise state are collected in real time by sensors, including the friction velocity and surface kinematic viscosity of the moving skin. These two values ​​are used to correct the spanwise oscillation parameters in real time, and the corrected spanwise oscillation parameters are used to drive and control the moving skin in real time.

[0014] Furthermore, the hydrodynamic parameters of the aircraft entering the turbulent stage during cruise include: the position of the wing entering the turbulent stage, the boundary layer thickness δ, the surface kinematic viscosity coefficient ν, and the surface friction velocity u. τ The fluid dynamic parameters are obtained through actual flight tests or numerical simulations after modeling the aircraft.

[0015] Furthermore, the preset area is defined as follows: in the heading direction, starting from the position where the wing enters the turbulent stage, extending to a distance of twelve times the boundary layer thickness δ from the aileron of the aircraft; in the spanwise direction, starting from a distance of twelve times the boundary layer thickness δ from the wing root, extending to a distance of twelve times the boundary layer thickness δ from the wingtip.

[0016] Furthermore, the formula for calculating the preset length L is as follows:

[0017]

[0018] Among them, L + ν is a dimensionless length representing the average flow-direction length of the vortex encountered by the aircraft during cruise. This length can be obtained through numerical simulation of the flow field and subsequent post-processing analysis; ν represents the surface kinematic viscosity coefficient. τ This indicates the surface friction speed.

[0019] Furthermore, within the preset region, it is divided into segments according to a preset length L, as follows:

[0020]

[0021] in, This indicates rounding down, and M represents the length of the preset region in the heading direction;

[0022] That is, an integer number of active skins will be placed within the preset area. If the remaining part is not long enough for one L, it will not be placed.

[0023] Furthermore, the spanwise oscillation parameters of the active skin are:

[0024]

[0025] Where w wall(t) represents the spanwise oscillation velocity, A represents the maximum spanwise oscillation velocity amplitude, T0 represents the spanwise oscillation period, and t represents the oscillation time. The maximum spanwise oscillation velocity A = A + ×u τ , stretching oscillation period A + and T + These are the dimensionless maximum spanwise velocity and the dimensionless oscillation period, respectively, obtained through numerical simulation.

[0026] Furthermore, the friction velocity and surface kinematic viscosity coefficient of the moving skin surface are collected in real time by sensors under the current cruise state, and these two values ​​are used as parameters u. τ Substituting ν into the calculation formulas for A and T0, w can be calculated in real time. wall The value of (t) is used to continuously adjust the movement of the active skin.

[0027] An aircraft having movable skin designed in the aircraft drag reduction method based on segmented skin rotational oscillation on its wings.

[0028] Compared with the prior art, the present invention has the following technical features:

[0029] This invention divides the wing skin into sections along the flow direction, with adjacent sections vibrating in opposite directions, thereby neutralizing the torque generated by the skin vibration. This method can not only significantly reduce the frictional drag of the aircraft, but also reduce the noise generated by the aircraft body due to high-speed flight, significantly improve the performance parameters of the aircraft, and is easier to implement in engineering. Attached Figure Description

[0030] Figure 1 A schematic diagram of the structure of an aircraft wing with movable skin;

[0031] Figure 2 The drag reduction curve for the active skin;

[0032] Figure 3 The near-wall vortex distributions are shown for fixed skin and movable skin, where (a) is for fixed skin, (b) is for movable skin with a large drag coefficient, and (c) is for movable skin with a small drag coefficient. Detailed Implementation

[0033] See appendix Figure 1This invention provides a drag reduction method for aircraft based on segmented skin rotational oscillation. The method involves setting segmented movable skins on the surface of the aircraft wing and performing segmented spanwise oscillations along the flow direction. Adjacent movable skins vibrate in opposite phases, thereby canceling out the torque generated by the spanwise oscillation. Simulation results show that spanwise oscillation can achieve drag reduction and noise reduction by altering the near-wall self-sustaining process of the boundary layer. The invention specifically includes the following steps:

[0034] Step 1: Determine the hydrodynamic parameters of the aircraft when it enters the turbulent phase during cruise, including the wing's position when it enters the turbulent phase, boundary layer thickness δ, surface kinematic viscosity coefficient ν, and surface friction velocity u. τ .

[0035] For aircraft undergoing drag reduction modifications, the position of the aircraft wing entering the turbulent stage and the relevant hydrodynamic parameters at this time can be obtained through actual flight tests or numerical simulations after modeling the aircraft.

