CN118025352A - Distributed porous micron-structure drag reduction film - Google Patents

Abstract

The invention discloses a distributed porous micron-structure drag reduction membrane, which comprises the following components: the film body covered on the object is uniformly arranged in small rib areas on the film body, exhaust holes are arranged between adjacent small rib areas, and small rib structures are uniformly arranged on the small rib areas; the small rib area comprises a parallel small rib area and an inclined small rib area, the parallel small rib area is parallel to the streamline direction, the inclined small rib area is inclined to the streamline direction, and the near wall surface of the drag reduction film flows parallel to the small rib structure through distributed small rib arrangement, so that on one hand, the drag reduction effect can be improved, and on the other hand, the small rib structure is prevented from being damaged and deformed due to larger shape resistance under the high-speed motion state. The multi-vent structure is convenient for the installation of drag reduction membrane on complicated curved surface, prevents to form the swell in the installation, influences drag reduction effect and little rib membrane life.

Description

Distributed porous micron-structure drag reduction film

Technical Field

The invention relates to the technical field of drag reduction films, in particular to a distributed porous micron-structure drag reduction film.

Background

The object (car, train or aircraft) generates resistance when moving in liquid or gas, and the resistance can prevent the movement of the object, so that the resistance can reduce the movement speed of the object or increase the oil consumption of the object when moving or accelerating. Taking a minibus as an example, the energy expended for aerodynamic drag when traveling at a speed of 100km/h is about 50% of the fuel consumption. The energy consumed by the larger common truck for aerodynamic drag at a speed of 100km/h is about 32%. Data statistics show that when the running speed of an object is 80km/h to 300km/h, the fuel consumption caused by aerodynamic resistance occupies a very significant proportion of the total fuel consumption, which is typically above 30%, and when the running speed of the object exceeds 300km/h, the proportion of the fuel consumption caused by aerodynamic resistance occupies more.

Reducing the frictional resistance of a vehicle in motion is one of the main means of reducing its fuel consumption. Pneumatic friction resistance is the main component of total friction, resulting from the interaction between the fluid and the wall. Related researches show that the small rib structure with a specific configuration can effectively reduce the pneumatic friction resistance, so that the utilization efficiency of fuel is improved.

In the prior art, most research and design has focused on improving drag reduction by optimizing the rib structure parameters. However, drag reducing films with small rib structures still present problems during practical use. On the one hand, the drag reduction effect is directly influenced by the included angle between the airflow flowing direction and the arrangement direction of the small rib structure. If the included angle is too large, the effect of increasing resistance may be generated. On the other hand, the surface requiring drag reduction in practical application often has a complex curved surface appearance structure, so that the whole drag reduction film with a small rib structure is difficult to be flatly adhered to the surface.

For example, chinese patent CN 103496405A discloses a drag reducing film, the surface of the drag reducing film is formed with pockets, the pockets are spaced apart and form an array, the depth of the pockets is smaller than the diameter of the pockets, the drag reducing film covers the surface of the moving object, and the pockets enable the boundary of the laminar flow to extend backward along the length direction of the moving object. The drag reduction film is covered on the surface of a moving object, such as a shell of an automobile, a rail transit vehicle, a train or a low-speed aircraft, turbulence is reduced by using a turbulence guiding structure formed by a concave cavity array, and a laminar boundary extends backwards along the length direction of the moving object. The drag reduction film with the structure can reduce aerodynamic drag by reducing pressure difference in front of and behind an object so as to reduce fuel consumption, but the drag reduction film with the 'concave' structure in the technical scheme is not suitable for the object in a high-speed motion state, and the drag reduction film with the 'concave' structure is easily damaged and deformed due to larger shape resistance in the high-speed motion state.

