Exhaust duct of a turbine test bench with double tube

Abstract

The invention relates to an exhaust duct of a gas turbine test bench comprising an outer tube (10) extending along a longitudinal axis (X1) with an inlet (11) adapted to recover the exhaust gases displaced by a gas turbine (90). This exhaust duct comprises at least one inner tube (20) extending along a longitudinal axis (X2) with an inlet (21) and which is located inside the outer tube (10) such that in operation an internal flow (F20) of gas circulates in the at least one inner tube (20) and an external flow (F10) of gas, separated from the internal flow (F20), circulates in the outer tube (10) outside the at least one inner tube (20). Figure 2

Description

Title of the invention: Exhaust duct of a turbine test bench with double tube

[0001] The present invention relates to a gas turbine test bench. More specifically, the invention relates, in such a test bench, to an exhaust duct of a gas turbine test bench comprising an outer tube extending along a longitudinal axis with an inlet capable of recovering the gases displaced by a gas turbine and an outlet. In particular, the invention relates to a turbomachine test bench.

[0002] Such a test bench is described in document EP 3021102. With reference to [Fig.7] which represents the prior art, the test bench comprises, from upstream to downstream (in the normal direction of air circulation) an intake chimney 181, a test room 182, an exhaust duct of a turbine test bench and an exhaust chimney 183. The air enters the test room 182 through the vertical intake chimney 181 which is open to the outside at its entrance. The test room 182 comprises a turbomachine 190 which is mounted on a thrust balance 191. Downstream of the turbomachine 190 being tested, there is an exhaust duct of a turbine test bench which comprises a tube 110 which is intended to receive at its inlet 111 (upstream end) the exhaust gases which escape from the turbomachine 190 during its test.This tube 110 is provided at its outlet 112 (downstream end) with a burster basket 113 which is a cylinder closed downstream by a concave cover and pierced on its side wall with holes. The exhaust gases exit the burster basket through these holes and rise in the exhaust chimney 183 then exit into the atmosphere.

[0003] During operation of the turbomachine, three air flows are distinguished which circulate in the test room 182:

[0004] the primary flow (FP), which passes through the combustion chamber (HP (High Pressure) core) of the turbomachine 190 and participates in the combustion. This primary flow FP is therefore at the outlet loaded with CO2 but also with water, Sox, Nox and other particles;

[0005] the secondary flow (FS), which is compressed by the fan of the turbomachine 190 and which generates the majority of the thrust;

[0006] the induced air flow (induced flow FI), which is sucked in by the depression at the outlet of the turbomachine 190. Indeed, the engine flow, the sum of the primary flow FP and the secondary flow FS, upon entering the tube 110 of the exhaust duct, causes, by jet pump effect, a so-called “induced” flow which circulates in the test room 182 without passing through the turbomachine 190.

[0007] These different flows are illustrated in [Fig.8] by arrows, [Fig.8] being a longitudinal view of the turbomachine 190 and the upstream part of the tube 110 of [Fig.7]. For the sake of clarity, the thrust balance 191 is not shown. All these flows circulate in the tube 110 of the exhaust duct of a turbine test bench.

[0008] Due to the combustion in the turbomachine 190, the above flows which mix and circulate in the exhaust duct of a turbine test bench include carbon dioxide CO2 which is released into the atmosphere at the outlet of the exhaust stack 183. This release of carbon dioxide is undesirable. It is possible to place in the exhaust stack 183 a carbon dioxide filtration device 170. However, the concentration of carbon dioxide in the flow which circulates in the exhaust stack 183 is low, which makes such a filtration device ineffective. Description of the invention

[0009] The present invention aims to remedy these drawbacks.

[0010] The invention aims to propose a device which contributes to making the capture of carbon dioxide CO2, carbonaceous particles and other pollutants generated by a gas turbine test bench as efficient as possible.

