DE3305756A1 - Method of delaying the separation of the boundary layer on a wall having an incident fluid flow, and application thereof - Google Patents

Abstract

In a method of delaying the separation of the boundary layer on a wall (3) having an incident fluid flow, smooth fibres (15) or the like pointing approximately in the flow direction (2) are attached to the wall (3). In order to be able to apply this method economically for walls (3) in the building of fluid-flow machines, the fibres (15) are connected to the wall (3) in a stepless fashion at their end (16) pointing against the flow direction (2), and arranged at their opposite end (17) freely movable relative to the wall (3), so that the free end (17) aligns itself automatically parallel and/or perpendicular to the wall (3) in accordance with the forces of the fluid acting at this end. <IMAGE>

Description

Method of delaying the separation of the boundary layer one from one Fluid laminar flow against wall and application of the same The present The invention relates to a method for delaying the separation of the boundary layer of a wall against which a fluid flows in a laminar manner according to the preamble of Claim 1 and its application.

In the publication "Structure - Form - Movement, BIOLOGY AND TECHNOLOGY by Heinrich Hertel, Vol. 1 (1963), Krauskopf-Verlag GmbH, Mainz, page 191, Paragraph 3, line 16 ff, a method is indicated in which to stabilize the laminar flow and damping of the boundary layer on a wall thin wires next to each other be arranged in the direction of flow. Measures for performing and applying the However, procedures are not specified in this publication.

The invention characterized in claim 1 is based on the object a method of delaying the separation of the boundary layer on one of a fluid to create the flowed wall of the type mentioned, which for walls of the fluid mechanical engineering is easy and economical to use.

With the invention according to claim 1 it is achieved that the fluid, So gas (air) or liquid (water), along the smooth fibers or the like. the wall is held and guided in the laminar state. The free movable ends of the fibers automatically aligned in the direction of the flow. The transition of the flow on the wall from the laminar to the turbulent state occurs relatively late or is prevented entirely. The laminar or turbulent flow The boundary layer does not come off the wall. This results in an advantageous small flow resistance on the wall. The fibers or the like. Can simple, for example by pouring into a wall of cast material or by welding, Connect to the wall without a step.

Appropriate measures for carrying out or applying the invention Process are characterized in the subclaims.

The measure of claim 2 causes the free end of the fibers or the like. Without attaching structurally complex flaps (with joints) themselves can align.

With the measure according to claim 3, the advantage is achieved that the the machine element supporting the wall can be produced economically because a part the surface of the wall simply, i.e. without attaching fibers or the like can be.

The measure according to claim 4 has the consequence that the fibers or the like. the flow also in the area of the outflow end or the outflow edge of the wall calm down, so that there are fewer separation vortices, which give rise to annoying noise can arise.

When using the method according to the invention for a laminar flow Wing according to claim 5, the flow around the wing then takes place relatively low noise, if this is in the range of different angles of attack works relative to the direction of flow of the fluid.

In particular, in the case of an airfoil, the backflow is that at the rear End of the suction side blocked boundary layer prevented, so that an advantageously smaller induced wing drag arises. It is also due to the on the wall of the suction side and / or fibers arranged at the downstream end of the wing or the like. A harmful lateral outflow of the fluid (towards the ends of the wing) at least inhibited.

In the event that the fibers or the like. According to claim 5 on the suction side and / or at the outflow end of a flat or continuously curved wall of a hydrodynamic or bearing sliding surface against a hydrostatic flow, results an advantageously low bearing friction.

In the claims 6 to 8 are appropriate measures for adaptation of the fibers or the like. Given different flow conditions, so that with this in each individual application a detachment of the boundary layer from the wall prevented or delayed.

The arrangement of the fibers or the like. According to claim 9 causes by Pressure surges of the fluid caused vibrations of the fibers from the vibration-damping, compressible material, e.g. rubber, is absorbed between the fibers and the wall will.

The pressure waves can be applied to the (film-shaped) fibers or the like automatically develop surface waves adapted to the fluid.

The measure according to claim 10 causes an oscillation and mutual Movement of the fibers is dampened and thus the fibers collide with each other during operation is avoided, because the neighboring fibers with the same polarity collide with one another from, The fibers, which are made of a suitable electrostatically chargeable material, e.g.

Plastic, can be made by the friction of the fluid flowing past be continuously charged.

The electrostatic charge can also be caused by electrical influence be done by adding a constant or a at one end or inside the fibers Depending on the flow conditions, controllable electrical voltage is applied will. Finally, the fibers can also be used together with the associated wall, the can also consist of an electrostatically chargeable plastic, of the same name be poled electrostatically. The fibers are then also in their movement to the Wall braked.

