An aerodynamic metasurface and applications thereof

Abstract

The application discloses an aerodynamic super surface technology, and the super surface comprises a base body, and a plurality of periodic microstructures are arranged on the surface of the base body; the size of the microstructures is 10 mu m, and the microstructures can naturally form a stable micro secondary vortex under the action of airflow, so that a dense micro vortex layer is formed above the original solid wall surface layer. The application relates to the field of aerodynamic drag reduction, and when the super surface is used as the surface of a high-speed aircraft, a relatively low pressure area is formed in each microstructure due to the low-speed backflow vortex, a weak deformation of the streamline appears in the near-wall area, a relatively high pressure is formed on the inclined surface, the stability of the backflow vortex can be ensured, and meanwhile, the interaction between the main flow and the vortex structure forms a velocity slip boundary layer; since the scale of the microstructure is within the control range of the viscous bottom layer, the existence of the velocity slip boundary layer can obviously reduce the velocity gradient of the actual boundary layer, so that the frictional resistance can be greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aircraft aerodynamic drag reduction technology, and particularly relates to an aerodynamic super surface and application thereof. BACKGROUND

[0002] Aerodynamic frictional resistance is caused by the shearing action between airflow and wall surface. The energy and heat exchange between airflow and wall surface occurs in the boundary layer. There is a temperature gradient and a velocity gradient from the wall surface to the outer edge of the boundary layer, which determines the size of the shear force. When the flow is in a high-speed state, the viscous effect in the boundary layer will be enhanced, and the velocity gradient will increase, resulting in an increase in frictional resistance. For an aircraft, an increase in frictional resistance means that more power is needed, and usually the frictional resistance can account for more than 40% of the total resistance of the aircraft, which is a major limiting factor for further speed increase of the aircraft. Therefore, aircraft drag reduction technology has become a front hot spot in aircraft design engineering.

[0003] The existing researches on reducing surface friction can be divided into passive and active methods.

[0004] The passive method mainly simplifies the micro-groove structure according to the bionic principle, which is divided into two ways of arranging in the flow direction and transversely. The main principle is to suppress the turbulent burst process at the bottom of the boundary layer by weakening and limiting the turbulent kinetic energy and energy exchange in the turbulent flow, so as to reduce the viscous resistance in the boundary layer and achieve the purpose of drag reduction. However, the passive method is currently limited to the low-speed field, the drag reduction mechanism has not been unified, and the actual drag reduction efficiency is less than 10%, which is not good.

[0005] In the active method, the patent CN114476029A discloses a heat-proof and drag-reducing method based on a bottom base microcavity and a heavy gas ablation material. The ablation material generates heavy gas when ablated, which can absorb the energy of the second mode wave and inhibit the occurrence of transition, thereby reducing the drag. However, this method is more suitable for the second mode in the boundary layer transition, which has obvious limitations, and the ablation material method cannot guarantee the effective time.

[0006] A method for generating wall normal cold jets and / or wall tangential cold jets on the wall surface of a hypersonic aircraft to form a surface cold gas film on the surface boundary layer of the hypersonic aircraft, isolate the direct interaction between the hypersonic main flow and the wall, change the original gas-solid shear layer into a gas-gas shear layer, reduce the original velocity gradient of the boundary layer, and thereby realize the reduction of the hypersonic boundary layer friction drag is described in CN115384759A patent "A hypersonic aircraft heat reduction and drag reduction method". However, this active method will bring extra structure to the aircraft shape, affect the flow field, and on the other hand, it needs a large amount of gas working medium, and has poor adaptability to three-dimensional complex shapes. SUMMARY

[0007] In view of the deficiencies in the prior art, the present application provides an aerodynamic metasurface and its application, which can effectively realize efficient aerodynamic drag reduction of the aircraft in high-speed state, and has small implementation difficulty, strong applicability, and does not need additional working medium or filling material.

[0008] To achieve the above purpose, the present application provides an aerodynamic metasurface, comprising a substrate, a plurality of microstructures are arranged on the surface of the substrate along the flow direction, the length direction of the microstructure is perpendicular to the flow direction;

[0009] And the width and depth of the microstructure are both on the order of 10μm, so that a micro stable secondary vortex flow is naturally formed in the microstructure under the action of the incoming flow, thereby forming a dense micro vortex layer above the original solid wall surface layer.

