Leaf seal

[0002] 1. Field of the Invention

[0003] The invention relates to a sealing device, referred to herein as a leaf seal, which uses a thin sheet or leaf to ensure fluid tightness between two zones of fluid flow. It is of use in particular with turbomachine nozzle rings to ensure fluid tightness between an aerodynamic flow path in which there is a hot gas flow and a chamber supplying air for cooling a nozzle ring.

[0004] 2. Summary of the Prior Art

[0005] Leaf seals are often used to ensure fluid tightness between two adjacent structural elements of a turbomachine in which there is a considerable pressure difference between the structural elements.

[0006] When the structural elements are of annular shape, as in the case with many turbomachine elements, a number of curved leaf seals are used and arranged in contact with one another so as to form a substantially continuous annular seal between the structural elements.

[0007] The known leaf seals comprise a thin flexible leaf formed with an aperture in which a pin secured to one of the adjacent structural elements slides.

[0008] To retain the leaf in a sealing position the seal may also comprise, as described, for example, in French patent No. 2649463, a spring comprising a first part mounted on one of the structural elements and a second part mounted on the seal support pin. The problem with this seal is that leakages occur through the aperture in which the pin slides.

[0009] It is an object of the invention to solve this problem and to provide an effective leaf seal which is not permanently mounted on the structural elements, the seal comprising a pinless retaining system which is easy to demount and manufacture and which retains the seal stably in its operative sealing position.

[0010] To this end, the invention provides a leaf seal for ensuring fluid tightness between a first and a second structural element having a space therebetween, said leaf seal comprising at least one flexible sealing leaf disposed in a sealing position in said space between said first and said second structural elements, said sealing leaf having first and second contact generators bearing on said first and second structural elements respectively, and a retaining bracket having a first end bearing on said sealing leaf and a second end which is bent back and engaged in a groove provided in said second structural element in order to locate said sealing leaf axially and to retain said sealing leaf permanently in said sealing position by clamping said leaf between said retaining bracket and said first and second structural elements.

[0011] Preferably, the sealing leaf is retained radially in position by retaining means in the form of lateral lugs provided on the retaining bracket and lugs which are bent at right-angles at the lower end of the leaf and which engage under the lateral lugs of the bracket.

[0012] In the case in which the seal comprises at least two adjacent leaves placed edge to edge, the seal also comprises a flat cover strip or plate disposed between the leaves and the bracket so as to cover the joint between the two adjacent leaves.

[0013] Further preferred features and advantages of the invention will become apparent from the following description of the preferred embodiments, given by way of example only, with reference to the accompanying drawings.

[0014] FIG. 1 is a diagrammatic longitudinal sectional view of part of a turbomachine incorporating a leaf seal in accordance with the invention.

[0015] FIG. 2 is a sectional view illustrating one embodiment of a leaf seal in accordance with the invention.

[0016] FIG. 3 is a view similar to FIG. 2 but showing another embodiment.

[0017] FIG. 4 is a rear elevational view of the leaf seal shown in FIG. 3 with the retaining bracket removed.

[0018] FIG. 5 is a view similar to FIG. 4 but showing the retaining bracket in place.

[0019] FIG. 1 shows a turbomachine comprising a combustion chamber 10 and a high pressure turbine 11 having one or more stages. Each turbine stage comprises a row of guide vanes 12 and a row of rotor blades 13 disposed alternately in a known manner. The high pressure turbine is supported by a structure comprising, on the radially outer side of the turbine, an outer casing 14 of the combustion chamber, an outer turbine ring 15 and a turbine casing 16 which are all bolted together. On the radially inner side of the turbine, an inner casing 17 of the combustion chamber is connected to an inner ring 18 of the turbine. In conventional manner high pressure cooling air flows around the annular combustion chamber in the annular chamber disposed between the casing and the liner of the combustion chamber. The cooling air also flows downstream through orifices 19, 20 to cool the turbine guides.

[0020] Air leaks between the structural elements of the turbomachine which are disposed between the combustion chamber 10 and the guide vane stage 12 must be avoided to ensure the required cooling air flow in the elements of the engine. To this end, a seal in accordance with the invention is disposed in the space separating the structural elements of the engine which are situated between the combustion chamber 10 and the guide vane stage 12. The seal comprises a leaf 31 having an inner end in contact with the front wall of an outer casing 33 of the guide vane stage 12, and an outer end in contact with the rear wall 34 of the combustion chamber. The leaf is retained in its sealing position by retaining means which is described hereinafter with reference to FIGS. 2 to 5.

[0021] FIG. 2 illustrates one embodiment of the leaf seal in accordance with the invention. The seal comprises a flexible leaf 31, which is intended to form a seal between two structural elements 40 and 41, and a retaining bracket 42 intended to maintain the flexible leaf axially and radially in its sealing position. The flexible leaf is disposed in a space separating the first and second structural elements 40, 41 and comprises a first contact generator or surface 35 and a second contact generator or surface 36 which, in the sealing position, bear on the first and second structural elements 40, 41 respectively. The retaining bracket 42 comprises a first end 43 bearing on the sealing leaf 31 and a second end 44 bent back in the form of a pin engaged in a groove 46 in the second structural element 41. The second end 44 of the bracket 42 is retained by the groove, and the bracket acts to retain the leaf 31 in its operative sealing position by a clamping action. The first end 43 of the bracket 42 is preferably curved in a direction away from the leaf to increase the bearing force acting on the leaf. Advantageously, the bracket 42 is mounted in a prestressed state to provide a spring effect.

[0022] The bracket 42 retains the sealing leaf 31 radially in position, for example by means of interengaging lugs on the leaf and the bracket. In the embodiment shown in FIG. 2, the sealing leaf 31 has lugs 37 cut in its lower edge and bent at right angles so that they engage below lateral lugs 45 provided on the bracket 42.

[0023] FIG. 3 is a sectional view of an embodiment of the leaf seal for use with annular structural elements. In this case a number of curved leaf seals are used, and the sealing leaves are disposed edge to edge to form a substantially continuous annular seal between the structural elements.

[0024] To prevent leaks between two adjacent leaves the seal also comprises a flexible cover strip or plate 50 disposed between the sealing leaves and a retaining bracket so as to cover the joint between the two adjacent leaves. The two adjacent sealing leaves and the cover plate are retained axially in position by the retaining bracket.

[0025] The retaining bracket 42, cover plate 50 and sealing leaves 31 retain one another radially in position, for example by means of a system of lugs which engage one below another. In the embodiment of FIGS. 3 to 5, the adjacent sealing leaves have right-angled lugs which engage below lateral lugs of the retaining bracket; and the cover plate 50 comprises two lateral lugs 51 bent twice at right-angles so that they engage below the lugs of the two adjacent sealing leaves 31.

[0026] The whole assembly is retained in its operative sealing position by the bracket 42 being engaged and retained in a groove 46 in the second structural element 41, in a manner similar to that described with reference to FIG. 2.

[0027] The invention has the advantage that all of the components of the seal may consist of sheet metal stampings, which are easy to produce. The seal is light, compact and inexpensive.

[0028] The invention is of course not limited to the embodiments which have been described in detail. In particular, the retaining bracket illustrated is shown as being disposed obliquely relative to the sealing leaf, but it can also be disposed parallel thereto. Also, the retaining bracket may or may not be prestressed, and other systems for radially retaining the sealing leaves in position may be used. The use of lugs is merely one particularly simple embodiment requiring no additional parts.