Device generating low-altitude atmospheric turbulence and associated wind tunnel

Abstract

Turbulence-generating device for a wind tunnel, the device comprising at least a first bar (11) and a second bar (12) both intended to be arranged in a convergent part of a wind tunnel, the two bars forming two independent elements intended to be arranged spaced apart from each other in the convergent part, wherein in use the two bars extend through the convergent part such that they are inclined relative to one another. The invention further relates to a corresponding wind tunnel.

Description

[0001]Low Altitude Atmospheric Turbulence Generator Device and Associated Wind Tunnel The invention relates to a low altitude atmospheric turbulence generator device in a wind tunnel. The invention also relates to a wind tunnel equipped with such a device. BACKGROUND OF THE INVENTION To accurately study the effects of wind on a structure, particularly atmospheric wind at low altitudes, it is necessary to be able to reproduce such effects in wind tunnels. Currently, the techniques developed from the work and methods of Counihan are only applicable to very specific wind tunnels, such as long-flow wind tunnels. However, such installations are few in number because they are expensive to build and operate. Generally, more standard wind tunnels, known as short-flow wind tunnels, are preferred, in which one or more grids are arranged to generate turbulence in the airflow.However, such grids do not sufficiently modify the airflow to accurately reproduce the effects of low-altitude wind. OBJECT OF THE INVENTION The invention aims, in particular, to provide a solution for more accurately simulating the effects of low-altitude wind in a wind tunnel. SUMMARY OF THE INVENTION To this end, the invention provides a turbulence-generating device for a wind tunnel, the device comprising at least two bars intended to be arranged in a convergent section of a wind tunnel, the two bars forming two independent elements intended to be spaced apart from each other in the convergent section, the two bars extending in operation through the convergent section at an angle to each other. The use of these two bars makes it possible to introduce turbulence (i.e.disturbances) in an airflow circulating in the convergent section: the disturbed airflow thus faithfully reproduces the behavior of atmospheric wind at low altitude. By "low-altitude atmospheric wind," we mean a wind present at an altitude of less than 200 meters above the area under consideration (therefore not necessarily above sea level). The inventor was particularly able to observe that the arrangement of the bars transverse to the direction of the flow made it possible to create a detachment of alternating vortices formed behind the bars, vortices which are then diffused and accelerated by the downstream section of the convergent section before reaching a test section. Advantageously, the invention is a passive device. It makes it possible to generate turbulence without needing to move relative to the wind tunnel and in particular to the convergent section. Moreover, the invention proves to be simple in structure.The invention also operates without power. The invention is also inexpensive to manufacture. The invention can also be easily implemented in existing wind tunnels. Hereafter, the terms "upstream" and "downstream" shall be understood as referring to the direction of airflow in the wind tunnel, from its inlet chamber to at least its divergent point. Hereafter, the terms "upper," "top," "lower," "bottom," etc., shall be understood as referring to the operating position of the wind tunnel and the turbulence-generating device when the wind tunnel rests on a base or on the ground and the device is arranged in the wind tunnel and ready for testing. Optionally, at least one of the bars has a polygonal cross-section. Optionally, the first and second bars have the same cross-section for at least one section of the first bar and at least one section of the second bar.The invention also relates to a wind tunnel comprising at least successively an air inlet chamber, a convergent section, a test section, and a divergent section, the wind tunnel comprising at least one device according to one of the preceding claims arranged in the convergent section. Optionally, the first bar is arranged in the second half of the convergent section. Optionally, the second bar is arranged in the third third of the convergent section. Optionally, the first bar is arranged upstream of the second bar, the first bar being arranged so that one of its edges forms its end closest to the inlet of the convergent section. Optionally, the second bar is arranged so that one of its flat faces forms its end closest to the inlet of the convergent section. Optionally, the device comprises an additional bar arranged between the first and second bars.Optionally, the additional bar extends vertically in the convergent section. Other features and advantages of the invention will become apparent from the following description of particular, non-limiting embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Reference will be made to the accompanying drawings, among which: [Fig. 1] Figure 1 is a schematic cross-sectional view of a portion of a wind tunnel according to a first embodiment of the invention; [Fig. 2] Figure 2 is a cross-sectional view of a convergent section of the wind tunnel shown in Figure 1; [Fig. 3] Figure 3 is a schematic cross-sectional view of a portion of a wind tunnel according to a second embodiment of the invention; [Fig. 4] Figure 4 is a cross-sectional view of a convergent section of the wind tunnel shown in Figure 3.DETAILED DESCRIPTION OF THE INVENTION With reference to Figures 1 to 2, a wind tunnel 1 according to a first embodiment will now be described. The wind tunnel 1 comprises at least one section extending longitudinally along a first longitudinal axis X. Said axis X is horizontal when the wind tunnel 1 rests on the horizontal ground or a horizontal base. A cross-section of said section can thus be defined by a second axis Y which is orthogonal to the first axis X, and a third axis Z which is orthogonal to the first axis X and to the second axis Y. When the first axis X is horizontal, the second axis Y is vertical and the third axis Z is horizontal.In this section, the following are arranged successively (along the first X-axis): an inlet chamber 2 (sometimes