Patent Description:
Gas turbine engines have bearing compartments wherein the bearings for rotating components within the engine are housed. These bearing compartments require oil and typically include dynamic seals with an air buffered cavity to contain oil within the compartment. A passive drainback system is sometimes desired to ensure oil cannot enter the buffered air cavity and eventually make its way into the flow path of a gas turbine engine. A gutter system is sometimes located directly outboard of the bearing compartment seals, and is attached to a drain tube which passes the captured oil from the gutter system back into the bearing compartment and thereby prevents the oil from reaching the flow path of the engine. One non-limiting example of such a gutter system is that disclosed in <CIT>.

Typically, bearing compartments operate at a different pressure relative to the surrounding buffer air cavity to maintain the oil containment function of the seals. Because of the need to maintain this pressure differential there is a limited ability for the bearing compartment to process additional air flow from other sources such as a drain feature.

It is usually desired to locate the end of the drain tube, which returns oil to the bearing compartment, as low into the compartment strut (and therefore as close to the drain port or sump) as possible. This is due to the desire to keep the tube in a relatively calm part of the strut to avoid potential for back flow, to increase the overall head height in the tube (again to help prevent back flow), and finally to reduce the impact that any debris from the buffer cavity will have on components within the bearing compartment.

During positive differential pressures, where pressure in the buffer cavity is higher than pressure in the bearing compartment, managing additional airflow into the bearing compartment through the drain tube, both in terms of overall mass flow and velocity, can become a significant factor in proper functioning of the oil drainback system.

Modern gas turbine engine bearing compartments are highly optimized designs to accommodate high oil flows in a relatively small amount of space. Many factors impact the ability of the sump to effectively scavenge oil, but typically they are heavily influenced by the operating pressures inside and outside of the compartment. Additionally, the quality of the oil entering the drain tube can affect the ability of the scavenge pump to scavenge oil. Further, high air content entrained within the oil can significantly impact the drain efficiency of the sump.

Introducing a drain tube into a sealed bearing compartment that is under a positive delta pressure results in significant amounts of airflow through the drain tube and into the sump or at least the area of the sump. This additional airflow can impact the scavenge capability of the sump (even with a breathed compartment), especially in small, high speed, bearing compartments.

One response to this problem has been to introduce a restriction device (for example an orifice) into the drain tube to reduce the mass flow of the air entering the compartment and thereby reduce velocity of the air. This is an effective way of reducing the impact that the airflow has on scavenge capability, but significantly reduces the ability of the drainback system to tolerate debris that may likely be in the system. The size of the orifice needed to create acceptable air flow conditions is sufficiently small that the orifice may become blocked by debris.

The present disclosure addresses this problem.

<CIT>, <CIT>, <CIT> and <CIT> disclose diffusers of the prior art.

In one aspect, a diffuser for an oil drainback system drain tube is provided according to claim <NUM>.

In another non-limiting embodiment, flow area of the openings in the side wall is greater than flow area of the end opening.

In an embodiment, an oil drainback system for a bearing compartment of a gas turbine engine is provided according to claim <NUM>.

In another aspect, a method is provided for upgrading an oil drainback system for a gas turbine engine according to claim <NUM>.

In another non-limiting embodiment, the drain tube contains an orifice for restricting flow through the drain tube, and wherein the method further comprises removing the orifice from the drain tube in advance of the mounting step.

These features and elements as well as the operation of the invention will become more apparent in light of the following description and the accompanying drawings.

The invention relates to fluid diffusion device for an oil recirculation or drainback system and, more particularly, to such a device for an oil drainback system in a gas turbine engine.

<FIG> shows a side partial cross-section view of a gas turbine engine <NUM> and includes axial centerline <NUM>, upstream airflow inlet <NUM>, downstream airflow exhaust outlet <NUM>, fan section <NUM>, compressor section <NUM> (with low pressure compressor ("LPC") section 20A and high pressure compressor ("HPC") section 20B), combustor section <NUM>, turbine section <NUM> (with high pressure turbine ("HPT") section 24A and low pressure turbine ("LPT") section 24B), engine housing <NUM> (with core case <NUM> and fan case <NUM>), fan rotor <NUM>, LPC rotor <NUM>, HPC rotor <NUM>, HPT rotor <NUM>, LPT rotor <NUM>, gear train <NUM>, fan shaft <NUM>, low speed shaft <NUM>, high speed shaft <NUM>, bearing compartments 50A, 50B, and 50C, plurality of bearings <NUM>, core gas path <NUM>, bypass gas path <NUM>, combustion chamber <NUM>, and combustor <NUM>.

