# Patent

## Title
Gas turbine engine systems and related methods involving vane-blade count ratios greater than unity

## Abstract

Gas turbine engine systems and related methods involving vane-blade count ratios greater than unity are provided. In this regard, a representative turbine stage for a gas turbine engine includes a first set of rotatable blades operative to be positioned downstream of and adjacent to a first set of vanes, a number of blades of the first set of blades being less than a number of vanes of the first set of vanes.

## Background
This application is a divisional of U.S. patent application Ser. No. 11/850,787 filed Sep. 6, 2007, which is hereby incorporated by reference.


BACKGROUND
1. Technical Field
The disclosure generally relates to gas turbine engines.
2. Description of the Related Art
Turbine durability for high inlet temperature/high fuel-to-air ratio gas turbine engine designs can be compromised by gas path temperature and/or chemical species non-uniformities occurring at the exit of a combustor. Chemical species variation is particularly relevant to high-fuel-to-air ratio turbine designs in that the combustion process may not be completed at the exit plane of the combustor section with the result that partial products of reaction (PPR's) enter the turbine section. The anticipated presence of such temperature non-uniformities contributes to the use of conservative cooling designs for the turbine in order to prevent damage that can be caused by a failure to account for such temperature/PPR's non-uniformities.
SUMMARY
Gas turbine engine systems and related methods involving vane-blade count ratios greater than unity are provided. In this regard, an exemplary embodiment of a gas turbine engine comprises: a compressor section; a combustion section operative to receive compressed gas from the compressor section; and a turbine section operative to impart rotational energy to the compressor section, the turbine section having a first set of vanes positioned adjacent the combustion section and a first set of rotatable blades positioned downstream of and adjacent to the first set of vanes, a number of vanes of the first set of vanes exceeding a number of blades of the first set of blades.
An exemplary embodiment of a turbine stage for a gas turbine engine also is provided. The engine has a combustion section and a first set of vanes positioned adjacent to and downstream of the combustion section. The turbine stage comprises a first set of rotatable blades operative to be positioned downstream of and adjacent to the first set of vanes, a number of blades of the first set of blades being less than a number of vanes of the first set of vanes.
An exemplary embodiment of a method for designing a gas turbine engine comprises: selecting a number (N) of vanes and a corresponding number (N) of blades for a turbine stage of a gas turbine engine; increasing the number of the vanes by M; and decreasing the number of blades by at least M such that the number of vanes of the turbine stage exceeds the number of blades of the turbine stage.
An exemplary embodiment of a method for operating a gas turbine engine comprises: providing a gas turbine engine having a combustion section and a turbine stage, the turbine stage having a first set of vanes and a first set of blades, the first set of blades being located downstream from and adjacent to the first set of vanes; and completing a combustion reaction prior to a plane defined by downstream portions of the first set of blades.
Other systems, methods, features and/or advantages of this disclosure will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be within the scope of the present disclosure.



BRIEF DESCRIPTION OF THE DRAWINGS
Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
FIG. 1 is a schematic diagram depicting an embodiment of a gas turbine engine.
FIG. 2 is a schematic diagram depicting the embodiment of FIG. 1, showing detail of the first and second stages of the turbine section.
FIG. 3 is a flowchart depicting an embodiment of a method for operating a gas turbine engine.
FIG. 4 is a flowchart depicting an embodiment of a method for designing a gas turbine engine.