[0010] In one embodiment, the cross section of the microstructure is a trapezoidal structure, which includes a first side wall, a bottom wall and a second side wall connected in sequence;

[0011] The first side wall is located upstream and perpendicular to the substrate surface, the bottom wall is parallel to the substrate surface, and the second end of the second side wall is connected to the bottom wall, and the second end is connected to the substrate surface and extends downstream.

[0012] In one embodiment, the second end of the second side wall and the substrate surface are connected by a circular arc transition.

[0013] In one embodiment, the height of the first side wall is 20μm~30μm.

[0014] In one embodiment, the width of the bottom wall is 10μm~20μm.

[0015] In one embodiment, the included angle between the bottom wall and the second side wall is in the range of 100°~170°.

[0016] In one of the embodiments, the interval between two adjacent microstructures is a geometric multiple of the first side wall,

[0017] All the microstructures are arranged periodically.

[0018] To achieve the above object, the application further provides an application of the aerodynamic super surface, characterized in that the aerodynamic super surface is used as a wall surface of a hypersonic aircraft.

[0019] In each microstructure of the aerodynamic super surface, due to the relatively low pressure area formed by the low-speed backflow vortex, the flow line in the near-wall area is slightly deformed, and a relatively high pressure is formed on the slope, which can ensure the stability of the backflow vortex, and there is an interaction between the main flow and the vortex structure, forming a velocity slip boundary layer, and due to the scale of the microstructure being within the control range of the viscous bottom layer, the existence of the velocity slip boundary layer can significantly reduce the velocity gradient of the actual boundary layer, thereby greatly reducing the frictional resistance.

[0020] Compared with the prior art, the application has the following beneficial technical effects:

[0021] In the application, a plurality of microstructures are arranged along the flow direction on the surface of the base body, the length direction of the microstructure is perpendicular to the flow direction, and the width and depth of the microstructure are controlled to be about 10 microns, so as to form a super surface structure, and when the super surface structure is applied to the surface of a hypersonic aircraft, in each microstructure, due to the relatively low pressure area formed by the low-speed backflow vortex, the flow line in the near-wall area is slightly deformed, and a relatively high pressure is formed on the slope, which can ensure the stability of the backflow vortex, and there is an interaction between the main flow and the vortex structure, forming a velocity slip boundary layer, and due to the scale of the microstructure being within the control range of the viscous bottom layer, the existence of the velocity slip boundary layer can significantly reduce the velocity gradient of the actual boundary layer, thereby greatly reducing the frictional resistance. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from the drawings shown without creative labor.

[0023] Figure 1 The figure is a structure schematic diagram of the aerodynamic super surface in the embodiment of the application.

[0024] Figure 2 The figure is a principle schematic diagram of the aerodynamic super surface in the embodiment of the application.

[0025] Reference numerals: substrate 1 , microstructure 2 , first side wall 201 , bottom wall 202 , second side wall 203 , secondary vortex 3 .

[0026] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0029] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0030] like Figure 1 The figure shows an aerodynamic metasurface disclosed in this embodiment, which mainly includes a substrate 1, and a plurality of microstructures 2 are provided on the surface of the substrate 1 along the flow direction. The length direction of the microstructure 2 is perpendicular to the flow direction, and the width and depth dimensions of the microstructure 2 are both on the order of 10 μm. Among them, the aerodynamic metasurface refers to a wall material with an artificially designed and processed micron-scale array-type periodic microstructure. Since the scale of the artificial microstructure on the surface of the material is only on the order of 10 μm, for the macroscopic aircraft scale, the naked eye cannot distinguish the periodic artificial microstructure on the surface. When the aerodynamic metasurface in this embodiment is used as the wall of an aircraft, under the action of the incoming flow, micron-scale stable secondary vortices 3 will naturally form in the microstructure 2. From a macroscopic point of view, the secondary vortices 3 in the numerous microstructures 2 can form a dense microvortex layer above the original solid wall surface. The existence of the microvortex layer changes the original solid surface properties into a gas surface.

[0031] refer to Figure 2The cross section of the microstructure 2 is a trapezoidal structure, which comprises a first side wall 201, a bottom wall 202 and a second side wall 203 connected in sequence. The first side wall 201 is located upstream and perpendicular to the surface of the base body 1, the bottom wall 202 is parallel to the surface of the base body 1, the first end of the second side wall 203 is connected with the bottom wall 202, and the second end is connected with the surface of the base body 1 and extends downstream. Among them, the height of the first side wall 201 is 20-30 μm, and the width of the bottom wall 202 is 10-20 μm.

