BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a bearing compartment within an engine;
FIG. 2 illustrates an embodiment of a dual mode scavenge scoop in accordance with the present invention;
FIG. 3 illustrates an alternative embodiment of a dual mode scavenge scoop in accordance with the present invention; and
FIG. 4 is a graph showing breather flow as a percentage of oil supply vs. oil flow for the embodiments of FIGS. 2 and 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Referring now to FIG. 1, there is shown a bearing compartment 10 for an engine. At one end of the compartment 10, there is a rotating disk 12 and an upstream cavity 14. Sealing airflow is provided to the upstream cavity 14 via the buffer port 16 and a suitable conduit or piping system. The sealing airflow enters the bearing compartment 10 through holes 17 inside the rotating disk 12. Additional seal airflows are provided to the seals 18 and 20 to prevent oil leakage out of the compartment's outer and inner rotor/stator interfaces 22 and 24.
The compartment 10 contains one or more bearings 26. Oil is provided through the oil supply nozzle 28 for the purpose of bearing lubrication and compartment cooling. In general, air and oil flows mix inside the bearing compartment 10 and generates a high velocity swirling flow pattern that forms a liquid wall film along the internal compartment walls. In the case of an oil film flow along a rotating wall 30, the oil film will be pumped by the centrifugal acceleration to the free end of the shaft 32, where it will separate, disintegrate into droplets, and flow radially outwards until it coalesces on another surface. As noted before, in the case of oil coalescence on a stationary surface 34, superimposed effects of interfacial shear and gravitational forces will dominate the oil film motion.
The compartment 10 is provided with one or more breather ports 40 through which an air/oil mist is carried out of the compartment 10. The compartment 10 is also provided with a scavenge port 42 through which oil is carried out of the compartment.
Referring now to FIG. 2, there is shown a first embodiment of a tangential scavenge scoop 44 in accordance with the present invention. As can be seen from this figure, the scavenge scoop 44 has a first wall 46 which extends into the scavenge port 42 and a second wall 48 at an angle to the first wall 46. A separation wall 50 is connected to the scavenge scoop 44 at the second wall 48 to create a settling cavity or sump region 52 with the compartment end wall 54. If desired, the separation wall 50 may be integrally formed with the second wall 48 of the scavenge scoop 44. The separation wall 50 serves to shield the settling cavity or sump region 52 against the rotor. As can be seen from this figure, the settling cavity or sump region 52 connects directly into the exit pipe 56 of the scavenge port 42. As can be seen from this figure, half of the diameter of the exit pipe 56 has been dedicated to the downstream portion of the sump, where as the other half is still sufficient to process the upstream air/oil mixture that is captured by the tangential scavenge scoop 44. The separation wall 50 is advantageous in that it reduces the size of any recirculation zone and maintains it substantially within the sump region 52.
Referring now to FIG. 3, there is shown an alternative embodiment of the present invention. In this embodiment, the tangential scavenge scoop 44′ has a first wall 46′, which does not extend into the exit pipe 56′, and a second wall 48′. The first wall 46′ terminates at an end 47′ which is at a distance from the entrance 49′ of the exit pipe 56′. A baffle 58′ is mounted to the compartment end wall 54′ just upstream of the entrance 49′ to the exit pipe 56′ to create a small recirculation region 60′. In this way, excessive scavenge inlet pressure losses that may be expected from a cross flow of oil may be avoided. As before, the settling cavity or sump region 52′ created by the separation wall 48′ connects directly into the exit pipe 56′ of the scavenge port 42. The exit pipe 56′ also receives the upstream air/oil mixture that is captured by the tangential scavenge scoop 44′.
Referring now to FIG. 4, there is shown the results of a test where the embodiments shown in FIGS. 2 and 3 (Modifications B and C respectively) were compared to a tangential scavenge scoop arrangement without the separation wall (Modification A). It can be seen from this figure that the breather oil flow rate for the modifications B and C (shaded area 70) is at a very desirable level of less than 2% of the total, whereas the breather oil flow rate for modification A as a function of oil flow increases above 2% of the total as oil flow increases. It also has been found that the relative breather oil flow rate for modifications B and C is independent of total oil, which indicates sufficient scavenging capacity.
The dual mode oil scavenge scoop of the present invention is a novel solution in that the single scavenge port 42 works well on both high and low power regimes. As used herein, the terms “high” and “low” power regimes are primarily characterized by the rotational speed of the rotor. The rotor imposes an interracial shear on the liquid wall film and, therefore, drives the oil film in circumferential (rotational) direction. Depending on the location around the circumference, gravitational forces may assist or counteract that driving force. If one envisions a situation where the oil film would have to flow uphill, it takes a significant interfacial shear to overcome gravitation forces that want to keep the oil at the bottom. In this sense, a high power setting is one that imposes enough interfacial shear to drive all the oil over top-dead center.
The dual mode scavenge scoop of the present invention offers significant cost and weight benefits to more conventional solutions, and is therefore desirable for aircraft applications.
If desired, two scavenge lines and pump stages can be added to capture the oil and all operating conditions.
It is apparent that there has been provided in accordance with the present invention a dual mode scavenge scoop which fully satisfies the objects, means, and advantages set forth hereinbefore. While the present invention has been described in the context of specific embodiments thereof, other unforeseen alternatives, modifications, and variations may become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.
Patent Application
20080078617
