DE10027938A1 - Aerofoil section with lift-increasing trailing edge, in which trailing edge has spoilers on one or both sides to cause flow breakaway - Google Patents

Abstract

The aerofoil section has a suction side and a compression side when a flow passes round it. The trailing edge (2) diverges or is angled away from the rest of the section. The trailing edge has spoilers on both sides to produce a periodic flow breakaway or to stabilize the flow. Anti-backflow spoilers may also be included.

Description

The invention relates to a wing profile, on which there is an inflow by a fluid forms a suction side and a pressure side, in particular aircraft wing or blade of a turbomachine, and that a divergent thickened or has angled trailing edge.

Kinked trailing edges to increase lift on wings, in the following Gurney-Flap were first from the racing driver and designer Dan Gurney was used in the 1970s. The downforce generating As a result, wings at the rear of racing cars were able to improve their performance become; this has resulted in better traction. The aerodynamicist Liebeck then recognized the potential of these modified trailing edges Increase in lift of aircraft wings and reported about it in the essay "Design of subsonic airfoils for high lift" in the US magazine Journal of Aircraft, Vol. 15, No. 9, Sept. 1978, pp. 547-561.

Wings with wedge-shaped diverging trailing edges have been extensively developed by Hen examined with a view to the use in the cruise of Commercial aircraft, printed under "Innovation with computational aerodynamics: The divergent trailing-edge airfoil "in" Applied Computational Aerodynamics ", Progress in Astronautics and Aeronautics, Vol. 125 (1990), p. 221-261, American Institute of Aeronautics and Astronautics, Inc., Washington). It was shown that wedge-shaped diverging wing trailing edges for Commercial aircraft in cruise at high subsonic speed clear Bring advantages. For the commercial aircraft MacDonnell-Douglas MD11 is therefore such a trailing edge of the wing is already in use. They are also successful Test flights have been carried out on a Boeing B 747.  

An increase in lift due to kinked trailing edges, Gurney flaps, is also used in the high lift configuration of aircraft for takeoff and Landing reached (Ross, J.C., Storms, B.L. & Carrannanto, P.G. "Lift-enhancing tabs on multielement airfoils ", Journal of Aircraft, Vol. 32, No. 3, May-June 1995, p. 649-655).

Furthermore, an increase in performance through Gurney flaps was also used Proven wind turbines, evident from an essay by Kentfield, "Theoretically and experimentally obtained performances of Gurney-Flap equipped wind turbines ", US Journal: Wind Engineering, 1994, Vol. 18, No. 2, pp. 63-74.

The results of simplified theories of aerofoil aerodynamics already show that the outflow angle at the rear edge is of particular importance, shown schematically in Dubbel, Taschenbuch für den Maschinenbau, 18th ed. 1995, Springer, Berlin, p. B61, hydrofoils and blades. However, these simplified theories, which presuppose continuous flow, are only of very limited significance here. But they make it plausible why a very small Gurney flap delivers such a high lift gain. More detailed aerodynamic studies of the flow behind a bent or divergent trailing edge before Congress paper by Sauvage, P., Pailhas, G. & Coustols, E. "Detailed flow pattern around thick cambered trailing edges", 7 ^th Asian Congress of Fluid Mechanics, Chennai, Madras, IN, Dec. 8-12, 1997.

Through a kinked or wedge-shaped diverging trailing edge A wing's lift can be increased. The change in The trailing edge is very small and consists of e.g. B. in a kink, the one Only about 0.3-2% of the wing profile depth. This will make one substantial increase in wing lift of 5-25% achieved. Behind the however, a bent or diverging trailing edge forms locally  limited flow separation that causes resistance.

Therefore, the invention addresses the problem in all of these Applications lower resistance and resultant additional noise to decrease that these trailing edges produce.

The problem is solved according to the invention by the features of claims 1, 6 and 12. Advantageous developments of the invention are in the subclaims detected.

