GB2177661A - Adaptive working section of a transonic wind tunnel - Google Patents

Abstract

The working section has a smooth inner surface and can be bent in the flow direction 23 by means of a plurality of adjusting elements 7. The wall 1, 2, 3 is made perforated and has a plurality of recesses 9 and closing pieces 10. The closing pieces 10 are adjustable by means of adjusting devices 14 at least partially, for example perpendicularly relative to the recesses 9 in the wall, so that, in the closed position, the smooth continuous inner surface 31 is obtained, whilst in the other positions an opening ratio differing from zero can beset. <IMAGE>

Description

SPECIFICATION Adaptive working section of a transonic wind tunnel The invention relates to an adaptive working section of a transonic wind tunnel, with a wall which has a smooth inner surface and which can be bent in the flow direction by means of a plurality of adjusting elements. By a transonic wind tunnel is meant one which can be used in both the subsonic range and the supersonic range, that is to say, for example, between Mach 0.5 to 1.3.

The publication "Wall interference in Wind Tunnel" (AGARD-CP-335), published in London on 20th May 1982, makes known a treatise entitled "The status of two- and three-dimensional testing in the University of Southampton Transonic Self-Streamlining Wind Tunnel" (Wolf, Cook, Goodyer) which shows an adaptive working section having the features indicated in the pre-characterizing clause of Claim 1. The wall consists of a bendable metal plate which has a continuous smooth inner surface. Arranged on the outside of this wall is a plurality of adjusting elements in the form of adjusting spindles, by means of which the wall can be bent continuously within the range of elasticity of the metal. This ensures that the wall is matched closely to the flow conditions in the subsonic range. This working section cannot be used in the supersonic range.If a working section were used in the supersonic range, the compression shocks occurring in this range would not be cancelled, but reflected. Consequently, it is possible for the measurement result to be falsified.

The same publication makes known a treatise entitled "Development of a three-dimensional adaptive wall test section with perforated walls" (Parker and Erickson) which shows an adaptive working section already intended for a wide flow range of between Mach 0.6 and 1.2. However, a wall consisting of two shells surrounding one an other without a clearance is used here. The outer shell is sub-divided into a plurality of segments, whilst the inner shell is made continuous. In both shells there are recesses in the form of bores.

When a segment of the outer shell is shifted in the flow direction relative to the inner shell, the bores at the inner and outer shells overlap to a greater or lesser extent, depending on the particular position.

It is thus possible to set a variable opening ratio, specifically both in the flow direction and transversely relative to this. There is, however, no pro vision for adjusting the two shells relative to one another so as to obtain a continuous wall. Even if the segments of the outer shell had such mobility that the opening ratio could be adjusted towards zero, the recesses in the inner shell would nevertheless still remain, so that the inner shell would present a rough surface as a whole and under all measuring conditions. Even in the subsonic range, this working section is used with an opening ratio differing from zero. This is disadvantageous.

Nevertheless, in the flow range of Mach > 1, the compression shocks are advantageously cancelled in this working section as a result of the performation. But a disadvantage here again is that there is no possibility of measuring the flow components near the wall. Consequently, it has already been proposed there to measure the characteristic data representing the flow, in particular the pressure and velocity, by means of a separate device consisting of two measuring rods which are axially continuous in the flow direction. In actual fact, this known measuring section produces satisfactory results only in a very narrow flow range, for example around Mach 1. In contrast, in the subsonic range the disadvantages described are accepted. This working section is not intended for measurements in a range higher than Mach 1.2.

The WGLR 1966 year book, "The Transonic Wind Tunnel of the Gottingen Aerodynamic Test Institute" (Ludwieg, Lorenz-Meyer, Schneider), makes known a working strip in which there are actually two working sections arranged in succession in the flow direction. The first working section has a continuous wall with a smooth inner surface, whilst the second working section is made perforated. By "perforations" are meant, in the present application also, recesses of relatively small size closed round their edges, that is to say particularly in contrast to slits which usually have a substantially greater extension in the axial direction than transversely to this. The first working section has a nozzle design with an adjustable surface for producing different flow Mach numbers. This applies to the supersonic range.The other working section, which is therefore made "perforated", is used in the subsonic range up into the transonic range right up to Mach 1.2. Here, the advantageous cancellation of the shock waves is utilized in the transonic range, whereas the disadvantages of the perforation come into play in the subsonic range.

