WO2021185389A1

WO2021185389A1 - Wind tunnel

Info

Publication number: WO2021185389A1
Application number: PCT/CZ2020/050012
Authority: WO
Inventors: Jan JEDELSKY; Milan MALY; Ondrej CEJPEK
Original assignee: Vysoké Uceni Technické V Brne
Priority date: 2020-03-16
Filing date: 2020-03-16
Publication date: 2021-09-23
Also published as: CZ202218A3; CZ309563B6

Abstract

A wind tunnel, comprising: - an inlet diffuser (4), - a settling chamber (5) having its inlet end fluidly connected to the outlet end of the inlet diffuser (4). - a confuser (6) having its inlet end fluidly connected to the outlet end of the settling chamber (5), - a Iaminarization pipeline (7) having its inlet end fluidly connected to the outlet end of the confuser (6), - a test section (8) having its inlet end fluidly connected to the outlet end of the Iaminarization pipeline (7) and having at least a part of its wall made of a transparent material, the inlet diffuser (4), the settling chamber (5), the confuser (6), the Iaminarization pipeline (7) and the test section (8) being arranged one after the other along a common longitudinal axis, - an inlet compensator (3) having its inlet end adapted to be fluidly connected to an outlet end of a Mower (i) a having its outlet end fluidly connected to the inlet end of the diffuser (4), and - an outlet compensator (9) having its inlet end fluidly connected to the outlet end of the test section, wherein the compensators (3, 9) are flexible pipelines having variable lengths.

Description

Wind Tunnel

Field of the invention

The present invention relates to a wind tunnel, particularly an open blow-down type one, such wind tunnel comprising an inlet diffuser, a settling chamber, a confuser, a laminarization pipeline and a test section, the latter having at least a part of its wall made of a transparent material, wherein the inlet diffuser, the settling chamber, the confuser, the laminarization pipeline and the test section being arranged one after the other along a common longitudinal axis and mutually fluidly connected.

Background of the invention

Various types of wind tunnels, which constitute the prior art concerned, are used for exploring the aerodynamic properties of bodies within the framework of the research focused on the behaviour of objects in an air stream, and the like.

The known wind tunnels, which constitute the prior art, have a number of drawbacks. In particular, the variability of the available measurement options in such tunnels is very limited. Wind tunnels are usually intended for exploring specific behaviour schemes of particular objects within an air stream. This means that, such wind tunnels can be used neither to explore different objects nor to explore identical objects under significantly different or gradually changing conditions of an air stream.

An operation of the wind tunnels, which would allow alteration of measurement parameters, such as the tunnel length or the like, is connected with a subsequent, very time-consuming re-adjustment procedure of the optical systems used for recording the processes taking place within the test section.

Wind tunnels comprise test sections. Usually, a test section is formed by a portion of the tunnel having transparent walls. External optical measuring systems, which are assigned to a test section, are used for recording the behaviour data of objects within such test section. Such measurement systems are very sensitive to vibration and to motional influences and simultaneously require procedures for precise adjustments despite of being focusable on a very small area, mostly in the order of mm³. The acquisition of findings relating to the behaviour of objects within a substantial part of the profile of the test section requires readjustments and/or relocations of the respective measurement systems. Such procedures, however, are very time-consuming. Moreover, there is a risk of damage such expensive measurement systems.

Hence, the object of the present invention is to improve the aforesaid type of wind tunnels by making it variably usable for different measurement procedures and for observing the behaviour of different objects within a substantial part of the profile of the test section, in addition, such advanced wind tunnels should be simple from the viewpoint of design and production.

Summary of the invention

The above object is fulfilled by means of a wind tunnel, comprising:

- an inlet diffuser,

- a settling chamber having its inlet end fluidly connected to the outlet end of the inlet diffuser,

- a confuser having its inlet end fluidly connected to the outlet end of the settling chamber,

- a laminarization pipeline having its inlet end fluidly connected to the outlet end of the confuser,

- a test section having its inlet end fluidly connected to the outlet end of the laminarization pipeline and having at least a pari of its wall made of a transparent material, the inlet diffuser, the settling chamber, the confuser, the laminarization pipeline and the test section being arranged one after the other aiong a common longitudinal axis,

- an inlet compensator having its inlet end adapted to be fluidly connected to an outlet end of a blower a having its outlet end f lui dly connected to the inlet end of the diffuser, and

- an outlet compensator having its inlet end fluidly connected to the outlet end of the test section, wherein the compensators arc flexible pipelines having variable lengths.

