CN113460284A

CN113460284A - Low-Reynolds-number lower wing with inclined grooves

Info

Publication number: CN113460284A
Application number: CN202110967608.1A
Authority: CN
Inventors: 张鹏; 孙爽
Original assignee: Civil Aviation University of China
Current assignee: Civil Aviation University of China
Priority date: 2021-08-23
Filing date: 2021-08-23
Publication date: 2021-10-01
Anticipated expiration: 2041-08-23
Also published as: CN113460284B

Abstract

A low Reynolds number lower wing with oblique grooves. A plurality of left-inclined and right-inclined oblique groove groups which are alternately distributed are arranged near the tail edge of the upper surface; each oblique groove group consists of a plurality of oblique grooves which are arranged in parallel along the chord direction at intervals, so that an spanwise array is formed; the adjacent oblique groove groups are arranged at intervals, so that the whole oblique groove groups are zigzag. According to the invention, the oblique groove is arranged at the tail edge of the upper surface of the wing, so that on one hand, a stable secondary vortex can be formed in the oblique groove, the rolling bearing in machinery is played, and the effect of reducing viscous resistance is achieved; on the other hand, the inclined grooves have the effect of vortex generators, secondary flow is formed in the boundary layer of the upper wing surface of the wing, the mixing of high-speed flow of the main flow and low-speed flow of the boundary layer is enhanced, the propagation of the low-speed flow to the main flow is blocked, the capability of resisting the adverse pressure gradient is stronger, the separation of the boundary layer can be inhibited, and the lift-drag ratio is effectively increased.

Description

Low-Reynolds-number lower wing with inclined grooves

Technical Field

The invention belongs to the technical field of civil aviation aircraft parts, and particularly relates to a low Reynolds number lower wing with an inclined groove.

Background

With the rise of micro aircrafts and unmanned planes, the aerodynamic performance of wings under low reynolds numbers is more and more concerned by researchers. The reduction of the Reynolds number enables the viscous friction force on the surface of the wing to be enhanced, and statistics shows that the wall friction resistance accounts for about 40% of the total resistance in the cruising state; in addition, due to the existence of the laminar boundary layer and the flow transition phenomenon, the boundary layer on the upper surface of the wing is easy to separate, and the separation can cause serious lift loss. Therefore, aiming at the working condition of low Reynolds number, an effective flow control method is developed, and the inhibition of flow separation and resistance reduction and lift increase are of great importance to the wing design.

At present, the flow control technologies for separation of boundary layer on the surface of the wing and stall mainly include active control and passive control. The active control technology mainly comprises plasma excitation, boundary layer blowing and sucking technology, synthetic jet flow and the like; passive control techniques include sinusoidal leading edges, vortex generators, wall microstructures, and the like.

The fine structure of the wall surface represented by the longitudinal small ribs/grooves imitating the sharkskin has better performance in the aspect of resistance reduction of the wall surface, and attracts extensive attention of researchers, however, the research shows that when the longitudinal small ribs are positioned on a laminar boundary layer, extra resistance can be generated, and the resistance reduction effect cannot be achieved; the transverse small ribs are considered to play a role of an air bearing and reduce the friction force of the wall surface, but the transverse small ribs cannot effectively inhibit negative layer separation and cannot play a role of reducing resistance and increasing lift for the wings with large attack angles. Therefore, the resistance-reducing and lift-increasing method based on the wall surface fine structure needs further research.

Disclosure of Invention

In order to solve the problems, the invention aims to provide a low Reynolds number lower wing with an inclined groove.

In order to achieve the aim, the low Reynolds number lower wing with the inclined grooves is characterized in that a plurality of inclined groove groups which are alternately distributed in a left-inclined mode and a right-inclined mode are arranged near the tail edge of the upper surface; each oblique groove group consists of a plurality of oblique grooves which are arranged in parallel along the chord direction at intervals, so that an spanwise array is formed; the adjacent oblique groove groups are arranged at intervals, so that the whole oblique groove groups are zigzag.

The number of the oblique grooves in each oblique groove group is 5-10.

The distance c between adjacent oblique grooves is 0.001 l-0.005 l, wherein l is the chord length of the wing.

The extending direction of the oblique grooves forms an included angle beta of 30-60 degrees with the incoming flow direction.

The spanwise width a of each oblique groove group is 0.05l to 0.15 l; the distance b between adjacent oblique groove groups is 0.005 l-0.01 l.

The cross section of the oblique groove is in a semiellipse shape, the major axis dimension d is 0.004 l-0.01 l, and the minor axis dimension e is 0.003 l-0.005 l.

The low Reynolds number lower wing with the oblique grooves provided by the invention has the following beneficial effects:

by arranging the inclined groove at the tail edge of the upper surface of the wing, on one hand, stable secondary vortex can be formed in the inclined groove until the function of a rolling bearing in machinery is achieved, and the effect of reducing viscous resistance is achieved; on the other hand, the inclined grooves have the effect of vortex generators, secondary flow is formed in the boundary layer of the upper wing surface of the wing, the mixing of high-speed flow of the main flow and low-speed flow of the boundary layer is enhanced, the propagation of the low-speed flow to the main flow is blocked, the capability of resisting the adverse pressure gradient is stronger, the separation of the boundary layer can be inhibited, and the lift-drag ratio is effectively increased. Compared with the longitudinal small ribs imitating the sharkskin, the oblique grooves are more suitable for resistance reduction and lift increase of the wings under the condition of low Reynolds number, and compared with the transverse small ribs/grooves, the oblique grooves can obviously play a role in inhibiting separation of boundary layers and have better resistance reduction and lift increase effects.

Drawings

FIG. 1 is a perspective view of a low Reynolds number lower airfoil with angled grooves according to the present invention.