[0011] This object is achieved by virtue of the fact that the exhaust duct of the gas turbine test bench comprises at least one inner tube extending along a longitudinal axis with an inlet and an outlet and which is located inside the outer tube such that in operation an internal flow of gas circulates in the at least one inner tube and an external flow of gas separate from the internal flow circulates in the outer tube outside the at least one inner tube.

[0012] Thanks to these arrangements, a gas flow is obtained (which in this case circulates in the inner tube) which is mainly made up of the primary flow resulting from the combustion. Consequently, this gas flow has a concentration of carbon dioxide and carbonaceous and polluting particles which is maximized, which facilitates the decontamination of this flow and makes it possible to reduce the size of the decontamination system for this gas. In addition, this gas flow has a higher temperature than a flow circulating in the outer tube without an inner tube. The heat from this gas flow can thus be recovered more efficiently.

[0013] Advantageously, the internal tube is unique and is coaxial with the external tube.

[0014] Advantageously, the internal tube is unique and the longitudinal axis of the internal tube is located in a vertical plane above the longitudinal axis of the outer tube and parallel to this longitudinal axis.

[0015] Advantageously, the inlet of the at least one internal tube is located downstream of the inlet of the external tube by a longitudinal distance.

[0016] Advantageously, the at least one internal tube is fixed to the external tube by a fixing mechanism.

[0017] Thus, the assembly of the exhaust duct is simplified.

[0018] Advantageously, the external tube comprises an outlet and the at least one internal tube comprises an outlet which is located downstream of the outlet of the external tube.

[0019] Advantageously, the outer tube comprises an outlet and the at least one inner tube comprises an outlet, and the at least one inner tube comprises, upstream of its outlet and downstream of said outlet of the outer tube, a diffuser which is a conduit whose cross-section increases from upstream to downstream so as to reduce the flow rate of the gases which pass through this diffuser.

[0020] The invention also relates to an assembly consisting of an exhaust duct of a turbine test bench according to the invention and a pollution control system located downstream of the outlet of the at least one internal tube and capable of receiving the internal flow.

[0021] The invention also relates to a gas turbine test bench which comprises a building which has an air inlet stack at a first end of the building and a gas exhaust stack at a second end of the building, a test room extending between the inlet stack and the exhaust stack, a thrust balance located in the test room and adapted to receive the gas turbine for testing, an exhaust duct of a gas turbine test bench according to the invention, this exhaust duct being located downstream of the gas turbine when it is mounted on the thrust balance and being positioned relative to the gas turbine such that the central axis of the gas turbine passes through the at least one inner tube and the outer tube is adapted to receive the flow of gas displaced by the gas turbine,and the test bench further comprises a pollution control system which is located downstream of the outlet of the at least one internal tube and which is capable of receiving the internal flow which circulates in the at least one internal tube.

[0022] Advantageously, the maximum dimension of the at least one internal tube is greater than or equal to the equivalent diameter of the ejection nozzle of the gas turbine.

[0023] The invention will be better understood and its advantages will appear better on reading the detailed description which follows, of embodiments shown as non-limiting examples. The description refers to the appended drawings in which:

[0024] [Fig-1] [Fig. 1] is a perspective view of a turbomachine test bench according to a first embodiment of the invention.

[0025] [Fig.2] [Fig.2] is a perspective view of a turbomachine test bench according to a variant of the first embodiment of the invention illustrated in [Fig.l].

[0026] [Fig.3] [Fig.3] is a side view of the upstream portion of an exhaust duct of a turbine test bench according to the invention.

[0027] [Fig.4] [Fig.4] is a side view of the upstream portion of an exhaust duct of a turbine test bench according to a variant of the invention.

[0028] [Fig.5] [Fig.5] is a perspective view of the upstream portion of an exhaust duct according to the invention which shows the fixing mechanism between the inner and outer tubes.

[0029] [Fig.6] [Fig.6] is a perspective view of a turbomachine test bench according to a second embodiment of the invention.