Preferably, the compensators have the form of bellows with folded walls. Advantageously the wind tunnel further comprises a carrier with a positioning mechanism enabling the inlet diffuser, the settling chamber, the eonfuser, the laminarization pipeline and the test section to be displaced together and simultaneously.

Preferably, the positioning mechanism comprises a rail system with travellers, the top surfaces of the positioning mechanism constituting support areas for carrying the settling chamber.

The positioning mechanism preferably comprises a lifting device for displacing the rail system with the travellers in the vertical direction. The lifting device is preferably a screw-type lifting device having the transmission ratio of not more than 1 mm per revolution and/or having the range of motion at least 150 mm.

Preferably, the wind tunnel further comprises support arms attached to the settling chamber, carrying arms attached to the test section and/or to the laminarization pipeline and a coupling beam attached both to the support arms and to the carrying arms.

The wind tunnel may further comprise an outlet diffuser, wherein the outlet compensator interconnects the test section and said outlet diffuser or the inlet end of the outlet compensator is connected to the outlet end of the outlet diffuser.

Preferably, the wind tunnel further comprises at least one separator for elimination droplets from the gas stream, said separator having its inlet end fluidly connected to the outl et end of the outlet diffuser.

The wind tunnel further comprises a blower having its outlet end connected to the inlet end of the inlet compensator, wherein it may further comprise a frequency converter, which is electrically connected to the blower, for modifying the output power of the blower in a continuous manner. The inlet diffuser, the settling chamber, the eonfuser, the laminarization pipeline and the test section are arranged in mutually fixed positions forming an assembly, said assembly being moveable with respect to the blower while maintaining the fluid connection between the outlet orifice of the blower and the test section.

Preferably, there are following components arranged within the settling chamber:

- a straightener, which is arranged in a plane extending perpendicularly to the longitudinal axis of the settling chamber and compri ses an array of thin channels extending in parallel to the longitudinal axis of the settling chamber, and/or - an array of sieves or meshes arranged in parallel to each other and perpendicularly to the longitudinal axis of the settling chamber, the fineness grade of the individual sieves or meshes increasing in the direction from the inlet end towards the outlet one of the settling chamber.

Preferably, the laminarization pipeline as well as the test section arranged downstream of the former have the form of a duct with an octagonal or rectangular cross- section.

Preferably, at least two walls of the test section are formed by transparent panes, preferably by panes made of glass or polymethyi methacrylate.

Explanation of the drawings

An exemplary embodiment of the invention is further schematically depicted in the attached drawings; wherein Fig. 1 sho ws a schematic view of a wind tunnel assembly, Fig. 2 shows an inlet diffuser with an array of stream straighteners, Fig. 3 shows a confuser; Fig. 4 shows a test section equipped with a high-speed camera and a laser- source, Fig. 5 shows an outlet diffuser; Fig. 6 shows a wind tunnel comprising a carrying structure and Figs. 7A to 7D show multiple images exemplifying the processes taking place within the test section.

Exemplary embodiments of the invention

The exemplary embodiment of the wind tunnel according to the present invention, which is shown in Fig. 1 , comprises a blower L In the present particular case, a radial blower is provided (for example, the blower RFC 355-15/3-3-P-Z made by Alteko). Nevertheless, other types of blowers, such as axial ones, can also be used.

The blower I is connected to a frequency converter 2. enabling the output power of the blower and, in turn, the velocity of the air stream produced by the latter to be modified.

The wind tunnel further comprises a feed assembly for supplying the air stream produced by the blower 1 into the test section _.8, the outlet end of the blower l being fluidly connected to the inlet end of the feed assembly through an inlet compensator 3, the latter being constituted by a duct made of a fabric provided with a bonding coat and with bellows-like folds. Thereby, the inlet compensator 3 enables the relative movement of the blower 1 and the feed assembly to be effected in a certain range and, simultaneously, prevents the vibration produced by the blower 1 to be transferred into the feed assembly. In general, the compensator 3 can be constituted by any type of air impervious flexible duct, the length of which is at least partially variable.

The feed assembly comprises an inlet diffuser 4, a settling chamber 5, a confuser 6 and a laminarization pipeline 7, which are arranged one after the other downstream of the inlet compensator 3.

