Patent Abstract:
A gas turbine engine has a fan at an axially outer location. The fan rotates about an axis of rotation. The fan delivers air into an outer bypass duct, and across a booster fan positioned radially inwardly of the outer bypass duct. The booster fan delivers air into a radially middle duct, and across a cold turbine into a radially inner core duct being directed into a compressor. From the compressor, air flows axially in a direction back toward the fan through a combustor section, and across an exhaust of the turbine section as directed into the middle duct. A gear reduction drives the fan from a fan drive turbine section. A method is also disclosed.

Full Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under Contract No. FA8650-09-D-2923/D013 awarded by the United States Air Force. The Government has certain rights in this invention. 
    
    
     BACKGROUND 
     This application relates to a reverse core geared turbofan engine having a turbine driven by fan air. 
     Gas turbine engines are known, and typically include a fan delivering air into a compressor section. The fan may also deliver air into a bypass duct to provide propulsion. The air delivered into the compressor is compressed and moved into a combustion section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors, driving them to rotate. The rotation of the turbine rotors in turn drives the fan and compressor sections. 
     Recently a speed reduction has been incorporated between a fan drive turbine and the fan. This allows the fan to rotate at a slower speed than other components that may be driven by the same turbine. As an example, a low or intermediate compressor is often driven by the fan drive turbine. 
     Another feature that has been incorporated into gas turbines is a “reverse core” engine. In a reverse core engine, the compressor delivers air in an axial direction toward a front of the aircraft and into a combustion section. The products of combustion pass downstream over turbine rotors, however, those turbine rotors are located in an axial direction toward the front of the engine, and typically the fan. 
     SUMMARY 
     In a featured embodiment, a gas turbine engine has a fan at an axially outer location. The fan rotates about an axis of rotation. The fan delivers air into an outer bypass duct, and across a booster fan positioned radially inwardly of the outer bypass duct. The booster fan delivers air into a radially middle duct, and across a cold turbine into a radially inner core duct. Air from the inner core duct is directed into a compressor, and then flows axially in a direction back toward the fan through a combustor section, and across a core turbine section. Air is then directed into the middle duct. A gear reduction drives the fan from a fan drive turbine section. 
     In another embodiment according to the previous embodiment, a shaft downstream of the gear reduction relative to the fan drive turbine section also drives the booster fan. 
     In another embodiment according to the previous embodiment, a shaft downstream of the gear reduction is also connected to rotate with the cold turbine. 
     In another embodiment according to the previous embodiment, the fan booster and the cold turbine rotate with a clutched shaft separate from a fan shaft driving the fan. A clutch selectively connects the clutched shaft to the fan shaft such that the fan shaft can selectively drive the clutched shaft. 
     In another embodiment according to the previous embodiment, there are at least a plurality of core turbine sections, with one of the plurality of core turbine sections driving the fan through the gear reduction and a second of the core turbine sections driving the fan booster. 
     In another embodiment according to the previous embodiment, the compressor section includes at least a first compressor section and a second compressor section downstream of the first compressor section. The core turbine section includes at least a first core turbine section and a second core turbine section. The first core turbine section drives the second compressor section and the second core turbine section drives the first compressor section. The second turbine section and first compressor section operate at a slower speed and at lower pressures than the first turbine section and the second compressor section. 
     In another embodiment according to the previous embodiment, a first cold turbine section is positioned adjacent the booster fan. A second cold turbine section is positioned downstream of the first cold turbine section in the path of air flowing through the inner core duct, and upstream of the compressor section. 
     In another embodiment according to the previous embodiment, one of the first and second cold turbine sections is provided with a flow diverter that allows bypass of air around a rotor associated with one of the cold turbine sections. 
     In another embodiment according to the previous embodiment, a radially outer extent of blades associated with one of the cold turbine sections is spaced inwardly of a radially outer position for the flow diverter to allow bypass of air radially outwardly of the radially outermost extent of the blades of one of the cold turbine sections. 
     In another embodiment according to the previous embodiment, there are a pair of flow diverters, being movable between a position allowing the bulk of the air delivered to the compressor section to bypass the turbine rotors by passing radially outwardly of the radially outermost extent of the blades, and the flow diverters being movable to an alternative position wherein the great bulk of the air delivered across one of the cold turbine sections passes radially inwardly of the radially outermost extent of the fan turbine blades. 
     In another embodiment according to the previous embodiment, the flow diverter is associated with the first cold turbine section. 
     In another embodiment according to the previous embodiment, the flow diverter is associated with the second cold turbine section. 
     In another embodiment according to the previous embodiment, the cold turbine section is provided with a flow diverter that allows bypass of air around a rotor associated with the cold turbine section. 
     In another embodiment according to the previous embodiment, a radially outer extent of blades associated with the cold turbine section is spaced inwardly of a radially outer position for the flow diverter to allow bypass of air radially outwardly of the radially outermost extent of the blades in the cold turbine section. 