[0030] [Fig.7] [Fig.7], already described, is a perspective view of a test bench of turbomachine according to the prior art.

[0031] [Fig.8] [Fig.8], already described, is a side view of the upstream part of the turbomachine test bench of [Fig.7]. Detailed description of the invention

[0032] In the description below, the terms "upstream" and "downstream" are defined with respect to the normal direction of circulation of gas and air in the test bench, in the gas turbine and in the exhaust duct of a turbine test bench during normal operation of this turbine.

[0033] The invention is described below in the case where the gas turbine 90 is a turbomachine, but applies to any gas turbine where the displaced gas must be depolluted.

[0034] [Fig.l] shows a turbomachine test bench 90 comprising an exhaust duct of a turbine test bench (of this turbomachine) according to the invention. This test bench 80 comprises a building 88 which comprises, from upstream to downstream (in the normal direction of air circulation during operation of the turbomachine 90) an intake chimney 81, a test room 82 and a (first) exhaust chimney 83. The air enters the test room 82 through the vertical intake chimney 81 which is open to the outside at its inlet. The test room 82 comprises a turbomachine 90 which is mounted on a thrust balance 91. Downstream of the turbomachine 90 tested, there is an exhaust duct of a turbine test bench which comprises a tube 10 which extends along a longitudinal axis XI and which is intended to receive at its inlet 11 (upstream end) the exhaust gases which escape from the turbomachine 90 during its test.The longitudinal axis XI is substantially the longitudinal axis along which the turbomachine 90 extends. The tube 10 is provided at its outlet 12 (downstream end) with a burster basket 13 which is a cylinder closed at its downstream end by a concave cover (convex seen by the gas flow) and pierced on its side wall with holes. The gas flow F10 which circulates in the tube 10 outside the internal tube 20 (see description below and in [Fig. 3]) leaves the burster basket 13 through these holes and rises in the exhaust chimney 83 then leaves into the atmosphere. This . tube 10 is referred to as outer tube 10 as opposed to inner tube 20 which is described below.

[0035] The exhaust duct of a turbine test bench comprises an inner tube 20 which extends along a longitudinal axis X2 with an inlet 21 and an outlet 22 and which is located inside the outer tube 10 and in the same direction.

[0036] During operation of the turbomachine 90, three air flows are distinguished which circulate in the test room 82:

[0037] the primary flow (FP), which passes through the combustion chamber (HP (High Pressure) core) of the turbomachine 90 and participates in the combustion. This primary flow FP is therefore at the outlet loaded with CO2 but also with water, Sox, Nox and other particles.

[0038] the secondary flow (FS), which is compressed by the fan of the turbomachine 90 and which generates the majority of the thrust. This secondary flow FS initially circulates around the primary flow FP.

[0039] the induced air flow (FI), which is sucked in by the depression at the outlet of the turbomachine 90. Indeed, the engine flow, the sum of the primary flow FP and the secondary flow FS, upon entering the external tube 10, causes by jet pump effect a so-called “induced” flow which circulates in the test room 82 without passing through the turbomachine 90. This induced flow FI initially circulates around the secondary flow FS.

[0040] In operation, the primary FP, secondary FS and induced FI flows enter and then circulate in the outer tube 10, as illustrated in [Fig. 3] by arrows. The term "gas displaced by the turbomachine" refers to the gases and air constituting all of these primary FP, secondary FS and induced FI flows. [Fig. 3] is a longitudinal view of the turbomachine 90 and the upstream part of the outer tube 10 and the inner tube 20 of [Fig. 1]. For the sake of clarity, the thrust balance 91 is not shown.

[0041] In operation, an internal flow F20 of gas circulates inside the internal tube 20 and an external flow F10 of gas separated from the internal flow F20 circulates in the external tube 10 outside the internal tube 20.