The first solution consists in a wing profile, which can flow through when there is an inflow a fluid forms a suction side and a pressure side, in particular Aircraft wing or blade of a turbomachine, and the one has divergent thickened or angled trailing edge, the Trailing edge on the suction side and the pressure side with means for disturbing one periodic flow separation and / or flow stabilization is.

The means for the printed page are selected from a group of means, comprehensive: arranged on the print side in front of the rear edge or up to incisions or webs extending there, to the pressure side and / or from the Trailing edge extending individual elements, perforations of the Angle, in the vertical direction on the pressure side and at the same time horizontally extending sawtooth or wavy elements. Furthermore, the means for the suction side include: arranged in front of the rear edge or elements or webs extending up to there, which are preferably in the Cross-section have the shape of a triangle, trapezoid or a wave. The webs, which are designed as ribs in front of the rear edge, are in Direction of flow aligned.  

In all wing profiles according to the invention, the means extend over a length or height of up to about 5%, preferably 0.3% to 2%, of defined by the distance from the front edge to the rear edge of a wing Wing depth.

The second solution comprises a wing profile, on which the air flows through Fluid forms a suction side and a pressure side, in particular Aircraft wing or blade of a turbomachine, and the one has divergent thickened or angled trailing edge, behind which the Trailing edge means arranged to prevent backflow of the fluid are.

These include the means: band-shaped, in particular parallel to the rear edge arranged profiled bodies, the basic shape of which is approximately in cross section is rectangular, triangular or teardrop-shaped.

The profiled bodies are preferably perpendicular to the bars Flow direction arranged on the suction or pressure side and with the Trailing edge are connected by webs, with, particularly preferably, the profiled body are spaced in the direction of flow from the trailing edge and several profiled bodies in the direction of flow at intervals from one another are arranged.

Ultimately, at least one of the profiled bodies should be movably mounted and for Printing side be adjustable.

This wing profile of the second solution according to the invention can additionally have the characteristics of the first solution.

The invention is illustrated by means of schematic exemplary embodiments explained. Show it

Fig. 1 flow of a wing profile (A) and the enlarged kinked or diverging trailing edge (AA);

FIG. 2 diagram of the spectrum of the speed fluctuations at the edge of the dead water as shown in FIG. 1;

Fig. 3 shows a schematic perspective of the divergent trailing edge / Gurney flap with a perforated back edge;

Fig. 4 principle perspective of the divergent trailing edge / Gurney flap with slotted trailing edge;

Fig. 5 divergent trailing edge shown in perspective with suction and pressure-side interference means;

Fig. 6 divergent trailing edge shown in perspective with trailing bodies;

Fig. 7 diagram of the polar of a reference measuring wing without and with Gurney flap;

Fig. 8 wing profile with kinked or diverging trailing edge in section, equipped with trailing bodies;

Fig. 9 of the polar diagram to compare different measures for tracking stabilization,

Fig. 10 compressor blade with diverging trailing edge, with interference on the pressure side (B) and the suction side (A);

Fig. 11 Technically schematic design of a wing with diverging trailing edge and trailing body, in perspective view on the suction side (A) and partially enlarged on the suction side (AA) or on the pressure side (B) and partially enlarged (BB).

The inventive solutions are described in the following with their operating principles Connection shown without the protection area on the schematic Want to limit embodiments. Identify the same reference numerals in the following the same or equivalent elements.

In principle, a profile of the mean flow of a fluid is found in wing profiles with a divergent or kinked trailing edge, as shown in FIG. 1 in partial image A with a section through the entire wing, in partial image AA in accordance with the dot-dash circle of partial image A. The flow behind a bent rear edge 2 of an airfoil 1 has a flow separation with dead water 3 . A backflow 4 forms in the dead water. In the outer area above the dead water, the boundary layer flow 5 continues almost undisturbed from the wing upper side / suction side of the profile, but is deflected somewhat downwards by the suction from the lower edge 6 of the dead water. An increased downward deflection is synonymous with increased lift. The increased lift must also be reflected in a change in the pressure distribution on the wing profile. An increased buoyancy force on the upper side of the profile arises from the fact that the somewhat lower pressure of the dead water 3 on the upper side of the wing, the suction side, is noticeable in comparison with the surroundings. The reduced pressure is equivalent to an additional suction force that increases the buoyancy.