The method according to the invention for delaying the Detachment of the boundary layer at a laminar flow against which a fluid flows Wall together with application examples shown in the drawing, explained in more detail. 1 shows a profile cross section through an airfoil with arranged on its wall of the suction side, protruding over the trailing edge film-shaped fibers, FIG. 2 shows a partial plan view of the wall of the suction side of the wing shown in Figure 1, 3 shows a profile cross section by a modified wing, Fig. 4 is a profile cross section through a Another modified wing, Fig. 5 shows a central cross section through a transverse Circular plate flowed against it with film-shaped fibers arranged on its edge, Fig. 6 shows a partial cross-section through a stepped sliding bearing with at the trailing edge film-shaped fibers arranged at each stage and FIG. 7 is a partial plan view onto the sliding surface provided with steps of the step sliding bearing shown in FIG.

In Figures 1 and 2, 1 is a wing of an aircraft, a fan or a propeller turbine called by a gaseous or the flow of liquid fluid in the direction of arrow 2 is laminar. This fluid flows around the wing 1 and moves along the convex curved wall 3 on the suction side and along the convex at the front end and then (at the rear end) concave curved wall 4 on the pressure side to the trailing edge 5 of the wing 1. On the walls 3 and 4 forms in is known from the stagnation point 6 of the wing 1 from a laminar or turbulent Boundary layer.

Starting from stagnation point 6 is in the front area of the wing 1 a thin, smooth and flexible one Foil 8 made of metal or Plastic glued onto the wing body 7. The wall 3 is the suction side in the front area of the wing 1 through the smooth outer surface section 9 of the film 8 and in the rear area through the opposite to the surface section 9 inwardly offset rear surface section 10 of the wing body 7 is formed.

Between the film 8 and the rear surface section 10 of the wing body 7 there is a narrow gap 11.

In this gap 11 there are webs aligned in the direction of flow 2 12 introduced from an elastically compressible and stretchable elastomer adhesive, so that they connect the film 8 to the wing body 7 in sections.

From the illustration in Figure 2 it can be seen that the film 8 in the risk of detachment rear area of the wing 1 in the direction of flow 2 extending long slots 13 and short slots 14, which alternate transversely to the direction of flow 2 arranged side by side and open to the trailing edge 5. Through these slots 13, 14 are at the rear end of the film 8 pointing approximately in the direction of flow 2 Fibers 15 formed. The film-shaped fibers 15 have an inwardly facing Foil surface that is approximately parallel to surface section 10 at a small distance the wall 3 runs.

At its freely movable end 17 pointing in the direction of flow 2 the fibers 15 are branched. At its opposite end 16, which shows against the flow direction 2, the fibers 15 are with the surface section 9 of the wall 3 in one piece and connected without a step.

The branches 18 of the fibers 15 partly protrude over the trailing edge 5 backwards forwards. The free mobility of the ends 17 of the fibers 15 relative to the Surface section 10 of the wing body 7 grows along its length in the direction of flow 2. The ends 17 can thus in particular as a result of their own flexural elasticity but also as a result of the elastic resilience of the webs 12 corresponding to that of these automatically align the forces acting on the fluid, any bending vibrations the fibers 15 are in operation by the vibration-damping elastomer adhesive the webs 12 dampened, which extends almost to the rear end of the branches 18, When the fibers 15 are automatically aligned, the gap 11 can move towards the outflow end 5 expand or narrow.

The gap 11 can, however, also become wavy during operation, that is to say in Alternately expand and narrow the direction of flow 2. A break in the boundary layer flow on the rear surface section 10 of the wall 3 is thus prevented.

In Figure 3 is the profile cross-section of a modified wing 19, which is flown against in a laminar manner in flow direction 2 from the front. This The wing 19 is made of an electrically insulating plastic in a casting process manufactured. Just below the wall 3 of the wing 19 is a parallel to this running braid 20 cast from electrically conductive steel wire. This Braid 20 has smooth fibers 21 pointing approximately in the direction of flow 2, which consist of a steel wire coated with electrostatically chargeable plastic.

The fibers are at their end pointing against the direction of flow 2 21 with the braid 20 firmly, so also electrically tied together. the free ends 22 of these coated fibers 21, which have a circular cross-section have, emerge from the wall 3 to the outside without a step. You have a mutual Distance transversely to flow direction 2, the one towards the rear (in flow direction 2) gradually gets smaller.

As a result of their own flexibility in bending, the free ends 22 of the fibers 21 according to the forces of the fluid acting on them Move both parallel and perpendicular to wall 3 and align automatically.