The present disclosure related to an oil drainback system for the bearing compartments 50A, 50B, 50C. After consideration of the following disclosure, it will be appreciated that while this disclosure is made in terms of a gas turbine engine as shown in <FIG>, the subject matter disclosed herein would be equally useful in other engine or turbine settings wherein bearing compartments have an oil drainback system which reintroduces oil to the bearing compartment at a potentially elevated pressure and/or accompanied by a high velocity gas stream.

<FIG> is an enlarged view of components of bearing compartment 50B of <FIG>, and shows surrounding buffer air cavity <NUM> separated from bearing compartment 50B by a seal support <NUM>. A drain tube assembly <NUM> is schematically shown in the lower portion of this drawing and shows the position of oil being re-introduced into the bearing compartment 50B near the sump after being collected from the buffer air cavity <NUM>.

<FIG> is a completely schematic illustration of oil flow through and around the bearing compartment 50B and an accompanying oil drainback system <NUM>. A sump <NUM> allows oil to flow to a storage tank (not shown) with filters and the like where oil can then be drawn or fed back to the bearing compartment as needed, schematically illustrated by arrow <NUM>. In addition, oil which has reached the buffer air cavity <NUM> is collected in an oil drainback system <NUM> and returned to the bearing compartment 50B. This oil can be collected, for example by centripetal force and gravity, in a gutter system schematically illustrated at <NUM> and then flows at pressure typically influenced by pressure in the buffer air area <NUM>, through an oil flow path <NUM> to an oil drain tube <NUM> which typically introduces the collected oil near sump <NUM>. Oil and air in the oil flow path are typically exposed to the higher pressure which can be present in the buffer air cavity <NUM>, and therefore gas (air) and entrained oil can frequently be introduced back into bearing compartment 50B at a high velocity from drain tube <NUM>, which high velocity is schematically illustrated at arrow <NUM>.

High velocity flow <NUM> can interfere with proper scavenging and flow of oil through sump <NUM>, resulting in this area of the bearing compartment becoming flooded with oil. In order to prevent this, and as shown in <FIG>, an orifice <NUM> or other flow restriction has been placed in drain tube <NUM> to reduce the impact of air flow into the bearing compartment. To effectively address the problem, orifices as small as <NUM> inches (<NUM>) in diameter have been utilized. However, an orifice this small is extremely prone to blockage with debris that can frequently be present in the flow of air and oil from the sump.

An in-line orifice as shown in <FIG> restricts air flow and this restricted flow is then able to expand into the tube after the restriction, slowing down before exiting the tube into the compartment.

The diffusers as disclosed herein do not restrict mass flow like the orifice. Rather, they increase the flow area at the exit to allow the mass flow from the drain tube to diffuse as opposed to exiting from the tube and acting like a single jet of air/oil.

Diffusers as disclosed herein are configured to produce in-line flow velocity less than or equal to that which is produced using an orifice in the line. In other words, an orifice as shown in <FIG> can be used and optimized until an acceptable in-line flow velocity is achieved, that is, one which does not interfere with proper flow to the sump. Once this acceptable in-line flow velocity is determined, a diffuser such as those disclosed herein can be configured with side openings in various configurations to produce an in-line flow velocity less than or equal to the acceptable in-line velocity, while doing so with diffusion and larger flow openings, thereby reducing the chance of blockage due to debris.

<FIG> shows drain tube <NUM> mounted to a structure <NUM> which could be a portion of the structure of bearing compartment 50B such as a strut or the like. As shown, a diffuser device <NUM> can be affixed to an end <NUM> of drain tube <NUM>. Diffuser device <NUM> receives flow at end <NUM> of drain tube <NUM> and diffuses and redirects flow from drain tube <NUM> to remove negative effects of high pressure, high velocity flow into the bearing compartment 50B. Further, diffuser device <NUM> is also configured to minimize the possibility of blockage from debris. In addition to the illustration in <FIG>, <FIG> illustrate different non-limiting configurations of a diffuser device and these different configurations are discussed below.

<FIG> show diffuser device <NUM> defined by a sidewall <NUM> having openings <NUM> passing through sidewall <NUM>. These openings are sized and arranged to direct flow laterally out of diffuser device <NUM>, which both slows the velocity of the flow and also directs it away from the sump in the typical configuration wherein drain tube <NUM> is pointed at the sump. In this configuration, end wall <NUM> also has an end opening <NUM>. The size and amount of side openings <NUM> and end opening <NUM> are configured to reduce velocity of flow out of drain tube <NUM> in the axial direction of drain tube <NUM>, while still maintaining the size of all openings large enough to avoid potential blockage by debris.

