Cooling duct arrangement within a hollow-cast casting

A cooling passage arrangement is provided inside a hollow-cast cast part, with a flow region, delimited by at least two spaced apart cast-part walls, for a cooling medium. The flow region is divided in the flow direction into two cooling passages by at least one rib line which is connected to the two cast-part walls. At least one gap is provided along the at least one rib line. At the least one gap, two rib ends are oppositely disposed a distance apart, of which one rib end has a contour in the style of a “wish bone -“Y”-cross-section”.

TECHNICAL FIELD

The invention relates to a cooling passage arrangement inside a hollow-cast cast part, with a flow region, delimited by at least two spaced apart cast-part walls, for a cooling medium, which flow region is divided in the flow direction into two cooling passages by at least one rib line which is connected to the two cast-part walls.

BACKGROUND OF THE INVENTION

Hollow-cast cast parts with cooling passage arrangements inside the walls refer within the spirit of the invention primarily to components which are to be integrated into gas and steam turbine plants and are exposed to high process temperatures for service-induced reasons and require effective cooling for avoiding thermally induced material degradations. Especially stator blades and rotor blades within turbine stages, which are directly exposed to the hot gases of a gas turbine process, constitute such cast parts. As a rule, the cooling of such blading arrangements is carried out by means of cooling air which is tapped off on the compressor side and fed via openings inside the respective blade roots into the blade airfoils, which have cavities, for cooling purposes.

For illustration of the previously applied cooling technique of stator blades for use in gas turbine plants reference may be made toFIGS. 2aandbwhich show a known per se stator blade with a stator-blade platform1and also a stator-blade shroud2, between which extends the stator-blade airfoil3with a stator-blade leading edge4and a stator-blade trailing edge5. For cooling the stator blade3, formed hollow inside, which is shown partially cut away inFIG. 2afor illustrating the inner hollow cooling passage arrangement, cooling air K finds its way both through openings inside the stator-blade shroud2and inside the stator-blade platform1. For effective cooling of the stator-blade airfoil3, in the interior of the stator blade there are flow contours which ensure a thermal contact which is as intimate as possible between the supplied cooling air and the inner side, which is to be cooled, of the stator-blade wall. In particular, in the flow region directly upstream to the trailing edge5, which is shown enlarged inFIG. 2b, there are rib lines6, extending in the flow direction, which delimit individual cooling passages7from each other in each case. The rib lines6, which are oriented parallel to each other, are connected in each case on both sides to the oppositely disposed stator-blade inner walls and therefore close off two directly adjacent cooling passages7from each other. For improving the cooling effect in this flow region, provision is made along the cooling passages7for a large number of individual peg-like connecting lands, so-called pins8, between the spaced-apart oppositely disposed inner sides of the stator-blade walls, as a result of which cooling air experiences an effective mixing-through and therefore comes into intimate contact with the inner sides of the stator-blade walls.

For producing such filigrane cooling structures inside a stator blade or rotor blade which is to be produced by way of a casting process, so-called lost cores are required for the casting process, in which core the negative contours of all the structures which are to be provided inside the cast part, especially the flow contours which influence the cooling air flow, are to be incorporated. In order to form for example the rib lines6which are shown in the detailed view according toFIG. 2band also the peg-like pins8, which for better illustration are shown again inFIG. 3ain a plan view, it is necessary to provide a casting core9, similarly shown inFIG. 3bin plan view, which has to be provided for creating the individual rib lines via groove-like recesses10and for creating through-holes11corresponding to the peg-like pins8. The entirety of all the recesses which are to be provided inside the casting core9lead eventually to extensive perforation of the casting core and contributes decisively towards mechanical weakening of the casting core so that ultimately mechanical stability limits are reached and exceeded, these limits no longer allowing a damage-free machining and ultimately the forming of the extremely small flow contours inside the cast part. In order to stabilize the casting core, modifications have been undertaken especially during the forming of the previously described rib lines so that the casting core provides connecting lands12, which stabilize the casting core, transversely to the longitudinal extent of the respective rib lines. As a result of this measure, however, the rib lines6are no longer formed continuously in the finished-cast cast part, as is to be gathered from the view inFIG. 4, but where the connecting lands12were provided in the casting core now have corresponding gaps13(seeFIG. 4b).

If previously continuously formed rib lines6were able to completely separate the cooling air flows K contained inside the cooling passages7from each other, as is shown in the schematized plan view inFIG. 4a, then by providing corresponding gaps13along the rib lines6, attributable to the stabilizing connecting lands12inside the casting core, cooling air flows K′, which branch off through the gaps13, now occur and are able to irritate the cooling air flow in the adjacent cooling passages. This, however, reduces the cooling efficiency of the cooling air which passes through the cooling passages7so that measures have to be sought with which the cooling air flow portions which pass through the gaps13can be avoided.

SUMMARY OF THE INVENTION

The invention is based on the object of further developing a cooling arrangement inside a hollow-cast cast part, with a flow region, delimited by at least two spaced apart cast-part walls, for a cooling medium, which flow region is divided in the flow direction into two cooling passages by at least one rib line, which is connected to the two cast-part walls, in such a way that on the one hand the adopted measures for stabilizing the casting core which is required for producing the cast part shall largely remain uninfluenced, but the cooling effect of the cooling medium which passes through the cooling passage arrangement shall be noticeably improved.

The achieving of the object which forms the basis of the invention is disclosed in the exemplary embodiments below. Advantageous features which develop the inventive idea are to be gathered from the further description with reference to the exemplary embodiments.