also called a settling chamber), a convergent section 3 following the inlet chamber 2, a test section 4 following the convergent section 3, a divergent section 5 following the section 4, and an outlet chamber following the divergent section 5. The wind tunnel 1 can be an open-circuit wind tunnel (the inlet chamber 2 and the outlet chamber are thus open to the outside) or a closed-circuit wind tunnel (the wind tunnel 1 then includes an additional section connecting the outlet chamber to the inlet chamber 2). Preferably, the wind tunnel 1 is a closed-section wind tunnel. The section 4 is therefore not open to the outside. Preferably, the wind tunnel 1 is a short-section wind tunnel 4 (as opposed to a long-section wind tunnel).A "long" vein is a vein whose length (along the first X-axis) is at least twenty times greater than its height (considered along the second Y-axis). A "short" vein is a vein whose length is X times the height of its cross-section, where X is less than 10 and preferably less than 5 and preferably less than 4 and preferably between 3 and 4 times. In this application, the term "diameter" should be understood in its geometric sense, namely, the upper bound of the set of distances between any two points in a subset A of a metric space. The cross-section of vein 4, whose plane of section has its normal to the first X-axis, is therefore not necessarily circular. Optionally, vein 4 may have a cross-section with rectangular or square internal and external contours.The diameter of said cross-section is therefore the diagonal connecting opposite corners of the outer contour of the duct 4. Preferably, the duct 4 has the same cross-section along its entire length. With such a wind tunnel 1, the airflow 6 originates from the inlet chamber 2 and arrives at the inlet of the convergent nozzle 3. The airflow 6 is usually hypoturbulent (with an intensity of less than 1-2%). Said airflow 6 thus propagates in the inlet chamber 2 and at the inlet of the convergent nozzle 3 along a general propagation direction G. The general direction G is here parallel (and preferably coincident) with the first axis X. According to the invention, a turbulence-generating device 10 is arranged in the wind tunnel 1. The device 10 comprises at least two bars 11, 12. In the first embodiment, the device 10 comprises strictly two bars 11, 12.Preferably, the device 10 consists solely of these two bars 11, 12 (with optional attachment means for bars 11, 12, up to a point of convergence 3). We will now describe the first bar 11. The first bar 11 is solid. The first bar 11 extends longitudinally along a longitudinal direction B1. The first bar 11 has a polygonal cross-section (along a section plane whose normal is the longitudinal direction B1). Preferably, this cross-section is in the shape of a quadrilateral. Preferably, this cross-section is in the shape of a square. The first bar 11 is identical along its entire length (considered along the longitudinal direction B1). The first bar 11 thus has the same cross-section along its entire length.At least the height and / or width (one side) of the cross-section of the first bar 11 is equal to between 5 and 20% of the height (considered along the second Y-axis) of the duct 4, and is, for example, between 8 and 18% and is, for example, 10%. The first bar 11 is, for example, made of or based on wood, plastic, etc. We will now describe the positioning of the first bar 11 in the wind tunnel 1. The first bar 11 is arranged in the convergent section 3. Preferably, the first bar 11 is arranged in the second half of the convergent section 3, that is, in the lower half of the convergent section 3.Preferably, for a convergent length L (length considered along the first X-axis), the center of a first end 3a of the first bar 11 (i.e., the lowest end of the first bar 11 when the first bar 3 is in place in the convergent) is positioned at a distance d1 from the outlet of the convergent 3 (corresponding to the inlet of the vein 4) less than 0.5L and preferably less than 0.4L. Preferably, the distance d1 is also greater than 0.2L. Optionally, the first bar 11 is fixed to the convergent 3. This fixing may be permanent or temporary. This fixing may be achieved by any known means of attachment (removable or not): adhesive, screw and nut, welding, etc. At least one, and optionally both ends of the first bar 11 are here fixed to the convergent 3. The first bar 11 is arranged so as to extend through the convergent 3.The first bar 11 is of such a length that both its ends touch at least one wall of the convergent section 3. The first bar 11 is of such a length that the first end 11a of the first bar 11 touches at least one wall of the convergent section 3, and that a second end 11b of the first bar 11 touches at least one wall of the convergent section 3 opposite the first wall. Hereafter, "touch" means that the contact between the first bar 11 and the wall of the convergent section 3 is direct (optionally apart from the attachment means). In this case, the convergent section 3 has four walls that are opposite each other in pairs. The first end 11a of the first bar 11 touches here the first wall 21 and the second wall 22 and the second end 11b of the first bar touches here the third wall 23 (opposite to the first wall 21) and the fourth wall 24 (opposite to the second wall 22).More specifically, here, the first bar 11 extends such that its first end 11a is positioned at the junction between the first wall 21 and the second wall 22, and its second end is positioned at the junction between the third wall 23 and the fourth wall 24. The first bar 11 thus extends through the entire convergent section 3. In particular, the first bar 11 traverses the entire cross-section of the convergent section 3. It is therefore understood that the first bar 11 is arranged such that the longitudinal direction B1 is inclined (i.e., neither parallel nor orthogonal) with respect to the second Y-axis and the third Z-axis. Preferably, the first bar 11 is also arranged such that the longitudinal direction B1 is inclined with respect to the first X-axis (i.e., neither parallel nor orthogonal to the first X-axis). The first bar 11 thus does not extend straight, vertically, or horizontally in the convergent 3.For example, the second end 11b of the first bar 11 (i.e., the highest end) is closer to the outlet of the convergent 3 than the first end 11a of the first bar 1 (i.e., the lowest