Turbine blade with internal cooling passage

Abstract: Object of the present invention is to make it possible to cool members to be cooled effectively with small amount of cooling air. According to the present invention, turbulence promotor ribs are so formed that cooling fluid along a wall flows from center of the wall to both ends portions of the wall. In accordance with the above described structure, highly enhanced thermal conducting effect, namely high cooling heat transfer coefficient, can be obtained, and it becomes possible to cool members effectively with small amount of cooling air.

Description: The present invention relates to improvement of a member having at least one internal cooling passage, especially, to improvement of a member having an internal cooling passage whose wall possesses cooling ribs. There are various members having internal cooling passages, but prior art is explained hereinafter taking the most representative gas turbine blade for an example. A gas turbine is an apparatus for converting high temperature and high pressure gas generated by combustion of fuel with high pressure air compressed by a compressor as an oxidant to such an energy as electricity by driving a turbine. Consequently, the more electrical energy obtained by consumption of a unit of fuel as possible is naturally preferable, and in view of the above described aspect, improvement of the gas turbine performance is expected. And, as one of the methods for improvement of the gas turbine, elevation of temperature and higher pressurizing of operating gas have been studied. On the other hand, a method for improvement of total energy conversion efficiency including the gas turbines and steam turbines by elevation of operating gas temperature of the gas turbine and combining with the steam turbine system utilizing high temperature exhausting gas in forming a combined plant has been proposed. Operating gas temperature of the gas turbine is restricted by durable capacity of the turbine blade material against hot corrosion resistance and thermal stress caused by the gas temperature. In elevating of the operating gas temperature higher, a method for cooling the turbine blade by providing hollowed portions, namely cooling flow passage, in the turbine blade itself, and flowing coolant such as air in the cooling flow passage is conventionally well adopted. Concretely saying, at least one cooling flow passage is formed inside of the turbine blade, cooling the turbine blade from inside by flowing cooling air through the cooling flow passage, and, further, surface, top end, and trailing edge of the turbine blade are cooled by releasing cooling air out of the blade through cooling holes provided at the above described cooling portions. As for the above described cooling air, a part of air bled from a compressor is generally utilized. Accordingly, a large amount of cooling air consumption causes dillution of gas temperature and increase of pressure loss. Therefore, it is important to cool effectively with less quantity of cooling air. For realizing a gas turbine using higher temperature, it is important to improve heat transfer characteristics inside of the turbine blade for increased cooling effect of supplied cooling air, and various methods for heat transfer enhancement are used. As one of the methods for heat transfer enhancement, there is a method to provide a plurality of ribs on the wall of cooling passages inside of the turbine blade because it is well known that heat transfer coefficient can be improved by making air flow on thermal conducting plane surface turbulent or breaking thermal boundary layers etc. An example of the methods using a structure for heat transfer enhancement is disclosed in the reference, "Effects of Length and Configuration of Transverse Discrete Ribs on Heat Transfer and Friction for Turbulent Flow in a Square Channel", ASME/JSME Thermal Engineering Joint Conference, Vol. 3, pp. 213-218 (1991). The disclosed structure for heat transfer enhancement aims to improve heat transfer coefficient by arranging ribs having a half length of flow path width at right and left sides of the flow path alternatively in perpendicular direction to the cooling air flow in order to break down the flow boundary layer and to increase turbulence of the cooling air flow with re-attaching flow, and ratio of the ribs pitch and the rib height is preferably about 10. The second example of the methods using a structure for heat transfer enhancement is disclosed in the reference, "Heat Transfer Enhancement in Channels with Turbulence Promoters", ASME/84-WT/HT-72 (1984). The disclosed structure for heat transfer enhancement aims to improve heat transfer coefficient by ribs arranged perpendicularly or slantingly to the cooling air flow in order to obtain same effect as the above described first example, and the slanting angle of the rib to the air flow is preferably from 60° to 70° view of heat transfer coefficient. And, ratio of the