Abstract:
A gas turbine engine comprises a fan drive turbine for driving a gear reduction. The gear reduction drives a fan rotor. A lubrication system supplies oil to the gear reduction. The lubrication system includes a lubricant pump supplying a mixed air and oil to a deaerator inlet. The deaerator includes a separator that for separating oil, and delivering separated air to an air outlet, and for delivering separated oil back into an oil tank. The separator includes a member having lubricant flow paths on both of two opposed sides. A method of designing a gas turbine engine is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/019,452, filed Jul. 1, 2014. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This application relates to a gas turbine engine having a gear reduction driving a fan wherein an oil tank has an improved deaerator. 
         [0003]    Gas turbine engines are known and, typically, include a fan delivering air into a bypass duct as propulsion air. The fan also delivers air into a core engine where it passes to a compressor. The air is compressed in the compressor and delivered downstream 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. 
         [0004]    Historically, the fan rotor and a fan drive turbine rotor have been driven at the same speed. This placed a restriction on the desirable speed of both the fan and the fan drive turbine. 
         [0005]    More recently, it has been proposed to provide a gear reduction between the fan drive turbine and the fan rotor. 
         [0006]    The gear reduction is a source of increased heat loss. As an example, a geared turbofan engine creates about twice as much heat loss as a non-geared turbofan engine. In addition, the weight of the engine increases due to the weight of the gear reduction. 
         [0007]    It has typically been the case that a designer of a gas turbine engine sizes an oil tank such that the oil can sit in the oil tank long enough to de-aerate. On a normal turbofan engine, this had been approximately at least ten seconds. 
       SUMMARY OF THE INVENTION 
       [0008]    In a featured embodiment, a gas turbine engine comprises a fan drive turbine for driving a gear reduction. The gear reduction drives a fan rotor. A lubrication system supplies oil to the gear reduction. The lubrication system includes a lubricant pump supplying a mixed air and oil to a deaerator inlet. The deaerator includes a separator that for separating oil, and delivering separated air to an air outlet, and for delivering separated oil back into an oil tank. The separator includes a member having lubricant flow paths on both of two opposed sides. 
         [0009]    In another embodiment according to the previous embodiment, the separator has a splitter at an intermediate position in the inlet. 
         [0010]    In another embodiment according to any of the previous embodiments, the air outlet has a tube extending downwardly into a deaerator shell. 
         [0011]    In another embodiment according to any of the previous embodiments, an inlet velocity to the deaerator is less than or equal to 14 feet/second, and an exit velocity from the deaerator of the separated air is less than or equal to 14 feet/second. 
         [0012]    In another embodiment according to any of the previous embodiments, a deaerator exit delivers oil into the oil tank at least 2 inches (5.08 centimeters) between a freestanding oil level within the tank. 
         [0013]    In another embodiment according to any of the previous embodiments, a dwell time of oil in the tank as removed by the oil pump, on average, is five seconds or less. 
         [0014]    In another embodiment according to any of the previous embodiments, the oil tank may hold greater than or equal to 25 and less than or equal to 35 quarts of oil. 
         [0015]    In another embodiment according to any of the previous embodiments, the engine is rated greater than or equal to 15,000 and less than or equal to 35,000 lbs in rated thrust at take-off. 
         [0016]    In another embodiment according to any of the previous embodiments, the oil tank holds greater than or equal to 35 and less than or equal to 50 quarts of oil. 
         [0017]    In another embodiment according to any of the previous embodiments, the oil tank is associated with an engine having greater than or equal to 35,000 and less than or equal to 100,000 lbs in rated thrust at take-off. 
         [0018]    In another embodiment according to any of the previous embodiments, the gear reduction includes a sun gear for driving intermediate gears. Oil baffles are located circumferentially between the intermediate gears. 
         [0019]    In another embodiment according to any of the previous embodiments, an oil capture gutter surrounds the gear reduction. 
         [0020]    In another embodiment according to any of the previous embodiments, an oil capture gutter surrounds the gear reduction. 