The inlet diffuser 4 has its inlet end fluidly connected to the out let end of the inlet compensator 3 and its outlet end to the inlet end of the settling chamber 5 and serves as a transition piece between the cross-section Si of the inlet compensator 3 and the cross- section $2 of the settling chamber 5.

The settling chamber 5 comprises so-called stream straighteners which are arranged inside said chamber where they contribute to make the stream-velocity profile more uniform and to mitigate turbulence. Each stream siraightener can be constituted by a honeycomb straightener 50 followed by an array of sieves or meshes 51. The honeycomb straightener 50 is a structure which partitions the settling chamber 5 in a plane extending perpendicularly to the longitudinal axis of the feed assembly, said structure comprising thin through channels having hexagonal cross-sections and extending in parallel to said longitudinal axis. Preferably, the length of a channel is 6 to 8 times greater than the hydraulic diameter of the same. The honeycomb straightener 50 can be made by means of a suitable 3D printing technique or by machining workpieces of wood or plastics. Alternatively, the honeycomb straightener 50 can be replaced, for example, by a triangular or rectangular stream straightener (not shown) differing from the honeycomb one in having a triangular and rectangular cross-sections of the thin channels, respectively.

The sieves or meshes 51 are also arranged perpendicularly to the longitudinal axis of the feed assembly, the finest mesh 51 (i.e., that having the smallest apertures) being arranged as the last one with respect to the direction of the air stream flowing through the feed assembly.

For example, the settling chamber 5 can contain one honeycomb straightener 50 and three meshes 51 having gradually increasing fineness grades, the aforesaid parts being arranged one after the other along the direction of the air stream. The purpose of the settling chamber 5 consists in reducing turbulences and eliminating l ateral components of the air stream.

According to an advantageous embodiment, the honeycomb straightener 50 and/or the mashes 51 are arranged in a manner enabling them to be removed from the settling chamber 5. Thus, the aforesaid parts can be combined and interchanged in accordance with the requirements of the particular measurement or, as the case may be, replaced or supplemented by additional elements influencing the streaming characteristics. For instance, it is also possible to increase the turbulence and to convert the laminar stream into a turbulent one by means of various inserted elements which are not shown herein.

The outlet end of the settling chamber 5 is connected to the inlet end of the eonfuser 6 which is arranged downstream of the settling chamber and provides a transition between the relatively large diameter S₂ of the settling chamber 5 and the relatively smal l diameter S3 of the Familiarization pipeline 7 or of the test section 8. The ratio S₂ / S₃ is preferably greater than 6.

The eonfuser 6 enables the air stream to be further smoothed and made more uniform and, simultaneously, the corresponding stream velocity to be increased in a desired manner. According to an exemplary embodiment, the eonfuser 6 may have a shape which is expressed, with respect to x, y coordinates of the points of the inner surface thereof, by the equation

wherein yo is the distance of the longitudinal axis of the eonfuser to the side wall of the inlet portion of the same, yi is the distance of the longitudinal axis of the eonfuser to the side wall of the outlet portion of the same, and

Leon is the length of the eonfuser, as measured bet ween the inlet and outlet ends of the same along the longitudinal axis of the same, the latter axis extending in parallel to the x axis.

However, other shapes of confusers are also conceivable. The outlet end of the eonfuser 6 is connected to the inlet end of the laminarization pipeline 7, the latter being arranged downstream of the eonfuser. The inner cross-section of the laminarization pipeline is the same as the inner cross-section of the test section 8 arranged farther in the downstream direction. The length of the laminarization pipeline 7 corresponds preferably at least to the twofold, more preferably at least to the fivefold and most preferably to the tenfold hydraulic diameter of the same, wherein the hydraulic diameter is equal to the ratio of the fourfold cross-sectional area to the wetted perimeter.

The outlet end of the laminarization pipeline 7 is connectedto the inlet end of the test section 8 which is arranged downstream of the laminarization pipeline and constituted by a duct having at least a part of its wall made of a transparent material in order to enable the processes taking place inside the test section 8 to be observed. Therefore, at least a part of said wail is made of a transparent material, such as glass or polymethyl methacrylate.

