Patent Application
20150033697
The invention relates to a cooling arrangement for a hot gas duct having significantly varying cooling requirements along its length.
Conventional gas turbine engines utilizing a can-annular combustion arrangement include a transition duct that receives hot combustion gases from a combustor can and guides the combustion gases toward a turbine inlet. Typically a guide vane between the downstream end of the transition duct and the turbine rotor inlet orients the hot gases for delivery onto the first row of turbine blades. The hot gases exhausting from the combustor outlet typically flow below 0.2 mach. The hot gases accelerate slightly as they travel within the transition duct, but most of the acceleration occurs as the hot gases flow through the guide vanes, where the hot gases are accelerated to approximately 0.7-0.9 mach.
Cooling requirements for the transition duct are influenced by the speed of the hot gases flowing through the transition duct. Since the speed of the hot gases flowing through conventional transition ducts remains reasonably constant along the length of the transition duct, conventional transition duct cooling arrangements have been designed to remove heat at relatively constant rates along the length of the transition duct.
In contrast to the conventional combustion arrangements, an emerging can-annular combustion arrangement reorients the combustors and directs the hot gases along a straight flow path toward the turbine inlet annulus. The associated transition duct technology uses the transition duct itself to accelerate the hot gases, thereby eliminating the guide vanes conventionally placed between the transition duct and the turbine rotor inlet. Accelerating the combustion gases within the transition duct increases the amount of heat transferred to the transition duct in those regions where the hot gases flow faster. Consequently, there remains room in the art for improved cooling arrangements.
The invention is explained in the following description in view of the drawings that show:
The present inventors have devised a unique cooling arrangement adapted to the unique cooling requirements for transition ducts associated with certain emerging can-annular combustion arrangements. In these combustion arrangements the combustors are oriented in a manner that permits delivery of the hot gases along a straight flow path and directly on to a first row of turbine blades via transition ducts that accelerate the hot gases and thereby eliminate the need for the conventional guide vanes immediately upstream of the turbine rotor inlet. The cooling arrangement forms various zones capable of meeting the cooling requirements or different regions of the transition duct by varying the type of cooling provided. Types of cooling provided including impingement cooling, convection cooling, and combination impingement and convection cooling.
Surrounding the transition cone 30 is a flow sleeve 50 which defines a cooling plenum 52 there between. Surrounding the flow sleeve 50 is a casing plenum 54 that contains compressed air received from the compressor and used as the cooling fluid. The cooling arrangement 56 may include an impingement cooling zone 60, an optional blended cooling zone 62, and a convection cooling zone 64. These zones represent zones of varying rates of heat transfer from the hot gases 16 to the transition cone 30. Both the impingement cooling zone 60 and the blended cooling zone 62 form a zone having impingement cooling.
In the convection cooling zone 64 hot gases 16 may be flowing at a speed below mach 0.2 and therefore transfer a relatively low amount of heat to the transition cone 30 in this zone. In the blended cooling zone 62 the diameter of the transition cone 30 decreases. This accelerates the hot gases 16 and this increased flow velocity increases the amount of heat transferred from the hot gases 16 to the transition cone 30 (i.e. the heat flux) in the blended cooling zone 62 when compared to the convection cooling zone 64. In the impingement cooling zone the diameter of the transition cone 30 continues to decrease. This continues to accelerate the hot gases 16 resulting in an even greater rate of heat transfer from the hot gases 16 to the transition cone 30 in the impingement zone 60 when compared to the blended cooling zone 62.
Readily available types of cooling include impingement cooling and convection cooling, both of which are used in the cooling arrangement 56. Impingement cooling is used in the impingement cooling zone 60 because it is extremely effective and therefore a good match for the extremely high cooling requirements of the narrowest portion of the transition cone 30 where hot gases may flow above approximately 0.5 mach. In an exemplary embodiment, in the impingement cooling zone 60 impingement cooling may be responsible for the majority of the heat removal from the transition cone 30, and convective cooling may be responsible for a minority of the heat removal. Here fast moving jets 70 of cooling fluid 72 are directed onto an outer surface 74 of the transition cone 30 to be cooled. Once spent, (i.e. post-impingement), the cooling fluid 72 becomes a cross-flow 76 of cooling fluid 72. The cross-flow 76 flows along and convectively cools the outer surface 74. However, as the cross-flow 76 flows along the outer surface 74 a volume of the cross-flow increases because more impingement jets 70 are feeding cooling fluid 72 into the cross-flow 76. This can interfere with the flow of the impingement jets 70, reducing the penetration of the impingement jets 70 to a point where the impingement cooling effect is reduced.
To reduce this interference the inventors have developed an innovative dimpled arrangement 80 where individual dimples 82 extend radially inward from an undimpled portion 84 of the flow sleeve 50, such as a sheet. Each dimple 82 includes an outlet 86 from which a respective impingement jet 70 emanates. The dimples 82 can be configured such that all outlets 86 are at any distance 88 desired from the outer surface 74. In one exemplary embodiment all of the outlets 86 are at a same distance from the outer surface 74. In an exemplary embodiment the ratio of distance 88 to diameter of the outlet 86 in the impingement cooling zone 60 may be set at 3-5. The closer the outlets 86 are to the outer surface 74, the less pressure necessary to form an effective impingement jet 70. Thus, this dimple arrangement can be used more effectively in areas where the driving pressure difference is relatively small. The dimples 82 may be aligned with each other and in a direction of the cross-flow 76 so that the cross-flow 76 is guided around the impingement jets 70 by the dimples 82 and is free to flow in the rows between the dimples. In this manner the cross-flow 76 does not interfere with the impingement jets 70.
