Patent Application
20080187436
This invention relates to a method of mounting a frequency probe in a turbine engine.
Microwave/radio frequency signals have been used to detect, for example, the position of a target component within a turbine engine. A microwave/radio generator produces a signal that is reflected by the target component and processed to detect information such as the position of the target component.
Current methods of instrumentation in a turbine structure require that a hole be drilled in the metal structure to allow the sensor to function. The hole is required to permit communication with a target component. A mechanical connection is required to attach the sensor to the metal structure to prevent leakage. The mechanical connections pose durability issues.
In one example, microwave/radio frequencies are used to detect the clearance of a turbine blade relative to an adjacent housing. The orifice used to accommodate the microwave/radio frequency instrumentation allows air and debris in the turbine gas path to collect within the sensor thereby degrading its performance. The hole also creates a potential pathway for high pressure secondary cooling air used to cool the blade outer air seal to leak through the hole and into the gas path, creating a performance loss.
With prior art methods it is difficult to reliably determine the proximity of the rotating turbine blades relative to the turbine case. What is needed is a method and apparatus for preventing contamination of the sensor and leakage between the cooling path and turbine gas path. What is also needed is a reliable way of establishing an absolute position of the sensor relative to the turbine blades.
A turbine engine includes a target structure, for example, a rotating turbine blade. A probe is arranged near the target structure for communicating a detection frequency relative to the target structure for gathering information such as tip clearance. A housing is arranged adjacent to the target structure. In one example, the housing is a blade outer air seal. The housing includes a structural material that supports a window material. In one example, the window material is secured within an aperture provided by the structural material of the housing. In one example, the window material is brazed to the structural material. The window material is arranged between the probe and the target structure. The window material is transparent to the detection frequency permitting the detection frequency to pass through the window to the target structure for measurement of its position relative to the housing. In one example, the window material is a metalized aluminum that is brazed to a housing constructed from an Inconel®. The window material prevents probe contamination and provides a seal between the cooling path and turbine gas flow path.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
A turbine section of a gas turbine engine 10 is shown in
Referring to
Referring to
The BOAS 16 is typically constructed from a metallic material such as an Inconel®. While Inconel® is a desirable structural material typically used in blade outer air seals, Inconel® blocks the passage of microwave/radio frequencies, which can prevent the communication between the turbine blades 14 and probe 24. In the example, a hole 25 is provided near the end of the probe 24. A window material 34 is supported within the hole 25. The window material 34 is transparent to the detection frequency, permitting communication between the detection frequency and the turbine blade 14. By “transparent” it is meant that the window material 34 permits desired passage of the detection frequency. Said another way, the window material 34 comparatively permits a better quality passage of the detection frequency relative to the housing.
The window material 34 is a polycrystalline, single crystalline or ceramic material, for example. In one example, the window material 34 is a metalized alumina. Other example materials include quartz, diamond, Zirconia toughened alumina, unmetalized alumina, or other materials that are transparent to the detection frequency as known by someone skilled in the art.
In the examples shown in
In one example, a shoulder 44 is provided at one end of the hole to axially locate the subassembly 38. The subassembly 38 including the window material 34 and carrier 36 are machined to a precise height H and diameter D for the typical application. The height H can be precisely machined by polishing, for example, so that an accurate determination of tip clearance can be made. The diameter D can be achieved using an electrical discharge machining process, for example. The window material 34 acts as a reference point to enable more precise measurement of the blade tip clearance. For example, another frequency can be transmitted through the probe 24 that will not pass through the window material 34. The signal reflected from the window material 34 can be used for reference when determining the clearance between the BOAS 16 and blade tip. The carrier 36 may extend radially beyond the channel ring 22 to include the channel ring 22 for better location of the end of the probe 24 relative to the housing 16. Such a carrier 36 is schematically illustrated by the dashed lines in
Referring to
Other example arrangements are shown in
Although preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
