Abstract:
In a featured embodiment, a gas turbine engine has a first compressor rotor driven by a first turbine rotor, and a second compressor rotor driven by a second turbine rotor. The second compressor rotor is upstream of the first compressor rotor and the first turbine rotor is upstream of the second turbine rotor. An air mixing system taps air from a location upstream of the first compressor rotor for delivery to an environmental control system. The air mixing system receives air from a first air source and a second air source. The first air source includes air at a first pressure upstream of the first compressor rotor. The second air source includes air at a lower second pressure. At least one valve controls a mixture of air from the first and second sources to achieve a predetermined pressure for the environmental control system.

Description:
BACKGROUND 
       [0001]    This application relates to a two spool gas generator for a gas turbine engine and a propulsor drive having improved porting for air to be utilized on an aircraft. 
         [0002]    Conventional gas turbine engines typically include a fan section, a compressor section and a turbine section. There are two general known architectures. In one architecture, a low speed spool includes a low pressure turbine driving a low pressure compressor and also driving a fan. A gear reduction may be placed between the spool and the fan in some applications. There are also direct drive engines. 
         [0003]    Another known architecture includes a third spool with a third turbine being positioned downstream of the low pressure turbine and driving the fan. The three spools have shafts connecting a turbine to the driven element, and the three shafts are mounted about each other. 
         [0004]    All of these architectures raise challenges. 
         [0005]    When gas turbine engines are utilized on an aircraft, the compressor is typically utilized to supply air for aircraft uses. As an example, cabin air supply systems typically tap air from a higher pressure compressor. A number of applications are typically provided, resulting in a good deal of plumbing, valves, etc. 
         [0006]    Another challenge is that the pressure of the air supplied by an engine compressor will vary during operation of the associated aircraft. 
       SUMMARY 
       [0007]    In a featured embodiment, a gas turbine engine has a first compressor rotor driven by a first turbine rotor, and a second compressor rotor driven by a second turbine rotor. The second compressor rotor is upstream of the first compressor rotor and the first turbine rotor is upstream of the second turbine rotor. An air mixing system taps air from a location upstream of the first compressor rotor for delivery to an environmental control system. The air mixing system receives air from a first air source and a second air source. The first air source includes air at a first pressure upstream of the first compressor rotor. The second air source includes air at a lower second pressure. At least one valve controls a mixture of air from the first and second sources to achieve a predetermined pressure for the environmental control system. 
         [0008]    In another embodiment according to the previous embodiment, the second compressor rotor has a first overall pressure ratio, and the first compressor rotor has a second overall pressure ratio. A ratio of the first overall pressure ratio to the second overall pressure ratio is greater than or equal to about 2.0. 
         [0009]    In another embodiment according to any of the previous embodiments, the ratio of the first overall pressure ratio to the second overall pressure ratio is greater than or equal to about 3.0. 
         [0010]    In another embodiment according to any of the previous embodiments, the ratio of the first overall pressure ratio to the second overall pressure ratio is greater than or equal to about 3.5. 
         [0011]    In another embodiment according to any of the previous embodiments, the ratio of the first overall pressure ratio to the second overall pressure ratio is less than or equal to about 8.0. 
         [0012]    In another embodiment according to any of the previous embodiments, a propulsor turbine is positioned downstream of the second turbine rotor. 
         [0013]    In another embodiment according to any of the previous embodiments, the propulsor turbine drives a propeller. 
         [0014]    In another embodiment according to any of the previous embodiments, the propulsor turbine drives a fan at an upstream end of the engine. 
         [0015]    In another embodiment according to any of the previous embodiments, an axially outer position is defined by the fan. The propulsor turbine is positioned between the fan and the first and second turbine rotors. The first and second compressor rotors are positioned further into the engine relative to the first and second turbine rotors. 
         [0016]    In another embodiment according to any of the previous embodiments, the second air source is positioned to be upstream of the second compressor rotor. 
         [0017]    In another embodiment according to any of the previous embodiments, the second air source delivers air across a heat exchanger, and includes a particle separator for separating impurity. 
         [0018]    In another embodiment according to any of the previous embodiments, the second air source communicates through a conduit to a connection leading into the mixing box. The second air source further selectively communicates with an outlet is associated with the first compressor rotor. 
         [0019]    In another embodiment according to any of the previous embodiments, the second air source communicates from a single conduit through a port leading into a mixing box and, alternatively, flowing to the outlet at the first compressor rotor. 
         [0020]    In another embodiment according to any of the previous embodiments, the second air source communicates into a branch of two lines, with the first line including a valve control to control the amount of air reaching the mixing box, and a second valve on a second line leading to the outlet. 
         [0021]    In another embodiment according to any of the previous embodiments, the at least one valve is a pair of valves associated with the supply port from the first air source, and also on the second air source. 
         [0022]    In another embodiment according to any of the previous embodiments, the location upstream of the first compressor rotor is in an intermediate case intermediate the first and second compressor rotors. 