Another disadvantage here is that, when a wide measuring range is covered, the measurement has to be interrupted, because the model has to be moved from one working section into the other.

The working sections with a ventilated wall, that is to say, perforated or slit, used nowadays for the entire transonic range have the following disadvantages: They do not provide interference-free measuring results in the subsonic range.

The measuring results to some extent cannot be corrected, one of the reasons for this being that the boundary conditions cannot be determined with sufficient accuracy.

Disturbingly high sound radiation occurs, so that walls ventilated in this way cannot be used, for example, to keep the flow laminar.

Only relatively small model dimensions are permitted, and the ratio of the cross-section of the model to the cross-section of the wind tunnel should be ~ 0.5%, which results in large cross-sections of the tunnel when the necessary accuracy of the model is adhered to.

On the other hand, continuous, that is to say non-ventilated, adaptive walls, which can be used free of interference in the subsonic range, are not suitable for cancelling compression shocks, such as occur in the supersonic range.

The object on which the invention is based is to provide an adaptive working section of a transonic wind tunnel, by means of which measurements can be made as free of interference as possible over a wide flow measuring range, in particular, for example, between Mach 0.5 and 1.3 (0.5 =' Ma = 1.3) continuously, that is to say without interrupting the wind supply, simply by adjusting or varying the parts of the wall.

According to the invention, this is achieved because the wall is made perforated and has a plurality of recesses and closing pieces, and because the closing pieces are adjustable by means of adjusting devices at least partially, for example perpendicularly relative to the recesses in the wall, so that, in the closed position, the smooth continuous inner surfaces obtained, whilst in the other positions an opening ratio differing from zero can be set. It is essential, in the first place, that the wall be perforated and not, for example, slit. The term "perforated" refers to recesses of relatively small size closed round their edges and usually arranged in a uniform distribution over the wall. A closing piece belongs to each recess. Of course, several closing pieces can also be combined in groups, so that they can be moved jointly. The closing pieces fit into the recesses.They are moved out of the recesses or inserted into them by means of adjusting devices. In the inserted position, the wall of the wind tunnel is closed, that is to say the opening ratio is equal to zero, and it is important that the inner surface of the closing pieces and the inner surface of the wall be aligned with one another, so that, overall, a smooth continuous inner surface is obtained on the wall. Furthermore, the wall can be bent by means of a plurality of adjusting elements, so that it can be adapted to the flow behaviour. It is thereby possible to set the ideal wall form for the particular measurement over the entire Mach number range between 0.5 and 1.3, without the measurement having to be interrupted. Measurement can be carried out continuously, that is to say without interrupting the wind supply.Because of the simple and accurate wall-pressure and position measurements, the closed adaptive wall of the working section is ideal for investigations in the range < 1. The working section can be used here both for two-dimensional and for three-dimensional measurements. In this case, the two-dimensional measurements are interference-free and the three-dimensional measurements are low in interference (and can be corrected). At Mach numbers Ma ~ 1 a supersonic flow has to be built up, and furthermore the compression shocks or expansion waves have to be cancelled at the wall. This is also possible by means of the working section according to the invention.In the front part, the working section is shaped in the form of a Laval nozzle with a closed wall, and in the rear part, that is to say where the model is positioned, the closing pieces are moved out of the recesses to a greater or lesser extent, so that a perforated wall is obtained here. The opening ratio in this region of the working section for cancelling compression shocks or expansion waves is dependent on the Mach num ber. The particular wall opening ratio required can easily be set by the degree to which the closing pieces are moved out of the recesses. It is possi ble, for example in a working section consisting of four wall parts approximately bounded by straight lines, to design and use according to the invention only one wall part, two wall parts or all four wall parts.