[0036] Step 2: Based on the fluid dynamic parameters, determine the preset area on the aircraft wing for arranging movable skin, and divide the wing within the preset area into segments of preset length along the aircraft's heading.

[0037] See appendix Figure 1 The preset region is defined as follows: in the heading direction, starting from the position where the wing enters the turbulent stage, and ending at a distance of twelve times the boundary layer thickness δ from the aileron of the aircraft; in the spanwise direction, starting from a distance of twelve times the boundary layer thickness δ from the wing root, and ending at a distance of twelve times the boundary layer thickness δ from the wingtip; within this region, the influence of spanwise oscillations on the flow field at the control surface position and the flow at the wingtip can be ignored, while the maximum drag reduction effect can be obtained.

[0038] The formula for calculating the preset length L is:

[0039]

[0040] Among them, L + The dimensionless length represents the average flow-direction length of the vortex faced by the aircraft during cruise. This length can be obtained by numerical simulation of the flow field and post-processing analysis of the flow field; in this scheme, it is determined to be 150.

[0041] Within the preset area, it is divided into segments according to a preset length L, represented as follows:

[0042]

[0043] in, This indicates rounding down, and M represents the length of the preset area in the heading direction.

[0044] That is, if the ratio of the length M to L of the preset area in the heading direction is not an integer, it is rounded down to the nearest integer as the final number of segments; that is, an integer number of active skins are finally arranged in the preset area, and the remaining part is not long enough to be one L, so it is not arranged.

[0045] Step 3: A movable skin is arranged on the outer side of the wing within the preset area. The directional length of the movable skin is the preset length. The movable skin is a strip-shaped structure arranged on the outside of the wing skin, with adjacent movable skins having a clearance fit. A drive mechanism is arranged between each segment of the movable skin and the fuselage to drive that segment of the movable skin to oscillate longitudinally on the wing surface. Adjacent movable skins oscillate in opposite directions. The drive mechanism is either a motor or a hydraulic mechanism.

[0046] Step 4: Determine the spanwise oscillation parameters of the active skin at the initial moment of the aircraft entering the cruise phase.

[0047] The spanwise oscillation parameters of the active skin are:

[0048]

[0049] Where w wall (t) represents the spanwise oscillation velocity, A represents the maximum spanwise oscillation velocity amplitude, T0 represents the spanwise oscillation period, and t represents the oscillation time. The maximum spanwise oscillation velocity A = A + ×u τ , stretching oscillation period A + and T + These are the dimensionless maximum spanwise velocity and the dimensionless oscillation period, respectively, obtained through numerical simulation.

[0050] This paper proposes a numerical simulation scheme. The wing skin is modeled in ICEM. To simplify the model, the wing is assumed to be a straight wing, and the boundary conditions on the wing surface are set to spanwise oscillating boundary conditions. During the simulation, the wing surface is assumed to be in a fully turbulent state, and the longitudinal length of the movable skin is a dimensionless length L. + =150, fixed dimensionless maximum spanwise oscillation velocity A + =12, the dimensionless oscillation period takes values ​​in the range of T. + =50-200; Simulation results under this condition show that when the dimensionless oscillation period is T + The maximum drag reduction effect can be obtained when the value is 100; therefore, in this scheme, the dimensionless maximum spanwise velocity A + =12, dimensionless oscillation period T + =100.

[0051] Step 5: During the actual flight of the aircraft, at the initial moment after entering the cruise phase, the movable skin on the wing is driven to oscillate in the spanwise direction using the drive mechanism according to the spanwise oscillation parameters determined in Step 4.

[0052] Furthermore, the hydrodynamic parameters of the wing under the current cruise state can be collected in real time by sensors, including the friction speed of the moving skin surface and the surface kinematic viscosity coefficient. These two values ​​are used to correct the spanwise oscillation parameters in real time, and the corrected spanwise oscillation parameters are used to drive and control the moving skin in real time.

[0053] In practical applications, after entering the cruise phase, the aircraft continuously collects the friction velocity and surface kinematic viscosity of the moving skin surface at the current moment, and uses these two values ​​as parameters u. τ Substituting ν into the calculation formulas for A and T0, w can be calculated in real time. wall The value of (t) is used to continuously adjust the movement of the active skin in order to achieve a better drag reduction effect.

[0054] Example:

[0055] Based on the above scheme, the inventors performed calculations for the movable skin and the fixed skin (i.e., the original skin of the wing) separately. In order to accurately simulate the flow details inside the boundary layer, a direct numerical simulation method based on the Navier-Stokes equations was used to calculate the local boundary layer flow. To reduce the amount of computation, the channel flow model, which is commonly used both domestically and internationally, was adopted, aiming to provide a detailed simulation of the flow inside the boundary layer.