The flow around the underside, the pressure side of the wing profile is changed even more seriously. The current is dammed up in the area in front of the Gurney flap. This increases the pressure there almost up to the value of the dynamic pressure of the flow. This leads to a significantly increased lift due to the contribution of the underside of the wing. After passing the edge 2 of the Gurney flap, however, the pressure of the dead water quickly returns to the free streamline of the boundary layer flow 6 of the dead water. This is slightly under the pressure of the environment. The flow velocity there is therefore approximately equal to the inflow velocity of the profile, or slightly above it, if Bernoulli's equation is used to estimate the velocity. This relatively high speed and the relatively thin shear layer, the boundary layer flow 6 , at the bottom of the dead water cause fluid to be drawn in downwards.

The previous considerations concerned buoyancy.

However, the Gurney flap also creates resistance; that can also be illustrated with FIG. 1. In front of the Gurney flap, high pressure acts on the Gurney flap in the direction of flow. The pressure behind the Gurney flap is slightly reduced. The parasitic resistance that the Gurney flap additionally generates results from the product of the projection of the surface of the Gurney flap in the direction of flow and the pressure difference on both sides, before and after. This parasitic resistance must be reduced.

In addition to the fluid values, as shown by arrows in FIG. 1, the transient portions of the flow behind the Gurney flap are also important. At the top and bottom 6 of the dead water you measure z. B. with a hot wire probe, not shown, speed fluctuations u 'in the direction of the mean flow u _medium . A frequency spectrum f (kHz) of the relative speed fluctuations u '/ u _{mean is found} , as shown in FIG. 2. On the one hand, there is a broadband spectrum 7 , which is generated by the stochastic fluctuations of the turbulent boundary layers of the wing profile. On the other hand, a sharp peak 8 is observed in the spectrum of the speed fluctuations. This is a periodic fluctuation or trailing dip, as is also known from the trailing flow behind a cylinder with a flow around it, as Karman's vortex street. For some years now it has been possible to predict the occurrence of this periodic fluctuation and its frequency. The occurrence of such a periodic fluctuation is called absolute instability. The presence of a backflow contributes particularly to the occurrence of the absolute instability. On the other hand, if the wake flow is particularly asymmetrical, ie the boundary layer on the profile suction side is much thicker than on the profile pressure side, then the absolute instability disappears. This leads to the disappearance of the sharp tip 8 shown in FIG. 2. Such a case occurs in reality at high angles of attack of the wing profile.

The occurrence of absolute instability with a periodic wake leads to strong periodic vortices, as are known from Karman's vortex street. The associated increased pulse exchange in the wake causes increased resistance. If the absolute instability can be suppressed, the resistance will decrease at the same time. The wake flow can be stabilized in the following ways:

• - hindrance of backflow in dead water behind the Gurney flap, and
• - Disruption of the two-dimensionality of the wake flow.

The backflow can be hindered by introducing suitable bodies into the dead water. The two-dimensionality in the wake of a cylinder can be disturbed by applying a spiral structure to the cylinder. This measure, which is often seen on industrial chimney pipes, suppresses the formation of periodic vortices. The slotted, perforated and serrated edges of the Gumey flap according to DE patent application 199 64 114.5 have a comparable function. These are trailing edge shapes e.g. As shown in FIGS. 3, 4, where a divergent trailing edge 2 or Gurney flap with holes 20 or slots is equipped 21st

A serrated trailing edge according to FIG. 5 had also already been mentioned there, but only on the pressure side of the wing profile.