According to the solution, a cooling arrangement inside a hollow-cast cast part according to the features of the exemplary embodiments disclosed herein is formed in such a way that provision is made along the at the least one line of ribs for at least one gap at which two rib ends face each other in a spaced apart manner, of which one rib end has a contour in the style of a “wish bone -“Y”-cross-section”. By means of such a flow contour, it is possible, as the further embodiments will show, to largely or completely prevent a flow of cooling medium through the gap along a rib line.

The measure according to the solution simply requires an additional contour along the rib line in the region of a gap, as a result of which the stability of a casting core is in no way negatively affected. Also, with the measure according to the solution it is possible to provide connecting regions between the cooling passages which are separated by the rib lines in order to realize a compact and mechanically stable casting core.

For illustration of the idea according to the solution, reference is made to the following illustrated exemplary embodiments.

WAYS OF IMPLEMENTING THE INVENTION, INDUSTRIAL APPLICABILITY

FIG. 1ashows the region of a gap13along a rib line6, wherein two rib ends61,62along the rib line6face each other a distance apart. In the pictorial representation according to theFIG. 1a, it may be assumed that a cooling medium flow K along the rib line heads in the flow direction which is indicated by means of the arrows. The rib end61, which is provided upstream to the gap13, in this case according to the solution has a contour14in the style of a wish bone -“Y”-cross-section, as a result of which the cooling medium flow K does not pass through the gaps13within the limits of crossflows K′, as in the illustrated exemplary case inFIG. 4b, but in each case flows past the gap13along the respective cooling passage7on both sides. As a result of the rib end contour14, which is formed in the style of a wish bone -“Y”-cross-section, at the rib end61, the flow portions which are contiguous to the rib6on both sides are deflected transversely to the longitudinal extent of the rib line6. The contour14which is formed in the style of a wish bone -“Y”-cross-section preferably has an extent, oriented transversely to the longitudinal extent of the rib, which corresponds at least to 1.5 times the respective rib width d. The rib-end contour14which is formed in the style of a wish bone -“Y”-cross-section is optimized from the flow-dynamics point of view and has a surface contour which is round and therefore reduces flow resistance. The axial distance between the two oppositely disposed rib ends61,62along the gap13should not exceed three times the length of the lateral extent D of the contour14which is formed in the shape of a wish bone -“Y”-cross-section.

By means of the fluidic simulations, the effect of avoiding a passage of cooling medium through the respectively existing gaps13along a rib line6could be demonstrated and proven. A graphic simulation result is shown inFIG. 1b. Here, the dark line regions indicate the presence of cooling medium and it may be assumed that the flow region which is shown inFIG. 1bis exposed to throughflow with cooling medium K from left to right. As a result of the rib-end contour14which is formed in the style of a wish bone -“Y”-cross-section, which is formed upstream of the gap13, those flow portions which find their way through the gap13from a cooling passage7into the adjacent cooling passage can be demonstrably reduced to a minimum. In this way, it is possible to ensure the cooling efficiency of the cooling medium K inside a cooling passage7, despite the provision of construction-related gaps13.

In a flow region which, as inFIG. 5, has a plurality of rib lines6, which are oriented parallel to each other, for mutual separation of cooling passages7, it has advantageously become apparent that particularly good flow results are achieved if the rib-end contours in the style of a wish bone -“Y”-cross-section are provided in an arrangement and distribution which is evident fromFIG. 5. Here, it may be assumed that provision is made for three rib lines6which extend next to each other and along which gaps13are provided in each case for reasons of a more stable forming of the casting core. It may be additionally assumed that the cooling passages7which are located between the rib lines6are exposed to throughflow by cooling air K with the flow direction which is indicated by means of the arrows. An additional view of the pins, which are formed in a peg-like manner and located along the cooling passages7, is dispensed with for reasons of improved clarity, although in reality these are to be correspondingly provided. Along the uppermost rib line6in the pictorial representation according toFIG. 5, the contours14which are formed in the style of a wish bone -“Y”-cross-section are provided in each case on the upstream rib end to each individual gap13. In the middle rib line which is directly adjacent thereto, however, the dog-bone contour14is provided on the downstream end to each individual gap13along the rib line. In the lower rib line, the contours14which are formed in the style of a wish bone -“Y”-cross-section are again uniformly on the upstream rib end in each case at the position of each gap13. In addition, in this rib-line arrangement it is necessary to take into consideration the fact that the gaps along a rib line in each case are not mutually overlapped by the gaps along an adjacent rib line in the direction transversely to the rib-line longitudinal extent, as is to be gathered fromFIG. 5.

It could be demonstrated that with the arrangement illustrated inFIG. 5of the rib-end contours14which are formed in the style of a wish bone -“Y”-cross-section, a very high cooling efficiency can be achieved, which can ultimately be accounted for by the minimizing of the flow portions which pass through the gaps13.

LIST OF DESIGNATIONS

1Stator blade platform2Stator blade shroud3Stator blade airfoil4Stator blade leading edge5Stator blade trailing edge6Rib line7Cooling passage8Pins of peg-like design9Casting core10Groove-like recess inside the casting core11Hole-like recesses inside the casting core12Connecting region, connecting land13Gap14Contour formed in the style of a wish bone -“Y”-cross-section61,62Rib endsK Cooling mediumD Lateral extent of the contour formed in the style of a wish bone -“Y”-cross-sectiond Rib thicknessK′ Cooling-medium flow portions which pass through the gap13