[0056] The Mach number of the incoming flow is 0.2, and the Reynolds number based on half-height of the channel is 3180; the maximum spanwise oscillation velocity is taken as A = 51.32 m / s, and the spanwise oscillation period is T0 = 7.69 × 10⁻⁶ m / s. -5 s; Atmospheric density, temperature, and viscosity coefficient are calculated using sea level parameters. Figure 2 It is the drag reduction curve of the active skin; Figure 3 The near-wall flow field vortex distribution is shown for fixed skin and movable skin; it can be seen that the frictional resistance of the movable skin with segmented oscillation is reduced by more than 30% compared with that of the fixed skin.

[0057] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for reducing spanwise vibration of segmented skin of an aircraft, characterized in that, include: Determine the hydrodynamic parameters of an aircraft entering the turbulent phase during cruise, including: the wing's position entering the turbulent phase, boundary layer thickness δ, and surface kinematic viscosity. ν and surface friction speed u τ The fluid dynamic parameters are obtained through actual flight tests or numerical simulations after modeling the aircraft. Based on the aforementioned fluid dynamics parameters, a predetermined region on the aircraft wing for arranging movable skin is determined. The wing within this predetermined region is then segmented along the aircraft's flight direction according to a predetermined length. The predetermined region extends along the flight direction from the point where the wing enters the turbulent phase to a distance of twelve times the boundary layer thickness δ from the aileron; and along the spanwise direction, it extends from a distance of twelve times the boundary layer thickness δ from the wing root to a distance of twelve times the boundary layer thickness δ from the wingtip. The predetermined length... L The calculation formula is: in, L + , a dimensionless length, represents the average flow-direction length of the vortex faced by the aircraft during cruise. This length can be obtained by numerical simulation of the flow field and post-processing analysis of the flow field. A movable skin is arranged on the outside of the wing within the preset area. The yaw length of the movable skin is the preset length. The movable skin is a strip structure. A drive mechanism is arranged between each segment of the movable skin and the fuselage to drive the segment of the movable skin to oscillate in the spanwise direction on the wing surface. The spanwise oscillation directions of adjacent movable skins are opposite. Determine the spanwise oscillation parameters of the active skin at the initial moment when the aircraft enters the cruise phase; During actual flight, when an aircraft enters the cruise phase, at the initial moment, it uses a drive mechanism to drive the movable skin on the wing to oscillate in the spanwise direction according to the determined spanwise oscillation parameters.

2. The drag reduction method for spanwise vibration of segmented aircraft skin according to claim 1, characterized in that, The method further includes: The hydrodynamic parameters of the wing under the current cruise state are collected in real time by sensors, including the friction velocity and surface kinematic viscosity of the moving skin. These two values ​​are used to correct the spanwise oscillation parameters in real time, and the corrected spanwise oscillation parameters are used to drive and control the moving skin in real time.

3. The drag reduction method for spanwise vibration of segmented aircraft skin according to claim 1, characterized in that, Within the preset area, according to the preset length L It is divided into segments, represented as: in, This indicates rounding down. M Indicates the length of the preset area in the heading; That is, an integer number of active skins will be placed within the preset area, with the remaining portion not enough for one. L If the length is too short, then no arrangement will be made.

4. The drag reduction method for spanwise vibration of segmented aircraft skin according to claim 2, characterized in that, The spanwise oscillation parameters of the movable skin are: in For spanwise oscillation velocity, A The maximum spanwise oscillation velocity amplitude, T 0 represents the period of the longitudinal oscillation. t Oscillation time, maximum spanwise oscillation velocity , stretching oscillation period ; A + and T + These are the dimensionless maximum spanwise velocity and the dimensionless oscillation period, respectively, obtained through numerical simulation.

5. The drag reduction method for spanwise vibration of segmented aircraft skin according to claim 4, characterized in that, The friction velocity and surface kinematic viscosity of the moving skin surface are collected in real time by sensors under the current cruise condition, and these two values ​​are used as parameters. u τ , ν Substitute into A , In the calculation formula, thus calculating in real time. The value is used to continuously adjust the movement of the active skin.

6. An aircraft, characterized in that, The aircraft wing is provided with a movable skin designed in the drag reduction method for spanwise vibration of segmented skin of an aircraft according to any one of claims 1-5.

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