The braid 20 is facing against the flow direction 2 on its End connected to an electrical cable 23 embedded in the wing 19. By this cable 23 can apply a certain electrical voltage to the wires of the braid 20 and the fibers 21 are applied, so that the plastic coating of the fibers 21 and the wall 3 of the wing 19 due to electrical influence homopolar electrostatically charged.

The ends 22 of the fibers 21 repel each other, so that a mutual contact between adjacent ends 22 prevented and a harmful flutter of fibers 21 is avoided. The movement of the ends 22 of the fibers 21 is also perpendicular damped to wall 3 with the same polarity.

In Figure 4, the profile cross section of a wing 24 is shown, which, like the wing 19 shown in FIG. 3, is made of plastic is. The smooth fibers 25 also face the wall 3 of the wing 24 again approximately in the direction of flow 2 and are at their counter to this direction 2-pointing end 26 connected to the wall 3 without a step.

In the present case, however, the fibers 25 are designed in the form of a film and in a row at a close distance from one another transversely to the direction of flow 2 arranged. The film surface of the fibers 25 is perpendicular to the wall 3 and the inner edge of the fibers 25 is cast in the plastic of the wing 24. When the fibers 25 are poured in, the plastic penetrates continuous circular ones Holes 27, which are incorporated in the front portion of the fibers 25. On the other hand the The end 26 of the fibers 25 facing the direction of flow 2 is thus in the plastic of the wing 24 firmly anchored.

At their end 28 pointing in the direction of flow 2 are the fibers 25 freely movable and protrude beyond the trailing edge 5 of the wing 24. As a result This end 28 of the fibers 25, which are made of metal or plastic can be produced, according to the forces acting on them align the fluid automatically.

In Figure 5, a thick rigid circular plate 30 is shown, which of a laminar flowing fluid is flowed against transversely. On the back Wall 31 of the circular plate 30 are a flexurally elastic film 32 and one on her radially outer edge 33 in the flow direction 2 bent over rigid sheet metal shell 34 Glued, welded or screwed attached. The film 32, which the entire circular rear wall 31 is covered, is in close contact with this wall 31. She owns one curved in flow direction 2 (to the rear) Edge 35, which is at a distance radially outside the edge 33 of the rigid sheet metal shell 34 is arranged.

The edge 35 of the film 32 is provided with continuous, open to the rear, narrow slots 36 provided, which are evenly distributed around the circumference. To this Way 32 smooth fibers 37 are present at the edge 35 of the film, which on their against the flow direction 2 pointing end 38 with the wall 3 of the lateral surface of the Circular plate are connected without a step.

On the circular plate 30 with the film 32 attached thereon are uniform arranged on the circumference, obliquely radially outward through bores 39 on his front wall incorporated. These bores 39 open into one between the edge 35 of the film 32 and the edge 33 of the sheet metal shell 34 formed annular space 40.

The intermediate space 40 is located on its in the flow direction 2 Side an annular gap-shaped opening 41, which between the rear ends of the two Edges 33 and 34 are present and the space 40 with the surroundings of the circular plate 30 communicating connects.

The fibers 37 are at their end pointing in the direction of flow 2 42 freely movable due to its own flexibility.

When the flow hits the circular plate 30, part of the arrives at the front Wall of the circular plate 30 jammed fluid in the holes 39. At their The bores 39 have a sieve (not shown) so that the flow of fluid upon entry is expanded into the space 40.

The fluid flowing through the bores 39 into the intermediate space 40 there forms a radially flexible pressure cushion (air cushion) for the one made of fibers 37 composite edge 35 of the film 32. From the space 40 flows from the largest Part of the fluid through the annular gap-shaped opening 41 into the environment to the rear.

Only a small part of the fluid flows in the intermediate space 40 through the relatively narrow slits 36 between the adjacent fibers 37 radially outward.

That which hits the front wall of the circular plate 30 perpendicularly Fluid first moves radially outward along this wall and flows then along the wall 3 of the lateral surface of the circular plate 30 to the rear to the trailing edge 5. From there, the fluid continues along the smooth fibers 37 headed backwards.

The free ends 42 of the fibers 37 are aligned according to these attacking forces of the fluid automatically from.

In Figure 6 and 7, a stepped sliding bearing 43 is shown which hydrodynamic with a gaseous or liquid fluid of the environment is lubricated.

This stepped sliding bearing 43 has rigid stepped projections 44 with the bearing load-bearing flat support surfaces, on each of which a flexurally elastic Foil 45 made of metal or plastic is glued on. The outer wall 3 of each film 45 is the flat sliding surface in the direction of arrow 46 perpendicular to the sliding surface loaded sliding plate 47 opposite, The slide plate 46 slides with their flat sliding surface on the walls 3 of the foils 45, so that in between a hydrodynamically stable lubricating film is created along its laminar flow the walls 3 takes place in the direction 2 (see Figure 6).