end). Preferably, the first bar 11 is oriented so that the airflow 6 arrives at an edge of the first bar 11. The first bar 11 is therefore oriented so that a longitudinal edge of the first bar 11 (which here has four) is the part of the first bar 11 arranged closest to the inlet of the convergent 3. The first bar 11 thus forms a point (extending through the entire convergent 3) for the arrival of the airflow 6 into the convergent 3. We will now describe the second bar 12. The second bar 12 is solid. The second bar 12 extends longitudinally along a longitudinal direction B2.The second bar 12 has a polygonal cross-section (along a section plane with its normal along the longitudinal direction B2). Preferably, this cross-section is quadrilateral. Preferably, this cross-section is square. The second bar 12 is identical along its entire length (considered along the longitudinal direction B2). The second bar 12 thus has the same cross-section along its entire length. The second bar 12 has the same cross-section (shape and dimensions) as the first bar 11. However, the second bar 12 is shorter than the first bar 11. At least the height and / or width (i.e., one side) of the cross-section of the second bar 12 is between 5 and 20% of the height (considered along the second Y-axis) of the vein 4 and is, for example, between 8 and 18% and is, for example, 10%.The second bar 12 is, for example, made of or based on wood, plastic, etc. The second bar 12 is, for example, made of the same material as the first bar 11. We will now describe the positioning of the second bar 12 in the wind tunnel 1. The second bar 12 is arranged downstream of the first bar 11. The second bar 12 is arranged in the convergent section 3. Preferably, the second bar 12 is arranged in the third third of the convergent section 3 (i.e., the most downstream third of the convergent section 3). Preferably, the center of a first end 12a of the second bar 12 (i.e., the lowest end of the second bar 12 when the second bar 12 is in place in the convergent section 3) is arranged at a distance d2 from the outlet of the convergent section 3 (corresponding to the inlet of the stream 4) of less than 0.3L. Preferably, the distance d2 is also greater than 0.1L and for example greater than 0.16L.Optionally, the second bar 12 is fixed to the converging bar 3. This fixing can be permanent or temporary. This fixing can be achieved by any known means of attachment (removable or not): adhesive, screw and nut, welding, etc. At least one, and optionally both ends of the second bar 12 are fixed to the convergent 3. The attachment means of the second bar 12 are optionally independent of those of the first bar 11. The second bar 12 is arranged to extend through the convergent 3. The second bar 12 is of a length such that both its ends each touch at least one wall of the convergent 3. The second bar 12 is of a length such that the first end 12a of the second bar 12 touches at least one wall of the convergent 3 and the second end 12b of the second bar 12a touches at least one wall of the convergent 3 opposite the first wall.Hereafter, "touch" means that the contact between the second bar 12 and the wall of the converging section 3 is direct (optionally, apart from the attachment means). In this case, the second end 12b of the second bar 12 touches the third wall 23 and the second wall 22, and the first end 12a of the second bar 12 touches the first wall 21 and the fourth wall 24. More precisely, the second bar 12 extends so that its first end 12a is positioned at the junction between the first wall 21 and the fourth wall 24, and so that its second end 12b is positioned at the junction between the third wall 23 and the second wall 22. The second bar 12 thus extends across the entire converging section 3. In particular, the second bar 12 traverses the entire cross-section of the converging section 3.It is therefore understood that the second bar 12 is arranged so that the longitudinal direction B2 is inclined with respect to the second Y-axis and the third Z-axis. The second bar 12 is also arranged so that the longitudinal direction B2 is inclined with respect to the first X-axis. The second bar 12 thus extends neither straight, nor vertically, nor horizontally into the convergent 3. For example, the first end 12a of the second bar 12 (i.e., the lower end) is closer to the outlet of the convergent 3 than the second end 12b of the second bar 12 (i.e., the higher end). Preferably, the second bar 12 is oriented here so that the airflow 6 arrives on a longitudinal face of the second bar 12 (in this case, four faces). The second bar 12 is therefore oriented so that a lateral face of the second bar 12 is the part of the second bar 12 arranged closest to the entrance of the convergent 3.The second bar 12 thus forms a plane (extending through the entire convergent section 3) for the airflow 6 from the first bar. Arranged in this way, the two bars 11 and 12 form two independent elements. In this arrangement, the two bars 11 and 12 are spaced apart from each other in the convergent section 3, particularly along the first axis X. The two bars 11 and 12 therefore do not touch. It is also understood that the two bars 11 and 12 extend at an angle to each other. In particular, the longitudinal directions B1 and B2 are inclined relative to each other. More precisely here, the two bars 11, 12 jointly draw a cross in the convergent 3. More precisely here, in a Euclidean frame linked to the first bar 11, with the longitudinal direction B1 forming one of the axes of this frame, the longitudinal direction B2 is inclined with respect to the three axes of this frame.With reference to Figures 3 and 4, a second embodiment will now be described. This second embodiment is identical to the first embodiment except that the device 10 includes an additional bar 13. The device 10 thus comprises at least three bars. In the second embodiment, the device consists strictly of three bars. Preferably, the device 10 is composed solely of these three bars 11, 12, 13 (apart from optional bar attachment means at the convergent point 3). The third bar 13 will now be described. The third bar 13 is solid. The third bar 13 extends longitudinally along a longitudinal direction B3. The third bar 13 has a polygonal cross-section (along a section plane whose normal is the longitudinal direction B3). Preferably, this cross-section is in the shape of a quadrilateral.Preferably, the cross-section