In certain cases (low stream velocities, large and rapid spray drops) the drops may happen to impinge the wail of the test section. Therefore, according to an advantageous embodiment, the transparent portion of the side wall is protected from being stained by the sprayed liquid by means of an array of aperture nozzles (not shown) arranged upstream of the respective transparent portion, said nozzles being arranged along the (inner) circumference of the test section, Such aperture nozzles, which are supplied by an auxiliary pressurized distribution system, enable a secondary air stream having a proportionate velocity to be fed into the respective section. Said array of aperture nozzles is appropriately directed so that it causes the air stream to impact the wail and to adhere due to the Coanda effect, while reducing the turbulence of the stream. Such additional stream contributes to the uniformity of the stream-velocity profile within the test section in an advantageous manner.

In an exemplary embodiment, the test section 8 can have a rectangularly shaped profile, at least two walls of the section comprising window panes made of a transparent rigid plate-type / planar material.

According to the exemplary embodiment, which is shown in the drawings, the test section 8 has 400 mm in length. The size of the square profile of the test section is 200 x 200 mm, the individual side walls comprising the glass panes 81 are interconnected by bars 80. The bars 80 can be replaced, for example, by aluminium profiles provided with receiving grooves for glass panes 8L

Preferably, the test section 8 is provided with at least one inlet orifice 82 for receiving a nozzle which opens into the interior space of the test section 8. According to the embodiment shown in the drawings, the inlet orifice 82 is arranged in the central area of the top wall of the test section 8. Nonetheless, different arrangements of the inlet orifice 82, or inlet orifices 82, are also conceivable. In accordance with particular requirements concerning the measurement process, the inlet orifice 82, which is intended for receiving a nozzle, may be omitted.

According to an advantageous embodiment, which is not shown in the drawing, the test secti on 8 has an octagonal tubular profile, the side wails of the latter comprising glass panes 81 interconnected by the bars 82. As a result, a further improvement of the air stream characteristics is achievable, which particularly regards an elimination of undesirable corner vortices.

The overall arrangement further comprises a measurement assembly assigned to the test section 8. According to the embodiment shown in Fig. 4, such assembly comprises a high-speed camera 100 and a laser source 110. The high-speed camera 100, which enables preferably at least 5 thousand, more preferably at least 15 thousand, most preferably at least 20 thousand frames per second to be acquired, faces the side wall of the test section 8, i.e. one of the glass panes 81 of the side wall of the test section 8, the optical axis of the objective lens of the high-speed camera 100 being perpendicular to said glass pane 81 of the side wall. The laser source 110 faces the bottom glass pane 81 of the test section. The path of the laser beam produced by the source also extends perpendicularly to said bottom glass pane _.81.

The laser source is preferably adapted for generating laser light beams impinging on a planar surface (as shown in Fig. 4), Such planar surface is also usable in connection with measurement procedures based on the use of the PIV (Particle Image Velocimetry) method. Other possible measurement methods, which are based on the use of a source of continuous laser beams, include the point methods, such as those performed by means of LDA or PDA systems, i.e. by systems for performing measurements based on Laser Doppler Anemometry and Phase Doppler Anemometry, respectively, or visualization procedures, such as those performed by means of high-speed cameras. Advantageously, the measurement assembly further comprises an electronic control unit connected both to the high-speed camera 100 and to the laser source U0 or, as the case may be, to the positioning mechanism.

In addition, a heating / cooling system can be incorporated into the wind tunnel according to the present invention, said system being preferably arranged in the outlet area of the blower T Such heating / cooling system is preferably controllable in a manner enabling the temperature of the medium fed into the test section 8 to be set and maintained with an accuracy of ± 1 °C. Advantageously, said heating / cooling system is also electronically connected / connectable to the electronic control unit of the measurement assembly.

The test section 8 is arranged coaxially to at least the laminarization pipeline 7, preferably to the entire feed assembly, particularly to the member that is connected to the outlet end of the test section 8.

The outlet end of the test secti on 8 is fluidly connected to the inlet end of the outlet, diffuser 10, the outlet end of the latter being, in turn, fluidly connected to the inlet end of the outlet compensator 9. Similarly to the inlet compensator 3, the o utlet compensator can be constituted by any type of an air impermeable flexible duct being at least partially variable in length. The outlet end of the outlet compensator 9 is fluidly connected to a distribution pipeline P_. having two branch pipes 11 A, the outlet ends of said branch

pipes 11 A, 11 B opening into separators 13 A, 13B.

