Patent Abstract:
A gas turbine engine is defined wherein the inlet guide vanes leading into a core engine flow path are sized and positioned such that flow paths positioned circumferentially intermediate the vane are sufficiently large that a hydraulic diameter of greater than or equal to about 1.5 is achieved. This will likely reduce the detrimental effect of icing.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 61/593,083, filed Jan. 31, 2012. 
    
    
     BACKGROUND OF THE INVENTION 
     This application relates to a gas turbine engine, wherein the size and number of core inlet stator vanes at an upstream end of a compressor section are positioned to minimize icing concerns. 
     Gas turbine engines are known, and typically include a fan delivering air into a compressor section as core flow, and also to a bypass path. The air entering the compressor section typically passes across inlet stator vanes, and towards a compressor rotor. The air is compressed in the compressor section, delivered into a combustion section, mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors, driving the rotors to rotate, and in turn drive the compressor and fan sections. 
     In one traditional type of gas turbine engine, a low pressure turbine drives a low pressure compressor, and a high pressure turbine drives a high pressure compressor. The low pressure turbine typically also drives the fan blade through a low spool. In such engines, the fan blade and low pressure compressor were constrained to rotate at the same speed as the low pressure turbine. 
     More recently, it has been proposed to incorporate a gear reduction between the low spool and the fan blade such that the fan blade may rotate at a distinct speed relative to the low pressure turbine. Such engines have a gear reduction typically positioned inwardly of a core engine gas flow. 
     One concern with gas turbine engines when utilized on airplanes is that ice may be passed downstream into the core flow. The ice may accumulate on an outer housing, known as a splitter, which defines an outer periphery of the core flow, and on the stator vanes. When the ice builds up, this is undesirable. The problem becomes particularly acute with a geared turbofan, as the core flow tends to be across a smaller cross-sectional area then in the prior systems. 
     SUMMARY 
     In a featured embodiment, a gas turbine engine has a fan, a turbine operatively connected to the fan, an inner core housing having an inner periphery, and a splitter housing having an outer periphery. The inner periphery of the inner core housing and the outer periphery of the splitter housing define a core path. A plurality of inlet stator vanes is located in the core path. The inner periphery of the inner core housing, the outer periphery of the splitter housing and the plurality of inlet stator vanes define a flow area having a hydraulic diameter. The hydraulic diameter of the flow area is greater than or equal to about 1.5 inches. 
     In another embodiment according to the previous embodiment, the hydraulic diameter is greater than or equal to about 1.7 inches. 
     In another embodiment according to the previous embodiment, the turbine is a low pressure turbine which also drives a low pressure compressor, and the fan as a low spool. 
     In another embodiment according to the previous embodiment, the low spool drives the fan through a gear reduction. 
     In another embodiment according to the previous embodiment, the gear reduction is positioned inwardly of the inner core housing. 
     In another embodiment according to the previous embodiment, the gear reduction has a gear reduction ratio greater than 2.3. 
     In another embodiment according to the previous embodiment, the gear reduction has a gear ratio of greater than 2.5. 
     In another embodiment according to the previous embodiment, the fan also delivers air into a bypass duct. 
     In another embodiment according to the previous embodiment, a bypass ratio of the amount of air delivered into the bypass duct compared to the amount of air delivered into the core path is greater than about 6. 
     In another embodiment according to the previous embodiment, the bypass ratio is greater than 10. 
     In another embodiment according to the previous embodiment, the fan has an outer diameter that is larger than an outer diameter of the rotors in the low pressure compressor. 
     In another embodiment according to the previous embodiment, the low pressure turbine has a pressure ratio that is greater than about 5:1. 
     In another featured embodiment, a gas turbine engine has a fan that delivers air into a core path and into a bypass duct as bypass air. The air in the core path reaches a low pressure compressor, and then a high pressure compressor. The air that is compressed by the high pressure compressor is delivered into a combustion section where it is mixed with fuel and ignited. Products of the combustion pass downstream over a high pressure turbine and then a low pressure turbine. The low pressure turbine drives the low pressure compressor as a low spool. A gear reduction is driven by the low spool to in turn drive the fan at a rate of speed lower than that of the low spool. The gear reduction is positioned inwardly of an inner core housing which defines an inner periphery of the core path. A splitter housing defines an outer periphery of the core path. A plurality of inlet stator vanes extend between the splitter and the inner core housing. There is a flow area between adjacent stator vanes, wherein a hydraulic diameter is defined as: Hydraulic diameter=(4×A)/(O+L+I+L), where A is the area between the trailing edge of one vane, the leading edge of an adjacent vane, the inner periphery of the splitter, and the outer periphery of the inner core housing. L is the length of the leading edge of each vane. I is the length of the inner periphery of the vanes and O is the length of the outer periphery between adjacent vanes. The hydraulic diameter is greater than or equal to about 1.5 inches. 