Fig. 2 is a partial enlarged view showing the geometric and distribution features of the diagonal grooves in the present invention.

Fig. 3 is a schematic cross-sectional view of the slanted groove of the present invention.

Fig. 4 is a flow field diagram of a prototype airfoil surface without angled grooves at the trailing edge of the upper surface.

FIG. 5 is a flow field diagram of an airfoil surface having angled grooves at the trailing edge of the upper surface in accordance with the present invention.

Fig. 6 is a comparison diagram of lift-drag ratios of the wing with the oblique groove at the upper surface trailing edge and the prototype wing without the oblique groove at the upper surface trailing edge under different attack angles.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

As shown in FIG. 1, the low Reynolds number lower wing 1 with oblique grooves provided by the invention is provided with a plurality of oblique groove groups which are alternately distributed in a left-leaning way and a right-leaning way near the trailing edge 3 of an upper surface 2; each oblique groove group consists of a plurality of oblique grooves 4 which are arranged in parallel along the chord direction at intervals, so that an spanwise array is formed; the adjacent oblique groove groups are arranged at intervals, so that the whole oblique groove groups are zigzag.

As shown in fig. 2, for reynolds number of 5 × 10⁵The boundary layer separation will develop from the trailing edge 3 to the leading edge as the angle of attack of the wing 1 increases, so that inclined groove groups are arranged from the trailing edge 3 of the wing 1, the number of the inclined grooves 4 in each inclined groove group is adjustable, usually 5-10, and 8 are selected in the invention.

The distance c between adjacent oblique grooves 4 is adjustable, the size of the distance c determines the density of the oblique grooves 4 along the chord direction, the distance c is usually 0.001 l-0.005 l, and the distance c is selected to be 0.003l in the invention, wherein l is the chord length of the wing 1.

The size of the included angle beta between the extending direction of the oblique groove 4 and the incoming flow direction and the cross-sectional shape of the oblique groove 4 influence the flow control effect together, wherein the size of the included angle beta is adjustable, and the included angle beta is usually 30-60 degrees. In the present invention, the angle β is selected to be 30 °.

The spanwise width a of each oblique groove group and the distance b between adjacent oblique groove groups are adjustable, and the spanwise width a of each oblique groove group is usually 0.05l to 0.15 l; the distance b between adjacent oblique groove groups is 0.005 l-0.01 l. In the present invention, the spanwise width a is 0.095l and the pitch b is 0.005 l.

As shown in fig. 3, the cross section of the oblique groove 4 is a semi-ellipse, and the major axis dimension d and the minor axis dimension e are both adjustable, typically the major axis dimension d is 0.004 l-0.01 l, and the minor axis dimension e is 0.003 l-0.005 l. In the invention, the values of the long axis and the short axis are selected to be d-e-0.005 l.

As shown in fig. 4 and 5, by comparing the flow charts of the front and rear wing surfaces provided with the oblique grooves 4, it can be found that the boundary layer separation flow area of the upper surface of the wing provided with the oblique grooves 4 is significantly reduced compared with the original wing provided with no oblique grooves on the upper surface of the wing provided with the low reynolds number lower wing provided with the oblique grooves 4 on the trailing edge of the upper surface, so that the occurrence of separation can be delayed and suppressed by providing the oblique grooves 4.

As shown in fig. 6, it can be seen from the results of the numerical simulation of the lift-drag ratio of the wing at different angles of attack that the low reynolds number lower wing provided with the oblique groove 4 on the trailing edge of the upper surface provided by the invention has a significantly improved lift-drag ratio at different angles of attack compared with the original wing, and the lift-drag ratio can be improved by 152.6% at most compared with the original wing.

Therefore, on one hand, the low Reynolds number lower wing with the oblique grooves can form stable secondary vortexes in the oblique grooves 4 to achieve the effect of reducing viscous resistance; on the other hand, by forming the secondary flow in the boundary layer of the upper airfoil surface of the wing, the mixing of the high-speed flow of the main flow and the low-speed flow of the boundary layer can be enhanced, the propagation of the low-speed flow to the main flow is blocked, and the capability of resisting the adverse pressure gradient is stronger, so that the separation of the boundary layer can be inhibited, and the lift-drag ratio is effectively increased.

Claims

1. The utility model provides a wing under low reynolds number with slant slot which characterized in that: the low Reynolds number lower wing (1) with the inclined grooves is characterized in that a plurality of inclined groove groups which are alternately distributed in a left-inclined mode and a right-inclined mode are arranged near the tail edge (3) of the upper surface (2); each oblique groove group consists of a plurality of oblique grooves (4) which are arranged in parallel along the chord direction at intervals, so that an spanwise array is formed; the adjacent oblique groove groups are arranged at intervals, so that the whole oblique groove groups are zigzag.

2. The low reynolds number lower wing with angled grooves of claim 1, wherein: the number of the oblique grooves (4) in each oblique groove group is 5-10.

3. The low reynolds number lower wing with angled grooves of claim 1, wherein: the distance c between adjacent oblique grooves (4) is 0.001 l-0.005 l, wherein l is the chord length of the wing (1).

4. The low reynolds number lower wing with angled grooves of claim 1, wherein: the extending direction of the oblique grooves (4) forms an included angle beta of 30-60 degrees with the incoming flow direction.

5. The low reynolds number lower wing with angled grooves of claim 1, wherein: the spanwise width a of each oblique groove group is 0.05l to 0.15 l; the distance b between adjacent oblique groove groups is 0.005 l-0.01 l.

6. The low reynolds number lower wing with angled grooves of claim 1, wherein: the cross section of the oblique groove (4) is semiellipse, the major axis dimension d is 0.004 l-0.01 l, and the minor axis dimension e is 0.003 l-0.005 l.