According to an alternative embodiment, which is not shown in the drawings, two outlet compensators 9 can be used instead of a single one, each interconnecting one of the branch pipes 11 A, 11B of the distribution pipeline jj_, with the respective one of the separators 13 A, 13B.

The separators 13_» 13 A, 13B can be constituted, for example, by devices for separating liquid droplets (larger than 1 pin) from gas streams, so-called demisters, such as those made by United Enviro System, Maharasthra, India.

The number of the separators 13, 13 A, 13B is selected in dependence on the output power of the blower 1 since the separator / separators must be able to adequately purify the supplied air volume by eliminating liquid and/or other particles which have been previously introduced into the ah stream within the test section 8 (or in another portion of the wind tunnel). As clearly shown in Fig. 1 , the wind tunnel according to the present invention further comprises a carrier J4 that provides a support surface for placing the corresponding part of the feed assembly, namely the settling chamber 5. The earner 14 is provided with a positioning mechanism for displacing the support surface of the carrier 14 in at least two directions / axes, preferably in two mutually perpendicular horizontal ayes x, y and one vertical axis z.

According to an advantageous embodiment, the positioning mechanism can comprise a lifting device 16 for displacing the support surface in the vertical direction, on the one hand, and a guide rail system 1_.5 with travellers 25 for displacing the support surface in a horizontal plane, on the other hand.

According to a preferred embodiment, the lifting device Jj5 is formed by a screw- type jack, having a fine-pitch transmission ratio of not more than 1 mm per revolution, more advantageously 0,25 mm per revolution, and the range of motion of at least 150 mm, more advantageously 300 mm. An example of a suitable lifting device 16 can be represented by the type MSZ-5-A-SL-Tr-l 804-1 -H0200-SRO-VS-BF made by Zimin GmbH, Austria.

The guide rail system 15 preferably comprises guide rails arranged in a horizontal plane and carrying guided travellers 25, being controlled by a ball-screw spindle to achieve fine positioning movements in two mutually perpendicular horizontal axes. In other words, one pair of guide rails with the travellers 25 operated by means of a ball- screw spindle enables movement in the direction of the x-axis, whereas another pair of guide rails with travellers 25 operated by means of another ball-screw spindle and arranged over or below the former pair of guide rails enables the movement in the direction of the y-axis. In the embodiment shown in the drawings, the top surface of the upper pair of travellers 25 constitutes the support area for receiving the settling chamber 5. The aforesaid rail system 15 can be lifted by means of the lifting device 16 described above and arranged underneath the guide rail system 15.

Nevertheless, other embodiments of the positioning mechanism are also conceivable. For example, the lifting device 16 can be arranged directly on the guide rail system 15 with the travellers 25, thereby enabling the setling chamber 5 to be placed on the carrying surface of the lifting device 16, said surface being movable on the guide rail in the directions x, y of the horizontal plane. According to a particularly preferred embodiment, which is shown in Fig. 6, the wind tunnel further comprises a reinforcing frame consisting of support amis G 7 and carrying arms 18, said arms being interconnected by means of a coupling beam 19, in the exemplary embodiment shown in the drawings, the support amis 17 are attached to the settling chamber 5 and the carrying arms 18 are attached to the laminarization pipeline 7 as well as to the inlet end of the outlet diffuser 10. Both the support arms 17 and the carrying arms 18 have the flipped U -shape. All the arms, however, can be shaped in any manner enabling the individual parts of the respective wind tunnel to be comiected to the coupling beam 19. in general, the support arms can be advantageously connected to that part of the wind tunnel, which is placed on the support plane of the carrier 14, whereas the carrying amis can be attached to the test section 8 or to any other part of the wind tunnel adjoining the test section 8.

However, as a matter of course, the structural rigidity of the assembly, particularly the desired fixed interconnection of that part of the wind tunnel, which is arranged on the carrier 14, and the test section 8, can be achieved by any other suitable reinforcement means,

As mentioned above, the positioning mechanism is electronically connected to the measurement assembly, thereby enabling the positioning data of the test section 8 to be advantageously transferred into the evaluation unit of the measurement assembly. Additionally or alternatively, the positioning data of the test section 8 can be supplied to said evaluation unit on the basis of the motion of reference points being monitored on the test section 8.