     In another embodiment according to the previous embodiment, the hydraulic diameter is greater than or equal to about 1.7 inches. 
     In another embodiment according to the previous embodiment, the gear reduction is positioned inwardly of the inner core housing. 
     In another embodiment according to the previous embodiment, a bypass ratio of the amount of air delivered into the bypass duct compared to the amount of air delivered into the core path is greater than about 6. 
     In another embodiment according to the previous embodiment, the bypass ratio is greater than 10. 
     In another embodiment according to the previous embodiment, the gear reduction has a gear reduction ratio greater than 2.3. 
     In another embodiment according to the previous embodiment, the low pressure turbine has a pressure ratio that is greater than about 5:1. 
     In another embodiment according to the previous embodiment, the gear reduction has a gear reduction ratio greater than 2.3. 
     In another featured embodiment, a compressor module has a compressor rotor, a plurality of inlet stator vanes adjacent the rotor, a flow area defined between leading edges of two adjacent stator vanes, and an outer boundary and an inner boundary. The hydraulic diameter is greater than or equal to about 1.5 inches. 
     In another embodiment according to the previous embodiment, the hydraulic diameter is greater than or equal to about 1.7 inches. 
     These and other features may be best understood from the following drawings and specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a gas turbine engine somewhat schematically. 
         FIG. 2  is a cross-sectional view through an upstream end of a gas turbine engine. 
         FIG. 3  is a forward view of a portion of the  FIG. 2  gas turbine engine. 
         FIG. 4  is a schematic view. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section  22  drives air along a bypass flow path while the compressor section  24  drives air along a core flow path for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
     The engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a geared architecture  48  to drive the fan  42  at a lower speed than the low speed spool  30 . The high speed spool  32  includes an outer shaft  50  that interconnects a high pressure compressor  52  and high pressure turbine  54 . A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  further supports bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
     The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
     The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about 5. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.5:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
     A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tambient deg R)/518.7)^0.5]. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second. 
       FIG. 2  shows a portion of the gas turbine engine  20 . In particular, an outer housing, known as a splitter  80  defines an outer periphery for the core flow path C. A row of stator vanes  82  is positioned at a forward end. Air from the fan blade is divided into the bypass flow path B, and into the core flow path C, as mentioned above. The gear reduction  48  is positioned inwardly of an inner housing  83 . 
     As shown in  FIGS. 3 and 4 , the spacing and number of stator vanes  82  is selected such that the total flow area A between the vanes  82  is selected to reduce the likelihood of icing. As shown, a pair of spaced vanes  82  are circumferentially spaced by area A. The area A is defined by a leading edge L of one vane  82 , a leading edge L of an adjacent vane  82 , the inner periphery O of the splitter  80 , and the outer periphery I of the inner housing  83 . A perimeter is defined by the sum of L, O, L and I. The hydraulic diameter may be defined as 4 times the area A divided by the perimeter. This would be equation 1 as follows:
 
Hydraulic diameter=(4× A )/( O+L+I+L )  Equation 1
 
     The hydraulic diameter is desirably greater than or equal to about 1.5 in (3.8 cm). In preferred embodiments, it would be greater than or equal to about 1.7 in (4.3 cm). 
     The hydraulic diameter can be calculated for a compressor module in a similar manner by measuring the leading edges and measuring the distances along the outer and inner boundaries of the flow area, even though the module is not mounted in a splitter or outward of an inner housing. 
     Of course,  FIG. 3  shows a small circumferential segment, and it should be understood that the spacing would typically be equal across the entire circumference. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Technology Classification (CPC): 1