DETAILED DESCRIPTION
Gas turbine engine systems and related methods involving vane-blade count ratios greater than unity are provided, several exemplary embodiments of which will be described. In this regard, an increased vane count could increase the probability that a temperature/PPR's non-uniformity (“hot and/or fuel-rich streak”) will mix with cooler gases and, therefore, dissipate before propagating beyond the rotating blades of the first stage of the turbine. In some embodiments, the cooler gases used for dissipating such a hot streak are provided as cooling air, which is provided for film-cooling the vanes of the first turbine stage. In some embodiments, the vane and blade counts deviate from a nominal number so that overall parasitic drag and weight directly attributable to the vanes and blades are comparable to a gas turbine engine containing an equal number of vanes and blades. For example, in a first stage turbine design incorporating forty-eight (48) vanes and sixty two (62) blades, the number of vanes could be increased to fifty-six (48+8=56), whereas the number of blades could be decreased to fifty four (62−8=54). It should be noted that increasing the number of vanes can potentially enhance mixing of the gases departing the combustion section, thereby reducing the requirement for conservative cooling of downstream vanes. Thus, an overall weight reduction may be achieved by reducing the requirements of cooling air in some embodiments. Additionally, aerodynamic efficiency may be improved as an increased number of vanes can yield higher levels of unsteady flow in the downstream rotor passages. As such the formation of rotor passage secondary flow vortices and losses can be inhibited.
Referring now in detail to the drawings, FIG. 1 is a schematic diagram depicting an embodiment of a gas turbine engine 100. As shown in FIG. 1, engine 100 includes a compressor section 102, a combustion section 104 and a turbine section 106. Notably, engine 100 is a turbofan although it should be noted that the concepts described herein should not be considered limited to use with gas turbine engines configured as turbofans.
Turbine section 106 incorporates multiple stages, each of which includes a set of stationary vanes and a corresponding set of rotating blades. In this regard, a first stage 108 of the turbine section includes a first set of vanes 110 and a first set of blades 112. The first stage of the turbine section is located immediately downstream of the combustion section and immediately upstream of a second stage 114 of the turbine, which includes a second set of stationary vanes 116.
As shown in FIG. 2, blades 112 are located downstream of vanes 110, whereas vanes 116 are located downstream of blades 112. Notably, downstream portions of the blades 112 define an exit plane 120. Notably, interaction of gas 122 flowing along the gas path defined by the vanes and blades causes combustion products to mix and complete a combustion reaction prior to traversing the exit plane of the first set of blades 112. This is accomplished, at least in part, by providing a greater number of vanes 110 than there are blades 112, i.e., the vane-blade count ratio of the first turbine stage is greater than unity (1).
In the embodiment of FIGS. 1 and 2, vanes 110 and 116 incorporate film-cooling holes that direct cooling air for film-cooling the vanes. By way of example, vane 110 includes cooling holes 130, and vane 116 includes cooling holes 132. Note that although the number of cooling holes in vane 110 exceeds the number of cooling holes in vane 116, various other numbers and arrangements of cooling holes can be provided in other embodiments.
Because of work extraction in a first turbine stage, the temperature of gas is reduced at exit plane of that stage relative to the temperature at the entrance of the first vanes. As a result, for conventional turbine designs, cooling requirements for the downstream vanes are usually much lower than the cooling requirements for the first vanes. However, for high-fuel-to-air ratio turbine designs (i.e., designs that exhibit significant PPR concentrations at the inlet to the first stage), the oxygen included in the cooling air provided in the first stage 108 completes the combustion reaction and can significantly increase the temperature of gas 122 temperature at exit plane 120. The degree of circumferential and radial uniformity of this hot and/or fuel-rich streak temperature increase is a factor that should be considered for the cooling design of vanes 116. If the hot and/or fuel-rich streaks are highly concentrated (non-uniform temperature at station 120), then all of the vanes 116 should be designed to accommodate the hottest possible streak. However, if the hot and/or fuel-rich streak s are diffused by the first stage 108 (a highly uniform temperature at station 120), then the vanes 116 can be designed to accommodate a lower peak temperature. This can result in a weight reduction of the gas turbine engine as lighter and/or fewer components associated with routing of the cooling air may be provided.
In this regard, FIG. 3 is a flowchart depicting an embodiment of a method for operating a gas turbine engine. As shown in FIG. 3, the method may be construed as beginning at block 302, in which a gas turbine engine having a combustion section and a turbine stage is provided. Notably, the turbine stage includes a first set of vanes and a first set of blades, with the first set of blades being located downstream from and adjacent to the first set of vanes. In block 304, a combustion reaction is completed along a gas flow path prior to a plane defined by downstream portions of the first set of blades. In some embodiments, design of such a first stage incorporates, through the use of both CFD analysis and empirical correlations, any combination of (a) Vane(N)/Blade(N) ratio, (b) vane and/or blade film-cooling schemes or (c) vane and/or blade aerodynamic designs such that temperature and PPR's nonuniformities at the exit plane of the turbine stage are reduced, e.g., minimized or eliminated.
FIG. 4 is a flowchart depicting another embodiment of a method. Specifically, the flowchart of FIG. 4 involves a method for designing a gas turbine engine. That method may be construed as beginning at block 402, in which a number (N) of vanes and a corresponding number (N) of blades for a turbine stage of a gas turbine engine are selected. In block 404, the number of the vanes is increased by M. In block 406, the number of blades is decreased by at least M such that the number of vanes of the turbine stage exceeds the number of blades of the turbine stage. In some embodiments, the turbine stage is a first turbine stage downstream of a combustor.
A set of numerical experiments were conducted to quantify the impact of change in the number of first vanes on the temperature non-uniformity at the exit of a representative turbine stage. These simulations were conducted by changing the number of airfoils in the vane row while holding the airfoil count for the rotor row constant. The ratio of vanes to blades in these studies were 2/3, 1/1 and 3/2. The temperature at inlet to the stage was held constant at a typical combustor exit temperature value while the metal temperature for the vane was maintained at a constant value consistent with the airfoil durability requirements. The rotor airfoils and end-walls, however, were maintained at adiabatic wall temperatures. An unsteady 3-D Reynolds-Averaged-Navier-Stokes CFD code was used to conduct these simulations. Results from these simulations indicated that the absolute temperature distortion at the exit of the rotor was about 60%, 30% and 16% of the inlet distortion to the rotor, which was constant for the above three numerical experiments. These simulations clearly indicate that increasing the number of vanes relative to the blades enhances mixing between the hot and cold stream in the rotor passages. Interrogation of numerical data from these simulations also indicated that the loss levels in the rotor passages were also reduced as the number of vanes was increased. In addition, increasing the number of vanes was also found to reduce the hot spot temperature on the rotor airfoil pressure side indicating that the cooling air in the rotor passages may also be favorably impacted by increased vane count.
It should be emphasized that the above-described embodiments are merely possible examples of implementations set forth for a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the accompanying claims

