WO1998021091A1

WO1998021091A1 - Flow form

Info

Publication number: WO1998021091A1
Application number: PCT/EP1997/006193
Authority: WO
Inventors: Philippe Arribi
Original assignee: Philippe Arribi
Priority date: 1996-11-14
Filing date: 1997-11-07
Publication date: 1998-05-22
Also published as: DE19647102A1; AU7179098A

Abstract

The present invention relates to a flow form to be used in gaseous or liquid moving fluids, comprising a leading edge (4) defining a dividing line for the flowing medium, two opposite lying surfaces (6, 7) along which the medium flows over the flow form, and a downstream end behind which the medium divided by the flow form converges once again. In order to provide a flow form with enhanced energy utilization and/or energy conversion when compared with known flow forms, and which exhibits specially lower flow losses, the invention proposes that the downstream end should consist of an end section (3) which can be elastically folded around a theoretical axis running almost perpendicular to the direction of flow and lying parallel to a surface defined by the leading edge (4) and the direction of flow, wherein the flexibility of the end section (3) is a multiple of that of the main part (2) of the flow form (1) lying in front of the end section (3) in the direction of flow.

Description

Flow body

The present invention relates to a flow body for use in gaseous or liquid flow media with a front leading edge running along a line dividing the flow, and two opposite side surfaces, along which the flow is directed past the flow body, and with a downstream end behind which the medium divided by the flow body meets again.

Examples of such flow bodies are the wings of airplanes, boat keels and swords, the fins of surfboards, rigid sails, but also the rotor blades of wind turbines or propellers and turbine blades and the wings of propellers. When using such flow bodies in liquid or gaseous media, it is basically a matter of optimally extracting or utilizing energy, either to move the flow body and / or parts connected therewith in the flow medium, which also includes moving a rotor in a circle, or but in order to move the medium in reverse, or both if the recoil of the moving medium also simultaneously drives a concrete object, generally a water, land or aircraft. In general, such a flow body has a widely varying, generally aerodynamic shape, which is characterized by a more or less drop-shaped cross section, although the drop cross section in question often appears very elongated in the longitudinal direction. As an example, we would like to remind you of the wing profile of airplanes and the profile of the sword or the fin of a surfboard. While the latter is symmetrical with respect to a longitudinal median plane, since it is intended to make it easier for a surfboard loaded from the right and sometimes from the left in the same way, a wing profile is generally asymmetrical, ie the top and bottom of a wing are not exactly mirror images of one another.

In the context of the present invention, the term “leading edge” is generally not intended to mean a sharp front edge of the flow body which is in the form of a kink or even a cutting edge (although such a design is of course also intended to be encompassed by the term leading edge), but merely the front region of the flow body, which extends essentially along a line and projects most in the flow direction. The flowing medium must necessarily divide in the region of the front section of the flow body and the connecting line of all points along which the individual parallel flow threads divide is referred to here as the "leading edge".

Such flow bodies are usually relatively rigid structures, even if it cannot be ruled out that, in the case of very long flow bodies, such as the wings of aircraft, the ends of which can be bent up or down. Such a deflection about an axis running parallel to the direction of flow can also occur with heavy loads even with the mentioned fins and swords of surfboards or with rotor blades, but is not absolutely desirable and does not relate to the present invention. Viewed in the width direction, corresponding flow bodies are almost completely stiff, i.e. For example, it is not possible to significantly or even visibly bend the rear edge or the leading leading edge vis-à-vis the rest of the wing. This would be undesirable, if only because it changes the flow profile of the flow body, which is generally optimized for the fulfillment of its task, that is, for the generation of a lift and / or propulsion.

Nevertheless, it can always be found in concrete, practical situations that, depending on the respective flow medium and the flow velocities that occur, considerable flow resistances occur, which can primarily be explained by premature stall and vortex formation. If the flow body is used as a drive and / or buoyancy or control element, the flow losses which occur lead to corresponding losses in the drive power, that is to say either to higher energy consumption or to a reduction in the maximum possible drive speeds.