ribs pitch and the rib height is preferably about 10. An example utilizing the above described second example and further being improved in heat transfer coefficient is disclosed in JP-A-60-101202 (1985). The disclosed structure for heat transfer enhancement in the above described reference is a structure having ribs arranged slantingly to the cooling air flow and additionally machined slits. With the above described rib structure for heat transfer enhancement, it is said that further high cooling performance is realized by turbulence of air flow behind the slit, and the slit hinders accumulation of dust around the ribs and, consequently, prevents lowering of heat transfer coefficient. As extracted air sent by a compressor is used for cooling of the turbine blade as previously described, increasing of cooling air consumption lowers thermal efficiency of the gas turbine. Accordingly, it is important to cool the gas turbine effectively with small amount of cooling air. But, the above described conventional cooling structure of turbine blade needed more amount of cooling air in order to meet elevating of operation gas temperature to higher temperature, and improving effect of thermal efficiency of the gas turbine was generally small. US-A-4416585 discloses a turbine blade in which the internal cooling flow passages have an array of turbulence prompting ribs on opposed facing walls. The ribs define chevron shapes between the walls, so that there are first ribs extending obliquely away from the centre line of the array and one side of the centre line, and second ribs extending obliquely away from the centre line on the other side of the centre line. It is stated that the chevrons may point upstream or downstream so that the ends of the ribs nearer the centre line are downstream of upstream of the ends of the ribs further from the centre line. In the illustrated embodiment the chevrons point downstream. Thus, this document discloses the features of the precharacterising part of claim 1. The present invention seeks to provide an enhanced, heat transferring rib structure having a further increased heat transfer coefficient, for taking a gas turbine as an example, which enables the gas turbine blade be effectively cooled with small amount of cooling air, and consequently, to realise a high temperature gas turbine having a high thermal efficiency. According to the present invention there is provided a member having at least one internal cooling flow passage as set out in claim 1. The present invention permits a large heat transfer coefficient to be obtained because the cooling air flow becomes refracted flow in two directions by the ribs, three dimensional turbulent eddy is generated, re-attaching distance of the air flow behind the rib becomes short by the three dimensional turbulent eddy, and vortex generation at the top edge of the rib etc. Embodiments of the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a partial vertical cross section of a turbine blade; Fig. 2 is a cross section along the A-A line in Fig. 1; Fig. 3 is a cross section along the B-B line in Fig. 2; Fig. 4 is a cross section along the C-C line in Fig. 2, Fig. 5 is a perspective view illustrating cooling passages; Fig. 6 is a graph illustrating experimental results on thermal conducting characteristics; Fig. 7 is a graph illustrating experimental results on thermal conducting characteristics, FIG. 8 is a cross section around a cooling flow passage, FIG. 9 is a cross section around a cooling flow passage, FIG. 10 is a cross section around a cooling flow passage, FIG. 11 is a cross section around a cooling flow passage, FIG. 12 is a cross section around a cooling flow passage, FIG. 13 is a cross section around a cooling flow passage, FIG. 14 is a cross section around a cooling flow passage, FIG. 15 is a cross section around a cooling flow passage, and FIG. 16 is a perspective view illustrating cooling flow passages. Details of the present invention is explained based on the embodiments referring to drawings. FIG. 1 illustrates a vertical cross section of a gas turbine blade (a member) 1 adopting the present invention, wherein each of the numerical, 2 is the shank, 3 is the blade portion, 4 and 5 are a plurality of internal flow passage (cooling medium flow passages) provided from internal of the shank 2 to internal of the blade portion 3. The internal flow passages 4 and 5 are separated at the blade portion 3 by a plurality of partition walls 6a, 6b, 6c, and 6d into a plurality of cooling flow passages 7a, 7b, 7c, and 7d, and form surpentine flow passages with top end bending portions, 8a and 8b, and lower end bending portions, 9a and 9b. That means, in the present embodiment, the first internal flow passage 4 is composed of the cooling flow passage 7a, the top end bending portion 8a, the flow passage 7b, the lower end bending portion 9a, the flow passage 7c, and the blowout hole 11 provided at the top end wall of the blade 10. Similarly, the second