The present invention relates to a component of a flow machine, particularly a turbine blade, which has a cooling channel through which a cooling medium can flow and which has at least one deflection formed by the wall of the cooling channel and deflecting the flow of the cooling medium from a first channel section into a downstream second channel section, wherein at least one flow guiding element, by which the cooling channel is divided in the deflection into an inner and an outer flow channel, is arranged in the cooling channel in the region of the deflection.
In the field of flow machines, particularly gas turbines, increasingly higher temperatures are sought and put into practice for increasing the power output. The higher temperatures are attained on the one hand by advances in materials technology toward higher permissible material temperatures, and on the other hand by improved cooling of the components which are exposed to the high temperatures. Precisely in the gas turbine field, the necessity exist here to further improve the cooling for new generations of gas turbine blades.
A known cooling method for the cooling of gas turbine blades is internal, convective cooling. In this cooling method, cooling air is introduced through the rotor shaft into the blade foot and from there into cooling channels running within the turbine blade, in which it takes up the heat of the turbine blade. The heated cooling air is finally blown out of the turbine blade through suitably arranged bores and slits.
An exemplary course of the cooling air channels in a gas turbine blade (according to Thalin et al., 1982: NASA CR 1656087) is shown in FIG. 1. The cooling air enters the turbine blade via the blade foot 1, is conducted via a cooling channel 2 as far as the rear side of the blade, and is finally blown out through corresponding aperture slits 3. In the example shown in FIG. 1, a separate cooling channel 2a is additionally provided, via which a portion of the cooling air is conducted to the front side and tip of the blade, to emerge there via corresponding apertures 4. The flow course of the cooling air within the turbine blade is indicated by the arrows.
In a typical course of the cooling air channel, 180xc2x0 deflections 5 are required in the neighborhood of the blade tip or blade foot, to connect together the different sections of the cooling air channel 2. However, complicated flow patterns develop in the region of this deflection 5, with eddies which lead to large pressure losses over the length of the cooling air channel 2 and thus require an increased pump power for the transport of the cooling air. Furthermore, areas of low heat transfer to the turbine blade arise in these regions and lead to local temperature peaks on the outer skin of the turbine blade.
FIG. 2 shows schematically a detail of a cooling air channel 2 with a deflection 5, in which the recirculation areas, i.e., the areas which generate the high pressure losses, are denoted by the reference numeral 6. The flow course of the cooling medium is again shown by the arrows. Besides the pressure loss, the recirculation areas have only a small throughflow, so that areas of low heat transfer are present here.
The pressure loss over the length of the cooling channel is reduced by the technical developments known heretofore, by suitable arrangement of flow-conducting elements such as are apparent from FIG. 1.
An arrangement is known from U.S. Pat. No. 5,073,086 in which a flow guiding element is arranged in the cooling channel in the region of the deflection, and divides the cooling channel completely into an inner and an outer flow channel. The pressure loss brought about by the deflection can admittedly be reduced by this complete division of the flow; however, a clearly homogeneous removal of heat from the region of the deflection is not thereby attained. On the contrary, new areas of low heat transfer arise in the region of the flow guiding element constituted as a deflection guiding metal sheet.
The present invention has as its object to provide a component of a flow machine with improved cooling, by which the pressure loss is reduced in the region of the deflections of the cooling channel, and a homogeneous heat transfer is attained.
The object is attained with the component according to patent claim 1. Advantageous embodiments of the component are the subject of the dependent claims.
The proposed component of the flow machine, as a rule a turbine blade, has in a known manner a cooling channel through which cooling medium can flow, with at least one deflection formed by the wall of the cooling channel and deflecting the flow of the cooling medium from a first canal section into a downstream second channel section. In the region of this deflection, a flow guiding element, for example, in the form of a deflection guiding metal sheet, is arranged in the cooling channel in the present component, and divides the cooling channel completely into an inner and an outer flow channel in the deflection. The present component is distinguished in that the inner flow channel has a constriction in the flow cross section. By means of this constriction, i.e., a narrowing followed by a widening again of the flow cross section, a nozzle effect occurs in the inner flow channel and advantageously increases, and at the same time homogenizes, the heat transfer by means of the acceleration of the flow. The constriction is preferably formed by a suitable shaping or contouring of the flow guiding element and/or of the wall of the cooling channel in the region of the deflection.