However, wind tunnel tests have shown that the trailing instability can be suppressed much more effectively if spikes 111 , 112 or similar edge geometries for interference agents are attached to both sides of the trailing edge 113 , that is to say on the pressure side and on the suction side 110 A. It is irrelevant whether the prongs are directly opposite one another or are offset from one another.

Completely new is a configuration according to Fig. 6, a perspective view of a suction side 110 A of a wing profile with rectangular cross bodies 15 in the dead water behind the trailing edge 152, which may be connected by webs 151 therewith. This arrangement hinders the backflow in the dead water and stabilizes the backflow, which is also expressed in a reduction in resistance.

In order to obtain reliable statements about the achievable reduction in resistance, wind tunnel tests were carried out. A typical gliding profile called HQ17 was equipped with a Gurney flap. This consisted of a 90-degree angle, the height of which was 1% of the profile depth. The Reynolds number of the experimental wing was Re = 1 × 10 ⁶ . Buoyancy and resistance were measured with a precise wind tunnel balance. The inherently very low resistance of the selected profile made it possible to precisely determine changes in the resistance of the Gurney flap. Typical polar measurements of the drag coefficient C _w - in the range from 0 to the value 0.03 - and the lift coefficient C _a - in the range from 0 to the value 1.5 - can be seen in FIG. 7. The polar 9 for a reference wing without a Gurney flap naturally has the lowest drag coefficient C _w . In the conventional Gurney flap without means for interfering with periodic flow separation, the resistance increases considerably, and the polar 10 of the wing with Gurney flap is therefore shifted to a higher resistance. On the other hand, the considerable gain in lift can also be clearly seen in FIG. 7. The difference in resistance between the polar 9 and 10 is shown as a parasitic opponent 13 . This can be reduced by 20-30% by overtravel stabilization or disruptive means in combination with the rear edge configurations according to Fig. 3-6.

The data of the configuration with the trailing edge of FIG. 5 shows the graph 11 in FIG. 7. The data of the trailing edge with cross bodies in Totwasser of FIG. 6 are shown in curve 12 of Fig. 7.

The hot wire measurements show that the configurations according to FIGS. 3 to 5 completely suppress the periodic vortex formation. This property is particularly useful when the noise emission from the Gurney flap has to be particularly low, e.g. B. in wind turbines.

The stabilization of the wake of the Gurney flap has only a limited potential for reducing the parasitic resistance, in the order of magnitude of approximately 25%, shown in FIG. 7. However, there is a possibility of further reducing the parasitic resistance, namely by Filling the wake, as shown schematically in Fig. 8. Suction forces are shown as a minus sign and pressure forces as a plus sign. This achieves the following:

• - The wake is stabilized by the wake body behind the Gurney flap.
• - The trailing body 14 is preferably additionally supplemented by a vertical profile body 15 which hinders the backflow in the area between the Gurney flap and trailing body.
• - Nevertheless, pressure equalization between the suction side and the pressure side is complete the distance between the Gurney flap and the trailing body is possible, d. H. the Buoyancy gain of the Gurney flap is retained.
• - The resistance is reduced dramatically by the following situation: The resistance-increasing suction power behind the Gurney flap also affects the Front of the trailing body. The resulting toughness will thereby partially canceled. The rear part of the trailing body works due to its tapering like a diffuser. It is therefore based on the increased pressure on the rear part of the trailing body. The resulting one Force from this increased pressure affects the resistance from increased pressure in front of the Gurney flap. The total resistance of the  Gurney flap with trailing body must therefore be considerable sink.
• - The lossy detached flow behind the Gurney flap is back brought together by the flow on the trailing body. This leads to a drastic reduction in the lag dent or absolute instability in the speed profile behind the wing. This is synonymous with a decrease in resistance.