internal flow passage 5 is composed of the cooling flow passage 7d, the top end bending portion 8b, the flow passage 7e, the lower end bending portion 9b, the flow passage 7f, and the blowout portion 13 provided at the blade trailing edge 12. Cooling air is supplied from a rotor shaft(not shown in the figure), on which the blade 1 is installed, to the air flow inlet 14, and cools the blade from inside during passing through the internal flow passages 4 and 5. After cooling the blade, the air flow 15 is blown off into main operating gas through the blowout hole 11 provided at the top end wall of the blade 10 and the blow out portion 13 provided at the blade trailing edge 12. The ribs for improvement of heat transfer coefficient according to the present invention are provided integrally on cooling wall surface of the cooling flow passages 7a, 7b, 7c, and 7d. The rib for improvement of heat transfer coefficient is formed in a special shape slanting to the flow direction of cooling air in the cooling flow passage. That is, the rib for improvement of heat transfer coefficient is so formed that cooling medium along the wall flows from center of the wall to both end portions of the wall as FIG. 1 illustrated. Further detail of the structure and the operation is explained hereinafter referring to FIGs. 2 to 5. Referring to FIG. 2, the numerical 20 and 21 indicate blade suction side wall and blade pressure side wall respectively which compose blade portion 3 of the turbine blade 1, and the cooling flow passages 7a, 7b, 7c, and 7d are composed of the blade suction side wall 20, the blade pressure side wall 21, and partition walls 6a, 6b, 6c, and 6d. For instance, the cooling flow passage 7c is composed of the blade suction side wall 20, the blade pressure side wall 21, and partition walls 6b and 6c. Shape of the above described cooling flow passage differs depending on the design, and the shape is trapezoid or rhombus but mostly rectangle. The ribs for improvement of heat transfer coefficient 25a and 25b, which are formed integrally with the blade suction side wall 20, are provided on the back side cooling plane 23 of the cooling flow passage 7c, and the ribs for improvement of heat transfer coefficient 26a and 26b, which are formed integrally with the blade pressure side wall 21, are provided on the front side cooling plane 24. FIG. 3 is a vertical cross section of the cooling flow passage illustrating the B-B cross section in the FIG. 2, and the ribs for improvement of heat transfer coefficient, 25a and 25b, at the back side cooling plane 23 are arranged right and left alternatively from almost center of the back side cooling plane 23 with different angles to the cooling air flow direction. That is, the rib for improvement of heat transfer coefficient 25a is provided with an angle α in a counterclock direction to the cooling air flow direction and the rib for improvement of heat transfer coefficient 25b is provided with an angle β, as if the V-shaped staggered ribs are arranged in a manner to place the rib tops 29a and 29b at upstream side to the cooling air flow. Similarly, FIG. 4 illustrates the C-C cross section in FIG. 2. In FIG. 4, the ribs for improvement of heat transfer coefficient 26a and 26b at the front side cooling plane 24 are arranged right and left alternatively from almost center of the front side cooling plane 24 with different angles to the cooling air flow direction. That is, the rib for improvement of heat transfer coefficient 26a is provided with an angle α to the cooling air flow direction and the rib for improvement of heat transfer coefficient 26b is provided with an angle β, and forms the V-shaped staggered ribs structure. Value of the α is preferably between 95°and 140°, and value of the β is preferably between 40° and 85°. The cooling flow passage 7c for cooling air ascending flow (in FIG. 1)is illustrated in FIGs. 3 and 4. In case of the cooling flow passage for cooling air descending flow, the same V-shaped staggered ribs structure is naturally applied. Next, cooling air flow in the vicinity of the cooling wall depending on the ribs for improvement of heat transfer coefficient relating to the present invention is explained referring to FIG. 5. FIG. 5 is a schematic perspective view of the cooling flow passage 7c. The cooling air flow 15 becomes a saw toothed refractive turbulent flow 27a and 27b by the ribs for improvement of heat transfer coefficient 25a and 25b which are slanting to the air flow direction reversely each other at the back side cooling plane 23, and three dimensional rotating turbulent eddy 28a and 28b are generated behind the ribs. Consequently, increased cooling side heat transfer coefficient can be obtained. Further, the top end edge (head portion) of the ribs 29a and 29b are exposed to the cooling air flow, and much higher cooling heat transfer coefficient can be obtained by synergetic effects. Same effects to improve heat transfer coefficient exist at the front side cooling