For example, chinese patent CN 113479287a discloses a marine drag reducing film comprising micropores, grooves, gum, etc. After bubbles are generated in the ship body, the bubbles move backwards along the grooves on the membrane through micropores on the ship bottom to form a layer of air film layer so as to limit the transverse movement of liquid at the bottom of the boundary layer on the surface of the aircraft, improve the characteristics of a flow field near the wall surface of the aircraft, effectively reduce the friction resistance of the wall surface, further obtain higher speed, reduce energy consumption and fully play the advantages of energy conservation and emission reduction in the aspect of environmental protection. In addition, if the corresponding conditions exist, the number and the partition of the gas generating pore channels can be controlled through a wetting step effect, so that one part of the gas generating pore channels generates gas while the other part does not generate gas, and the gas film is restrained by the aggregation of a plurality of grooves, so that the existence time of the gas film is prolonged. The drag reduction membrane of the structure forms a stable air film at the bottom of the ship through the constraint action of the drainage and the grooves, and finally achieves the purpose of effectively reducing drag of the ship, but cannot be applied to objects running at high speed, and if the grooves and the micropores are arranged on an aircraft running at high speed, the grooves and the micropores can be rapidly damaged and deformed.

For example, chinese patent CN104908828 discloses a device for adding air film drag reduction and pressure difference drag reduction to a vehicle body and a method for reducing wind resistance, wherein the device is a cover body with a top wall and two side walls and mounted on the outer surface of the vehicle body; the top wall and the two side walls of the cover body are formed by sandwich plates with a plurality of air chambers inside, and each air chamber is provided with a plurality of air seepage holes facing the outside of the cover body: the front end of the car body is provided with a high-pressure air pump, the high-pressure air pump conveys air flow to each air chamber from the front end of the cover body through a pipeline, the air flow is ejected out of the outer surface of the cover body through the top wall of the cover body and the air seepage holes of the two side walls, and an air film is formed on the outer surface of the cover body. The air film is contacted and mixed with external air flow, so that the speed difference between the air film and the cover body is reduced, the speed gradient of a boundary layer outside the vehicle body is reduced, the friction effect of viscous force is weakened, and the wind resistance in the running process of the vehicle is reduced. According to the technical scheme, the drag reduction effect exists on a vehicle running at a low speed, the drag increase effect is easy to occur on an aircraft running at a high speed due to the particularity of the inner cover body and the outer cover body, and the cover body is easy to be damaged and deformed due to larger shape resistance in the high-speed movement state.

Disclosure of Invention

The invention aims to: the invention aims to solve the defects in the prior art, and provides a distributed porous micro-structure drag reduction film, which has improved drag reduction effect through a small rib structure distributed and arranged, and has a multi-scale exhaust hole structure, so that the drag reduction film is convenient to paste and install on a complex curved surface.

The technical scheme is as follows: in order to achieve the above object, the present invention provides a drag reducing film of distributed porous micrometer structure, comprising: the film body covered on the object is uniformly arranged in small rib areas on the film body, exhaust holes are arranged between adjacent small rib areas, and small rib structures are uniformly arranged on the small rib areas;

The small rib areas comprise parallel small rib areas and inclined small rib areas, the parallel small rib areas are parallel to the streamline direction, the inclined small rib areas are inclined to the streamline direction, and at least 1 parallel small rib area is arranged between every two adjacent inclined small rib areas;

The four inclined small ribs are respectively positioned at the left and right limit positions of the first row and the left and right limit positions of the last row, and the inclined small ribs arranged at the two ends are respectively used for introducing and guiding out gas.

As a further preferable mode of the invention, the cross section of each small rib structure is triangular, a trapezoid groove is arranged between two adjacent small rib structures, and each small rib structure is used for guiding the flow direction of the gas so as to minimize the resistance of an object under the condition of high-speed running.

As a further preferred aspect of the present invention, the distance between adjacent small rib areas is 2.5mm to 5mm.

As a further preferable aspect of the present invention, the diameter of the vent hole is 0.5mm to 1mm.

As a further preferable mode of the invention, the distance between two adjacent circular vent holes is 5 mm-8 mm, and the circular vent holes are arranged on the gap between the areas, and the vent holes can uniformly discharge the residual air between the film and the wall surface in the adhesive mounting process, so that the residual air is prevented from forming a bulge.

As a further preferred aspect of the present invention, the exhaust holes are aligned in a straight line along the length direction.

As a further preferred aspect of the present invention, the small rib structures on the inclined small rib regions have an inclination angle ψ with respect to the streamline direction, and the inclination angle is: the inclined angle of the small rib structures on the adjacent inclined small rib areas is equal to or less than 0 DEG and equal to or less than 20 DEG, the inclined small rib areas are positioned at two sides of the parallel small rib areas, and the inclined small rib areas are used for leading gas flow into the parallel small rib areas and leading the gas flow out of the parallel small rib areas.

