Patent Description:
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.

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.

More recently, it has been proposed to provide a gear reduction between the fan drive turbine and the fan rotor.

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.

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.

<CIT> discloses a prior art gas turbine engine according to the preamble of claim <NUM>.

In a featured embodiment, a method of operating a gas turbine engine is provided as set forth in claim <NUM>.

In another embodiment according to the previous embodiment, the separator is at an intermediate position in the inlet.

In another embodiment according to any of the previous embodiments, the air outlet has a tube extending downwardly into a deaerator shell.

In another embodiment according to any of the previous embodiments, the flow separator includes a scroll spiraling from the inlet to a deaerator exit.

In another embodiment according to the previous embodiment, said exit includes a plurality of holes in a shell.

In a further example, the engine <NUM> bypass ratio is greater than or equal to about six (<NUM>:<NUM>), with an example embodiment being greater than about ten (<NUM>:<NUM>), the geared architecture <NUM> is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM> and the low pressure turbine <NUM> has a pressure ratio that is greater than about five (<NUM>:<NUM>). In one disclosed embodiment, the engine <NUM> bypass ratio is greater than or equal to about ten (<NUM>:<NUM>), the fan diameter is significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> has a pressure ratio that is greater than about five (<NUM>:<NUM>). The geared architecture <NUM> 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 <NUM>:<NUM>.

The fan section <NUM> of the engine <NUM> is designed for a particular flight condition -- typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>,<NUM>). The flight condition of <NUM> Mach and <NUM>,<NUM> ft (<NUM>,<NUM>), 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 corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (<NUM> °R)]<NUM> (K=R * <NUM>/<NUM>).

The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about <NUM> ft / second (<NUM>/s).

As shown in <FIG>, a flexible shaft <NUM>, which is driven by the turbine <NUM>, drives a sun gear <NUM> which, in turn, engages and drives intermediate gears <NUM>. In some embodiments, the intermediate gears <NUM> may be planet gears of a planetary epicyclic gear system. In other embodiments, the intermediate gears <NUM> may be star gears of a star epicyclic gear system. The intermediate gears <NUM> engage and drive a ring gear <NUM> to, in turn, drive an output shaft <NUM>, which then drives the fan rotor <NUM>. 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 <NUM>, to the intermediate gears <NUM> and to other locations within the gear reduction <NUM>.

<FIG> shows baffles <NUM> which are placed circumferentially between adjacent planet gears <NUM>.

A gutter <NUM> surrounds the gear reduction <NUM> and captures oil that has left the gear reduction. Oil from the gear reduction <NUM> is returned to a pump <NUM> (See <FIG>) or a tank <NUM> as shown schematically in <FIG>. As shown, a lubricant system <NUM> includes the gear reduction <NUM> which may be structured as shown in <FIG> and <FIG>. Notably, complete details of the operation of the baffle, the gutter and the other portions of the gear reduction may be as disclosed in <CIT>.

Oil flows from an oil pump <NUM> to a filter <NUM> through a pressure relief valve <NUM> to an air/oil cooler <NUM> and then to a fuel/oil cooler <NUM>. The oil may pass through an oil pressure trim orifice <NUM> and back to the tank <NUM>. Alternatively, the oil may pass through a strainer <NUM> and then to the gear reduction <NUM>. Oil returning from the gear reduction and, in particular, from the gutter, may pass back directly to the pump <NUM> or to the tank <NUM>. This is a simplification of the overall lubricant system and, as appreciated, there may be other components.

Applicant has recognized that by utilizing baffles <NUM> and a gutter <NUM> on the gear reduction <NUM>, which may be generally as disclosed in the above-mentioned U. Patent, the oil need not sit in the oil tank for ten seconds in order to de-aerate. Thus, the size of the tank <NUM> may be made much smaller.

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.

Applicant has discovered that oil is de-aerated by the baffles <NUM> 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 <NUM> seconds. This allows the use of oil tank <NUM> to be of a size roughly equivalent to the size utilized in prior non-geared gas turbine engines. A deaerator <NUM> is shown incorporated into the oil tank <NUM>.