In the configuration shown, sidewall <NUM> defines a substantially cylindrical shaped structure, with openings <NUM> arranged around the circumference of the cylinder and also along the length of the cylinder, and with a substantially flat end wall <NUM> with one centered end opening <NUM>. It should be appreciated that other positioning and configuration of the openings <NUM>, <NUM> could be effective as well. In this regard, it has been found particularly useful for a ratio of flow area of openings <NUM> to end opening <NUM> to be at least high enough to produce an exit velocity from the diffuser that is equivalent to or less than the exit velocity of an in-line orifice configuration (such as is shown in <FIG>) that is known to produce acceptable results, while nevertheless reducing or avoiding the risk of plugging of the diffuser from debris.

<FIG> also show an enlarged portion <NUM> at one end of diffuser device <NUM> and this serves to configure diffuser device <NUM> for attachment to drain tube <NUM>. This can be by way of a press fit, or with a tightening strap (not shown) or any other mechanism including threads, adhesive or the like. Further, in some instances it may be desirable to manufacture the diffuser device integrally with the end of the drain tube instead of as a separate part. Of course, maintaining diffuser device <NUM> as a separate part may be more practical for maintenance and cleaning as necessary, and also for the purpose of retro-fitting oil drainback systems with either a straight drain tube or a drain tube with an orifice or other flow restriction.

<FIG> illustrate configuration of a diffuser device <NUM> wherein openings <NUM> are positioned in sidewall <NUM> as mentioned above. In this configuration, a plurality of end openings <NUM> are positioned in end wall <NUM>. Further, a baffle, or central flow opening <NUM> is positioned within diffuser device <NUM> as shown. In this configuration, it should be appreciated that the plurality of end openings <NUM> are all off direct-center, such that even the end openings produce at least some redirection of flow along the axis of drain tube <NUM> and diffuser device <NUM>. In this configuration, there are provided openings upstream and downstream of baffle <NUM> having different sizes, for example with smaller size openings upstream of the baffle and larger size openings downstream of the baffle. The configuration of these different size openings, as with other features of the diffuser, can be based on achieving equivalent air exit velocity compared to a conventional orifice design which produces acceptable results with respect to flow at the sump.

In the configuration of <FIG>, as with the previously discussed configurations, the sizing and placement of the different holes in the diffuser can be configured to produce a flow velocity of similar or less impact than what can be accomplished with an in-line orifice, while greatly reducing susceptibility to plugging due to debris.

In operation, the oil drainback system such as that illustrated in <FIG> collects oil from the buffered air cavity and returns this oil back to the bearing compartment to prevent migration of the oil to areas of the engine where oil is not desired. This is accomplished with a gutter system <NUM> which collects such oil typically assisted by centripetal force and gravity. This collected oil then flows through gas flow path <NUM> to drain tube <NUM>. When pressure in the buffer air cavity results in elevated pressure differential as compared to the sealed bearing compartment, the diffuser device as disclosed herein prevents a high velocity stream of air directly from exiting drain tube <NUM> at a high velocity directed at the sump, and therefore helps to avoid flooding of the sump and excessive air ingestion. Further, the diffuser device is configured to reduce the chance of blockage with debris, thereby providing an oil drainback system which addresses the issues identified above.

It should also be appreciated that the present disclosure lends itself to retro-fitting of existing systems which have either a non-restricted drain tube, or a drain tube with an orifice or other flow restriction. In such a situation, any orifice or flow restriction can be removed from the drain tube and replaced with a diffuser device as disclosed herein, thereby improving functionality of the drainback system without increasing issues of blockage from debris.

Claim 1:
A diffuser (<NUM>) for an oil drainback system drain tube, comprising:
a flow chamber configured for attachment to an open end (<NUM>) of a drain tube (<NUM>), wherein the flow chamber has a side wall (<NUM>) and an end wall (<NUM>), and openings (<NUM>) in at least the side wall (<NUM>),
wherein the side wall (<NUM>) defines a cylinder,
wherein the openings (<NUM>) are distributed around a circumference and along a length of the cylinder,
wherein the flow chamber further comprises at least one end opening (<NUM>) in the end wall (<NUM>),
the diffuser further comprising at least one baffle (<NUM>) in the flow chamber between an inlet end where the flow chamber connects to the drain tube (<NUM>), and the end opening (<NUM>),
wherein the openings (<NUM>) in the side wall (<NUM>) are distributed upstream and downstream of the baffle (<NUM>),
characterised in that openings (<NUM>) upstream of the baffle (<NUM>) have a smaller diameter than openings (<NUM>) downstream of the baffle (<NUM>).