The present invention is therefore based on the object of creating a flow body whose energy utilization and / or energy conversion is improved compared to the known flow bodies, which therefore also has, in particular, lower flow losses.

This object is achieved in that the downstream end of the flow body consists of an end section which extends out of the area spanned essentially by the leading edge and the flow direction and around an axis lying parallel to this area and approximately perpendicular to the flow direction, is preferably elastically bendable, the flexibility of this end section being a multiple of the flexibility of the main part of the flow body lying in front of it in the flow direction.

The flow body according to the invention thus consists of an essentially rigid main part, which largely or identically corresponds to a conventional flow body. Only the downstream end of this flow body is designed to be substantially more flexible than a conventional flow body and can therefore adapt to the pressure conditions prevailing due to the flow. The bending takes place about an axis which runs essentially parallel to the rear free edge and thus also approximately parallel to the front leading edge. This imaginary axis only identifies the bending direction and generally has no fixed position and the curvature can change both in time and in space across the width of the end section. The imaginary bending axis can also run more or less curved and the flow body or its surfaces can also be twisted about its longitudinal axis, as is known from rotor blades or propellers. In this case, the bending axis lies in a surface which is essentially spanned by the flow direction and the rear edge of the end section or the rear edge of the main part, to which the end section adjoins, and which corresponds to the course of this rear edge along a steep helix is twisted.

For example, take-off and landing flaps which are movable from aircraft wings are known, which in principle can be moved with respect to the same plane or about an axis which is approximately parallel to the wing edges, as the flexible end sections according to the present invention Invention, however such take-off and landing flaps are extended to generate additional lift and also to produce a braking effect and they are adjusted relative to the main part of the wing so that the pressure difference on the top and bottom of the wings rather increases or at least additional Areas are provided along which the relevant pressure differences occur in order to increase the lift at the slow take-off and landing speeds compared to the cruising speed. Energy consumption and energy conversion are less efficient, which is why they remain retracted even during normal cruising and at higher cruising speeds.

These flaps do not adapt to the prevailing flow conditions, but are held actively and firmly in a desired position, which is opposite to the self-adjusting orientation of an elastic, flexible end section due to the pressure conditions.

In general, the effect of flow bodies is based on the generation of a pressure difference on the two sides of the flow body due to different speeds of the medium flowing along these sides. The different flow velocities of the medium on the two sides of the flow body can either be achieved by a corresponding profile shape, for example the typical asymmetrical airfoil profile, which forces a longer flow path on the top and thus higher flow velocities, which in turn create a negative pressure relative to that on the bottom Generates pressure, the pressure difference on the underside and top of the wing providing the desired buoyancy. However, this effect can also be achieved with a symmetrical design of the two sides of a flow body by appropriately adjusting the plane of symmetry of such a flow body against the direction of flow. This effect is used, for example, when controlling surfboards and sailing boats, whereby the rudders of motor boats and larger ships also have a similar effect. The pressure on a sail, especially on a half wind or upwind course, not only propels a sailboat or surfboard forward, but also exerts a sideways pressure that pushes the surfboard or hull sideways. The water currents attacking the hull, rudder, fins and keel do not run exactly in the direction from the bow to the stern of the vehicle in question, but come diagonally from the windward side. The pressure on the sail, which is lashed in a certain position relative to the hull or by a surfer in a certain position relative to his board is held, tends to turn the boat or surfboard into the wind, ie the torque acting on the sail and thus on the entire hull pushes the rear of the vehicle away from the wind and the bow against the wind direction.

However, the fin attached to the stern of a surfboard or a corresponding rudder on a boat experiences pressure from the windward side and a corresponding suction or oppression due to the water flow which is oblique relative to the entire hull when the fin or rudder is aligned straight from the stern to the bow on the windward side. Since the rudder or fin are attached to the rear of the vehicle, they cause the desired counter-torque, so that the vehicle is kept on course.