[0042] The outer tube 10 and the inner tube 20 are coaxial, as illustrated in Figures 1 and 2 (as well as in Figures 3, 5, and 6). The longitudinal axes XI and X2 are therefore coincident. The outer tube 10 and the inner tube 20 are concentric.

[0043] Thanks to its central position in the space of the external tube 10, the internal tube 20 preferentially accommodates the gas flow which is the most central, that is to say the closest to the longitudinal axis XL. Thus, the internal flow F20 is made up of the majority, or even almost all, of the primary flow FP, and a part of the secondary flow FS. The external flow F10 is made up of the remainder of the secondary flow FS and almost all of the induced flow FL. For example, the external flow F10 is made up of the majority of the secondary flow FS and all of the induced flow FI.

[0044] The tests carried out by the inventors show that in the inner tube 20 it is possible to capture up to 92% of the primary flow FP. Given that the primary flow FP is that of the three flows (FP, FS, FI) which is by far the most loaded with carbon dioxide, carbonaceous particles and other pollutants, it is possible, thanks to the invention, to increase the concentration of carbon dioxide, carbonaceous particles and other pollutants in the flow treated by the filtration system (depollution system) 70 located downstream of the inner tube 10 (see below), in comparison with the flow which circulates in an exhaust duct without an inner tube 20.

[0045] Conversely, the gas flow F10 which circulates in the tube 10 outside the internal tube 20 and which leaves the burster basket 13 then rises in the exhaust chimney 83 is very little loaded with pollutants (even less than in the flow which circulates in the exhaust duct without internal tube 20). It is therefore possible to let this gas flow F10 exit through the extraction chimney 83 without filtering / treating it.

[0046] Alternatively to the configuration where the outer tube 10 and the inner tube 20 are coaxial, the longitudinal axis X2 of the inner tube 20 is located in a vertical plane above the longitudinal axis XI of the outer tube 10 and parallel to this longitudinal axis XL. In other words, the inner tube 20 is translated in a vertical plane (containing the longitudinal axis XI) relative to the position where the outer tube 10 and the inner tube 20 are concentric. This configuration is illustrated in [Fig.4]. This configuration has the advantage that more gases from the combustion are captured in the inner tube 20 since the natural ejection trajectory of the gases from the turbomachine 90 can be upwards.

[0047] The longitudinal central axis of the turbomachine 90 extends in the same direction as the longitudinal axis XI and the longitudinal axis X2. In all cases, the turbomachine 90 is positioned relative to the inner tube 20 such that this central axis of the turbomachine 90 passes into the inner tube 20 (and extends in the same direction as the inner tube 20).

[0048] In all cases, the maximum dimension D2 of the inner tube 20 is strictly less than the maximum dimension DI of the outer tube 10. For example, the maximum dimension D2 is less than or equal to half of the maximum dimension DI. In the case where the inner tube 20 and the outer tube 10 are of circular cross-section (their section is a circle) as illustrated in all the figures, the maximum dimensions DI and D2 are the diameters of these circles. The diameters DI and D2 are indicated in [Fig.3].

[0049] Alternatively, the inner tube 20 and the outer tube 10 each have an ellipse as their cross-section. Alternatively, the inner tube 20 and the outer tube 10 each have a polygon as their cross-section, for example a square or a rectangle.

[0050] According to a variant (not shown), the internal tube 20 is divided transversely, that is to say by a wall which extends along the longitudinal axis X2, over all or part of its length.

[0051] According to a variant (not shown), the external tube 10 is divided transversely into two half-tubes by a wall which extends over its entire length along the longitudinal axis XI. In this variant, the internal tube 20 is for example formed by one of these half-tubes, or for example is housed in one of these half-tubes.

[0052] According to a variant, the maximum dimension D2 of the internal tube 20 is greater than or equal to the diameter of the primary flow FP which is emitted by the combustion chamber of the turbomachine 90, measured immediately at the outlet of this combustion chamber. In other words, the maximum dimension D2 is greater than or equal to the equivalent diameter of the ejection nozzle of the turbomachine 90. Thus, all or almost all of the primary flow FP passes into the internal tube 20.