As a further preferred aspect of the present invention, the relationship function between the small rib drag reduction amount γ of the small rib structure and the inclination angle ψ is:

γ＝-0.0795+8×10^-5ψ+0.0001ψ²。

The beneficial effects are that: according to the distributed porous micro-structure drag reduction film, the distributed small ribs are distributed to enable the near-wall surface flow to be parallel to the small rib structures, so that on one hand, the drag reduction effect can be improved, and on the other hand, the small rib structures are prevented from being damaged and deformed due to larger shape resistance in a high-speed motion state. The multi-vent structure is convenient for the installation of drag reduction membrane on complicated curved surface, prevents to form the swell in the installation, influences drag reduction effect and little rib membrane life.

Drawings

FIG. 1 is a simplified pictorial illustration of a simplified top view of the present invention;

FIG. 2 is a schematic view of the direction of the rib structures and the direction of the streamline;

FIG. 3 is a schematic view of a longitudinal interface of a small rib structure;

FIG. 4 is a schematic diagram of the relationship between the small rib angle and drag reduction ratio;

FIG. 5 is a schematic diagram of example 1;

FIG. 6 is a schematic diagram of example 2.

Detailed Description

The invention is further elucidated below in conjunction with the drawings.

As shown in fig. 1, 2 and 3, the drag reducing film with distributed porous microstructure according to the present invention includes: the membrane comprises a membrane body 1 covered on an object, a small rib area 2 and an exhaust hole 3, wherein the small rib area 2 is uniformly arranged on the membrane body 1, the small rib area 2 comprises a parallel small rib area 21 and an inclined small rib area 22, the parallel small rib area 21 is parallel to the streamline direction, and the inclined small rib area 22 is inclined to the streamline direction;

four inclined rib areas 22 are located at the left and right extreme positions of the first row and the left and right extreme positions of the last row, respectively.

According to the related research conclusion in the prior art, the included angle between the small rib structure 23 and the incoming flow can influence the drag reduction effect of the drag reducing film. The small rib structures 23 provide the best drag reduction when parallel to the flow direction. Therefore, the distributed arrangement can ensure that the small rib structures 23 in each small rib area 2 are parallel to the local streamline as much as possible, so that the whole drag reduction film achieves the optimal efficiency. The relation function between the drag reduction amount of the small rib and the included angle is that

γ＝-0.0795+8×10^-5ψ+0.0001ψ² (1)

Wherein, psi represents the included angle between the small rib structure and the streamline direction, and gamma represents the drag reduction ratio (negative number is drag reduction and positive number is drag increase). According to this equation, the small rib structure 23 will instead have a drag increasing effect when the included angle is greater than 26 °. Therefore, in order to reduce the influence of the included angle of the streamline on the drag reduction effect, the included angle between the rib structure 23 and the local streamline in each subarea needs to be ensured to be smaller than 20 degrees as much as possible in the practical design process.

The calculation mode of the included angle phi between the small rib structure and the streamline direction is as follows:

Since the streamline direction is the same as the velocity direction, the included angle can be calculated by the velocity vector direction, and the velocity vector on the surface is set under the same coordinate system Local surface normal vector/>The projection vector of velocity at that location of the surface, i.e. tangential velocity direction is/>Let the direction vector of the small rib structure 23 in the same space coordinate system be/>The following needs to be satisfied:

Based on the above constraint conditions, the design of the small rib region 2 is performed in combination with the specific curved streamline direction in the actual design process, and a proper partition mode and the orientation of the small rib structure 23 in the small rib region 2 are determined.

Example 1

When the film body 1 is a rectangular flat plate, it is mounted on a plane. The flat surface drag reducing film is divided into two small rib areas 2 as shown in fig. 5. Gaps of 2.5mm exist between the small rib areas 2, the diameters of the exhaust holes 3 are 0.5mm, the distance between two adjacent exhaust holes 3 is 5mm, and the size of the small ribs is determined according to the flow field characteristics;

Surface normal vector The direction of the average streamline/>, in the parallel small rib region 21Direction of average streamline/>, in inclined rib region 22It can be found that the tangential velocity direction in the two small rib areas 2 is/>, respectivelyAnd/>

If it is expected that the average angle ψ=0, the direction vector of the rib structures 23 in the two rib areas 2 can be found according to equations (2) (4) (5)

And (3) taking the direction of the small rib structures 23 on the parallel small rib areas 21 as a reference, calculating the included angle between the actual flow field direction of each point on the surface and the small rib structures 23, calculating the drag reduction amount of each point through an equation (1), and integrating to obtain the integral drag reduction amount which is about gamma= -0.0763, namely the friction resistance is reduced by 7.63%.

