Patent Application
20160208823
The subject matter disclosed herein generally relates to the field of fan rotors and more particularly to shrouded fan rotors.
The subject matter also generally relates to environmental control systems. In particular, the subject matter relates to a ram air fan assembly and fan rotors thereof for environmental control systems for aircraft.
An environmental control system (ECS) aboard an aircraft provides conditioned air to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressurized air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the ECS before the air is delivered to the aircraft cabin. As heat is removed from the air, it is dissipated by the ECS into a separate stream of air that flows into the ECS, across heat exchangers in the ECS, and out of the aircraft, carrying the excess heat with it. Under conditions where the aircraft is moving fast enough, the pressure of air ramming into the aircraft is sufficient to move enough air through the ECS and over the heat exchangers to remove the excess heat.
While ram air works well under normal flight conditions, at lower flight speeds, or when the aircraft is on the ground, ram air pressure may be too low to provide enough air flow across the heat exchangers for sufficient heat removal from the ECS. Under these conditions, a fan within the ECS is employed to provide the necessary airflow across the ECS heat exchangers. This fan is called a ram air fan.
According to one embodiment, a fan rotor for an aircraft environmental control system ram fan is provided. The fan rotor includes central body defining a central axis and a radius having a first radial distance that is defined as a distance from the central axis to an edge of the central body. A plurality of fan blades extend radially from the edge of the central body to a second radial distance, the second radial distance defined as a distance from the central axis to a tip of the fan blades. A shroud extends circumferentially between and connecting each of the plurality of fan blades. The shroud is located at a radial distance from the central axis that is greater than the first radial distance and includes one or more tuning features configured to mistune a vibration of the fan rotor during operation.
According to another embodiment, a method of manufacturing a fan rotor for an air cycle machine is provided. The method includes providing a material for a fan rotor, forming a central body of the fan rotor from the material, the central body defining a central axis and a radius having a first radial distance that is defined as a distance from the central axis to an edge of the central body, removing material to form a plurality of fan blades extending radially from the edge of the central body to a second radial distance defined as a distance from the central axis to a tip of the fan blades, forming a shroud that extends circumferentially between and connects each of the plurality of fan blades, the shroud located at a radial distance from the central axis that is greater than the first radial distance, and forming one or more tuning features in the shroud, the one or more tuning features configured to mistune a vibration of the fan rotor during operation.
Technical features of the invention include a ram air fan rotor having a shroud that provides improved structural stability and strength to the fan rotor such that failure or damage during surge events may be prevented.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Turning now to
A first radial distance 216 is defined as the radial distance from the central axis 206 of fan rotor 200 to the edge 208 of the central body. Thus, the central body 202 generally defines a circular or disk shape with a radius of 216. A second radial distance 218 is defined as the radial distance from the central axis 206 to the blade tip 214. Thus, the length of the fan blades 210 is the second distance minus the first distance.
Although fan rotor 200 may be configured to operate as a ram air fan for an aircraft environmental control system, such as that shown in
As noted, the fan blades 210 have free ends at tips 214, and thus the end of the blades are free floating and may be subject to vibrations and stresses. For example, due to operational stresses, the fan blades 210 may fail during a surge event. A surge event may occur when there is a blockage upstream of the fan within the system, such as in a partially blocked heat exchanger in an environmental control system of an aircraft, which may result in increased stresses within the system. Thus, the stresses imposed on the fan rotor 200 are increased, and specifically the stresses imposed on the fan blades 210 are increased, which can result in failure, damage, or breaking of the fan blades 210.
Turning now to
Shroud 320, as shown in
Further, in some embodiments, the shroud 320 does not need to be uniform in its construction and/or configuration. For example, as shown in
In the example of
As another example, the radial thickness of the tuning feature of the shroud may be varied, depending on the requirements of use or engineering. A thicker shroud, whether thicker in a radial or axial direction, will provide more material and thus rigidity between the fan blades. However, the additional material will add more weight to the fan rotor, and thus a trade-off may be made depending on the design and needs of the particular fan rotor. In some embodiments, the radial and/or axial thickness of the shroud may be varied to form the tuning feature. In some embodiments that include a varying axial thickness, the tuning feature may be formed with an undulating form or contour along the circumference of the shroud. In some embodiments the contour or shape of the tuning feature may be configured with a repeating pattern or wave pattern. For example, the tuning feature may be formed as a wave pattern or frequency around the circumference of the shroud with the pattern of frequency defining the axial thickness of the shroud.
For example, with reference to
Advantageously, in embodiments that include a tuning feature with a frequency pattern formed in the shroud, either radially or axially, a mistuning of the fan rotor during operation may be provided. Specifically, an asymmetry of the thickness of the shroud can ensure that the vibrations of each of the fan blades do not ring in unison, and thus prevent the fan rotor from vibrating at a single frequency. It is advantageous to prevent vibration at a single frequency because such vibrations may result in additional stress on and/or failure of the blades. The single frequency is prevented, in part, because of an asymmetric distribution of weight around the fan rotor. Thus, while still providing structural strengthening by connecting each of the fan blades of the fan rotor, the variations in thicknesses can be configured to prevent undesirable frequency vibrations within the rotor and blades thereof
Turning now to
At step 406 material is removed, by known methods, from the stock between the first distance, defined as a distance from a central axis to the edge of the central body, and a second distance, defined as a distance from the central axis to the outer rim of the fan rotor, i.e., the fan blade tips, to form the fan blades. At step 408 a shroud is formed on the fan rotor. The shroud may be formed at the second distance (i.e., at the terminal edge of the fan blades), or at some third distance that is between the first distance and the second distance. At step 410, the shroud may be modified to have variable thicknesses in the radial, axial, and/or circumferential directions, i.e., to form one or more tuning features. Process 400 thus may form a fan rotor similar to that shown in
Although process 400 is described as a sequence of steps, those of skill in the art will appreciate that the order of steps is not restricted to that presented above. For example, the machining may all occur at once, and thus steps 404-410 may occur simultaneously, without departing from the scope of the invention. Further, in some embodiments, the steps may be performed in a different order as presented above, or various sub-combinations of steps may be performed simultaneously, without departing from the scope of the invention.
Advantageously, in accordance with various embodiments of the invention, a shrouded fan rotor can significantly reduce the cyclic stress during a surge event, thus prolonging the life of the fan rotor and reducing the need to service or perform maintenance thereon. Specifically, embodiments of the invention may provide a fan rotor that can survive surge events without damage being done to the fan rotor.
Furthermore, advantageously, providing a shroud increases the weight of the fan rotor and thus can push the frequency of modes of operation of the fan rotor out of fan operating speed ranges. For example, the addition of the shroud, due to the weight and the structural integrity, may enable a fan rotor to operate at higher speeds than traditional fan rotors.
Moreover, advantageously, in accordance with various embodiments of the invention, varying the construction of the shroud may provide additional and/or alternative advantages. For example, by providing a pattern of frequency in the shape of the shroud, either in terms of axially thickness or radial thickness, may enable a mistuning of the fan rotor to thus prevent the rotor from operating at specific frequencies that may enable damage to occur to the blades and/or the rotor fan.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments and/or features.
For example, although shown in
Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