[0053] As illustrated in [Fig.l], the inlet 21 of the inner tube 20 is located downstream of the inlet 11 of the outer tube 10 by a longitudinal distance LT. This longitudinal distance LT is therefore non-zero.

[0054] For example, the longitudinal distance LT between the inlets (11, 21) is less than half the length L of the outer tube 10 (see [Fig.l]). For example, the longitudinal distance LT is preferably greater than 0.8 times the maximum dimension DI of the outer tube 10.

[0055] Alternatively, the inlet 21 of the inner tube 20 and the inlet 11 of the outer tube 10 are located in the same transverse plane (relative to the longitudinal axis XI).

[0056] The inner tube 20 is fixed to the outer tube 10 by a fixing mechanism 30. For example, this fixing mechanism 30 consists of a plurality of radial fins 31 which are regularly distributed along the circumference of the inner tube 20 in the space between the inner tube 20 and the outer tube 10. Each fin 31 extends longitudinally in the direction of the longitudinal axis X2. For example, the number of fins is equal to four, as illustrated in [Fig. 5] in the case where the inner tube 20 and the outer tube 10 are coaxial. Alternatively, the fixing mechanism consists of a plurality of radial rods which are distributed in the space between the inner tube 20 and the outer tube 10 along the inner tube 20 in several transverse planes, and regularly distributed, in each transverse plane, along the circumference of the inner tube 20.

[0057] The outlet 22 of the inner tube 20 is located downstream of the outlet 12 of the outer tube 10. Thus the inner tube 20 extends downstream of the outer tube 10 with a constant cross-section, as illustrated in [Fig.l].

[0058] Advantageously, the internal tube 20 is provided at its outlet 22 with a burster basket 23 which is a cylinder closed downstream by a concave cover and pierced on its wall. side of holes. The internal flow F20 exits the burster basket 23 through these holes and rises in a second exhaust chimney 84 which includes the outlet 22 and the burster basket 23. The second exhaust chimney 84 is part of the building 88, as illustrated in [Fig.l] (or in [Fig.2] which is a variant of the embodiment of [Fig.l], described below).

[0059] The invention also relates to an assembly consisting of an exhaust duct of a turbine test bench as described above, and a pollution control system 70 which is located downstream of the outlet 22 of the internal tube 20 and which is capable of receiving the internal flow F20 which circulates in the internal tube 20. The pollution control system 70 comprises a pollution control filter 71. The pollution control system 70 is located in the second exhaust chimney 84, for example directly above the spark gap basket 23, as illustrated in [Fig.l] (or in [Fig.2]). This pollution control system 70, thanks to its filter, is capable of capturing the carbon dioxide CO2, the carbonaceous particles and the other polluting particles which are in the internal flow F20 such that, downstream of the pollution control system 70, the gas of the internal flow F20 is depolluted by this pollution control filter 71.This decontamination process is made more efficient thanks to the higher density of carbon dioxide CO2, carbonaceous particles and other polluting particles which are in the internal flow F20 (this density is higher than if the internal tube 20 were absent).

[0060] According to a first embodiment, described above with reference to [Fig.l], the decontamination system 70 is part of the test bench 80 and the building 88.

[0061] In this first embodiment, according to a variant, the internal tube 20 comprises, upstream of its outlet 22 and downstream of the outlet 12 of the external tube 10, a diffuser 24 which is a conduit, for example a conical conduit, the cross-section of which increases from upstream to downstream. Thus, the flow rate of the gases which pass through this diffuser 24 is reduced, which makes it possible to increase the quantity of gas captured and the pressure drop available for the depollution system 70 positioned downstream of the burster basket 23. This situation is illustrated in [Fig.2].