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.

As an example, an oil tank that holds <NUM> to <NUM> quarts of oil (<NUM> to <NUM> litres) may be utilized on a geared gas turbine engine with <NUM>,<NUM> to <NUM>,<NUM> lbs (<NUM>,<NUM> to <NUM>,<NUM>) in rated thrust at take-off. Further, an oil tank may be <NUM> quarts to <NUM> quarts (<NUM> to <NUM> litres) of oil for an engine with <NUM>,<NUM> to <NUM>,<NUM> lbs (<NUM>,<NUM> to <NUM>,<NUM>) in rated thrust at take-off.

<FIG> shows a deaerator embodiment <NUM>. A line <NUM> receives an air/oil mixture such as from the pump <NUM>. Air leaves through an air outlet <NUM>, as shown in <FIG>.

A plurality of oil outlets <NUM> are shown in an outer shell <NUM> of the deaerator. An oil level <NUM> is shown schematically, and would be the oil level within the oil tank <NUM> of <FIG>.

As shown in <FIG>, a flow splitter or separator <NUM> is provided inline to the inlet <NUM> and serves to split the air/oil flow into two paths, and at an intermediate location in inlet <NUM>. This will hasten the deaeration of the mixed oil and air from the inlet <NUM>. The air will be at the radially outer locations, and will pass through a tube <NUM> into the air outlet <NUM>. As shown, air outlet <NUM> has an end <NUM> extending into a shell <NUM> of deaerator <NUM>.

As shown in <FIG>, the oil will flow downwardly along an upper path <NUM> of a scroll or spiral, and along a lower path <NUM>. 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.

A deaerator exit <NUM> delivers oil into the oil tank <NUM> at least <NUM> inches (<NUM> centimeters) below a freestanding oil level <NUM> within the tank <NUM>. An inlet velocity to the deaerator <NUM> is less than or equal to <NUM> feet/second (<NUM>/s). An exit velocity from the deaerator <NUM> into the air outlet <NUM> is less than or equal to <NUM> feet/second (<NUM>/s).

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 (<NUM>) below a free surface. As an example, if the oil were sprayed into the free surface, this could cause splashing and foaming.

As to the velocity, high velocity oil and air mixtures entering the tank may cause re-aeration. The <NUM> feet/second (<NUM>/s) is a very good goal to reduce the chances of re-aeration.

Claim 1:
A method of operating a gas turbine engine (<NUM>) comprising:
driving a gear reduction (<NUM>) using a fan drive turbine, said gear reduction (<NUM>) for driving a fan rotor (<NUM>);
supplying oil to said gear reduction (<NUM>) using a lubrication system (<NUM>), with an oil tank (<NUM>), the lubrication system (<NUM>) including a lubricant pump (<NUM>); and
supplying a mixture of air and oil to an inlet (<NUM>) of a deaerator (<NUM>, <NUM>), said deaerator (<NUM>, <NUM>) including a separator (<NUM>) for separating oil, and delivering separated air to an air outlet (<NUM>), and delivering separated oil back into an oil tank (<NUM>);
characterised in that:
said separator (<NUM>) includes a member having lubricant flow paths (<NUM>, <NUM>) on both of two opposed sides;
an inlet velocity to the deaerator (<NUM>, <NUM>) is less than or equal to <NUM> feet /second (<NUM>/s), and an exit velocity from the deaerator (<NUM>, <NUM>) of the separated air is less than or equal to <NUM> feet/second (<NUM>/s);
said gear reduction (<NUM>) includes a sun gear (<NUM>) for driving intermediate gears (<NUM>) and oil baffles (<NUM>) are located circumferentially between said intermediate gears (<NUM>);
an oil capture gutter (<NUM>) surrounds said gear reduction (<NUM>); and
a dwell time of oil in the oil tank (<NUM>) as removed by said lubricant pump (<NUM>), on average, is five seconds or less.