         [0023]    In another featured embodiment, a gas turbine engine has a first shaft connecting a first compressor rotor to be driven by a first turbine rotor, and a second shaft connecting a second compressor rotor to be driven by a second turbine rotor. The second compressor rotor is upstream of the first compressor and the first turbine rotor is upstream of the second turbine rotor. An air mixing system taps air from a location upstream of the first compressor rotor for delivery to an environmental control system. The air mixing system receives air from a first air source and a second air source. The first air source includes air at a first pressure upstream of the first compressor rotor. The second air source includes air at a lower second pressure. At least one valve controls a mixture of air from the first and second sources to achieve a predetermined pressure for the environmental control system. A propulsor turbine outwardly connects to drive one of a fan or propeller through a third shaft. The first shaft surrounds the second shaft, but the first and second shafts do not surround the third shaft. The second compressor rotor has a first overall pressure ratio. The first compressor rotor has a second overall pressure ratio. A ratio of the first overall pressure ratio to the second overall pressure ratio is greater than or equal to about 2.0. The source of lower pressure air is positioned to be upstream of the second compressor rotor. 
         [0024]    In another embodiment according to the previous embodiment, the second air source communicates through a conduit to a connection leading into a mixing box. The second air source further selectively communicates with an outlet which is associated with the first compressor rotor. 
         [0025]    In another embodiment according to any of the previous embodiments, the at least one valve is a pair of valves associated with a supply port for the first air source, and also on the supply of the lower pressure air. 
         [0026]    In another embodiment according to any of the previous embodiments, the first air source is in an intermediate case intermediate the first and second compressor rotors. 
         [0027]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  schematically shows a three spool gas turbine engine. 
           [0029]      FIG. 2  shows a second embodiment. 
           [0030]      FIG. 3  shows a first embodiment air supply system. 
           [0031]      FIG. 4  shows a second embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    A gas turbine engine  19  is schematically illustrated in  FIG. 1 . A core engine, or gas generator  20 , includes high speed shaft  21  is part of a high speed spool along with a high pressure turbine rotor  28  and a high pressure compressor rotor  26 . A combustion section  24  is positioned intermediate the high pressure compressor rotor  26  and the high pressure turbine rotor  28 . A shaft  22  of a low pressure spool connects a low pressure compressor rotor  30  to a low pressure turbine rotor  32 . 
         [0033]    Engine  19  also includes a free turbine  34  is shown positioned downstream of the low pressure turbine rotor  32  and serves to drive a propeller  36 . 
         [0034]    Various embodiments are within the scope of the disclosed engine. These include embodiments in which:
       a good deal more work is down by the low pressure compressor rotor  30  than is done by the high pressure compressor rotor  26 ;   the combination of the low pressure compressor rotor  30  and high pressure compressor rotor  26  provides an overall pressure ratio equal to or above about  30 ;   the low pressure compressor rotor  30  includes eight stages and has a pressure ratio at cruise conditions of 14.5;   the high pressure compressor rotor  26  had six stages and an overall pressure ratio of 3.6 at cruise;   a ratio of the low pressure compressor pressure ratio to the high pressure compressor ratio is greater than or equal to about 2.0, and less than or equal to about 8.0;   more narrowly, the ratio of the two pressure ratios is between or equal to about 3.0 and less than or equal to about 8;   even more narrowly, the ratio of the two pressure ratios is greater than about 3.5.       
 
         [0042]    In the above embodiments, the high pressure compressor rotor  26  will rotate at slower speeds than in the prior art. If the pressure ratio through the fan and low pressure compressor are not modified, this could result in a somewhat reduced overall pressure ratio. The mechanical requirements for the high pressure spool, in any event, are relaxed. 
         [0043]    With the lower compressor, the high pressure turbine rotor  28  may include a single stage. In addition, the low pressure turbine rotor  32  may include two stages. 
         [0044]    By moving more of the work to the low pressure compressor rotor  30 , there is less work being done at the high pressure compressor rotor  26 . In addition, the temperature at the exit of the high pressure compressor rotor  26  may be higher than is the case in the prior art, without undue challenges in maintaining the operation. 
         [0045]    A bleed line or port  40  is positioned between the low pressure compressor rotor  30  and the high pressure compressor rotor  26 . Details of this porting are disclosed below. 
         [0046]    Variable vanes are less necessary for the high pressure compressor rotor  26  since it is doing less work. Moreover, the overall core size of the combined compressor rotors  30  and  26  is reduced compared to the prior art. 