plane 24, but explanation on the effects is omitted. The above described effects of heat transfer enhancement were confirmed by model heat transfer coefficient experiments. The experiments were performed on the first example of prior art structure, the second example having slanting ribs structure possessing slits disclosed in JP-A-60-101202 (1985), and the structure relating to the present invention, and heat transfer coefficient characteristics of each examples were compared. Shapes of each experimental models and experimental conditions are shown in Table 1. ITEMS PRIOR ART 1 PRIOR ART 2 PRESENT INVENTION SHAPE OF RIB RIB HEIGHT 0.7 mm 0.7 mm 0.7 mm RIB WIDTH 0.7 mm 0.7 mm 0.7 mm RIB PITCH 7 mm 7 mm 7 mm α 110° RIB ANGLE 90 ° 110° β 70° SLIT WIDTH - 0.5 mm - PATH WIDTH 10 mm 10 mm 10 mm PATH HEIGHT 10 mm 10 mm 10 mm EXPERIMENTAL CONDITION MEDIUM AIR AIR AIR EXPERIMENTAL 1.5×10 4 ∼ 1.5×10 4 ∼ 1.5×10 4 ∼ RANGE, Re 1.5×10 5 1.5×10 5 1.5×10 5 Re: Reynolds number The experimental model formed a rectangular flow passage which was 10 mm wide and 10 mm high, and a pair of facing planes was used as heat transferring planes having the ribs for improvement of heat transfer coefficient, and another pair of facing planes was used as insulating layers. As Table 1 reveals, each of the ribs for improvement for heat transfer coefficient is almost equivalent in its shape (because rib height, rib width, and rib pitch (pitch/rib height = 10) are all same). The experiment were performed in such a manner that heat transferring plane side was heated and low temperature air was supplied into the cooling flow passage. Results of the experiments on heat transfer coefficient characteristics are shown in FIG. 6 in comparison of the results each other. Referring to FIG. 6, the comparison was performed with the abscissa indicating Reynolds numbers which express flow condition of the cooling air and the ordinate indicating a ratio of a average Nusselt number which expresses flow condition of heat and an average Nusselt number of flat heat transfer surface without ribs for improvement of heat transfer coefficient. In FIG. 6, the larger value in the ordinates with a constant Reynolds number (same cooling condition) indicates preferable cooling performance. As FIG. 6 reveals, thermal conducting performance of the structure relating to the present invention is clearly preferable in comparison with the conventional structures. Under the condition of Reynolds number 10 which is close to the cooling air supply condition in rated gas turbine operation, the structure relating to the present invention has higher heat transfer coefficient by about 18 % in comparison with the prior art 1, and by about 20 % in comparison with the prior art 2. That reveals superior performance of the structure relating to the present invention. In the model heat transfer coefficient experiment, effect of the ratio of the pitch and height of the ribs for improvement in heat transfer coefficient with the structure relating to the present invention on heat transferring performance was confirmed. In FIG. 7, the effect of improvement in heat transfer coefficient is shown with the abscissa which indicates the ratio of pitch and height of the ribs for improvement of heat transfer coefficient. The case shown in FIG. 7 is under the cooling condition of Reynolds number 10 . As FIG. 7 reveals, remarkable effect for improvement of heat transfer coefficient is realized in a range of the ratio of pitch and height of the ribs for improvement of heat transfer coefficient between 4 and 15. The improving effect of heat transfer coefficient of the above described conventional structure is said to be remarkable when the ratio of pitch and height of the ribs for improvement of heat transfer coefficient is about 10, but the structure relating to the present invention realizes the remarkable improving effect of heat transfer coefficient in a wider range of the ratio. The reasons are that the cooling air flow becomes saw teethed refractive turbulent flow by the ribs for improvement of heat transfer coefficient which are provided reverse-slantingly each other to the cooling air flow, further, three dimensional rotating turbulent eddy is generated behind the ribs, and high cooling heat conductance is obtained by exposing the top end edge of the rib to the cooling air flow. Especially, the three dimensional rotating turbulent eddy behind the rib shortens the reattaching distance of the cooling air behind the rib by rotating power of the eddy itself, and more preferable effect to the prior art is obtained. The above description explains a fundamental structure of the present invention, but, further, various embodiments, modifications, and applications are available. Other structure examples of the ribs for improvement of heat transfer coefficient being applied the present invention are illustrated in FIGs. 8-11 all of which are shown as B-B cross sections of the cooling flow passage 7c as same as the