In between the dimples 82, the undimpled portion 84 forming the cross-flow channels may be characterized by a diameter 90 having a rate of taper 92. This rate of taper 92 may be tailored with respect to a rate of taper 94 of the outer surface 74 so a cross sectional area of the cooling plenum 52 is increased, or optionally, maintained or even reduced. By increasing the cross sectional area of the cooling plenum 52, the cooling plenum 52 can be configured to maintain a same flow velocity of the cross-flow 76 along a length of the cooling plenum 52 despite the addition of cooling fluid 72 with each impingement jet 70 in a direction 96 of flow of the cross-flow 76. Having a slower flow velocity reduces an interference between the cross-flow 76 and the impingement jets 70. Alternately, the flow velocity of the cross-flow 76 could be decreased or increased based on other design considerations. This unique arrangement allows for individual tailoring of the flow velocity of the cross-flow 76 and the number of impingement jets 70 and their distance 88 from the outer surface 74. By controlling the flow velocity of the cross-flow 76 one can also control the amount of convective cooling that is achieved via the cross-flow 76. Together, the impingement cooling and the convection cooling are effective to meet the cooling requirements of the transition cone 30 in this zone that might not be met by convection cooling along.
The blended cooling zone 62 is similar to the impingement cooling zone 60 in that both impingement cooling jets 70 and cross-flow 76 convective cooling may be used, but in this zone and in an exemplary embodiment the convective cooling effects of the cross-flow 76 may be predominant, and the impingement jets 70 are responsible for a minority of the heat transfer from the transition cone 30. This blended cooling is sufficient to meet the needs of the transition cone 30 in this zone where hot gases 16 may flow at rates between approximately 0.5 mach and 0.2 mach. In an exemplary embodiment the ratio of distance 88 to diameter of the outlet 86 in the blended cooling zone 62 may be set at 3-5.
In the convective cooling zone 64 all cooling is accomplished by convection. While the cooling requirements are lowest in this zone, the cross-flow 76 must still be accelerated so it can transfer enough heat from the transition cone 30. Consequently, in this zone the flow velocity of the cross-flow 76 is greater than the flow velocity of the cross-flow 76 in the impingement cooling zone 60 and in the blended cooling zone 64. The acceleration of the cross-flow 76 can be accomplished in at least two ways. In a first configuration a cross sectional area of the cooling plenum 52 may be reduced in the convection cooling zone 60 and this will accelerate the cross-flow 76 to the desired flow velocity. This may be accomplished in an exemplary embodiment by having a diameter 100 at an upstream end 102 of the convection cooling zone 64 be less than a diameter 104 of the undimpled portion 84 immediately upstream of the upstream end 102 of the convection cooling zone 64 with respect to a direction of flow of the cross-flow 76.
Alternately, or in addition, a flow sleeve opening 106 may be positioned to allow cooling fluid 72 into the convection zone 64. The increased volume of cooling fluid will cause the cross-flow velocity to increase. The increase can be tailored as necessary by sizing the size of the flow sleeve opening 106 alone or together with the diameter 100 at the upstream end 102 of the convection cooling zone 64 or anywhere else in the convection cooling zone 64 as desired. Alternately, or in addition, the flow sleeve opening 106 may be angled as shown so that a momentum of the cooling fluid 72 traveling through the flow sleeve opening 106 and entering the cross-flow 76 may contribute to an acceleration of the cross-flow 76.
In a transition region 110 between the blended cooling zone 62 and the convection cooling zone 64 the flow sleeve 50 may be configured to take advantage of the changing diameters of the flow sleeve 50. For example, a ramp 112 may be formed that directs circumferential portions of all of the converging cross-flow 76 toward the transition cone 30 as indicated by arrow 114. This ramp 112 can be configured at any angle desired or may undulate circumferentially, resulting in regions of greater and lesser impact on the transition cone 30 circumferentially. Such circumferential undulation may be a natural result of the last circumferential ring 116 of dimples 82.
Cooling fluid 72 exhausting from an outlet 118 of the convection cooling zone 64 may exhaust into an inlet of the combustor and used for further cooling and/or combustion.
From the foregoing it is apparent that the inventors have devised an innovative solution to new cooling requirements created by a new combustion arrangement. The cooling arrangement is responsive to the much greater variation in cooling requirements of different regions of the duct than exists in prior art combustion arrangements. Consequently, the cooling arrangement is able to satisfy the varying cooling needs of these regions, but does so using cooling fluid in a much more efficient manner than would be possible if the prior art cooling arrangements were applied. Thus, the cooling arrangement represents an improvement in the art.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
Development for this invention was supported in part by Contract No. DE-FC26-05NT42644, awarded by the United States Department of Energy. Accordingly, the United States Government may have certain rights in this invention.