     In another embodiment according to the previous embodiment, there are a pair of flow diverters, being movable to a position allowing the bulk of the air delivered to the compressor section to bypass the turbine rotor by passing radially outwardly of the radially outermost extent of the blades, and being movable to an alternative position with a great bulk of the air delivered across one of the cold turbine sections passes radially inwardly of the radially outermost extent of the fan turbine blades. 
     In another embodiment according to the previous embodiment, the cold turbine section associated with the flow diverter is positioned adjacent to the booster fan. 
     In another embodiment according to the previous embodiment, the cold turbine section associated with the flow diverter is positioned at a location adjacent to the compressor on an axial side of the compressor spaced away from the fan. 
     In another embodiment according to the previous embodiment, the cold turbine section associated with the flow diverter is positioned adjacent to the booster fan. 
     In another embodiment according to the previous embodiment, the cold turbine section associated with the flow diverter is positioned at a location adjacent to the compressor on an axial side of the compressor spaced away from the fan. 
     In another embodiment according to the previous embodiment, the cold turbine section associated with the flow diverter is positioned adjacent to the booster fan. 
     In another featured embodiment, a method of operating a gas turbine engine includes having blades with a radially outermost extent, and a flow diverter that is operable to divert air radially inwardly of the radially outermost extent of the turbine blades, or allow air to pass radially outwardly of the radially outermost extent of the turbine blades. The flow diverter is positioned to increase or decrease the amount of gas passing across that turbine rotor to increase or decrease a power output by said turbine rotor. 
     In another embodiment according to the previous embodiment, there are a pair of flow diverters moving between a position which passes all of the gas radially inwardly of the radially outermost extent of the turbine rotors, and to a position which diverts the gas radially outwardly of the radially outermost extent. 
     In another embodiment according to the previous embodiment, the flow diverter is moved to the position to allow bypass of the gases in low power conditions, such as when a gas turbine associated with the turbine section is in a aircraft at cruise conditions, and the flow diverter is moved to direct the air radially inwardly of the radially outermost extent at high power conditions, such as take-off for that aircraft. 
     These and other features of the invention would be better understood from the following specifications and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first embodiment. 
         FIG. 2  shows a second embodiment. 
         FIG. 3  shows a third embodiment. 
         FIG. 4A  shows a feature which may be incorporated into any one of the  FIG. 1-3  embodiments. 
         FIG. 4B  shows the first embodiment feature in a second operative position. 
         FIG. 5A  shows another embodiment feature which can be incorporated into any of the  FIGS. 1-3  embodiments. 
         FIG. 5B  shows the second embodiment feature in a second operative position. 
         FIG. 6A  shows another embodiment feature which can be incorporated into anyone of the  FIGS. 1-3  embodiments. 
         FIG. 6B  shows the third embodiment feature in a second mode of operative position. 
         FIG. 7A  shows a fourth embodiment feature which can be incorporated into any one of the  FIGS. 1-3  embodiments. 
         FIG. 7B  shows the fourth embodiment feature and a second operative position. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a gas turbine engine  20  having a fan  22  delivering air into three flowpaths, as an outer bypass propulsion flowpath  24 , a middle flowpath  26  wherein the air will mix with exhaust from an exhaust duct  54 , and an inner flow duct  28  which will deliver air into a core inlet duct  32  for the reverse core engine  20 . 
     A fan booster  50  is positioned downstream of the fan  22  and further drives the air into the flowpaths  26  and  28 . A turbine  52  (or cold turbine) receives the air from the inner flowpath  28  and extracts energy from the air as it is driven to rotate. 
     The air from the turbine  52  passes into the inner core flowpath  28 , the duct  32 , and into a low pressure compressor  30 . The air is compressed and delivered into a high pressure compressor  34 . The air is mixed with fuel in a combustion section  36  and ignited. 
     Products of the combustion pass downstream over a high pressure turbine  38 , a low pressure turbine  40  and another low pressure turbine  44 . Downstream of the low pressure turbine  44 , exhaust gases exhaust from the duct  54 , and into the middle airflow duct  26 . 
     The turbine  40  drives a spool  42  to drive the low pressure compressor  30 . The high pressure turbine  38  drives a spool  39  to in turn drive a high pressure compressor  34 . 
     The turbine  44  is a fan drive turbine, and drives a gear reduction  46  to in turn drive a shaft  48 . The shaft  48  is operatively connected to drive the fan blade  22 , the fan booster  50  and the turbine  52 . Notably, the turbine  52  may also extract energy from the air delivered by the fan booster  50  to rotate the shaft  48 . 
     The provision of a turbine driven by the “cold” air downstream of the fan booster  50  provides greater efficiency to the overall arrangement. 
       FIG. 2  shows another embodiment  120 . In embodiment  120 , components which are generally the same as the  FIG. 1  embodiment bear like numbers, however, increased by 100. Embodiment  120  differs in that the gear reduction  146  drives a shaft  147 . The shaft  147  is clutched by clutch  160  to a shaft  148  which drives the fan booster  150 , and the turbine  152 . 