above described FIG. 3. The structures of the ribs for improvement of heat transfer coefficient, 30a and 30b, illustrated in FIG. 8 are curved structures in circular arc shape, heads of which, 35a and 35b, are oriented to upstream side of the cooling air flow 15, and the ribs are staggeringly arranged right and left alternatively to the cooling air flow direction. The structures of the ribs for improvement of heat transfer coefficient, 31a and 31b, illustrated in FIG. 9 are same structures as the ribs in the above described first embodiment except that top ends of the partition plates, 5a and 6b, of the ribs for improvement of heat transfer coefficient, 25a and 25b, are perpendicularly arranged to the cooling air flow direction, heads of which, 36a and 36b, are oriented to upstream side of the cooling air flow 15, and the ribs are staggeringly arranged right and left alternatively to the cooling air flow direction. The ribs for improvement of heat transfer coefficient, 32a and 32b, illustrated in FIG. 10 have structures having a staggering arrangement of chevron shape ribs, of which lower portions, 37a and 37b, are oriented to upstream side of the cooling air flow direction, and, further, the ribs for improvement of heat transfer coefficient, 33a and 33b, illustrated in FIG. 11 have structures having a staggering arrangement of inverted chevron shape ribs, of which head portions, 38a and 38b, are oriented to upstream side of the cooling air flow direction. In any of above described additional embodiments, a large cooling heat transfer coefficient as same as the previously described first embodiment is obtainable without changing aim of the present invention by making saw-teethed refractive turbulent cooling air flow, generating three dimensional rotating turbulent eddy behind the ribs, and exposing the top end edge of the ribs to the cooling air flow. In other words, various shapes such as straight line type, curved line type, and chevron type etc. are usable as for the ribs relating to the present invention, but substantially at least the ribs are staggeringly arranged right and left alternatively to the cooling air flow direction on the cooling planes in the cooling flow passage so that the head portions of the ribs at central side of the cooling planes are oriented to upstream side of the cooling air flow. Modified examples of the present invention are explained taking modification of the previously described first embodiment as examples referring to FIGs. 12-15. Referring to FIG. 12, a structure is illustrated in which gaps, 41a and 41b, are provided between the top ends, 40a and 40b, of the ribs for improvement of heat transfer coefficient, 25a and 25b, at the partition plate, 6a and 6b, side and the partition plates, 6a and 6b. Intensity of turbulence behind the ribs are increased by the cooling air flow flowing through the gaps, 41a and 41b, and accordingly, thermal conducting performance is improved and lowering of thermal conducting performance can be prevented by an effect to hinder stacking of dust. Referring to FIG. 13, a structure is illustrated in which a gap 42 is provided between head portions, 29a and 29b, of the ribs for improvement for heat transfer coefficient, 25a and 25b, at central side of the cooling air path. Referring to FIG. 14, a structure is illustrated in which the head portions, 29a and 29b, of the ribs for improvement for heat transfer coefficient, 25a and 25b, at central side of the cooling air path-are overlapped each other. Further, a structure in which the gaps, 41a and 41b, are provided between top end portions, 40a and 40b, of the ribs for improvement of heat transfer coefficient, 25a and 25b, at the partition plate, 6a and 6b, side and the partition, 6a and 6b, is illustrated in FIG. 15. In any of the modified examples, V-shaped staggered ribs arrangement is taken to be a base, and more improved effect of thermal conducting performance than the previously described embodiments and hindering effect of dust stacking are realized without losing the aim of the present invention. The modified examples illustrated in FIGs. 12-15 are all based on the previously described first embodiment, same modification of other embodiments illustrated in FIGs. 8-11 are possible. The partition walls 6a, 6b, and 6c of the above described gas turbine blade 1 operate as cooling heat removal planes in addition to form the cooling air flow path. In a case of the gas turbine using operating gas of much higher temperature, positive utilization of the partition walls for cooling is preferable. An example of application of the present invention to positive cooling utilizing the partition walls is illustrated in FIG. 16. The example is illustrated in FIG. 16 as a perspective view in comparison with previous first embodiment which is illustrated in FIG. 5 as the perspective view. In FIG. 16, same members as those in FIG. 5 are indicated with same numerical as those in FIG. 5, and 45a and 45b are V-shaped