BACKGROUND OF THE INVENTION
Contemporary aircraft include fans used for various cooling purposes. In the current configuration, the size, shape, and rotational speed are such that high hoop stresses occur. Currently such contemporary fans are being removed from the aircraft regularly at very short intervals and returned to the factory for inspection. If any anomalies are detected, then the impeller is replaced, which results in a lengthy and expensive upkeep process.
BRIEF DESCRIPTION OF THE INVENTION
In one embodiment, the invention relates to a fan assembly including a housing having an inner peripheral wall defining a flow through opening, a stator located within the through opening, a rotor comprising a hub having a front wall supporting an outer peripheral wall having a forward balancing ring and an aft balancing ring, and an annular array of non-stationary blades extending from the outer peripheral wall. The hub is made of cast metal with a plurality of strengthening ribs located between the forward balancing ring and the aft balancing ring.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a cross-sectional view of a prior art fan assembly;
FIG. 2 is an enlarged view of a portion of the prior art fan assembly of FIG. 1;
FIG. 3 is a perspective view of the result of stresses found during numerical analysis of the prior art fan assembly of FIG. 1;
FIG. 4 is a front view of a fan assembly according to an embodiment of the invention;
FIG. 5 is a cross-sectional view of a portion of the fan assembly of FIG. 4; and
FIG. 6 is a perspective view of the result of stresses found during numerical analysis of the fan assembly of FIG. 4.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
FIG. 1 illustrates a partial cross-sectional view of a portion of a prior art fan assembly 10, which has been shown partially cross sectioned. The fan assembly 10 may be a cooling fan for an aircraft engine or other aircraft application having a housing 12 and a rotor 24, which may be moveably mounted within the housing 12 and a cooling air stream may be generated by the rotor 24 during operation of the fan assembly 10. A stator 20 may be located within the housing 12 and may include an annular array of stationary blades 22. The rotor 24 includes a hub 26 and an annular array of non-stationary blades 28 extending from the hub 26. Two spaced apart bearings 30 may be operably mounted to the stator 20. A shaft 32 may be rotatably supported by the bearings 30 for rotation about a rotational axis 34. The rotor 24 may be operably coupled to the shaft 32 such that both the shaft 32 and rotor 24 may be co-rotated.
As may more clearly be seen in FIG. 2, the hub 26 includes a front wall 40 and a side wall 42. The side wall 42 is thickened at two longitudinal locations forming a first balance ring 44 and a second balance ring 46. The fan assembly 10 is approximately 16 inches in diameter, made of a cast metal such as cast aluminum alloy. The use of casting is mainly based on cost-effectiveness and the casting goes through machining processes to finished dimensions, including the diameter. The configuration of the fan assembly 10 results in high hoop stresses that may be comparable to the yield strength of the cast aluminum alloy. For example, the result of numerical analysis run on the fan assembly 10 is shown in FIG. 3. The numerical analysis has been illustrated as a variety of portions 50-58 representing ranges of stresses found in the fan assembly 10 at a predetermined rotational speed of 8,000 rpm. It will be understood that this is merely for illustrative purposes and that the stresses within each portion may not be uniform throughout. The portions 50 represent 63 psi to 5019 psi, the portions 52 represent 5020 psi to 7561 psi, the portions 54 represent 7562 psi to 15184 psi, the portions 56 represent 15185 psi to 22808 psi, and the portions 58 represent 22809 psi to 30432 psi. As it can be seen the numerical analysis shows maximum stress levels above 30,000 psi.
Referring now to FIG. 4, a portion of a fan assembly 100 according to an embodiment of the invention is illustrated. The fan assembly 100 is similar to the prior art fan assembly 10. Therefore, like parts will be identified with like numerals increased by 100, with it being understood that the description of the like parts of the fan assembly 10 applies to the fan assembly 100, unless otherwise noted.
A housing 112 including an inner peripheral wall 114 defining a flow through opening 116 may be included in the fan assembly 100. A rotor 124 may be moveably mounted within the housing 112 and a cooling air stream may be generated by the rotor 124 during operation of the fan assembly 100.
Referring now to FIG. 5, a stator 120 may be located within the flow through opening 116 and may include an annular array of stationary blades 122 provided along the inner peripheral wall 114. It is also contemplated that the stator 120 may form a portion of the housing 112. The stator may have a diameter of at least 14 inches. In the illustrated example, it is contemplated that the stator has a diameter of at least 16 inches. A rotor 124 is also illustrated and includes a hub 126 having a front wall 140 supporting an outer peripheral wall 142 having a forward balancing ring 144 and an aft balancing ring 146 and an annular array of non-stationary blades 128 extending from the outer peripheral wall 142. In the illustrated example, the flow of air is left to right through the flow through opening 116. The front wall 140 may include a collar 148, with the front wall 140 extending between the collar 148 and the outer peripheral wall 142. As illustrated, the front wall 140 may have a convex cross section between the collar 148 and the outer peripheral wall 142.
It is contemplated that the hub 126 is made of cast metal with a plurality of strengthening ribs 160 located between the forward balancing ring 144 and the aft balancing ring 146. The strengthening ribs 160 may extend between the forward balancing ring 144 and the aft balancing ring 146 and have any suitable radial spacing. As illustrated, the strengthening ribs 160 may extend in a direction generally parallel to an axis of rotation 134 of the rotor 124. The strengthening ribs 160 may reduce in cross sectional area in a direction from the forward balancing ring 144 to the aft balancing ring 146 or may maintain a constant cross sectional area. If the strengthening ribs 160 do reduce in cross sectional area, they may continuously reduce in cross sectional area in a direction from the forward balancing ring 144 to the aft balancing ring 146. The strengthening ribs 160 may be sized and located in any manner suitable to reduce hoop stress in the outer peripheral wall 142. It is contemplated that the reduction of the hoop stress may be at least 20% than that of a stator without the strengthening ribs at a predetermined rotational speed.
For example, FIG. 6 illustrates the result of stresses found during numerical analysis of the fan assembly 100 having the illustrated configuration of strengthening ribs 160. The numerical analysis has been illustrated as a variety of portions 170-176 representing ranges of stresses found in the fan assembly 100 at a predetermined rotational speed of 8,000 rpm. It is contemplated that during operation, the fan assembly 100 may be rotated at a predetermined rotational speed of at least 7,000 rpm. Including that the predetermined rotational speed may be at least 8,000 rpm. It will be understood that this is merely for illustrative purposes and that the stresses within each portion may not be uniform throughout. The portions 170 represent 63 psi to 6870 psi, the portions 172 represent 6871 psi to 14425 psi, the portions 174 represent 14426 psi to 18202 psi, and the portions 176 represent 18203 psi to21980 psi. As it can be seen, the numerical analysis shows maximum stress levels less than 22,000 psi. In the illustrated example, the reduction of the hoop stress is at least 30%, this is a significant improvement from the prior art fan assembly 10.
The embodiments described above provide for a variety of benefits including that they have a high reliability and require less maintenance, including less preventative maintenance. The embodiments described above result in improved fan service life, which results in commercial advantages including reduced maintenance cost and reduced down time of the aircraft on which the fan assembly is installed. Further, the embodiments of the invention may be implemented with a minor modification to the casting tool, and thus cost and timing impacts would be minimal Further still, the weight increase is estimated at a mere 5 percent, which will not jeopardize weight specifications.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
Patent Application
20140064958