## Claims

1. A method for operating a gas turbine engine comprising:
providing a gas turbine engine having a combustion section and a turbine stage, the turbine stage having an inlet, a first set of vanes, and a first set of blades, the first set of vanes being located downstream and adjacent to the combustion section and downstream of the inlet, the first set of blades being located downstream from and adjacent to the first set of vanes, wherein the number of vanes of the first set of vanes exceeds the number of blades of the first set of blades; and
completing a combustion reaction along a gas flow path prior to a plane defined by downstream portions of the first set of blades;
wherein the engine exhibits a significant concentration of partially combusted products of the combustion reaction at the inlet of the turbine stage.

2. The method of claim 1, wherein:
completing the combustion reaction comprises mixing combustion products from the combustion section using the vanes of the first set of vanes.

3. The method of claim 2, wherein the engine is operative such that cooling air provided to the first set of vanes reacts with combustion products from the combustion section in order to complete the combustion reaction.

4. The method of claim 1, further comprising film-cooling the vanes of the first set of vanes.

5. The method of claim 4, wherein:
the gas turbine engine further comprises a second set of vanes located downstream from the first set of blades; and
the second set of vanes is film-cooled to a lesser extent than that provided to the first set of vanes.

6. The method of claim 5, wherein the engine is operative to complete the combustion reaction upstream of the second set of vanes.

7. The method of claim 1, wherein the engine is a turbofan.