ACTIVE FAN FLUTTER CONTROL

Abstract

A flutter control system for a turbomachine fan includes a plurality of fan case sensors located at a fan case of the turbomachine and configured to sense passing of blade tips of a fan of the turbomachine. A controller is operably connected to the plurality of fan case sensors. A variable fan area nozzle actuator is operably connected to the controller, such that the variable fan area nozzle actuator urges a change in fan nozzle area in response to data from the plurality of fan case sensors indicating flutter or near flutter conditions. A method of flutter control for a turbomachine fan includes sensing a blade tip passing of a plurality of fan blades. Data from a plurality of fan case sensors is compared to a threshold and a fan exit area is changed based on the comparison to dampen flutter of the plurality of fan blades.

Description

BACKGROUND OF THE INVENTION

[0001] The subject matter disclosed herein relate to turbine engines. More specifically, the subject disclosure relates to control of flutter of fan blades of turbine engines.

[0002] Turbine engines include a fan section having a number of airfoils, or fan blades, extending from a hub. In large turbine engines these fan blades can exceed five feet in length. The length and ratio of length to chord of fan blades leaves them susceptible to flow induced vibration, also known as flutter. Fan blade flutter can lead to structural damage to and failure of the fan blade, and liberation of the fan blade from the hub which results damage to components and potentially failure of the turbine engine. Fan blades typically are susceptible to flutter during certain operation conditions of the turbine engine. Typically, flutter is avoided by avoiding those operating conditions which may lead to flutter. This, however, places undesirable restrictions on the operation of the turbine engine.

BRIEF DESCRIPTION OF THE INVENTION

[0003] According to one aspect of the invention, a flutter control system for a turbomachine fan includes a plurality of fan case sensors located at a fan case of the turbomachine and configured to sense passing of blade tips of a fan of the turbomachine. A controller is operably connected to the plurality of fan case sensors. A variable fan area nozzle actuator is operably connected to the controller, such that the variable fan area nozzle actuator urges a change in fan nozzle area in response to data from the plurality of fan case sensors indicating flutter or near flutter conditions.

[0004] According to another aspect of the invention, a method of flutter control for a turbomachine fan includes sensing a blade tip passing of a plurality of fan blades via a plurality of fan case sensors disposed at a fan case of a turbomachine. Data from the plurality of fan case sensors is compared to a threshold and a fan exit area is changed based on the comparison to dampen flutter of the plurality of fan blades.

[0005] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] 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:

[0007] FIG. 1 is a schematic of an exemplary embodiment of an active flutter control system; and

[0008] FIG. 2 is a schematic of another exemplary embodiment of an active flutter control system.

[0009] The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Shown in FIG. 1 is a schematic of an embodiment of an active flutter control system 10. The system includes a plurality of tip timing probes 12 located in a fan case 14 of a turbomachine 16. The tip timing probes 12 are located to observe arrival timing of a plurality of fan blades 18 fixed to a fan shaft 20 as the plurality of fan blades 18 rotate about a fan axis 22. In the embodiment of FIG. 1, three tip timing probes 12 are utilized, located in the fan case 14 substantially to monitor passing of a leading edge 24, trailing edge 26, and mid-chord 28 of the plurality of fan blades 18. The tip timing probes 12 monitoring the leading edge 24 and trailing edge 26 are utilized to determine fan blade 18 twist. The tip timing probes 12 at mid-chord 28 monitor tip timing to determine flex of the fan blades 18. Even though three tip timing probes 12 are utilized in the embodiment of FIG. 1, it is to be appreciated that other quantities of tip timing probes 12, for example, five or six tip timing probes 12, may be used. Further, groups of tip timing probes 12 may be positioned radially around the fan case 14, for example at 12 o'clock, 4 o'clock, and 8 o'clock positions. This allows for collection of more tip passing data and correlation and/or verification of data when taken at multiple locations around the fan case 14.