A sword arranged centrally on the surfboard or boat or a corresponding keel are in principle subject to the same hydrodynamic effects, but because of their central arrangement generally do not exert any appreciable torque on the surfboard or the hull, but reduce due to their transverse resistance in the water and additionally due to the hydrodynamic effects mentioned, the lateral drift of the surfboard or boat.

Irrespective of the aerodynamic and hydrodynamic effects of known flow bodies explained above, considerable frictional losses occur due to stall and vortex formation, especially at high relative speeds or flow speeds. This is precisely where the present invention comes in, since it has been found in practical tests that flow separation and vortex formation are favorably influenced due to the flexible end section, so that the friction is reduced and an additional propulsion effect is produced, which will be explained later with reference to the figures .

Since, as already mentioned, due to the profile of the flow body or due to its position against the flow direction on one side of the flow body there is an overpressure in comparison to the opposite side and since this is of course also true for the area of the end section of the flow body, it fits flexible end section by appropriate deformation of this pressure difference. Compared to a tension-free rest position without any inflow, the flexible end section is also clearly visibly deflected or bent when there is a flow that generates a sufficiently large pressure difference. Of course, the flexible end section deviates in the direction of the lower pressure, as a result of which the Flow conditions change and the pressure difference is reduced.

A restoring force is provided either by additional inner components or else by the elasticity preferably inherent in the end section, which provides a return force corresponding to the pressure difference wherever the end section is deformed due to the acting pressure differences. Since the end section is preferably designed to be flexible (and elastic) over its entire length, the pressure difference decreases continuously from the attachment of the end section on the main part of the flow body to its free end and ideally to a value close to the free end of the end section . This results in a very trouble-free stall without significant eddy formation. The pressure difference still present along most of the end section results in an additional propulsive force due to the deformation of the end section relative to the main part.

The specific configuration of the flexible end section can vary within a very wide range both in terms of its shape and attachment to the main part of the flow body and in terms of the relative dimensions compared to the main part and in the specific elasticity and flexibility properties. The specific shapes, dimensions and flexibility properties to be selected depend on the respective application. For example, a relatively small flow body, which is also designed for low flow speeds, such as the fin on a beginner's surfboard, which is only used at low wind speeds and thus low driving and current speeds, can be comparatively flexible, i.e. more flexible than that End section on the fin of a surfboard, which is designed for high-speed trips. Likewise, the end section on the keel of a large sports yacht or on the sword or fin of a catamaran must be designed stiffer than on the keel or rudder of a cabin sailboat for the weekend sailor. In all cases, however, there is a noticeable and clearly visible deflection of the end section at those flow velocities to which the flow bodies in question are normally exposed or for which they are specifically designed, so that the free end of the end section is at least a few out of its rest position Degrees, possibly deviates by 20 or 30 ° or even more. The end section which is almost flat or even tapering in the rest position and which forms the continuation of the sides of the flow body which converge at a small angle then appears to be visibly curved in profile, the free end being bent toward one side.

The flexible end section preferably extends along the entire rear edge or at least along most of this trailing edge of the main part of the flow body. Its width is typically between 10% and 30% of the total width of the flow body, but depending on the application, significant deviations from this are also possible and the width of the flexible end section can, for example, only 3% of the total width in some applications and up to 80 in others % of the total width of the flow body, measured in the flow direction. In the vast majority of applications, however, it will be possible to limit the range to 10-50% of the total width of the flow body.

This width ratio can of course change along the length of the flow body, in particular if the width of the flow body decreases towards the ends anyway, as is the case, for example, with the wings of large aircraft. In general, however, the width of the flexible end portion of the flow body need not decrease in the same way as the width of the main portion of the flow body, but may, for example, either decrease only slightly towards the free ends or remain substantially constant. Alternatively, however, one could also change the flexibility characteristics of the flexible end section over the length of the flow body to be measured transversely to the flow direction, that is to say to make the end section more flexible and at the same time narrower in the direction of the free ends of the flow body.

