Method for discharging exhaust gas from a gas turbine and exhaust assembly having optimised configuration

Abstract

A method for discharging exhaust gas from a gas turbine wherein a number of sectors, position, and angle at the center of at least one sector of a peripheral opening capable of forming an area for reingestion of a primary flow into an engine bay are determined by correlation of interactions between secondary cooling flows and the primary flow, from following behavior parameters: air gyration and speed at an inlet of a pipe, geometry of an exhaust stream, routing of the secondary cooling flow for cooling the engine bay, and a geometry and position of inlets of the secondary flows. The peripheral opening is then closed over the identified at least one angular sector. The method prevents backflow of hot primary air into the peripheral opening formed between a pipe and an ejector of the exhaust stream of a gas turbine.

Claims

1. A method for discharging gas turbine exhaust gas from a gas turbine engine comprising: providing an engine bay and, the gas turbine engine, an exhaust pipe, and an ejector, wherein the engine bay has an exterior and an interior inlets, and encloses an interior space which is contiguous, the inlets fluidly connecting the exterior to the interior space, wherein the interior space encloses the gas turbine engine, the exhaust pipe, and the ejector, and wherein the exhaust pipe has a first end and a second end, the first end of the exhaust pipe being joined to the gas turbine engine: providing at least one circumferential opening radially between the second end of the exhaust pipe and the ejector, wherein the ejector radially overlays and is radially spaced from the second end of the exhaust pipe, and wherein each circumferential opening subtends a respective opening angle circumferentially with respect to a center of the ejector: providing at least one circumferential closure each subtending a respective closure angle circumferentially with respect to the center of the ejector, where for each circumferential closure the second end of the exhaust pipe is joined to the ejector by a respective seal thereby preventing fluid flow between the engine bay and the ejector via each circumferential closure; and discharging gas turbine exhaust into the exhaust pipe thereby causing ambient air from the inlets to flow into the ejector via the at least one circumferential opening thereby forming a mixture of gas turbine exhaust and ambient air, and causing the mixture to exit the ejector.

2. A method for discharging gas according to claim 1, wherein a radial spacing between the second end of the exhaust pipe and the ejector is determined based on air in circular or spiral motion and speed at the first end of the exhaust pipe, and geometry of the engine bay, the exhaust pipe, and the ejector.

3. A method for discharging gas according to claim 1, wherein each seal is at least partially diametrically opposite a respective circumferential opening.

4. A method for discharging gas according to claim 1, wherein the ejector forms an elbow to divert the mixture, an amplitude of an angle of the mixture in a region of the elbow and an axial position of the elbow correlate with an amplitude of the angle of the circumferential closure.

5. A method for discharging gas according to claim 4, wherein each seal is positioned on an upstream portion of external curvature formed by the elbow of the ejector.

6. A method for discharging gas according to claim 1, wherein each seal is produced using a technology chosen from among bonding of a strip of composite material, or welding of a strip of sheet metal, having appropriate curvature of the ejector which is then coupled to the exhaust pipe, and fixing of the ejector on the exhaust pipe by rigid connection of opposite extension parts.

7. A method for discharging gas according to claim 6, wherein the at least one circumferential closure comprises two circumferential closures that are separated by an intermediate open sector, the intermediate open sector being diametrically opposite a remainder of the at least one circumferential opening.

8. A method for discharging gas according to claim 1, wherein a sum of all of the respective opening angles is from 90 to 330 degrees, and a sum of all of the respective closure angles is from 30 to 270 degrees.

Description

DESCRIPTION OF THE DRAWINGS

(1) Other details, characteristics and advantages of the present invention will become apparent on reading the following description, which is not limited, with reference to the appended drawings, in which, respectively:

(2) FIG. 1 shows a schematic view in partial longitudinal cross-section of a rear end of a gas turbine according to the prior art (already mentioned);

(3) FIG. 2 shows a side view of the peripheral opening between a pipe and a bent ejector with an example of local closure of this pipe/ejector opening according to the invention;

(4) FIGS. 3a and 3b show schematic views in cross-section in the region of the pipe/ejector overlap with a coupling between the ejector and the pipe in order to form respectively one and two closed sectors according to the invention;

(5) FIG. 4 shows a schematic view in longitudinal cross-section located in the region of an open sector between the pipe and the ejector;

(6) FIG. 5 shows a view in partial longitudinal cross-section of a rear end of a gas turbine according to FIG. 1 with an example of location of a closed section of an opening depending on the position of the inlet of the secondary flow for cooling of the primary flow; and

(7) FIG. 6 shows a view in partial longitudinal cross-section of a rear end of a gas turbine according to FIG. 1 with an example of location of a closed section of an opening when the ejector is bent.