The wind tunnel according to the present invention works, for example, in the following manner: Both the wind tunnel itself and the measurement assembly are prepared, and the measurement assembly is precisely positioned and focused with respect to the test section 8 in a maimer enabling the processes taking place within the test section 8 to be scanned. The blower 1 is switched on, and the desired velocity of the air stream is adjusted by the frequency converter 2. A nozzle is joined to the test section 8. and by means of the nozzle the respective liquid is fed into the inlet orifice 82, The measurement assembly is used for scanning a particular area within the test section 8. Using the positioning mechanism the test section 8 is displaced along with the assigned parts of the wind tunnel without causing the coaxial alignment to get lost and, thus, without causing the turbulence of the air / gas stream fed into the test section 8. Due to the continual displacement of the test section 8. the test section 8 moves with respect to the measurement assembly such that, individual areas of the interior space of the test section 8 may be consecutively scanned. Thereby, data describing the processes taking place within a substantial portion of the interior space of the test section 8 can be acquired without having to relocate or readjust the respective measurement system in a considerably time-consuming manner and, in particular, without taking any risk of damage to the expensive parts of the measurement system. The use of the compensators 3 and 9 eliminate the necessity of readjusting the entire wind tunnel and, in particular, the necessity of relocating both the blower JL which has a considerable weight and is prone to vibrations, and the separators 13, 13 A, 13B.

Figs. 7A to 7D show' several exemplary images acquired inside the test chamber 8 during the injection of a liquid through a nozzle at different velocities.

The wind tunnel according to the present invention enables two-phase dispersed air streams to be observed / measured within the entire range thereof, a typical air stream being represented by a spray pattern produced by various spray nozzles (such as pressure- swirl ones). The test section, which provides easy visual access in an all-round manner, enables various measurement procedures by means of LD A/PDA and PIV systems and visualisation procedures by means of high-speed cameras to be performed.

The velocity of the air stream preferably ranges between 0 and 40 m/s, an exact value of said velocity being adjustable by means of the frequency converter.

Owing to the structural arrangement described above, a uniform stream- velocity profile having a very low turbulence intensity of < 0.5 % is achievable.

Pressure distribution on the surfaces of models can be measured by pressure sensors, thermovision cameras, or the like. Such measurements can be accompanied by visualisation of the air / gas streams by means of the high-speed camera using suitable particles (droplets, helium bubbles, smoke, or the like) introduced into the particular stream.

The positioning and data acquisition processes can be precisely 3D controlled by means of a computer. The wind tunnel, according to the present invention, enables the influence of lateral and longitudinal streams on real process liquids (such as fuels) sprayed by nozzles to be explored. Furthermore, experiments relating to the streaming in two-phase (liquid- gas) systems can be carried out, dynamic and ballistic properties of droplets and particles can be examined, stream trajectories can be explored, aerodynamic characteristics of 2D profiles and 3D models can be measured, interactions of bodies circumfluenced by air streams with the later can be observed, calibration of probes and measurement of the characteristic values of the same can be performed, etc. it is possible to introduce suitable particles (in a local manner and synchronously to the operation of the respective PDA system) to visualise the stream and to measure the velocity of the same, the particles being introduced e.g. from a condensing generator or aerosol generator.

A substantial advantage of the wind tunnel according to the present invention consists in the structural robustness thereof. The structural rigidity of the wind tunnel according to the present invention makes it possible to convert even the slightest motion induced by the positioning mechanism into the motion of the entire movable portion of the wind tunnel. Owing to the aforesaid arrangement, the measurement / optical instruments can remain stationary during the entire measurement process and the positional adjustment of the test section 8 along with the adjacent parts of the wind tunnel enables the region focused by the measurement assembly to be moved into all of the desired areas of the test section 8. In addition, the stationary arrangement of the blower l and the droplet separator 13 reduces the required load-bearing capacity of the support / positioning system.

The wind tunnel according to the present invention constitutes a compact, segmented open-loop solution that is, owing to its low weight and short accommodating length of the tunnel, suitable for being used in small test rooms / laboratories.

Although multiple exemplary, particularly advantageous embodiments are described above, it is obvious that those skilled in the art would easily appreciate further possible alternatives to those embodiments. Hence, the scope of the protection is not limited to the above exemplary embodiments and is rather defined by the appended patent claims.

