Patent Application
20110311355
The invention refers to an axial turbocompressor for a gas turbine, wherein the axial turbocompressor has low radial gap losses.
A gas turbine has a turbocompressor, for example in an axial type of construction. The turbocompressor has a casing with a stator attached thereupon, and a rotor which is enclosed by the casing. The rotor has a shaft on which the rotor can be rotationally driven. Provision is made for a shaft cover, encompassing the shaft, the outer contour of which together with the inner contour of the casing form a part of the flow passage through the turbocompressor. The flow passage has a cross section which widens in the flow direction so that the flow passage is formed as a diffuser.
The rotor has a multiplicity of rotor stages which are formed in each case by a rotor blade row. Also, the stator has a multiplicity of stator blade rows which, as seen in the axial direction, are arranged in a manner in which they alternate with the rotor blade rows. As seen in the flow direction, a guide vane row is customarily arranged after the last rotor blade row and a downstream guide vane row arranged after that.
The guide vane rows have a multiplicity of vanes which by their one end are fastened in each case on the casing and by their other end point towards the shaft. A vane tip, which faces the shaft cover and is arranged directly adjacent thereto, is formed on the other end of the guide vane. The distance between the vane tips and the shaft cover is formed as a radial gap which is dimensioned in such a way that on the one hand the vane tips do not butt against the shaft cover during operation of the gas turbine and on the other hand the leakage flow through the radial gap which ensues during operation of the gas turbine is as low as possible. This radial gap is therefore to be designed as small as possible so that high efficiency is achieved and the full blading potential of the compressor can be exploited. Alternatively to freestanding compressor vanes, it is also known from EP 1 079 075 A2, for example, to secure the hub-side ends of the vane airfoils, by means of a locking bolt, against an outwards movement from a hub-side fixed inner ring and to provide damping against vibration occurrences.
The casing of the turbocompressor is solidly constructed in order to be able to withstand the pressure stresses and temperature stresses during operation of the gas turbine. Also, the casing is of a rigid construction so that load transfer onto the casing during operation of the gas turbine results in only minor deformation of the casing. In contrast to this, the shaft cover is subjected to lower mechanical stresses during operation of the gas turbine, as a result of which the shaft cover is of a thinner and less solid construction than the casing.
Owing to the fact that the shaft cover is designed with lower wall thicknesses in comparison to the casing and as a rule has different material properties than the casing, the shaft cover heats up more quickly than the casing with the guide vane rows fastened thereupon. This has the result that for starting and shutting down the gas turbine the shaft cover and the casing have a different rate of thermal expansion so that during starting and shutting down of the gas turbine the depth of the radial gap alters, wherein the radial gap is temporarily smaller during starting and larger during shutting down.
So that the vane tips of the guide vane row do not butt against the shaft cover and damage this during operation of the turbocompressor, the radial gap is provided with a minimum depth which is dimensioned in such a way that in each operating state of the gas turbine—steady state as well as transient—the vane tips seldom if ever come into contact with the shaft cover. This has the result that a correspondingly dimensioned radial gap is provided at the vane tips which leads to a reduction of the efficiency of the gas turbine.
Also, the blockage which is created by the radial gap leads to a reduction of the main flow components, as a result of which the pressure recovery in the diffuser is reduced and disadvantageous separation phenomena can occur.
It is the object of the invention to create an axial turbocompressor for a gas turbine, which has high efficiency and high operational reliability.
The axial turbocompressor according to the invention for a gas turbine has a guide vane cascade, which is formed by guide vanes with vane tips which are free standing on the hub side, and a stationary shaft cover which is arranged directly adjacent to the vane tips on the hub side and delimits the flow passage of the axial compressor, wherein between the shaft cover and the vane tips a radial gap is formed and is minimally dimensioned in such a way that the assembly of the axial turbocompressor can only just be accomplished, and in the shaft cover provision is made for a multiplicity of blind hole-like recesses, wherein one of the recesses is associated with each vane tip and arranged directly adjacent to the vane tip which is associated therewith, and dimensioned in such a way that during operation of the axial turbocompressor each vane tip can sink into its associated recess without one of the vane tips coming into significant contact with the shaft cover.
As a result, the radial gap between the vane tip and the shaft cover is adjusted to the minimum required assembly gap so that the depth of the radial gap is reduced to the assembly-dependent minimum. The depth of the minimum required assembly gap is selected in such a way that the rolling in of the guide vane cascade, especially of the rear guide vane cascade, can be accomplished.
In a conventional turbocompressor, the radial gap between the vane tips and the shaft cover is provided with a minimum required depth which is selected in such a way that in practically all conceivable operating states of the gas turbine the vane tips scarcely come into contact with, or do not make contact with, the shaft cover. Consequently, the radial gap is created with such depth that an appreciable mass flow of leakage flow flows through the radial gap, which leads to an undesirable lowering of efficiency of the gas turbine.