         [0047]    The engine  60  as shown in  FIG. 2  includes a two spool core engine  120  including a low pressure compressor rotor  30 , a low pressure turbine rotor  32 , a high pressure compressor rotor  26 , and a high pressure turbine rotor  28 , and a combustor  24  as in the prior embodiments. This core engine  120  is a so called “reverse flow” engine meaning that the compressor  30 / 26  is spaced further into the engine than is the turbine  28 / 32 . Air downstream of the fan rotor  62  passes into a bypass duct  64 , and toward an exit  65 . However, a core inlet duct  66  catches a portion of this air and turns it to the low pressure compressor  30 . The air is compressed in the compressor rotors  30  and  26 , combusted in a combustor  24 , and products of this combustion pass downstream over the turbine rotors  28  and  32 . The products of combustion downstream of the turbine rotor  32  pass over a fan drive turbine  74 . Then, the products of combustion exit through an exit duct  76  back into the bypass duct  64  (downstream of inlet  66  such that hot gas is not re-ingested into the core inlet  65 ), and toward the exit  65 . A gear reduction  63  may be placed between the fan drive turbine  74  and fan  62 . 
         [0048]    The core engine  120 , as utilized in the engine  60 , may have characteristics similar to those described above with regard to the core engine  20 . 
         [0049]    The engines  19  and  60  are similar in that they have what may be called a propulsor turbine ( 34  or  74 ) which is spaced to be axially downstream of the low pressure turbine rotor  32 . Further, the high pressure spool radially surrounds the low pressure spool, but neither of the spools surround the propulsor turbine, nor the shaft  100  connecting the propulsor turbine to the propellers  36  or fan  62 . In this sense, the propulsor rotor is separate from the gas generator portion of the engine. 
         [0050]    The disclosed engine architecture creates a smaller core engine and yields higher overall pressure ratios and, therefore, higher performance. Further, uncoupling the low pressure turbine  32  from driving a fan  62  or prop  36  enables it to run at a lower compressor surge margin, which also increases efficiency. Moreover, shaft diameters can be decreased and, in particular, for the diameter of the low pressure shafts as it is no longer necessary to drive the fan  62  or prop  36  through that shaft. 
         [0051]    In the prior art, the ratio of the low pressure compressor pressure ratio to the high pressure compressor ratio was generally closer to 0.1 to 0.5. Known three spool engines have a ratio of the low pressure compressor pressure ratio to the high pressure compressor ratio of between 0.9 and 3.0. 
         [0052]    Further details of the bleed line or port  40  and an associated air supply system are shown in  FIGS. 3 and 4 . 
         [0053]    Particularly with an engine as disclosed above, the low pressure compressor  30  is supplying a higher pressure than is typically been the case in the past. As such, this compressor can be utilized as a source of air for environmental control systems on an associated aircraft. In the past, a higher pressure source has typically been required resulting in taps from the high pressure compressor. 
         [0054]    As shown in  FIG. 3 , an air supply system  190  incorporates a manifold  192  provided with a plurality of bleed lines or ports  194  and which communicate with an intermediate compressor case  200 . The intermediate compressor case  200  is positioned between the low pressure compressor  30  and the high pressure compressor  26 . 
         [0055]    The pressure of the air supplied by the low pressure compressor  30  will vary dramatically during operation of an associated engine. Thus, at some point, the air pressure delivered from the ports  194  may be undesirably high. 
         [0056]    A supply of lower pressure air is used to address this concern. An inlet  202  to a low pressure manifold  199  communicates through a heat exchanger  206 . The heat exchanger  206  may be utilized to cool oil at other locations. A particle separator  204  is positioned to filter dirt particles out of an air supply stream being delivered downstream through fans  208  to an air supply line  211 . Air supply line  211  may communicate through a valve  212  to a mixing box  198 . The valve  212  is controlled in combination with a valve  196  associated with the manifold  192 , such that the flow of air from the higher pressure manifold  192  and the lower pressure source  211 , are properly mixed to achieve a desired pressure at an outlet  310 . The outlet  310  leads to an environmental control system  400  for supplying air for use on an associated aircraft. 
         [0057]    A control, such as a full authority digital engine control, may control the valves  196  and  212 , based upon the pressure, temperature and any other variables within the operation of the associated engine. 
         [0058]    A worker of ordinary skill in the art would recognize how to achieve a desired pressure at the outlet  310 . The desired pressure at the outlet  310  may be dictated by the aircraft manufacturer. 
         [0059]    When the valve  212  is open, air flows from the source  211  through the mixing box  198 . However, as the valve  212  is moved toward a more closed position, that air is delivered through an outlet  214  downstream of the high pressure compressor  26 . 
         [0060]      FIG. 4  shows an alternative embodiment  250 . Alternative embodiment  250  is generally the same as the embodiment  190 . An inlet  302  leads into a low pressure supply manifold  300 . There is a dirt separator  304 , a heat exchanger  306  and fans  308 . Valves  312  and  296  are controlled to control the pressure of the air reaching a mixing box  298  which communicates with an outlet  311 , and eventually the environmental control system  400 . A pipe  410  communicating a lower pressure air supply into the mixing box  298  passes air through a one-way valve  420  and to the outlet  412 , similar to the first embodiment. 
         [0061]    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 disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.