In general, the elastic flexibility of the end section is at least one hundred times the flexibility of the main part, in each case based on the same bending axis. The main part of a corresponding flow body can essentially be described as rigid, although a minimal and barely visible deformation in the profile of a flow body may nevertheless occur if it is exposed to a flow and thus pressure differences on its top and bottom. Such deformations are fundamentally not wanted and intended and they can only be made visible with correspondingly sensitive measuring instruments. In contrast, the flexible end section is characterized by a clearly visible flexibility, which can be expressed in numbers by several orders of magnitude above the flexibility and deformability of the main part.

It is provided according to the invention that the transition from the main part to the flexible part takes place relatively quickly, but is essentially continuous. The flexibility of the flow body should expediently change in this transition area from the main part to the flexible end section by at least a factor of 10 in a transition area which does not make up more than 5% of the total width of the flow body, in the area of the flexible area End section, the flexibility can be substantially constant, but can also increase further in the direction of the free end or the rear edge of the end section.

The flexibility of the flow body preferably has an approximately step-shaped course, i.e. in the area of the main part, the flexibility of the main part with respect to bending or deforming in the direction of one of its sides is very low and can be set practically to zero or close to zero. At the transition to the flexible end section there is a still continuous but almost sudden increase in flexibility by at least a factor of 10, possibly also by a factor of 100 or more and within the flexible end section the flexibility then remains at this higher level and decreases Compared to the sudden increase in the transition area, there is only comparatively little to do.

Conveniently, the end section has the shape of a thin sheet or at least runs out as a thin sheet at its free end and is made of a fiber-reinforced plastic material. Because of the favorable weight and because of favorable elastic properties, plastic materials reinforced with carbon fibers are particularly suitable for the flexible end section. The main part and end section are designed in such a way that their upper and lower surfaces merge into one another essentially flush and without steps, kinks or other superficial irregularities. In particular, the main part and the end section can of course be formed in one piece or coated with a common outer layer. If the main part and the end section are produced essentially from the same material, the main part must of course have corresponding stiffening elements and / or be made substantially thicker and more solid than the end section in order to ensure the difference in flexibility between the main part and the end section.

When using fiber-reinforced materials, the fibers should run essentially in the direction of the expected flow, i.e. along the width direction of the flow body already defined above. However, flexible composite materials that are well suited for the end section can also be produced with the aid of fiber fabrics or with fiber mats with random orientation of the fibers.

The end section according to the invention can also be divided into a plurality of segments which independently adapt to the local flow conditions (which may differ at different positions in the longitudinal direction of the flow body). In practice, this is achieved, for example, by a series of more or less parallel ones Incisions at the same or different distances from the free rear edge of the end section more or less deep, possibly into the transition area. The segmentation can also be taken into account during the manufacture of the end section and the individual segments can be given different flexibility properties if this proves to be advantageous for certain applications. The end section can also consist of a plurality of individual segments which are completely separate from one another and are arranged next to one another at the rear end of the main part.

The following types and types of flow bodies, in each case individually or in combination with one another, are particularly suitable for the application of the present invention, but the following list is only exemplary and not exhaustive:

Fin and / or sword of surfboards, sword, rudder or keel of motor and sailing boats and other watercraft, wings and / or tail unit or empennage wing of aircraft, aircraft propellers, propellers or propellers, turbine blades, rotor blades of wind turbines or also of blowers, blades of hydrofoils, stabilizers for submarines, torpedoes, rockets and other water or air vehicles etc.

For dimensioning the flexibility and elasticity of the end section of a given flow resistance, it is best to take into account a design speed which is to be predetermined and which occurs most frequently in practice or at which the flow body in question is to be used. Flow bodies of this type can be provided interchangeably on an object, in particular with differently flexible end sections.

After determining the design speed, the flexibility of the end section is expediently dimensioned such that substantially the same pressure acts on both sides of this end section near the free end of the end section. This means that the pressure release, which is becoming more and more complete due to the flexible yielding of the end section behind, should preferably not take place too early, that is to say at a considerable distance from the free end, or too late, that is to say that it must not be completed before the free end is reached. Rather, the pressure curve recorded over the width of the end section (more precisely: pressure difference curve) should, with appropriate extrapolation, separate the zero line in the vicinity of the free end or the rear edge of the flexible end section. This may have to be determined by practical tests. With such an optimization, the flexible end section bears maximum for buoyancy and / or propulsion or for the optimal use of energy.