Part of the wall can be adjustable in the manner of a Laval nozzle. This will usually be the front part of the working section. This adjustment is used in the supersonic range, the nozzle being arranged in relation to the nozzle formation.

The closing pieces for varying the opening ratio can be adjustable individually or in groups both in the flow direction and transversely relative to this.

The recesses thereby exposed to a greater or lesser extent allow some of the flow to pass out of the tunnel to the outside and, if appropriate, also enter the tunnel again. It is also possible to com bine them with a suction system. Several closing pieces can be arranged on a common support. It is also possible, however, to provide closing pieces which can each be actuated individually. Where a group formation is used, the common support for the closing pieces can be a second wall, but one which is appropriately sub-divided into segments in the flow direction and transversely relative to this.

The recesses and the closing pieces appropri ately have conical forms matching one another, thus ensuring that the closed wall receives a smooth inner surface.

The adjusting devices for the closing pieces can be mechanical, motive, electromechanical, hy draulic or the like. There are many possibilities here for a person skilled in the art.

Finally, it is possible to make only part of the wall perforated according to the invention. This ap plies both over the cross-section and in the flow direction.

The invention is further illustrated and described with reference to some preferred exemplary em bodiments. In the drawing: Figure 1 shows, in a diagrammatic representation, a longitudinal section through a first embodi ment of the working section, taken along the line I I of Figure 2, Figure 2 shows a cross-section through the walls of the wind tunnel, Figure 3 shows a more basic representation of a longitudinal section through the working section set for a supersonic range, Figure4shows a detailed representation of a closing piece with an adjusting device, and Figure 5 shows a further possible embodiment of the closing piece with an adjusting device.

Figures 1 and 2 show highly diagrammatic representation of an embodiment of a working section of the wind tunnel in the form of a longitudinal section (Figure 1) and a cross-section (Figure 2). In the upper part of each of the Figures, the wall is shown in its closed state. The lower part illustrates the open recesses, that is to say a set opening ratio differing from zero. As can be seen in Figure 2, the wind tunnel is a rectangularly delimited tunnel which is bounded by the walls 1, 2, 3, 4. A window 5 is provided in the wall 2, so that it is possible to observe from outside the location in the tunnel where the model (not shown) is also arranged.The wall 1 has a bendable metal plate 6, on which a plurality of adjusting elements 7 is arranged distributed over its full extent both in the longitudinal direction (Figure 1) and in the transverse direction (Figure 2). By means of each adjusting element 7, it is possible to bend the metal plate 6 to a greater or lesser extent according to the arrows 8, in order thereby to adapt it to the flow. This is particularly important for the subsonic range, but also for the supersonic range in order to set a Laval nozzle (Figure 3).

The metal plate 6 has a plurality of recesses 9 closed round their edges, which are usually designed as round or conical bores. Here, the axes of the recesses 9 are arranged perpendicularly relative to the flow direction or relative to the wall. It is also possible, however, to make these axes oblique. A closing piece 10 belongs to each recess 9. Several closing pieces 10 can be arranged segmentally on a common support 11. As illustrated in Figure 1 as regards the wall 1, several such supports 11, 11', 11", etc. are arranged segmentally in succession in the flow direction, that is to say in the longitudinal direction of the working section.

As can be seen in Figure 2, several supports 11, 12, 13, likewise divided segmentally, are provided in the peripheral direction, that is to say transversely relative to the flow direction. In this way, the wall 1 is split into a plurality of segments in support form. However, this does not involve the continuous metal plate 6. As illustrated by reference to the wall 1, the other walls 2, 3, 4 can also be designed and divided in the same way. For the sake of clarity, however, this is no longer shown particularly in all its details. It goes without saying that only two walls, for example the walls 1 and 3, of a working section need be designed in this way, whilst the walls 2 and 4 can be made rigid in the form of a continuously closed wall. It is also possible to design only one of the walls 1, 2, 3, 4 according to the invention.