However, in the case of the axial turbocompressor according to the invention the radial gap is adjusted to the minimum possible radial gap, specifically to the minimum required assembly gap, so that the leakage flow through the radial gap is minimal. As a result, the axial turbocompressor has a high pressure recovery in the diffuser section and therefore high efficiency.
Also, the vane tips can sink into the recesses during operation of the axial turbocompressor so that although the radial gap is reduced to the minimum required assembly gap, a damaging contact of the vane tips with the shaft cover during operation of the axial turbocompressor is prevented.
If the vane tip sinks into its associated recess during a specific operating state, then the flow around the vane tip decreases, as a result of which the leakage flow at the vane tip also decreases. Consequently, the efficiency of the guide vane cascade increases and losses and also separations in the diffuser which lies downstream of the axial turbocompressor are reduced. In all, a good overall machine performance and high overall machine efficiency of the gas turbine result from the improved radial gap behavior. By implication, for this the divergence degree of the diffuser, i.e. the diffuser angle of the diffuser, can be selected larger than would be the case with a conventional diffuser. A reduction of the overall length of the gas turbine compared with a conventional gas turbine is associated with this.
It is preferred that a honeycomb-like and/or felt-like structure, which can yield during contact by the vane tip, is applied to the base of the recess. The honeycomb-like structure is preferably a honeycomb.
Consequently, the vane tip can sink into the honeycomb-like and/or felt-like structure, wherein the vane tip is not damaged. Resulting from this is the advantage that the distance between the vane tip and the honeycomb-like and/or felt-like structure is designed to be small. Therefore, the flow around the vane tip decreases if the vane tip sinks into its associated recess during a specific operating state and digs into the honeycomb-like and/or felt-like structure. As a result, the leakage flow at the vane tip advantageously additionally decreases.
Also, it is preferred that the recesses have an outline shape on the surface of the shaft cover which is adapted to the profile of the guide vanes associated therewith at the vane tip, and have a prespecified depth.
Therefore, the material of the shaft cover is arranged in such a way around the vane tip which is sunk into the recess that on the one hand the vane tip does not butt against the shaft cover when sinking into the recess and on the other hand the flow around the vane tip decreases.
It is preferred that the depth of the recesses is determined in such a way that during operation of the axial turbocompressor the radial relative movements between the vane tips and the shaft cover can be compensated.
As a result, prevention of a collision of the vane tip with the shaft cover during operation of the axial turbocompressor is advantageously achieved, so that the operational reliability of the axial turbocompressor is high.
Moreover, it is preferred that the outline shape of the recesses is determined in such a way that during operation of the axial turbocompressor the axial relative movements between the vane tips and the shaft cover can be compensated.
Therefore, the effect of the vane tips coming into contact with the shaft cover during axial relative movements between the vane tips and the shaft cover during operation of the axial turbocompressor is prevented, so that the operational reliability of the axial turbocompressor is high.
In the following, the invention is shown based on a preferred exemplary embodiment of an axial turbocompressor according to the invention, with reference to the attached schematic drawings. In the drawing:
As is evident from
Also, the axial turbocompressor 1 has a casing 5 on which the guide vanes 3 are fastened on the inner side. Facing away from the casing 5, the guide vanes 3 have a vane tip 4 which points inwardly into the casing 5.
On the hub side, a shaft cover 6, which is designed as a circumferentially symmetrical ring, is arranged directly at the vane tips 3. On the outer side of the shaft cover 6 which faces the vane tips 4, provision is made for a multiplicity of recesses 7. Each recess 7 is associated with a different vane tip 4, wherein the recess 7 is located directly adjacent to its associated guide vane tip 4. The recess 7 is formed like a blind hole and therefore terminates in a blind manner. That is to say, it is provided with a tightly sealed off base in order to avoid leakage losses.
Each recess 7, on the outer side of the shaft cover 6 facing the vane tips 4, has a contour 8 which is adapted to the profile shape of the guide vane 3 at the guide vane tip 4. Also, each recess 7 is provided with a depth 9 in the shaft cover 6. The shape of the contour 8 and the depth 9 are determined in such a way that during operation of the axial turbocompressor each vane tip 4 can sink into its associated recess 7, wherein during the sinking in the vane tip 4 does not come into contact, or barely comes into contact, with the shaft cover 6.
Applied to the base of each recess 7 is a honeycomb structure 10, as is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 09002056.1 | Feb 2009 | EP | regional |
This application is the US National Stage of International Application No. PCT/EP2010/050933, filed Jan. 27, 2010 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 09002056.1 EP filed Feb. 13, 2009. All of the applications are incorporated by reference herein in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP10/50933 | 1/27/2010 | WO | 00 | 8/11/2011 |