[0062] According to a second embodiment, the decontamination system 70 is part of the test bench 80 and is not part of the building 88. The decontamination system 70 then comprises a decontamination building 72, separate from the building 88, which contains the decontamination filter 71, and the outlet of the internal tube 20 is located in this decontamination building 72 such that the internal flow F20 passes through this filter 71.

[0063] In this second embodiment, according to a first variant (not illustrated), the decontamination system 70 is moved away from the building 88 and remains in the main direction of the building (from the inlet chimney 81 to the first exhaust chimney 83). Thus, the internal tube 20 extends along the longitudinal axis X2 outside the building 88 to this decontamination system 70. The outlet 22 of the tube internal 20 is either provided with a burster basket 23, or without this burster basket 23 (in this case the outlet 22 is provided with at least one orifice through which the gas exits into the decontamination building 72).

[0064] In this second embodiment, according to a second variant illustrated in [Fig. 6], the decontamination system 70 is offset relative to the building 88. Thus, the internal tube 20 extends in a curved manner (moving away from the longitudinal axis X2), outside the building 88 to this decontamination system 70. The outlet 22 of the internal tube 20 is either provided with a burster basket 23, or without this burster basket 23. In [Fig. 6] the case where the outlet of the internal tube 20 is provided with a burster basket 23 is illustrated.

[0065] An exhaust duct of a turbine test bench 90 according to the invention makes it possible to obtain a gas flow at a higher temperature than in an exhaust duct according to the prior art. Indeed, the internal flow F20 which circulates in the internal duct 20 is essentially composed of the primary flow FP, which leaves directly from the combustion chamber of the turbomachine 90 and which is therefore at a higher temperature than the secondary flow FS and the induced flow FI. Thus, the internal flow F20 has a higher temperature than the external flow F10 which circulates in the external tube 10 outside the internal tube 20, and a higher temperature than a flow circulating in the external tube without an internal tube in the prior art. Advantageously, the internal duct 20 is placed in thermal communication with a heat exchanger (not shown) which is capable of recovering this heat for a given application.This heat exchanger operates more efficiently because the internal flow F20 is at a higher temperature. Tests carried out by the inventors show that in the internal tube 20 it is possible to increase the temperature of the recovered flow by 50°C (compared to an exhaust duct without the internal tube 20).

[0066] The invention also relates to a gas turbine test bench 80 90 with a turbine test bench exhaust duct and a pollution control system 70 as described above.

[0067] Thus, the gas turbine 90 test bench 80 comprises a building 88 which has an air inlet chimney 81 at a first end of the building and at least one gas exhaust chimney (83, 84) at a second end of the building, a test room 82 extending between the inlet chimney 81 and the exhaust chimney (83, 84), a thrust balance 91 located in the test room 82 and adapted to receive the turbomachine 90 to be tested, an exhaust duct of a turbine test bench which is located downstream of the turbomachine 90 when it is mounted on the thrust balance 91 and which is positioned relative to the turbomachine such that the central axis of the turbomachine passes through the tube internal 20 of the exhaust duct and that the external tube 10 is capable of receiving the flow of gas displaced by the turbomachine. The test bench 80 further comprises a pollution control system 70 which is located downstream of the outlet 22 of the internal tube 20 and which is capable of receiving the internal flow F20 which circulates in the internal tube 20. According to one configuration, the building 88 comprises a single exhaust chimney 83, and the pollution control system 70 is located outside this building 88, either attached, or offset in the axis or offset relative to the main direction of this building. According to another configuration, the building comprises a (first) exhaust chimney 83 and a second exhaust chimney 84, and the pollution control system 70 is located in this second exhaust chimney 84.