staggered ribs for improvement of heat transfer coefficient formed integrally with the partition wall 6b on the partition wall 6b which forms the cooling flow passage 7c, and the ribs are so provided that the head portions, 46a and 46b, of the ribs are oriented to upstream side of the cooling air flow 15. Similarly, the partition wall 6c is provided with the ribs for improvement of heat transfer coefficient, 47a and 47b. In accordance with the above described structure, a turbine blade for a high temperature gas turbine using an operating gas of higher temperature can be provided. Further, as for shapes of the ribs, 45a, 45b, 47a, and 47b, for improvement of heat transfer coefficient, other structures illustrated in FIGs. 8-11 can be naturally used. Uniform temperature distribution in a gas turbine blade is preferable in view of strength of the blade. On the other hand, external thermal condition of the turbine blade differs depending on locations around the blade. Accordingly, in order to cool the blade to uniform temperature distribution, rib structures for improvement of heat transfer coefficient at suction side of the blade, pressure side of the blade, and partition wall are preferably designed to be matched structures to the external thermal condition. That is, concretely saying, structure, shape, and arrangement of the ribs for improvement of heat transfer coefficient are so selected as to match the requirement of each cooling planes from the ribs illustrated in the above described embodiments or modified examples. The gas turbine is hitherto taken as an example in the explanation, but the present invention is naturally applicable not only to the gas turbine but also to members having internal cooling flow passages as previously described. In the above described explanation, a return flow structure having two internal cooling flow passages is taken as an example, but the example does not give any restriction to number of cooling flow passages in application of the present invention. Further, although the rectangular cross sectional shape of the cooling flow passages is taken as an example in explanation of the above embodiments, shape of the cooling flow passage can be trapezoidal, rhomboidal, circular, oval, and semi-oval etc. And, the explanation is performed with taking air as a cooling medium, but other medium such as steam etc. are naturally usable. The gas turbine blade adopting the structure relating to the present invention has a simple composition and, accordingly, the blade can be manufactured by current precision casting.

Claims: A member (1) having external wall surfaces and at least one internal cooling flow passage (7) for the flow of cooling fluid to cool said member, wherein on a surface of a wall (20, 21) of said member (1) separating the cooling flow passage (7) from said external surface the cooling flow passage is provided with an array of turbulence promoting ribs; said array comprising a plurality of first ribs (25a,26a) and a plurality of second ribs (25b,26b), each of said first ribs extending obliquely away from the centreline of the array on one side of the centreline, and each of said second ribs extending obliquely away from the centreline on the other side of the centreline; the ends of the first and second ribs nearer the centreline in said array being upstream, with respect to the direction of cooling fluid flow, relative to the ends of the first and second ribs further from the centreline; characterised in that: said ends of the first and second ribs nearer the centreline are offset with respect to each other in the direction of the centreline. A member according to claim 1, wherein the first and second ribs are inclined at an angle of between 40 and 85 degrees to the flow direction of the cooling fluid (15). A member according to claim 1 or claim 2, wherein the ribs are curved along their length. A member according to any one of the preceding claims, wherein the ribs have a chevron shape. A member according to any one of the preceding claims wherein the ratio of the pitch of the ribs to the height of a rib is between 4 and 15. A member according to any one of the preceding claims, wherein the internal cooling flow passages (7) have rectangular cross-section. A member according to any one of the preceding claims, wherein the centreline intersects the first and second ribs. A member according to any one of claims 1 to 6, wherein the centreline does not intersect the first and second ribs. A member according to any one of the preceding claims, being a turbine blade. A member according to claim 9, wherein the array of ribs is formed on a curved wall, which corresponds to the leading edge of the turbine blade.

Inventors: ANZAI SHUNICHI, ISAO TAKEHARA, KAWAIKE KAZUHIKO, SASADA TETSUO, TORIYA HAJIME, ANZAI, SHUNICHI, ISAO, TAKEHARA, KAWAIKE, KAZUHIKO, SASADA, TETSUO, TORIYA, HAJIME
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1992
Main classification: F01D5
IPC codes: F01D5