In addition, the free end section should not be bent too much from its rest position. As a rule, the bend, i.e. the direction in which the free end of the end section, viewed in the profile of the flow body, points relative to its rest position, should not be greater than 40-50 °, and preferably not greater than 30 °.

Appropriate experiments and theoretical estimates have shown that the range of flexibility in various applications extends over several orders of magnitude. For example, an approximately 5-10 cm wide end section of the fin for a light wind surfboard with a pressure difference of only approximately 5000 Pa (approximately 0.05 kg / cm ² ) must assume a smallest radius of curvature between 10 and 50 cm. The end section on the keel of an ocean-going yacht, on the other hand, which is, for example, 50 cm to 1 m wide, will only reach a smallest radius of curvature of 2 to 10 m with a one-sided pressure load of up to 10 ^β Pa (approx. 1 kp / cm ² ). However, it should be pointed out that the pressure difference generally varies across the width of the end section and generally decreases towards the free end. So if you want a uniform curvature or at least a slow curvature decrease of the flexible end section from the transition area to the free end thereof, this effect of the pressure decrease can be compensated for by an increase in the flexibility of the end section from the transition area to the free end, for example, by making the end section somewhat thicker in the transition area and then allowing it to run out towards the free end as an increasingly thinner sheet.

For a preferred embodiment of the invention, the situation described above can generally be expressed in such a way that the flexibility of the end section should be dimensioned such that at a typical flow speed and in a normal application (e.g. windward course of a sailboat or surfboard at wind force 5 - 7 Beaufort) maximum pressure difference occurring, the minimum radius of curvature occurring at the flexible end section should be at most twenty times the width of the end section in this area. If the flexible end section then assumes this minimum radius of curvature along its entire width under these conditions, the free end is bent by at least about 2.8 ° from its unloaded rest position, provided that the radius of curvature of the flexible end section is in the unloaded state infinitely large, the surfaces of the end section are therefore essentially flat and, if need be, are twisted around the longitudinal direction of the flow body. Depending on the application, however, the above limit for the minimum Radius of curvature can also be set to 30 or 50 times the width of the flexible end section.

The attachment of the end section to the main section can be done in many different ways. For example, the end section and main part can be connected to one another via a tongue and groove connection, by means of bolts, dowels, a common outer or inner skin, and above all by gluing or a combination of the aforementioned types of fastening. In the case of more complex technical objects, such as, for example, the wings of aircraft, the flexible end section can also be retracted into the main part and can be extended again. In the case of wings, it would also be conceivable to attach the flexible end section to the rear edges of the take-off and landing flaps, which also define the rear edge of a wing when cruising.

Further advantages, features and possible uses of the present invention will become clear from the following description of preferred embodiments and the associated figures. Show it:

FIG. 1 shows a flow body according to the invention in profile,

Figure 2 is a plan view of a flow body interrupted in length, which in profile can essentially correspond to the flow body shown in Figure 1, Figure 3 shows the flexibility or flexibility of the flow body shown in Figure 1 as

Function of the width direction b, FIGS. 4 to 6 different fastening variants of the end section on the main part, and FIGS. 7 and 8

Two variants of ship propellers which implement the present invention.