     The clutch may be engaged to provide greater efficiency by either capturing the rotation of the turbine  152 , or allowing it to free rotate and drive the fan booster  150  on its own. 
       FIG. 3  shows yet another embodiment  220 . A turbine  256  drives the gear reduction  260  to drive the fan rotor  222 . Again, components which are similar to those in  FIGS. 1 and 2  are identified by the same reference numeral, only increased by 200. 
     A separate turbine  258  is connected to the cold turbine  262 , and the booster fan blade  250  by a spool  260 . In this regard, the power delivered to the fan booster  250 , and how the power generated by the turbine  262  is utilized, has some additional freedoms. 
       FIG. 3  also shows a second fan air turbine section  304  which is positioned downstream of the duct  232  and leading into the inlet for the compressor section  302 . The turbine section  304  is operable to rotate with a shaft  307  that rotates with the low pressure turbine  256  and the low pressure compressor  302 . 
       FIG. 4A  shows another feature which can be incorporated into any one of the three above-referenced embodiments. As shown, the turbine blades  262  have a relatively short radially outer edge  270 . A flow diverter, which could be a bypass door  272  of some sort is shown in an operative position to increase power flow. This position may be utilized such during takeoff of an associated aircraft on a hot day. 
     Notably, while the features of  FIGS. 4-7  are shown associated with the  FIG. 3  embodiment, they would have application into any one of the embodiments illustrated in this application. 
       FIG. 4B  shows another operative position wherein the door  272  is pivoted outwardly to create a bypass flowpath  274  which avoids the blades in the turbine section  262 . The bypass door could be opening during cruise conditions. In either case, the bypass flow  274  is still directed into the inner flow path  228 , and to the inlet duct  232  (for example, shown in  FIG. 3 ). 
       FIG. 5A  shows a second embodiment feature wherein a pair of flow diverters or doors  272  and  276  are utilized. During a cruise condition as shown in  FIG. 5A  the door of  272  is pivoted outwardly as is the door  276 . Now, all air is diverted away from the turbine section  262  and through the bypass path  274 . 
       FIG. 5B  shows an alternative operative position where the doors  272  and  276  are pivoted inwardly such that the great bulk of the air would now be directed across the turbine section  262 . This position would be utilized during high power conditions such as a takeoff on a hot day. 
       FIG. 6A  shows yet another embodiment  300 . In embodiment  300 , the turbine  302  is positioned downstream of the inlet duct  232 , and upstream of the low pressure compressor  302 . Door  308  operates similarly to the FIG.  4 A/ 4 B embodiment to direct all air across the turbine blades in turbine  304 , and within the radial extent of the blades (that is, radially inwardly of the radially outermost extent  306 ). 
       FIG. 6A  would be utilized in high power conditions such as during takeoff of an associated aircraft on a hot day. 
       FIG. 6B  shows the door  308  pivoted radially outwardly to provide a bypass flowpath  310  which is outward of the radially outer end  306  of the blades in the turbine  304 . This would be utilized at low power conditions such as cruise. 
       FIG. 7A  shows another embodiment  350 . Again, the turbine  304  is positioned downstream of the duct  232 , but upstream of the low pressure compressor  302 . A second door  354  is provided in addition to the door  352 . In the  FIG. 7A  position, the bypass  356  is opened, such as may be utilized during cruise conditions. The lower door  354  ensures that the great bulk of air avoids the turbine blades in turbine section  304 . 
       FIG. 7B  shows the position of the doors  352  and  254  during high power conditions such as takeoff on a hot day. In this position, the great bulk of the air is directed radially inward of the radially outermost extent  306  of the blades in the turbine section  304 . 
     A schematic control  800  is illustrated in the figures and would operate to control the various components disclosed across this application. The control can be incorporated into a FADEC for the entire engine. A worker of ordinary skill in the art would be able to design such a control given the teachings of this disclosure. 
     For purposes of this application, the terms “low” or “high” relative to pressure or speed, and in core turbine and compressor sections simply are to be taken as relative terms. That is, the “high” would rotate at higher pressures and typically higher speeds than would the “low,” although both might be at objectively high speeds and pressures. In addition, the term “cold” for the turbine sections downstream of the booster fan simply imply they are not part of the core engine. They may well operate at very high temperatures, even though they are referred to as “cold” in this application. The turbine sections which are in the core engine could be called “core turbine sections” for purposes of this application. The core turbine sections would typically be seeing higher temperature and pressure gases than would the “cold” turbine sections. 
     As should be understood, all of the gas turbine engines illustrated in all of these figures rotate about a central axis of rotation. The figures are generally illustrating only the upper half of that engine, and there is an axis of rotation shown generally in dashed line in each of the figures. 
     A worker of ordinary skill in this art would recognize that many modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this application.

Technology Classification (CPC): 5