Also for the configuration with trailing body of Fig. 8 were with the same airfoil profile (HQ17) was added and the same amount of the Gurney flap of 1% of the chord length, measured data in the wind tunnel. The Reynolds number was again, as commented on FIG. 7, Re = 1 × 10 ⁶ . The results are shown in FIG. 9. There, the person skilled in the art sees that the drag body once again achieves a dramatic reduction in resistance, in the order of 60% of the parasitic resistance. The quantitative comparison between reference wing or polar 9 , Gurney flap corresponding to polar 10 , Gurney flap with suction and pressure-side interference means on the rear edge according to FIG. 6 corresponding to polar 11 and Gurney flap with trailing body according to FIG. 8, corresponding to polar 16 , shows significant improvements. The ratio of lift to resistance is practically unchanged in the already very low-resistance wing according to FIG. 8.

In practice, this means, as the expert can easily calculate, that this wing behaves like a wing enlarged by approx. 12%. At a Airliner could reduce the weight by the same wing size by 12% increase. In the case of a glider, the sinking speed would be approx. 6% reduced.  

A wing or a blade of a turbomachine is to be shown below. The simplicity and rigidity of the rear edge construction are particularly important. An embodiment of the wing or blade trailing edge according to FIG. 3 or 5 is therefore particularly suitable. A compressor blade could e.g. B. can be designed according to FIG. 10. The trailing edge structures are exaggerated; the height or width of the rear edge or the height and length of the interference means is only max. 5%, preferably 0.3-2% of the wing or blade depth, which is defined by the distance from the leading edge to the trailing edge of the wing.

A scoop according to FIG. 10 can e.g. B. by casting, galvanic removal, drop forging or milling with suitable form cutters. The spikes can be made as one piece with the shovel as extended bars. On the other hand, a serrated metal or plastic band can be applied subsequently to the diverging thickened or kinked trailing edge, e.g. B. by gluing, soldering or welding. However, the easiest way to produce such a scoop with a serrated trailing edge is to cast it from a single piece.

Part B shows the pressure side 110 B and Part A shows the suction side 110 A of the compressor blade analogous to FIG. 5, the rear edge 113 of which is provided with rib-shaped or web-like disruptive means 114 , 115 , which start on the profile surfaces and run to the rear edge and end there, the cross-sectional shape of which is triangular.

When used on wind turbines, it is easiest if a trailing edge according to FIG. 4 or 5 is made from sheet metal and glued to a conventional profile as a sheet metal angle.

A trailing wing edge according to FIG. 8 is particularly suitable for the cruising of commercial aircraft. With transonic flow, as occurs there, the advantages of divergent trailing edges are further increased. The significant reduction in resistance, which is achieved by a divergent trailing edge of the wing with a trailing body, should therefore greatly promote an implementation of the invention in commercial aircraft, since lower fuel consumption and / or a higher payload are possible.

Another possible technical embodiment is shown in FIG. 11. Again, the real dimensions of the divergent trailing edge of the wing and the trailing body are very small and only a few centimeters in a commercial aircraft.

Part A shows the suction side 110 A or wing top side in perspective and part AA shows its partial enlargement in partial section. Likewise, partial image B shows the printed page 110 B or the underside of the wing in perspective and enlarged in partial section as partial image BB. The overall height of the divergent rear edge 152 with reinforcing ribs and interference means 153 placed on the pressure side ensures sufficient rigidity of the trailing edge of the wing. These reinforcing ribs merge into webs 151 and also carry the follower bodies 14 and 15 . Wind tunnel tests have shown that the reinforcement bars do not cause a measurable increase in resistance. The cross section of the wing trailing edge according to FIG. 11 corresponds to that of FIG. 8. The height of the Gurney flap or of the divergent trailing edge is in the range of approximately 0.3 to 1% of the wing depth. The width of the gap or distance between the Gurney flap 152 and the follower body 14 corresponds approximately to the height of the Gurney flap. Arranged in the gap in the rectangular shaped profiled body 15 for disturbing a return flow. The trailing body 14 is approximately triangular in cross section with the pressure side 140 b and the suction side 140 A tapering towards one another and has approximately the same thickness on its rounded front side 141 as the height of the Gurney flap. Its length to the rear edge 142 is approximately 3 to 4 times the thickness on its front side 141 .