A flow body 1 can be seen in FIG. 1, consisting of a main part 2 hatched in section and a flexible end section 3 which is not hatched. The main part has an upper side 6 and a lower side 7, the upper side 6 'and the lower side T of the end section 3 Connect flush to surfaces 6 and 7 without any kinks or other transitional irregularities. The front end of the flow body 1 facing the flow, which is indicated by arrows S, defines a flow edge 4 which corresponds to a dividing line for the flow S, a part of which extends over the upper side 6, 6 'and another part over the underside 7, 7 'of the flow body 1 flows out. In the transition area 5, the end section 3 is fastened to the main part 2 by a tongue and groove connection or the like. As can be seen, the end section 3 is shown in an upwardly bent position in FIG. 1, the free end of the end section 3 being deflected by an amount Y with respect to the rest position shown in broken lines. This bent position of the end section 3 arises due to a pressure difference on the two sides 6 ′, T of the end section 3, which is indicated by the reference symbols P ₊ and P. P ₊ stands for a higher pressure and P. stands for a negative pressure relative to P ₊ . These pressure ratios arise due to the profile of the flow body 1 or the main part 2 of the same and due to the inclination or inclination of the main axis of the flow body 1 relative to the main flow direction. The main axis of the flow body 1 is intended to denote a connecting line in the plane of FIG. 1 from the leading edge 4 to the tension-free, dashed end of the end section 3 in its rest position.

Due to the pressure difference, ie a higher pressure P ₊ on the underside 7, 7 'of the flow body in comparison to the pressure P. on the upper side 6, 6', the flexible end section 3 is pushed upwards, the flexibility of this end section 3 naturally being increased the pressure differences P ₊ - P. occurring specifically at realistic flow velocities are set and also bends in the desired manner when such a pressure difference occurs. The degree of deformation or the flexibility can be described, for example, as a change in the curvature of the surfaces 6 ', 7' as a function of an increase or decrease in the differential pressures that occur.

Due to the bending of the end section 3, of course, the flow against it changes, so that the pressure difference occurring in a straight alignment, as shown in the dashed position, is reduced and in the direction of the free end of the end section

3 continues to decrease. This also applies in particular if the end section 3 consists of an essentially homogeneous sheet of constant thickness, for example of carbon fiber-reinforced synthetic resin, the flexibility properties of which do not change from the transition region 5 to the free end of the end section 3. Since the pressure difference continues to decrease in the direction of the free end, the flexible end section 3 is also less and less curved there and the curvature disappears completely near the free end when the pressure difference P ₊ -

P. disappears. It is clear from the figures that in FIG. 1 the plane with respect to which the flexibility of the rear end section 3 is important is one from the front leading edge

4 and the plane spanned here as the horizontal direction of flow. Alternatively, this level could also be spanned by the front leading edge 4 and the main axis of the flow body 1, defined as a connecting line between the front leading edge 4 and the rear, free end of the end section 3 in the non-pressurized state becomes.

In FIG. 2, this plane is the paper plane and the rear end section 3, which can be seen on the right of a transition region 5 defined by dashed lines, can be flexibly bent up and down out of the paper plane. The main part 2 to the left of the transition area 5 is stiff and inflexible in comparison. As can be seen, the front leading edge of the flow body 1 shown broken off in length in FIG. 2 does not run along a straight line in this plane, but in particular clearly curved towards the free end (in the longitudinal direction) of the flow body 1, so that the free end of the flow body is significantly narrower than the flow body over most of its length. However, the free end section 3 is shown with a constant width over the entire length L of the flow body 1. The course of two flow lines or flow threads SL is indicated by dash-dotted lines. In FIG. 1, these lines run along the upper surfaces 6 and the lower surface 7 in the paper plane or parallel to it.

FIG. 3 schematically shows the course of the flexibility f of the flow body 1 shown in FIGS. 1 and 2 as a function of the width b of the flow body. In the area of the main part 2, the flexibility of the flow cross section is negligibly small and is characterized by a course close to the zero line of the flexibility. In the transition area 5, where the flexible end section 3 is connected to the main part 2, the flexibility then increases drastically and then at the end of the transition area and in the area of the end section 3 reaches an essentially constant, possibly slightly increasing value, which is the free one End, ie when the total width B is reached.

The flexibility f could be defined, for example, by the expression dk / dp, where k is the curvature d ² y / db ^{2 of} the surfaces 6 "or T which can be seen in the paper plane according to FIG. 1, and p is the pressure difference P which is dependent on the width position b ₊ - P. is on both sides 6 '7' of the end section 3.