         [0021]    In another embodiment according to any of the previous embodiments, the separator includes a scroll spiraling from the inlet to a deaerator exit. 
         [0022]    In another embodiment according to any of the previous embodiments, the exit includes a plurality of holes in a shell. 
         [0023]    In another featured embodiment, method of designing a gas turbine engine includes providing a fan drive turbine for driving a gear reduction. The gear reduction drives a fan rotor. A lubrication system is provided to supply oil to the gear reduction, with an oil tank, the lubrication system including a lubricant pump. Mixed air and oil are delivered to a deaerator inlet, the deaerator including a separator for separating oil, and delivering separated air to an air outlet, and delivering separated oil back into an oil tank. The lubricant separator includes a member having lubricant flow paths on both of two opposed sides. 
         [0024]    In another embodiment according to the previous embodiment, the separator is at an intermediate position in the inlet. 
         [0025]    In another embodiment according to any of the previous embodiments, the air outlet has a tube extending downwardly into a deaerator shell. 
         [0026]    In another embodiment according to any of the previous embodiments, the flow separator includes a scroll spiraling from the inlet to a deaerator exit. 
         [0027]    In another embodiment according to any of the previous embodiments, the separator is at an intermediate position in the inlet. 
         [0028]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a schematic view of a gas turbine engine. 
           [0030]      FIG. 2  shows a portion of a gear reduction. 
           [0031]      FIG. 3  shows another portion of a gear reduction. 
           [0032]      FIG. 4  shows a lubrication system. 
           [0033]      FIG. 5  shows a deaerator. 
           [0034]      FIG. 6  shows internal structure of the deaerator. 
           [0035]      FIG. 7  shows additional internal structure of the deaerator. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]      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 B in a bypass duct defined within a nacelle  15 , while the compressor section  24  drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool 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 two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
         [0037]    The exemplary 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, and the location of bearing systems  38  may be varied as appropriate to the application. 
         [0038]    The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a first (or low) pressure compressor  44  and a first (or low) pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in exemplary gas turbine engine  20  is illustrated as 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 second (or high) pressure compressor  52  and a second (or high) pressure turbine  54 . A combustor  56  is arranged in exemplary gas turbine  20  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. 
         [0039]    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 C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of combustor section  26  or even aft of turbine section  28 , and fan section  22  may be positioned forward or aft of the location of gear system  48 . 
         [0040]    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 or equal to about six (6), with an example embodiment being greater than about 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 five. In one disclosed embodiment, the engine  20  bypass ratio is greater than or equal to 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 five 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 2.3:1. 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. 
         [0041]    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 [(Tram°R)/(518.7°R)] 0.5 . The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second. 
         [0042]    As shown in  FIG. 2 , a flexible shaft  99 , which is driven by the turbine  46 , drives a sun gear  101  which, in turn, engages and drives intermediate gears  102 . In some embodiments, the intermediate gears  102  may be planet gears of a planetary epicyclic gear system. In other embodiments, the intermediate gears  102  may be star gears of a star epicyclic gear system. The intermediate gears  102  engage and drive a ring gear  103  to, in turn, drive an output shaft  106 , which then drives the fan rotor  42 . In other embodiments, a planetary gear carrier (not shown) driven by planetary gears may drive the fan shaft. Lubricant is supplied to a journal pin  108 , to the intermediate gears  102  and to other locations within the gear reduction  48 . 
         [0043]      FIG. 3  shows baffles  100  which are placed circumferentially between adjacent planet gears  102 . 
         [0044]    A gutter  104  surrounds the gear reduction  48  and captures oil that has left the gear reduction. Oil from the gear reduction  48  is returned to a pump  72  (See  FIG. 4 ) or a tank  90  as shown schematically in  FIG. 4 . As shown, a lubricant system  70  includes the gear reduction  48  which may be structured as shown in  FIGS. 2 and 3 . Notably, complete details of the operation of the baffle, the gutter and the other portions of the gear reduction may be as disclosed in U.S. Pat. No. 6,223,616, the disclosure of which with regard to the operation of the gear reduction is incorporated by reference. 