Regardless of this application in the commercial flight of commercial aircraft, Gurney flaps can also be used advantageously to increase lift when approaching and taking off. Even with conventional flap systems already fully extended, improvements in lift are still achieved. Gurney flaps with trailing edges according to FIGS. 3 to 5 are particularly suitable here.

Finally, there is also the possibility of movably supporting the trailing body 14 analogously to FIG. 8 on the web 15 or trailing edge 2 and swinging it down as a high-lift flap during landing and take-off.

Reference list

1

Wing profile

2

Divergent or kinked trailing edge (Gurney flap)

20th

hole

21

slot

3rd

Dead water

4

Backflow in dead water

5

Boundary layer flow over the dead water

6

Boundary layer flow under the dead water

7

Broad spectrum of turbulence

8th

Top in the spectrum

9

Polar of the reference wing without a bent rear edge

10th

Polar of the wing with bent rear edge (Gurney flap),

110

A, B suction side, pressure side

111

,

112

Disruptive means

113

Trailing edge

114

,

115

Disruptive means

11

Polar of the wing with the rear edge bent and interference means

12th

Polar of the wing with angled trailing edge and trailing body

13

Parasitic resistance

14

Trailing body

140

A, B suction side of the trailing body, pressure side of the trailing body

141

Front of the trailing body

142

Trailing edge of the trailing body

15

Trailing body to prevent backflow

151

web

152

Trailing edge

153

rib-like interference means or interference means

16

Polar of the wing with angled trailing edge and trailing body

Claims (12)

1. Wing profile, on which a suction side and a pressure side are formed when flowing through a fluid, in particular an aircraft wing or blade of a turbomachine, and which has a divergent thickened or angled rear edge, characterized in that the rear edge on the suction side and the pressure side with means is equipped to disrupt periodic flow separation and / or flow stabilization. 2. Wing profile according to claim 1, characterized in that the means for the printed page is selected from a group of means comprising: arranged on the print side in front of the trailing edge or up to there extending incisions or webs, to the pressure side and / or from the Trailing edge extending individual elements, perforations of the Angle, in the vertical direction on the pressure side and at the same time horizontally extending sawtooth or wavy elements. 3. Wing profile according to claim 1, characterized in that the means for the suction side include: arranged in front of the trailing edge or up to elements or webs extending there, preferably in cross section have the shape of a triangle, trapezoid or wave. 4. Wing profile according to one of the preceding claims, characterized characterized in that the means over a length or height of up to about 5%, preferably 0.3% to 2%, by the distance of Defined leading edge to trailing edge of a wing, wing depth extend.   5. Wing profile according to one of the preceding claims, characterized characterized in that the webs as ribs in front of the rear edge are designed, aligned in the direction of flow. 6. Wing profile, on which there is a suction side when flowing through a fluid and forms a printed page, in particular aircraft wing or Blade of a turbomachine, and that a divergent thickened or has angled trailing edge, characterized in that behind the trailing edge means to prevent backflow of the fluid are arranged. 7. Wing profile according to claim 6, characterized in that the means comprise: band-shaped, in particular arranged parallel to the rear edge profiled bodies, the basic shape of which is approximately rectangular in cross section, is triangular or teardrop-shaped. 8. Wing profile according to claim 6 or 7, characterized in that the profiled body as rods perpendicular to the mean flow direction of the Fluids are arranged and connected to the rear edge by webs. 9. Wing profile according to one of claims 6-8, characterized in that the profiled body in the direction of flow from the trailing edge are spaced. 10. Wing profile according to one of claims 6-9, characterized in that several profiled bodies in the direction of flow at intervals from one another are arranged.   11. Wing profile according to one of claims 6-10, characterized in that that at least one of the profiled bodies is movably supported and for Print side is adjustable. 12. Wing profile according to one of claims 6-11, on the pressure side and / or Suction side equipped with means according to one of claims 1-5.