It goes without saying that other definitions for the flexibility of the end section 3 can be chosen without this having any effect on the invention as defined in the claims.

FIGS. 4 to 6 show different variants of the connection between the main part 2 and the flexible end section 3. According to FIG. 4, the flexible end section 3 has a Y-shaped cross section, the two Y-legs from both sides on the opposite surfaces 6, 7 of the main part 2 are glued. So that the surfaces 6, 7 flush into the Merging surfaces 6 ', T of the end section 3, the main part 2 has surface depressions in its rear region, the depth of which corresponds precisely to the thickness of the two Y-legs of the flexible end section 3.

In Figure 5, a tongue and groove connection between the main part 2 and the flexible end portion 3 is shown. The rear end of the main part 2 is provided with a groove running in its longitudinal direction (perpendicular to the plane of the paper) into which a corresponding tongue of the end section 3 fits. Here, too, the corresponding surfaces 6, 6 'and 7, T are again designed such that they merge into one another smoothly and without a step at the junction between the main part 2 and the end section 3. It goes without saying that this tongue and groove connection can also be additionally fixed by an adhesive.

In Figure 6, the end section 3 is shown in one piece with the main part 2, specifically the outer skin of the main part 2 continues towards the rear either without the inner core shown with hatching or with another, more flexible core filled to the rear.

In all three FIGS. 4 to 6, a vertical, dashed line roughly denotes the transition region from the relatively rigid main part 2 to the flexible end section 3.

FIGS. 7 and 8 show two different ship propellers, whereby according to FIG. 7 the ship propeller has a straight, leading edge and a strongly curved trailing edge which has the flexible end section 3, which also extends into the area along the strongly curved trailing edge of the individual propeller blades the top of the wing extends. The width of this flexible end section also varies along the rear edge of the main part 2 and is approximately the maximum where the main part 2 also has a maximum width, but tapers towards the center.

In the embodiment according to FIG. 8, the individual propeller blades are contoured in opposite directions with respect to the direction of rotation as in the case of the embodiment according to FIG. 7, i.e. the leading edge of a propeller blade is the strongly curved front edge of the main part 2, the rear edge of which is essentially straight and has the flexible end section 3, in which case the flexible end section 3 extends beyond the tip of the propeller blade and even into the outer, front region of the main part 2. Due to the centrifugal forces caused by the rotation of the propeller, the flow medium receives a flow component in the radial direction to the outside, so that the flexible parts in the area of the propeller tips with respect to the Direction of flow are end portions of the propeller tube.

Claims

Patent claims

1. flow body for use in gaseous or liquid flow media, with a front leading edge (4) defining a dividing line for the inflowing medium, two opposite surfaces (6, 7) along which the medium flows around the flow body and with a downstream end, behind which the medium divided by the flow body meets again, characterized in that the downstream end consists of an end section (3) which is about an imaginary, approximately perpendicular to the flow direction and parallel to one of the leading edge (4) and the flow direction Axis lying on the spanned surface is elastically bendable, the flexibility of the end section (3) being a multiple of that of the main part (2) of the flow body (1) lying upstream of the end section (3).

2. Flow body according to claim 1, characterized in that the width of the end section measured in the direction of flow at least over most of the length of the flow body (1) measured essentially in the direction of the leading edge (4) is between 3 and 80%, preferably between 5 and 70%, the total width of the flow body.

3. Flow body according to claim 2, characterized in that the ratio of the width of the flexible end portion with the position in the longitudinal direction of the flow body varies continuously.

4. Flow body according to claim 2 or 3, characterized in that the width of the end portion (3) is substantially constant over most of the length (L) of the flow body.

5. Flow body according to one of claims 1 to 4, characterized in that the flexibility of the end section (3) is at least one hundred times the flexibility of the main part (2).

6. Flow body according to one of claims 1 to 5, characterized in that the flexibility of the flow body (1) in a maximum of 10% of the width of the Transition area (5) of the flow body changes by at least a factor of 10.