is square. The third bar 13 is identical along its entire length (considered along the longitudinal direction B3). The third bar 13 thus has the same cross-section along its entire length. The third bar 13 therefore has the same cross-section (shape and dimensions) as the first bar 11 and / or the second bar 12. However, the third bar 13 is shorter than the first bar 11 and / or the second bar 12. For example, the third bar 13 has a length between 10 and 30% of the vein height (considered along the second Y-axis) and, for example, between 15 and 20% of the vein height.Whether in the first or second embodiment, the first bar 11 and / or the second bar preferably have a length such that they are supported against opposite areas of the convergent section. At least the height and / or width (i.e., one side) of the cross-section of the second bar 12 is between 5 and 20% of the height (considered along the second Y-axis) of the vein 4, and is, for example, between 8 and 18% and is, for example, 10%. The third bar 13 is, for example, made of or based on wood, plastic, etc. The third bar 13 is, for example, made of the same material as the first bar 11 and / or the second bar 12. We will now describe the positioning of the third bar 13 in the wind tunnel 1. The third bar 13 is arranged here downstream of the first bar 11. The third bar 13 is arranged here upstream of the second bar 12.The third bar 13 is thus arranged between the first bar 11 and the second bar 12. For example, the third bar is arranged equidistant from the first bar 11 and the second bar 12. The third bar 13 is arranged in the converging joint 3. Optionally, the third bar 13 is fixed to the converging joint 3. This fixing may be permanent or temporary. This fixing may be achieved by any known means of attachment (removable or not): adhesive, screw and nut, welding, etc. This fixing is, for example, independent of that of the first bar 11 and / or the second bar 12. A single end of the third bar 13 is here fixed to the convergent 3. The third bar 13 is arranged so as to extend through the convergent 3. The third bar 13 is here of a length such that only one of its ends touches at least one wall of the convergent 3.The other end of the third bar 13 thus extends freely inside the convergent 3. Hereafter, "touch" means that the contact between the third bar 13 and the wall considered of the convergent 3 is direct (optionally apart from the means of attachment). The first end 13a of the third bar 13 (i.e., the lowest end) is the one fixed here to the first wall 21. More precisely, here, the third bar 13 extends so that its first end 13a is positioned opposite the first wall 21, i.e., the wall of the convergent 3 closest to the ground or the base on which the wind tunnel 1 rests. It is therefore understood that the third bar 13 does not extend through the entire convergent 3. In particular, the third bar 13 does not cross the entire cross-section of the convergent 3. The third bar 13 is arranged so that the longitudinal direction B3 is parallel to the second Y-axis and therefore orthogonal to the first X-axis.The third bar 13 thus extends straight and vertically into the convergent 3. Preferably, the third bar 13 is oriented here so that the airflow 6 arrives on an edge of the third bar 13. The third bar 13 is therefore oriented so that a longitudinal edge of the third bar 13 (which here has four) is the part of the third bar 13 arranged closest to the inlet of the convergent 3. The third bar 13 thus forms a point (extending only in the lower part of the convergent 3) for the arrival of the airflow from the first bar 11. Thus arranged, the three bars 11, 12, 13 form three independent elements. Arranged in this way, the three bars 11, 12, 13 are spaced apart, particularly along the first axis X. Therefore, the three bars 11, 12, 13 do not touch. It is also clear that the three bars 11, 12, 13 extend at an angle to one another.In particular, the longitudinal directions B1, B2, and B3 are inclined relative to each other. Apart from what has been stated above, everything said for the first embodiment (in particular with regard to the first bar 11 and the second bar 12) is also applicable to the second embodiment. Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims. Although here each bar has an identical cross-section along its entire length, at least one of the bars may have a variable cross-section along its length. For example, the cross-section of said bar may thus increase between one end of the bar and the other end of the bar. For example, said cross-section may increase progressively between the two ends of said bar.Although the cross-section of each bar is polygonal, at least one bar may have a rounded cross-section. For example, at least one bar may be shaped like a cone or a truncated cone. The first end of the first bar may be farther from the outlet of the convergent element than the second end of the first bar. In this case, it is preferable to have the second end of the second bar further from the outlet of the convergent element than the first end of the second bar. At least one of the first or second bars may be arranged so that its first end is as far from the outlet of the convergent element as its second end. This bar will thus extend orthogonally to the first X-axis (which defines) the length of the convergent element. In this case, it is preferable to have at least one bar with a cross-section that varies along its length.Although here the different bars are fixed to the convergent section, at least one of the first or second bars can simply be arranged within the convergent section until its two ends rest against one or more walls of the convergent section. The bar in question will then simply be wedged within the convergent section between one or more walls of the convergent section. At least one end of the bar can be fixed temporarily or permanently to the convergent section. At least one end of the bar can be fixed to the convergent section by adhesive, screws, etc. At least one of the bars can be made of wood, plastic, metal, etc. At least one of the bars can be made of a single material or multiple materials. Although here the vein has a square or rectangular cross-section, the vein can have a cross-section of a different shape, for example, oval or circular.The cross-section of the vein may therefore be of a different shape from the cross-section of at least one of the bars.