[0032] As a preferred embodiment, the second end of the second side wall 203 and the surface of the base body 1 are connected by a circular arc.

[0033] In the specific implementation process, the included angle between the bottom wall 202 and the second side wall 203 is 100-170°, and the spacing between the adjacent two microstructures 2 is a geometric multiple of the first side wall.

[0034] It is worth noting that in the specific application process, the cross-sectional shape of the microstructure 2 is not limited to the trapezoidal structure, but can also adopt other structural forms, such as a combination of circular arc and trapezoidal structure, etc.

[0035] In the specific application process, the size of the frictional resistance inside the boundary layer is related to the velocity gradient of the boundary layer along the direction perpendicular to the wall surface, that is:

[0036] ;

[0037] Among them, is the shear force (i.e. frictional resistance), is the viscosity coefficient, is the velocity gradient.

[0038] For the natural boundary layer of the solid wall surface, due to viscosity, the velocity of the gas at the wall surface is 0, and the outer edge of the boundary layer is equal to the velocity of the main flow, thereby forming the velocity gradient inside the boundary layer, wherein the height of the maximum velocity gradient is at the position of the viscous bottom layer of the boundary layer, in this range, the viscous force is dominant, there is the strongest energy transport and exchange, and the shear and heat exchange are also the highest. For the aerodynamic super surface in the present embodiment, when used as a wall surface of a hypersonic aircraft, in each microstructure 2, due to the relatively low pressure area formed by the low-speed backflow vortex, the streamline in the near-wall area will be slightly deformed, and a relatively high pressure will be formed on the inclined surface, which can ensure the stability of the backflow vortex, and there is an interaction between the main flow and the vortex structure, forming a velocity slip boundary layer. Since the size of the microstructure 2 is within the control range of the viscous bottom layer, the existence of the velocity slip boundary layer can significantly reduce the velocity gradient of the actual boundary layer, thereby greatly reducing the frictional resistance.

[0039] The above merely describes the preferred embodiments of the present application, and is not intended to limit the patent scope of the present application. Any equivalent structural changes made according to the content of the present application specification and drawings, or direct / indirect application in other related technical fields, are included in the patent protection scope of the present application.

Claims

1. An aerodynamic metasurface, characterized in that It comprises a substrate, wherein a plurality of microstructures are provided on the surface of the substrate along the flow direction, and the length direction of the microstructures is perpendicular to the flow direction; The width and depth of the microstructure are both on the order of 10 μm, so that under the action of the incoming flow, a microscopic stable secondary vortex is naturally formed in the microstructure, thereby forming a dense micro-vortex layer above the original solid wall surface; The cross-section of the microstructure is a trapezoidal structure, comprising a first side wall, a bottom wall, and a second side wall connected in sequence; the first side wall is located upstream and perpendicular to the substrate surface, the bottom wall is parallel to the substrate surface, a first end of the second side wall is connected to the bottom wall, and a second end is connected to the substrate surface and extends downstream; The height of the first sidewall is 20 μm to 30 μm, the width of the bottom wall is 10 μm to 20 μm, and the spacing between two adjacent microstructures is a geometric multiple of the first sidewall, and the microstructures are arranged periodically.

2. The aerodynamic metasurface according to claim 1, wherein: There is an arc transition between the second end of the second side wall and the surface of the base.

3. The aerodynamic metasurface according to claim 1 or 2, characterized in that The included angle between the bottom wall and the second side wall ranges from 100° to 170°.

4. An application of the aerodynamic metasurface according to any one of claims 1 to 3, characterized in that: Using the aerodynamic metasurface as the wall of a hypersonic vehicle; In each microstructure of the aerodynamic metasurface, due to the relatively low-pressure area formed by the low-speed recirculation vortex, the streamlines in the near-wall area will be slightly deformed, and a relatively high pressure will be formed on the inclined surface, which can ensure the stability of the recirculation vortex. At the same time, there is an interaction between the mainstream and the vortex structure to form a velocity slip boundary layer. Since the scale of the microstructure is within the control range of the viscous bottom layer, the existence of the velocity slip boundary layer reduces the velocity gradient of the actual boundary layer, resulting in a reduction in frictional resistance.

Images