         [0045]    Oil flows from an oil pump  72  to a filter  74  through a pressure relief valve  76  to an air/oil cooler  78  and then to a fuel/oil cooler  80 . The oil may pass through an oil pressure trim orifice  82  and back to the tank  90 . Alternatively, the oil may pass through a strainer  84  and then to the gear reduction  48 . Oil returning from the gear reduction and, in particular, from the gutter, may pass back directly to the pump  72  or to the tank  90 . This is a simplification of the overall lubricant system and, as appreciated, there may be other components. 
         [0046]    Applicant has recognized that by utilizing baffles  100  and a gutter  104  on the gear reduction  48 , which may be generally as disclosed in the above-mentioned U.S. patent, the oil need not sit in the oil tank for ten seconds in order to de-aerate. Thus, the size of the tank  90  may be made much smaller. 
         [0047]    Conventional turbofans allow the oil to dwell in an oil tank for approximately seven to ten seconds. The dwell time allows air bubbles to separate from the oil to prevent foaming. With the move to a geared gas turbine engine, the oil flow volumes may effectively double. This would require a much larger oil tank, and as much as twice as large if the same dwell time is allowed. Thus, it becomes important to reduce dwell time. 
         [0048]    Applicant has discovered that oil is de-aerated by the baffles  100  and gutter system and that a dwell time in the oil tank to remove air bubbles may be less than five seconds More preferably, it may be less than or equal to about 3.0 seconds. This allows the use of oil tank  90  to be of a size roughly equivalent to the size utilized in prior non-geared gas turbine engines. A deaerator  88  is shown incorporated into the oil tank  90 . 
         [0049]    The better the deaeration before the oil reaches the tank, the shorter the dwell time that can be achieved. The disclosed deaerator achieves these very low dwell times. 
         [0050]    As an example, an oil tank that holds 25 to 35 quarts of oil may be utilized on a geared gas turbine engine with 15,000 to 35,000 lbs in rated thrust at take-off. Further, an oil tank may be 35 quarts to 50 quarts of oil for an engine with 35,000 to 100,000 lbs in rated thrust at take-off. 
         [0051]      FIG. 5  shows a deaerator embodiment  188 . A line  190  receives an air/oil mixture such as from the pump  72 . Air leaves through an air outlet  192 , as shown in  FIG. 4 . 
         [0052]    A plurality of oil outlets  194  are shown in an outer shell  195  of the deaerator. An oil level  196  is shown schematically, and would be the oil level within the oil tank  90  of  FIG. 4 . 
         [0053]    As shown in  FIG. 6 , a flow splitter or separator  200  is provided inline to the inlet  190  and serves to split the air/oil flow into two paths, and at an intermediate location in inlet  190 . This will hasten the deaeration of the mixed oil and air from the inlet  190 . The air will be at the radially outer locations, and will pass through a tube  193  into the air outlet  192 . As shown, air outlet  192  has an end  300  extending into a shell  302  of deaerator  188 . 
         [0054]    As shown in  FIG. 7 , the oil will flow downwardly along an upper path  202  of a scroll or spiral, and along a lower path  204 . Although shown as vertically upper and lower sides, other opposed side orientations may be used. The inventive deaerator more quickly removes the oil, and thus facilitates the dwell times as mentioned above. 
         [0055]    A deaerator exit  194  delivers oil into the oil tank  90  at least 2 inches (5.08 centimeters) between a freestanding oil level  196  within the tank  90 . An inlet velocity to the deaerator  188  may be less than or equal to 14 feet/second. An exit velocity from the deaerator  188  into the air outlet  192  may be less than or equal to 14 feet/second. 
         [0056]    Applicant has found that introducing the oil and air mixture into an oil tank is much “quieter,” resulting in less re-aeration when it is delivered at least two inches below a free surface. As an example, if the oil were sprayed into the free surface, this could cause splashing and foaming. 
         [0057]    As to the velocity, high velocity oil and air mixtures entering the tank may cause re-aeration. The 14 feet/second is a very good goal to reduce the chances of re-aeration. 
         [0058]    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.