Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
2000-12-19
2002-11-19
Lopez, F. Daniel (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With heating, cooling or thermal insulation means
Changing state mass within or fluid flow through working...
C415S115000
Reexamination Certificate
active
06481966
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of guide elements, such as guide or turbine blades, used in gas turbines. It concerns a gas-turbine guide element around which hot air flows and having a trailing edge region at which the air flow separates from the guide element. At least the trailing edge region includes at least two walls arranged essentially in parallel and connected to one another by ribs in such a way as to form internal cooling passages. The guide element is cooled on the inside with cooling medium flowing through the cooling passages, the cooling medium discharging from the guide element at the trailing edge essentially parallel to and between the walls.
A gas turbine includes a multiplicity of components which are subjected to a flow of hot working air. Since the working air is at a high temperature which may lead to pronounced wear phenomena on many of the components, in particular during a prolonged operating period, it is necessary to cool many of these components. The cooling may be designed as internal cooling, in which the elements are designed as hollow profiles or are simply provided with internal cooling passages through which a cooling-air flow is directed. Alternatively or in addition, it is also possible to provide film cooling, in which a cooling-air film on the outside is applied to the elements.
Modem gas-turbine blades generally use a combination of the above methods, i.e. an internal convective cooling system which additionally has openings for film blowing at critical points is used. In order to increase the efficiency and the output of the gas turbine, and in order to reduce the emissions, the quantity of cooling air used must be minimized. This means that only a small cooling-air mass flow is available even for large components. In order to realize and control the small cooling mass flows with efficient internal heat transfer, which is required at the same time, the cross sections of flow must be reduced accordingly, or choke cross sections must be introduced.
In many of the known blade designs, the choking of the cooling mass flow takes place in the region of the trailing edge of a cast blade, in the vicinity of the cooling-air outlet. For reasons including production reasons, the end of the ribs which connect the pressure-side and suction-side walls in conventional blades are set back in the axial direction in order to avoid core fractures, i.e., the ribs end in the interior of the blade and do not extend up to the trailing edge.
FIG. 1
shows a section through a conventional guide blade, as often used in gas turbines. This is a section through a guide blade as typically used directly downstream of the combustion chamber and in front of the first moving row of the gas turbine. The section is taken axially to the main axis of the turbine and perpendicularly to the blade-body plane. The guide blade provides optimum incident flow to the moving blades. The blade is designed as a hollow profile, which is defined on the suction side by a wall
10
and on the pressure side by a further wall
11
. In the incident flow region, the blade is widened, the walls
10
and
11
are connected to one another in a rounded portion, and a central, radially running insert
12
, around which the cooling passage leads, is located between the walls
10
and
11
. In the rear or trailing edge region, the guide blade
30
is defined only by the two walls
10
and
11
, and cooling passages run in between the walls
10
and
11
, which are connected to one another by interrupted ribs running in the axial direction. The central insert
12
is often completely or partly enclosed by approximately axially running ribs. These ribs converge at the rear end of the insert (
16
in
FIG. 1
) and from this point on connect the suction- and pressure-side blade walls. Approximately axial passages, in which the cooling air is directed, are formed between the ribs.
In its further course, the rib bank may be interrupted in order to produce a plenum
18
running in the radial direction. The following rib bank
17
may be arranged both in line with or offset from the previous rib bank. In the region of the trailing edge, the pressure and suction-side walls are connected to one another by very short ribs or pin rows. In conventional guide blades, the built-in components, such as the ribs and pins, are positioned inwardly from the blade ends. This avoids the situation in which the core required for casting the blade has a large change in cross-sectional area at the trailing edge. A considerable nonuniformity in the core cross-sectional profile leads to a high number of core fractures during production. However, the above-described conventional method for forming a blade has the considerable disadvantage that the outlet cross section of the cooling air and thus of the cooling-air mass flow can not be adequately controlled.
In addition, the walls of a guide blade usually have film-cooling holes
13
-
15
, through which cooling air can flow to the outside.
This configuration of the internal convective cooling system has a number of disadvantages:
Since the cross section is small, even small tolerances during the production (casting) have an effect on the cooling-air mass rate of flow.
Since the choke point lies in the interior of the guide element, the effective choke cross section can only be measured and checked with difficulty.
Since the choke edge lies in the interior of the guide element, the effective choke cross section can only be subsequently modified with difficulty.
The two usually very thin walls are extremely susceptible to damage which is caused by foreign bodies in the hot gas and which may possibly even lead to a change in the choke cross sections.
Due to the gradual expansion of the cooling air (1) at the end of the ribs and (2) at the trailing blade edge, the cooling-air mass flow can be controlled and adjusted only with difficulty.
SUMMARY OF THE INVENTION
In view of the above-discussed disadvantages of conventional gas-turbine guide elements, the invention provides a gas-turbine guide element around which a hot air flows. The guide element has a trailing edge region at which the air flow separates from the guide element, with at least the trailing edge region including at least two walls arranged essentially in parallel and connected to one another by ribs in such a way as to form internal cooling passages. The guide element is cooled on the inside with cooling medium flowing through the cooling passages, and the cooling medium discharges from the guide element at the trailing edge essentially parallel to and between the walls.
The invention provides the guide element of the type described above with at least some of the ribs arranged so as to terminate essentially flush with the trailing edge. The arrangement of some of the ribs connecting the walls directly at and essentially flush with the trailing edge makes these ribs and the passages in between them more accessible and stabilizes the walls in the edge region more effectively. As a result, the walls in the trailing edge region are substantially less susceptible to damage caused by foreign bodies entrained in the working air flow. In addition, the rate of flow of cooling medium between the ribs arranged at the trailing edge can be reworked or adapted substantially more easily than with conventional guide elements after the production process or during maintenance as a result of the good accessibility.
In a first embodiment of the invention, the rate of flow of cooling medium through the guide element is essentially determined by the dimensioning of the outlet openings arranged between the ribs at the trailing edge, generally referred to as choke ribs. The better accessibility and ease of reworking due to the arrangement are especially advantageous when the choking of the cooling-air circulation is effected by the choke ribs arranged at the trailing edge, and the choking can easily be set or even measured from outside by boring or other processes.
In another embodiment of the inventio
Beeck Alexander
Ferber Jörgen
Nagler Christoph
Schneider Lothar
Semmler Klaus
Alstom (Switzerland) LTD
Burns Doane Swecker & Mathis L.L.P.
Lopez F. Daniel
McAleenan James M
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