Claims

1. A wind tunnel, comprising;

~ an inlet diffuser (4),

- a settling chamber (5) having its inlet end fluidly connected to the outlet end of the inlet diffuser (4),

- a confuser (6) having its inlet end fluidly connected to the outlet end of the settling chamber (5),

- a laminarization pipeline (7) having its inlet end fluidly connected to the outlet end of the confuser (6),

- a test section (8) having its inlet end fluidly connected to the outlet end of the laminarization pipeline (7) and having at least a part of its wall made of a transparent material, the inlet diffuser (4), the settling chamber (5), the confuser (6), the laminarization pipeline (7) and the test section (8) being arranged one after the other along a common longitudinal axis, characterized in that it further comprises

- an inlet compensator (3) having its inlet end adapted to be fluidly connected to an outlet end of a blower (1) a having its outlet end fluidly connected to the inlet end of the diffuser (4), and

~ an outlet compensator (9) having its inlet end fluidly connected to the outlet end of the test section, wherein the compensators (3, 9) are flexible pipelines having variable lengths.

2. The wind tunnel, according to claim 1, characterized in that the compensators (3, 9) have the form of bellows with folded walls,

3. The wind tunnel according to claim 1 or 2, characterized in that it further comprises a carrier (14) with a positioning mechanism enabling the inlet diffuser (4), the settling chamber (5), the confuser (6), the laminarization pipeline (7) and the test section (8) to be displaced together and simultaneously.

4. The wind tunnel according to claim 3, characterised in that the positioning mechanism comprises a rail system (15) with travellers (25), the upper surfaces of the positioning mechanism constituting support areas for carrying the settling chamber (5).

5. The wind tunnel according to claim 4, characterized in that the positioning mechanism further comprises a lifting device (16) for displacing the rail system (15) with the travellers (25) in the vertical direction.

6. The wind tunnel according to claim 5, characterized in that the lifting device (16) is a screw-type lifting device having its transmission ratio of not more than 1 mm per revolution and/or having the range of motion at least 150 mm.

7. The wind tunnel according to any of the preceding claims, characterized in that it further comprises support arms (17) attached to the settling chamber (5), carrying aims (18) attached to the test section (8) and/or to the lammarization pipeline (7) and a coupling beam (19) attached both to the support arms (17) and to the carrying arms (18).

8. The wind tunnel according to any of the preceding claims, characterized in that it further comprises an outlet diffuser (10), wherein the outlet compensator (9) interconnects the test section (8) and said outlet diffuser (10), or the inlet end of the outlet compensator (9) is connected to the outlet end of the outlet di ffuser (10).

9. The wind tunnel according to claim 8, characterized in that it further comprises at least one separator (13, 13 A, 13B) for elimination droplets from the gas stream, said separator having its inlet end fluidly connected to the outlet end of the outlet diffuser (10).

10. The wind tunnel according to any of the preceding claims, characterized in that it further comprises a blower (1) having its outlet end connected to the inlet end of the inlet compensator (3).

11. The wind tunnel according to claim 10, characterized hi that it further comprises a frequency converter (2), which is electrically connected to the blower (1), for modifying the output power of the blower (1) in a continuous manner.

12. The wind tunnel according to claim 10 or 11, characterized in that the inlet diffuser (4), the settling chamber (5), the confiiser (6), the Iaminarization pipeline (7) and the test section (8) are arranged in mutually fixed positions forming an assembly, said assembly being moveable with respect to the blower (1) while maintaining the fluid connection between the outlet orifice of the blower (1) and the test section (8).

13. The wind tunnel according to any of the preceding claims, characterized in that it further comprises the following components arranged within the settling chamber (5):

- a straightener (SO), which is arranged in a plane extending perpendicularly to the longitudinal axis of the settling chamber (5) and comprises an array of thin channels extending in parallel to the longitudinal axis of the settling chamber, and/or

- an array of sieves or meshes (51) arranged in parallel to each other and perpendicularly to the longitudinal axis of the settling chamber (5), the fineness grade of the individual sieves or meshes (51 ) increasing in the direction from the inlet end towards the outlet one of the settl ing chamber (5).

14. The wind tunnel according to any of the preceding claims, characterized in that the Iaminarization pipeline (7), as well as the test section (8), arranged downstream of the former have the form of a duet with an octagonal or rectangular cross-section.

15. The wind tunnel according to claim 14, characterized in that at least two walls of the test section (8) are formed by transparent panes, preferably by panes (81) made of glass or polymethyi methacrylate.