Patent Application
20070172355
(1) Field of the Invention
The present invention relates to a turbine engine component having improved cooling and a refractory metal core for forming the cooling passages.
(2) Prior Art
Rotational speeds for certain types of engines are very high as compared to large commercial turbofan engines. As a result, the main flow through the cooling circuits of turbine engine components, such as turbine blades, will be affected by secondary Coriolis forces and rotational buoyancy. The velocity profile of the main cooling flow is towards the trailing edge of the cooling passage. For a radial outward flow cooling passage with an aspect ratio of 3:1, there is a strong potential for cooling flow reversal, which in turn leads to poor heat transfer performance. Therefore, it is extremely important for cooling passages to maintain aspect ratios as close as possible to unity. This is needed to avoid main flow reversal and poor heat transfer performance.
There are existing cooling schemes currently in operation for different small engine applications. Even though the cooling technology for these designs has been very successful in the past, it has reached a culminating point in terms of durability. That is, to achieve superior cooling effectiveness, these designs have included many enhancing cooling features such as turbulating trip strips, shaped film holes, pedestals, leading edge impingement before film, and double impingement trailing edges. For these designs, the overall cooling effectiveness can be plotted in durability maps as shown in
The convective efficiency is a measure of heat pick-up or performance of the blade cooling circuit. In general, for advanced cooling designs, one targets high convective efficiency. However, trades are required as a balance between the ability of heat pick-up by the cooling circuit and the coolant temperature that characterizes the film cooling protection to the blade. This trade usually favors convective efficiency increases. For advanced designs, the target is to use design film parameters and convective efficiency to obtain an overall cooling effectiveness of 0.8 or higher, as illustrated in
In accordance with the present invention, there is provided a microcircuit cooling system with cooling passages which maintain aspect ratios as close as possible to one.
There is also provided a cooling scheme that has the means to (1) increase film protection, (2) increase heat pick-up, and (3) reduce airfoil metal temperature, denoted here as the overall cooling effectiveness, all at the same time. This may be achieved through the use of refractory metal core technology.
In accordance with the present invention, a turbine engine component broadly comprises an airfoil portion having a leading edge, a trailing edge, a pressure side, a suction side, a root, and a tip and at least one cooling circuit in a wall of the airfoil portion. The at least one cooling circuit has at least one passageway extending between the root and the tip, which at least one passageway has an aspect ratio which is less than 2:1, and preferably substantially unity.
Further in accordance with the present invention, there is provided a refractory metal core for forming at least one cooling circuit within a wall portion of the airfoil portion. The refractory metal core broadly comprises a tubular portion, and the tubular portion has an aspect ratio no greater than 2:1, and preferably substantially unity.
Other details of the microcircuit cooling with an aspect ratio of unity, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.
Referring now to
Referring now to
The pressure side 22 of the airfoil portion 12 also may be provided with a plurality of shaped holes 36. The holes 36 may be formed using any suitable conventional technique known in the art.
The airfoil portion 12 also may be provided with a trailing edge cooling microcircuit 38. The airfoil portion 12 may have a first supply cavity 40 for supplying cooling fluid to the trailing edge cooling microcircuit 38 and the cooling passage(s) 26.
The suction side 24 of the airfoil portion 12 may be provided with one or more cooling circuits or passages 42. The cooling circuit(s) or passage(s) 42 may be formed using refractory metal core technology and, as described hereinbelow, may have a serpentine configuration. As can be seen from
The leading edge 18 of the airfoil portion 12 may be provided with a plurality of film cooling holes 46. The cooling holes 46 may be formed using any suitable technology known in the art. The airfoil portion 12 may have a second supply cavity 48 for providing cooling fluid to the cooling circuit(s) or passage(s) 42 and the film cooling holes 46.
Referring now to
In a preferred embodiment of the present invention, each of the legs 52, 54, and 56 has an aspect ratio of about 2:1 or less, most preferably an aspect ratio of substantially unity. As used herein, the term “aspect ratio” is the ratio of the width to the height. To accomplish this, each of the legs 52, 54, and 56 may be circular in cross section. Alternatively, each of the legs 52, 54, and 56 may be square in cross section.
The airfoil portion 12 may also include a feed cavity 62 for supplying cooling fluid to the leading edge film cooling holes 46.
As can be seen in
The high coverage cooling fluid film may be accomplished by means of the slots 28 and 45 which are preferably made using one or more tabs 32 on a refractory metal core 30. The heat pick-up or convective efficiency may be accomplished by peripheral cooling with many turns and pedestals 61 as heat transfer enhancing mechanisms. The overall result of high film coverage and improved ability for heat pick-up leads to a cooling technology leap of high overall cooling effectiveness or lower airfoil metal temperature. This, in turn, can be used to decrease the cooling flow or increase part service life.
The rotational speeds for small engine applications can be very high as compared to large commercial turbofans, i.e. 40,000 RPM vs. 16,000 RPM. As a result, the main flow through the cooling microcircuits may be affected by the secondary forces of Coriolis and rotational buoyancy. For rotational environments, the velocity profile of the main flow is towards the trailing edge of the cooling passage. Studies have shown that for a radial outward flowing cooling passage, there is a strong potential for cooling flow reversal in a cooling passage if the aspect ratio is about 3:1. Therefore, it is important that any cooling passages formed using refractory metal core technology maintain aspect ratios as close as possible to unity. This is to avoid main flow reversal and poor heat transfer characteristics. As a consequence, the airfoil metal temperature would be high, leading to premature oxidation, fatigue, and creep.
As noted above, the various legs 52, 54, and 56 of the cooling circuit or passageway 42 may be formed using a refractory metal core 30. The refractory metal core 30 may have a serpentine shape that corresponds to the desired shape of the passageway 42. When a serpentine shaped refractory metal core is used, the refractory metal core 30 may have three tubular portions 70 that form the legs 52, 54, and 56. As shown in
The refractory metal core 30 may be formed from any suitable refractory metal material known in the art. For example, the refractory metal core 30 may be formed from molybdenum or a molybdenum alloy.
The foregoing refractory metal core technology shown in
The passageways 42 and 26 and the cooling film slots 45 and cooling passages 26 may be formed by placing the refractory metal cores 30 within the die and securing them in place with wax. Silica core elements may be placed in the die to form the supply cavities 40 and 48 as well as any other central core cavities in the airfoil portion 12. After the core elements have been positioned, molten metal is introduced into the die and allowed to solidify to form the walls and external surfaces of the airfoil portion 12. After the walls and external surfaces are formed, the silica core elements and the refractory core elements are removed. The silica core elements and the refractory core elements may be removed using any suitable technique known in the art. The pedestals 61 may be formed, using any suitable technique known in the art, after the cooling passageways 26 and 42 have been formed.
Microcircuit cooling systems in accordance with the present invention increases overall cooling effectiveness. As the overall cooling effectiveness increases from 0.5 to 0.8, it allows for cooling flow reduction by about 40% for the same external thermal load as conventional designs. This is particularly important for increasing turbine efficiency and overall cycle performance. The cooling systems have the means to increase film protection and heat pick-up, while reducing the metal temperature. This is denoted herein as the overall cooling effectiveness, all at the same time.
It is apparent that there has been provided in accordance with the present invention a microcircuit cooling with an aspect ratio of unity which fully satisfies the objects, means, and advantages set forth hereinbefore. While the present invention has been described in the context of specific embodiments thereof, other unforeseeable alternatives, modifications, and variations will become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.