By the proposed solution, a reduction of the pressure losses in the deflection is attained, with simultaneous homogenization of the heat transfer between the cooling medium and the wall material of the component. The present embodiment is independent of the further configuration of the component, and in particular independent of the rib configuration in the first and second channel sections, termed hereinafter the inlet channel and outlet channel, and also of possible roundings at the outer edge regions of the deflection. Such details, which occur in numerous gas turbine blades, have no influence on the advantageous effect of the present invention.
In a very advantageous further development of the component, one or more outlet bores for the cooling medium are additionally formed in the outer flow channel of the deflection, in the wall of the cooling channel for the cooling medium, via which bores a small portion of the cooling medium can emerge from the cooling channel. This so-called blowing out of cooling airxe2x80x94in the case of air as the cooling mediumxe2x80x94again contributes, in connection with the already explained features, to a distinct improvement of the heat transfer, so that a component is obtained in which, on the one hand, local temperature peaks no longer occur in the region of the deflection, and on the other hand, high average values of the heat transfer to the cooling medium are attained. By the arrangement of these outlet bores in corner regions of the deflection, in which eddy areas otherwise occur, a clearly improved heat transfer is attained just there. The bores lead to breaking up the eddy areas and thus contribute to a homogenization of the heat transfer. Furthermore, these bores bring about the desired side effect that dust particles in the cooling medium are blown out through the bores. To amplify this side effect, the longitudinal axes of the bores are aligned about in the direction of the local flow lines of the flow of the cooling medium in the cooling channel.
Because of the small boundary flow speed, the additional bores provide only a small contribution to the global pressure loss over the cooling channel, hardly perceptible, however, due to the advantageous effect of the abovementioned features for minimizing the pressure loss.
The constriction of the flow cross section in the inner flow channel of the deflection, i.e., in the flow channel which has the shortest flow path in the deflection, which is required for the best possible functioning of the present invention, can be attained on the one hand by corresponding shaping of the flow guiding element, for example, by a thickening, and on the other hand by a corresponding shaping of the channel wall opposite the flow guiding element in the inner flow channel. The constriction can of course also be attained by a corresponding shaping of both elements, or of the further wall regions surrounding the inner flow channel.
In an advantageous embodiment, in which the first and second channel sections run approximately parallel on either side of a partition which forms a side of the wall of the cooling channel, the thickness of the partition increases in the region of the deflection, in order to bring about the corresponding constriction within the inner flow channel by means of this increase of thickness. Different shapes are possible for the contouring of this partition which separates the outlet channel from the inlet channel in order to bring about the said effect.
The flow guiding element which divides the cooling channel in the deflection into an inner and an outer flow channel is as a rule constituted as a flow guiding metal sheet. Preferably this flow guiding element extends a certain distance as far as into the second channel section or outlet channel. The distance by which the flow guiding element extends into the second channel section preferably corresponds to about the distance between the flow guiding element and the opposite wall of the cooling channel in the inner flow channel at the inlet or outlet of the deflection. An extension of the division of the cooling channel into an inner and an outer flow channel is attained by the extension of the flow guiding element. A slight constriction or widening of the channel cross section can be provided at the outlet of the inner flow channel, so that the wall of the flow guiding element in this region does not have to run unconditionally parallel to the channel wall of the second channel section or outlet channel.
The flow guiding element is preferably constituted and arranged within the deflection such that about 25-45% of the mass flow of the flow entering the deflection from the inlet channel enters in the region within the flow guiding element, i.e., in the inner flow channel, and the remainder flows outside the flow guiding element, i.e., in the outer flow channel. The mass flow ratio corresponds to the inlet cross section surface ratio of the outer and inner flow channels. The surface ratio at the outlet channel should about correspond to that of the inlet channel, i.e., it is not to deviate by more than 20% from this ratio. The deflection guiding metal sheet, as a rule of a round shape, can of course vary in thickness, or else even furthermore be provided with guiding devices.
In a further preferred variant of the invention, the flow guiding element has means which prevent a collection of dust or dirt in one of the flow channels. This can, for example, be attained in that the flow guiding element is equipped with passage apertures or otherwise configured in a suitable manner.
By the total of the measures or features set out in the developments, i.e., by the optimizing of the geometry and by the blowing out of cooling air at critical places, an optimized cooling is attained in the region of the deflecting element, with minimized pressure loss. The individual measures are here independent of the specific geometry of the components and of the cooling channel, and can, for example, also be replaced with cooling channel deflections whose deflection angle is not equal to 180xc2x0. Furthermore, the present invention is not limited to turbine blades nor to gas-cooled components, but can also be used, in particular, for components with other flowing cooling media.