This example only demonstrates that after a drag reducing film is coated on a planar object, the partial position uses equation (1) to calculate the effect of the angle setting of the small rib structures 23 on the drag reducing film on drag reduction.

Example 2

The film body 1 is a rectangular flat plate and is arranged on a three-dimensional surface. The flat surface drag reducing film is divided into two small rib areas 2 as shown in fig. 6. A gap of 5mm exists between two adjacent small rib areas 2, the diameter of the exhaust hole 3 is 1mm, the distance between two adjacent exhaust holes 3 is 5mm, and the size of the small ribs is determined according to the flow field characteristics;

Surface normal vector in parallel rib region 21 Direction of average streamline/>Surface normal vector/>, in inclined rib region 22Direction of average streamline/>It can be found that the tangential velocity direction in the two small rib areas 2 is/>, respectivelyAnd/>

If it is expected that the average angle ψ=0, the rib direction vectors in the two rib areas 2 can be found according to equations (2) (4) (5)

And (3) taking the direction of the small rib structures 23 on the parallel small rib areas 21 as a reference, calculating the included angle between the actual flow field direction of each point on the surface and the direction of the small rib structures 23, calculating the drag reduction amount of each point through an equation (1), and integrating to obtain the integral drag reduction amount which is about gamma= -0.0795, namely the friction resistance is reduced by 7.95%.

This example is only to verify that after the drag reducing film is covered on the three-dimensional object, the partial position uses equation (1) to calculate the effect of the angle setting of the small rib structure 23 on the drag reducing film on the drag reducing.

The foregoing embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the present invention and to implement the same, not to limit the scope of the present invention. All changes and modifications that come within the meaning and range of equivalency of the invention are to be embraced within their scope.

Claims (10)

1. A distributed porous microstructured drag reducing film comprising: film body (1) on the object, its characterized in that: the membrane also comprises small rib areas (2) which are uniformly distributed on the membrane body (1), exhaust holes (3) are arranged between the adjacent small rib areas (2), and small rib structures (23) are uniformly distributed on the small rib areas (2);

the small rib area (2) comprises a parallel small rib area (21) and an inclined small rib area (22), the parallel small rib area (21) is parallel to the streamline direction, and the inclined small rib area (22) is inclined to the streamline direction;

Four inclined rib areas (22) are respectively positioned at the left and right limit positions of the first row and the left and right limit positions of the last row.

2. The distributed porous microstructured drag reducing film of claim 1, wherein: the cross section of the small rib structure (23) is triangular.

3. The distributed porous microstructured drag reducing film of claim 2, wherein: trapezoidal grooves (24) are arranged between two adjacent small rib structures (23).

4. The distributed porous microstructured drag reducing film of claim 1, wherein: the distance between the adjacent small rib areas (2) is 2.5 mm-5 mm.

5. The distributed porous microstructured drag reducing film of claim 1, wherein: the diameter of the exhaust hole (3) is 0.5 mm-1 mm.

6. The distributed porous, microstructured drag reducing film of claim 5, wherein: the distance between two adjacent circular exhaust holes (3) is 5 mm-8 mm.

7. The distributed porous, microstructured drag reducing film of claim 6, wherein: the exhaust holes (3) are arranged in a straight line along the length direction.

8. The distributed porous microstructured drag reducing film of claim 1, wherein: the inclination angle of the small rib structure (23) on the inclined small rib area (22) and the streamline direction is phi, and the inclination angle is: the phi is more than 0 DEG and less than or equal to 20 deg.

9. The distributed porous, microstructured drag reducing film of claim 8, wherein: the inclination angles of the small rib structures (23) on the adjacent inclined small rib areas (22) are mutually mirror surfaces.

10. The distributed porous, microstructured drag reducing film of claim 8, wherein: the relation function between the small rib drag reduction amount gamma of the small rib structure (23) and the inclined angle phi is as follows:

γ＝-0.0795+8×10^-5ψ+0.0001ψ²。