Each film 45 has an end 48 pointing in the direction of flow 2, that over the trailing edge 5 of the support surface of the relevant step projection 44 protrudes. In the vicinity of the trailing edge 5, this end 48 is elastically compressible Cushion 49 made of rubber supported between the base 50 of the stepped sliding bearing 43 and the end 48 is installed. At a greater distance from the trailing edge 5 is a gradually increasing gap 51 between the cushion 49 and the end 48 educated.

The fluid exits the end 48 of each sheet 45 at the transverse sharpened edge 52 running in the direction of flow 2. This edge 52 carries Narrow incisions 53 running in the direction of flow 2, so that therebetween foil-shaped smooth fibers 54 are formed.

The fibers 54 are pointing against the direction of flow 2 End connected to the wall 3 of the film 45 in question without a step. That in the direction of flow 2 pointing end 48 of the fibers 54 is due to inherent flexural compliance and as a result the compressible resilience of the associated cushion 49 in the direction of loading 46 freely movable; this can therefore move in accordance with that which acts on this end 48 Align the forces of the fluid automatically.

With the elastically compressible cushion 49 and with more or less viscous fluid filled narrow gap 51 between the fibers 54 and the The movement is inclined to the flow direction 2 surface of the cushion 49 the ends 48 hydraulically damped and braked in the loading direction so that the Fibers 54 do not flutter during operation of the stepped sliding bearing 43.

Between the edge 52 of the fibers 54 and the opposite boundary wall 55 of the adjacent step projection 44 is a throttle gap which the Inflow and outflow of the fluid from the space of the gap 51 to the space of the lubricating film between the sliding plate 46 and the walls 3 of the foils 45 throttles.

The application examples of the invention described above can be modify constructively.

For example, the fibers in a wall do not all need to be in the form of a film or to be designed in the form of a wire fiber.

Rather, fibers with different fibers can be attached to one and the same wall Be appropriate cross-sections.

Foil and wire fiber-shaped fibers can also be placed on the wall be arranged alternately one behind the other or next to one another. The fibers can with a be formed gradually decreasing cross-section towards its free end. To achieve certain ratios for retarding the separation of the boundary layer an arrangement of the fibers in groups on or on the wall is possible.

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Claims (1)

Method of delaying the separation of the boundary layer at one of a wall with a laminar flow against a fluid and application of the same patent claims 1. A method of delaying the separation of the boundary layer on one of a fluid Wall facing laminar flow by attaching v'gialttén't fibers pointing approximately in the direction of flow or the like on this wall, characterized in that the fibers or the like are attached their end pointing against the direction of flow connected to the wall without a step and at its opposite end facing in the flow direction relative to the Wall can be arranged freely movable, so that the free end of the fibers parallel and / or perpendicular to the wall according to the one acting on this end Aligns forces of the fluid automatically. 2. The method according to claim 1, characterized in that the fibers or the like. At least in sections in the direction parallel to the wall and / or in Direction perpendicular to the wall are designed to be flexible. 5. The method according to claim 1 or 2, characterized in that the fibers or the like. Only arranged in the area of the wall that is at risk of detachment will. 4. The method according to any one of the preceding claims 1, 2 or 3, in which the fibers or the like are attached to a wall having a trailing edge Are, characterized in that at least some of the fibers or the like. With their free ends are arranged protruding over the trailing edge. 5. Applying the method of retarding the separation of the boundary layer on a wall against which a fluid flows in a laminar manner according to one of the preceding Claims 1 to 4, characterized in that the fibers or the like (15, 21, 25, 54) on the suction side and / or on the trailing edge (5) of the wall (3) of a wing (1, 19, 24) or a bearing sliding surface. 6. Application of the method according to claim 5, characterized in that that at least some of the fibers or the like. (15) are branched at their free end (17). 7. Application of the method according to claim 5 or 6, characterized in that that at least some of the fibers or the like. (15, 25, 37, 54) at least at their free end (17, 28, 42, 48) be formed in the form of a film. 8. Application of the method according to claim 7, characterized in that that the film surface of the fibers or the like. (15, 54) is parallel to the wall (3) is arranged. 9. Application of the method according to one of the preceding claims 5 to 8, characterized in that the fibers or the like (15, 54) at least in sections by Introduction of a vibration-damping, compressible material be supported between the fibers (15, 54) and the wall (3). 10. Application of the method according to one of the preceding claims 5 to 9, characterized in that at least some of the transverse to the flow direction (2) adjacent fibers or the like. (21) made of an electrostatic material are homopolar and due to friction of the fluid or due to electrical influence electrostatically charged.