7. Flow body according to one of claims 1 to 6, characterized in that the flexibility as a function of the width of the flow body has an approximately step-shaped course.

8. Flow body according to claim 7, characterized in that the flexibility as a function of the width of the flow body in the region of the main part (2) is very small and substantially constant, increases steeply in the transition region and very large and essentially in the subsequent region of the elastic end section constant or continuously increasing in the direction of the free end of the end section (3).

9. Flow body according to one of claims 1 to 8, characterized in that the main part (2) and end section (3) are formed in one piece or in the form of two parts firmly connected to each other.

10. Flow body according to one of claims 1 to 9, characterized in that the surfaces (6, 7) of the main part (2) pass smoothly into the surfaces (6 ', 7') of the end section (3).

11. Flow body according to one of claims 1 to 10, characterized in that the end section consists of a fiber-reinforced plastic material.

12. Flow body according to claim 11, characterized in that the reinforcing fibers run essentially in the direction of the width of the flow body or in the flow direction or as a fabric in several preferred directions.

13. Flow body according to one of claims 1 to 12, characterized in that the shape and modulus of elasticity of the end section are set so that the deformation of the end section (3) remains in the entire design range of flow velocities in the elastic range.

14. Flow body according to one of claims 1 to 13, characterized in that the end section (3) of several in the longitudinal direction of the flow body side by side arranged segments.

15. Flow body according to claim 14, characterized in that the segments are formed by incisions extending from the free end of the end section (3) approximately parallel to the flow lines in the direction of the transition region.

16. Flow body according to claim 15, characterized in that the segments are completely separate parts.

17. Flow body according to one of claims 14 to 16, characterized in that at least some of the segments have a flexibility which differs from the other segments.

18. Flow body according to one of claims 1 to 17, characterized in that the flexibility of the end section in the longitudinal direction of the flow body varies continuously or stepwise from segment to segment.

19. Flow body according to one of claims 1 to 18, characterized in that the flexibility of the end section is designed such that at a flow velocity typical for the use of the flow body and the maximum pressure difference occurring in such use on both opposite surfaces (6 ', 7) of the end section (3), the minimum radius of curvature occurring at the end section is at most twenty to fifty times, preferably at most ten times the total width of the flexible end section (3).

20. Flow body according to one of claims 1 to 19, characterized in that it is designed as a fin or sword of a surfboard or sailboat.

21. Flow body according to one of claims 1 to 20, characterized in that it is designed as a keel or rudder of a boat or ship.

22. Flow body according to one of claims 1 to 20, characterized in that it is designed as a wing and / or tail unit of an aircraft.

23. Flow body according to one of claims 1 to 20, characterized in that it is designed as a propeller of an aircraft.

24. Flow body according to one of claims 1 to 20, characterized in that it is designed as a screw or propeller of a ship's drive.

25. Flow body according to one of claims 1 to 20, characterized in that it is designed as a rotor blade of a wind turbine.

26. Flow body according to one of claims 1 to 20, characterized in that it is designed as a turbine blade, in particular a jet engine.

27. Flow body according to one of claims 1 to 20, characterized in that it is designed as a blade of a blower or a compressor.

28. Flow body according to one of claims 1 to 27, characterized in that means for actively adjusting the deformability of the end section (3) are provided.

29. Flow body according to one of claims 1 to 28, characterized in that sensors for detecting the pressure conditions on the main part (2) and / or from the end section (3) of the flow body (1) are provided.

30. Flow body according to one of claims 1 to 29, characterized in that the end section can be made narrower or wider by at least partially moving in and out of the main part (2).

31. Flow body according to one of claims 1 to 30, characterized in that the flexibility and / or deformation of the end section is set such that, at a predetermined relative speed with respect to the flowing medium, the end section (3) bends in such a way that pressure difference (P ₊ - P.) on both sides of the end section is continuously reduced towards the free end of the end section (3) and preferably approaches zero in the vicinity of the free end.