[0011] Together, the information from the tip timing probes 12 is communicated to a full authority digital engine control (FADEC) 30. The FADEC 30 compares the passing timing of the fan blades 18 to a threshold, to determine if a fan blade 18 is approaching a flutter condition or is actively fluttering. Based on the comparison, the FADEC 30 sends commands to a variable fan area nozzle (VFAN) actuator 32. The VFAN actuator 32 drives a VFAN 34 to change a fan exit area 36. The change to fan exit area 36 ensures that sufficient back pressure is applied to the fan blades 18 to dampen out flutter as measured by the tip timing probes 12.

[0012] Another embodiment of a flutter control system 10 is shown in FIG. 2. In this embodiment, a plurality of radio frequency (RF) probes 38 located in the fan case 14 to observe arrival timing of the plurality of fan blades 18. As with the embodiment of FIG. 1, three RF probes 38 are utilized, located in the fan case 14 substantially to monitor passing of the leading edge 24, trailing edge 26, and mid-chord 28 of the plurality of fan blades 18. The RF probes 38 monitoring the leading edge 24 and trailing edge 26 are utilized to determine fan blade 18 twist. The tip timing probes 12 at mid-chord 28 monitor tip timing to determine flex of the fan blades 18.

[0013] A plurality of strain gauges 40 are arranged along a span 42 of the fan blade 18 and are connected to a radio frequency identification (RFID) tag 44 at the fan blade 18. In FIG. 2, the strain gauges 40 are arranged substantially linearly along the span 42, but this arrangement is merely exemplary. Any appropriate arrangement of strain gauges 40, for example, placement of strain gauges 40 at known high stress points, is contemplated within the present scope. The RFID tag 44 communicates with one or more of the RF probes 38 to relay data from the plurality of strain gauges 40 to the FADEC 30. The FADEC 30 utilizes data from the plurality of strain gauges 40 and the RF probes 38 to determine flutter status of the fan blades 18. Utilizing the plurality of strain gauges 40 and the RFID tag 44 provides the FADEC 30 with more data to more accurately determine the flutter status of the plurality of fan blades 18. As in the embodiment of FIG. 1, the FADEC 30 is linked to the VFAN actuator 32 to change the fan exit area 36 to mitigate flutter of the plurality of fan blades 18.

[0014] 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. 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.

Claims

1. A flutter control system for a turbomachine fan comprising: a plurality of fan case sensors disposed at a fan case of the turbomachine and configured to sense passing of blade tips of a fan of the turbomachine; a controller operably connected to the plurality of fan case sensors; and a variable fan area nozzle actuator operably connected to the controller, such that the variable fan area nozzle actuator urges a change in fan nozzle area in response to data from the plurality of fan case sensors indicating flutter or near flutter conditions.

2. The system of claim 1, further comprising at least one blade sensor disposed on a blade of the fan.

3. The system of claim 2, wherein the at least one blade sensor is operably communicative with the controller.

4. The system of claim 3, further comprising a radio frequency identification tag disposed at the blade and at least one radio frequency sensor disposed at the fan case.

5. The system of claim 2, wherein the at least one blade sensor is at least one strain gauge.

6. The system of claim 1, wherein the plurality of fan case sensors is three fan case sensors.

7. The system of claim 1, wherein the plurality of fan case sensors are a plurality of tip timing probes.

8. The system of claim 1, wherein the controller is a full authority digital engine control (FADEC).

9. A method of flutter control for a turbomachine fan comprising: sensing a blade tip passing of a plurality of fan blades via a plurality of fan case sensors disposed at a fan case of a turbomachine; comparing data from the plurality of fan case sensors to a threshold; and changing a fan exit area based on the comparison to dampen flutter of the plurality of fan blades.

10. The method of claim 9, further comprising: communicating the data from the plurality of fan case sensors to a controller; comparing the data to a threshold at the controller; and sending a command from the controller to a variable fan area nozzle actuator to change the fan exit area.

11. The method of claim 10, further comprising: collecting strain data via at least one fan blade sensor disposed at the plurality of fan blades; communicating the strain data to the controller; and comparing the strain data to a strain threshold.

12. The method of claim 11, further comprising communicating the strain data to the controller via a radio frequency identification tag.

13. The method of claim 9, further comprising: evaluating a twist of the plurality of fan blades via the plurality of fan case sensors; and evaluating a flex of the plurality of fan blades via the plurality of fan case sensors.

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