Claims

CLAIMS 1. A turbulence-generating device for a wind tunnel, the device comprising at least a first bar (11) and a second bar (12), both intended to be arranged in a convergent section of a wind tunnel, the two bars forming two independent elements intended to be arranged spaced apart from each other in the convergent section, the two bars extending in operation through the convergent section at an angle to each other.

2. A device according to claim 1, wherein at least one of the bars has a polygonal cross-section.

3. A device according to any one of the preceding claims, wherein the first bar (11) and the second bar (12) have, for at least one section of the first bar and at least one section of the second bar, the same cross-section. 4.A wind tunnel comprising at least successively an air inlet chamber (2), a convergent section (3), a test section (4), and a divergent section (5), the wind tunnel comprising at least one device according to any one of the preceding claims arranged in the convergent section.

5. A wind tunnel according to claim 4, wherein the first bar (11) is arranged in the second half of the convergent section (3).

6. A wind tunnel according to any one of claims 4 to 5, wherein the second bar (12) is arranged in the third third of the convergent section (3).

7. A wind tunnel according to any one of claims 4 to 6, wherein the first bar (11) is arranged upstream of the...

8. A second bar (12), the first bar (11) being arranged such that one of its edges forms its end closest to the inlet of the convergent (3).

9. A wind tunnel according to claim 7, wherein the second bar (12) is arranged such that one of its flat faces forms its end closest to the inlet of the convergent (3).

10. A wind tunnel according to any one of claims 4 to 8, wherein the device comprises an additional bar (13) arranged between the first bar (11) and the second bar (12).

11. A wind tunnel according to claim 9, wherein the additional bar (13) extends vertically into the convergent (3).

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