[0068] The invention has been described above in the configuration where the exhaust duct comprises a single inner tube 20. Alternatively, in another configuration, the exhaust duct comprises two or more inner tubes 20 which are parallel and which are located inside the outer tube 10. In a first variant of this configuration, these inner tubes 20 are arranged side by side, that is to say that each inner tube 20 has a longitudinal axis X2 which is parallel and distinct from the longitudinal axes X2 of the other inner tubes 20. For example, these inner tubes 20 all have the same diameter. In a second variant of this configuration, these inner tubes 20 are concentric. In other words, these inner tubes 20 are coaxial, that is to say that the longitudinal axes X2 of all these tubes are the same. The diameters D2 of any two inner tubes 20 are then necessarily different.

[0069] The invention has been described above in the case where the turbomachine is a double-spool turbofan. The invention also applies to a test bench of any type of turbomachine such as a turbojet, a triple-spool turbofan, a turboshaft, a military engine.

Claims

Claims

1. Exhaust duct of a gas turbine test bench comprising an outer tube (10) extending along a longitudinal axis (X1) with an inlet (11) capable of recovering gases displaced by a gas turbine (90), said exhaust duct being characterized in that it comprises at least one inner tube (20) extending along a longitudinal axis (X2) with an inlet (21) and which is located inside said outer tube (10) such that in operation an internal flow (F20) of gas circulates in said at least one inner tube (20) and an external flow (F10) of gas, separated from said internal flow (F20), circulates in said outer tube (10) outside said at least one inner tube (20), said outer tube (10) having an outlet (12) and said at least one inner tube (20) having an outlet (22) which is located downstream of the outlet (12) of said external tube (10).

2. An exhaust duct of a gas turbine test bench according to claim 1 such that said inner tube (20) is single and is coaxial with said outer tube (10).

3. Exhaust duct of a gas turbine test bench according to claim 1 such that said inner tube (20) is single and the longitudinal axis (X2) of said inner tube (20) is located in a vertical plane above the longitudinal axis (XI) of said outer tube (10) and parallel to this longitudinal axis (XI).

4. Exhaust duct of a gas turbine test bench according to any one of claims 1 to 3 such that said inlet (21) of the at least one inner tube (20) is located downstream of said inlet (11) of the outer tube (10) by a longitudinal distance (LT).

5. An exhaust duct of a gas turbine test bench according to any one of claims 1 to 4 such that said at least one inner tube (20) is fixed to the outer tube (10) by a fixing mechanism (30).

6. Exhaust duct of a gas turbine test bench according to any one of claims 1 to 5 such that said at least one inner tube (20) comprises, upstream of its outlet (22) and downstream of said outlet (12) of the outer tube (10), a diffuser (24) which is a duct whose cross-section increases from upstream to downstream. so as to reduce the flow rate of the gases passing through this diffuser (24).

7. Assembly consisting of an exhaust duct of a gas turbine test bench according to any one of the preceding claims and a pollution control system (70) located downstream of said outlet (22) of said at least one internal tube (20) and capable of receiving said internal flow (F20).

8. A gas turbine (90) test bench (80) characterized in that it comprises a building (88) which has an air inlet chimney (81) at a first end of the building (88) and a gas exhaust chimney (83, 84) at a second end of the building (88), a test room (82) extending between the inlet chimney (81) and the exhaust chimney (83, 84), a thrust balance (91) located in said test room (82) and adapted to receive said gas turbine (90) for testing, an exhaust duct of a gas turbine test bench according to any one of claims 1 to 6,said exhaust duct being located downstream of said gas turbine (90) when mounted on said thrust balance (91) and being positioned relative to said gas turbine (90) such that the central axis of said gas turbine (90) passes through said at least one inner tube (20) and said outer tube (10) is adapted to receive the gas flow displaced by said gas turbine (90), and said test bench (80) further comprises a depollution system (70) which is located downstream of the outlet (22) of said at least one inner tube (20) and which is adapted to receive said internal flow (F20) which circulates in said at least one inner tube (20).,

9. Test bench (80) for a gas turbine (90) according to claim 8 such that the maximum dimension (D2) of said at least one internal tube (20) is greater than or equal to the equivalent diameter of the exhaust nozzle of said gas turbine (90).

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