DETAILED DESCRIPTION

(8) In the present description, the term longitudinal means along the central line of the gas turbine, and the term transverse is defined as perpendicular to this axis and the term radial means extending in a transverse plane from this axis. The terms upstream and downstream relate to the overall flow direction of the air streams along the longitudinal axis of a gas turbine until their final discharge into the pipe. In the illustrated examples, helicopters are propelled by gas turbines. Moreover, identical reference signs refer to the passages in which these elements are described.

(9) With reference to the side view of the peripheral opening 1 of FIG. 2, an example of local closure of this opening 1 between a pipe 2 and a bent ejector 3 of a gas turbine is illustrated. This closure is produced by a part 20 attached to the pipe 2 and to the ejector 3 in the region of the upstream end 30 of the ejector forming the horn-shaped raised edge of this end. The part may be made of sheet metal or of composite material. Any appropriate rigid connection means can be used: welding, bonding, etc.

(10) In the example, the closure part 20 extends over an angular sector substantially equal to 120. According to other examples of embodiments illustrated by FIGS. 3a and 3b, the closed section 21 can extend respectively over a single sector 21a of approximately 180 (FIG. 3a) or over two sectors 21b and 21c each having an angle at the centre C equal to 60 (FIG. 3b). The closed sectors 21a and 21b-21c are complemented by open sectors 1a and 1b-1c.

(11) In the example according to FIG. 3, the closed sectors 21b and 21c have the same extension and are separated by an intermediate open sector 1c having an angle at the centre C equal to approximately 60, said intermediate open sector being overall diametrically opposite the rest of the peripheral opening 1b of greater amplitude than the intermediate sector 1c having an angle at the centre of approximately 180. More precisely, the open sectors 1a, 1b and 1c extend symmetrically around the radial axis xx oriented according to the position of the inlet of the secondary flow of fresh air, as described hereafter.

(12) Moreover, the pipe/ejector positioning has the geometry illustrated in FIG. 4 in longitudinal cross-section along the axis YY in the region of an open sector between the pipe 2 and the ejector 3. Two relative characteristics are advantageously determined on the basis of this geometry: the length of overlap Lr, between the edge 30 of the ejector 3 and the end of the pipe 2, relative to the height h radially separating the pipe from the ejector, with
1L.sub.r/h15 the amount of opening of the height h relative to the internal hydraulic diameter D.sub.hi of the pipe 2, with
3%h/D.sub.hi12%

(13) More generally, the position and the angle at the centre of the sectors of the peripheral opening are determined by correlation of the interactions by modelling for example with the aid of digital tools, between the secondary flows Fs and the primary flow Fp from the parameters of air gyration and speed at the inlet of the free turbine 12 (FIG. 1), geometries of the exhaust stream and the engine bay Mb, and also the geometry and position of the inlets of the secondary flows E1a and E1b. Said peripheral opening is therefore closed over the angular sectors identified in this way.

(14) An example of positioning of a closed section 21 of the peripheral opening 1 is presented with reference to the view in partial longitudinal cross-section of FIG. 5, relating to the rear end of a gas turbine. The closed section 21 extends with an appropriate curvature continuously from the upstream end 3a of the ejector 3 which is then coupled to the pipe 2. In this example, the last air inlet passage E1b of a secondary flow Fs is disposed radially in the same region as the intake of these secondary flows Fs into the opening 1 between the pipe 2 and the ejector 3. The section 21 in this case is positioned radially opposite the air inlet passage E1b of the secondary flow Fs through the engine cowling Mc of the engine bay Mb.

(15) In general, a connection of the continuous type or similar has the advantage of being able to eliminate the fixing tabs between the pipe and the ejector, in particular when the closed sectors extend over more than 180.

(16) With reference to the view in partial longitudinal cross-section of FIG. 6, the rear end of a gas turbine comprises a bent ejector 3. The closed section 21 extends over an angular sector positioned on an upstream portion of external curvature Ce formed by the elbow 33 of the ejector.

(17) The invention is not limited to the embodiments described and illustrated. In particular other configurations can be envisaged to guide the secondary flows in the engine bay in order to cool the primary flow.

(18) Moreover, the gyration of the air at the free turbine outlet is a fundamental parameter for determining the gyration of the air at the pipe inlet. The geometry of the flow of exhaust gases depends in particular on a configuration of the flow path of the pipe that is at least partly symmetrical axially, and on the presence and number of branches or obstacles in the exhaust stream. The pipe and the ejector may comprise several elbows: the number and the position of the elbows can likewise be factors to be taken into account. In addition, with regard to the geometry of the engine bay as a parameter, it may be useful to take into account the presence of obstacles in the bay and of walls in contact with the secondary flows, as well as the number, the position and the configuration of the inlets of the secondary flows.