Figure 3 illustrates a further-simplified representation of a longitudinal section through the working section. Here again, there can be the walls 1, 2, 3, etc. which each have a bendable metal plate 6. It is also possible, however, to select a rotationally symmetrical design and provide, instead of the metal plate 6, a wall made of multi-dimensionally deformable material, for example rubber. It can be seen by referring to Figure 3 how the closed wall, that is to say with the closing pieces (not shown separately) in the closed state, is deformed into a Laval nozzle 21 in the front region. The adjusting elements 7 serve for this purpose. The model 22 is arranged in the rear region. The flow direction is indicated by the arrow 23. In the rear region, the closing pieces 10 are moved out of the recesses 9, this being shown only with regard to the walls 1 and 3.A supersonic flow is obtained by means of the Laval nozzle 21. A Mach line 24 forms, and expansion waves 25 are generated, these being cancelled as a result of the perforated design of the walls with the set opening ratio.

Figure 4 shows a cut-out taken from the wall 1 with a single recess 9 and an associated closing piece 10. It is evident how each recess 9 can be equipped with its own closing piece 10 in this way, so that individual actuation is perfectly possible.

Fastened to the metal plate 6 via a perforated spacer ring 26 is a housing 27, in the cylinder of which a piston 28 is guided slideably and sealingly, its piston rod 29 being connected to the closing piece 10 or forming the closing piece 10 at its front end. A return spring 30 exerting stress in the direction of the closing position is arranged in the cylindrical housing 27. The metal plate 6, the recesses 9 and the closing piece 10 are designed and arranged so that, in the closed position as illustrated, a continuous smooth suface 31 is obtained on the inside of the metal plate 6. Connected to the housing 27 is a line 32, via which compressed air or hydraulic fluid can be fed to the adjusting device 14 according to the arrow 33, when the closing piece 10 is to be moved out of the recess 9 according to the arrow 19, that is to say when a specific opening ratio is to be set.The opening ratio can be adjusted or varied by means of the pressure of the air or the hydraulic medium in co-ordination with the force of the return spring 30.

It goes without saying that the individual adjusting devices shown in Figure 4 are arranged distributed in large numbers over the walls 1, 2, 3, 4. In addition to the adjusting devices 14, the adjusting elements 7 are of course always provided, in order to adjust or adapt the walls 1, 2, 3, 4 as a whole.

Figure 5 shows an electromagnetic design of the adjusting device 14. Here again, a housing 34 is fastened to the metal plate 6 by means of spacer pins 35 which are arranged distributed over the periphery. The housing 34 receives a coil 36, the core 37 of which carries or forms the closing piece 10.

Here again, the return spring 30 exerts stress in the direction of the closing position. The opening ratio is set according to the excitation of the coil 36.

Claims (9)

1. Adaptive working section of a transonic wind tunnel including a wall which has a smooth inner surface and which can be bent in the flow direction by means of a plurality of adjusting elements, the wall being perforated with a plurality of recesses closable by closure members, the closure members being adjustable so that, in the closed positions, the smooth continuous inner surface is obtained, whilst in other positions, an opening ratio differing from zero can be set.

2. An adaptive working section according to Claim 1, wherein part of the wall is adjustable in the manner of a Laval nozzle.

3. An adaptive working section according to Claim 1, to vary the opening ratio, the closure members are adjustable individually or in groups both in the flow direction and transversely relative to the flow direction.

4. An adaptive working section according to Claim 1,2 or 3, wherein several closure members are arranged on a common support.

5. An adaptive working section according to Claim 4, wherein the common support is a common wall.

6. An adaptive working section according to any preceding claim, wherein the recesses and the closure members have complementary conical formations.

7. An adaptive working section according to any preceding claim, wherein the adjusting devices for the closure members are mechanical, electromechanical, hydraulic or pneumatic.

8. An adaptive working section according to any preceding claim, wherein only part ofthe wall is made perforated.

9. An adaptive working section of a transonic wind tunnel substantially as herein described with reference to the accompanying drawings.