Patent Application
20110164653
The invention relates generally to thermal inspection systems and methods and, more particularly, to thermal inspection systems and methods that include external flow over the component under test to develop appropriate film cooling and aero distributions.
Various approaches to cooling hot gas path components, such as turbine airfoils, have been proposed and implemented to increase the upper operating temperature of the engines. For example, high pressure turbine blades typically include internal cooling comprising complex flow circuits with blind flow holes, such as impingement jets, which are formed in an interior shell for cooling the external shell of an integrally cast double-wall turbine airfoil. Conventionally, these cooled parts are inspected by indirect measurement methods to assess an associated effect. One example of these indirect measurement techniques is the measurement of airflow through a turbine airfoil and associating the readings with film cooling effectiveness. This is an indirect and extrapolated measurement of the desired film and cooling effectiveness and internal heat transfer coefficients, and the current indirect method provides at best a bulk indication whether a part has met its thermal design intent.
In practice, there are no inspection steps to directly measure film effectiveness and internal heat transfer coefficients for hot gas path components. Rather, airflow, backflow measurements, and pin-checking are the only measurements that extrapolate to heat transfer performance. Consequently, hot gas path components that do not perform thermally as intended (but that pass the indirect inspections) could enter the field. Other inspections and dimensional specifications of the component also impact the thermal performance of an airfoil. Again, a hot gas path component may dimensionally pass, but still fail thermally in the field. For example, film blow off can occur with subtle and geometrically immeasurable flaws in the film holes and film hole diffuser shapes.
It would therefore be desirable to provide a nondestructive inspection system and method to qualify a part's thermal performance directly.
One aspect of the present invention resides in a thermal inspection method that includes disposing a component in a wind tunnel configured to create a predetermined Mach number distribution for an external surface of the component. The thermal inspection method further includes supplying a gas at a known temperature T into the wind tunnel to create an external flow of gas over the external surface of the component in accordance with the predetermined Mach number distribution. One or more external surface temperatures of the component are directly or indirectly measured to generate an external surface temperature distribution for the external surface of the component. The thermal inspection method further includes using the external surface temperature distribution to perform a quality control inspection of the component.
Another aspect of the present invention resides in a thermal inspection system that includes a wind tunnel configured to create a predetermined Mach number distribution for an external surface of a component to be inspected. A gas supply is provided for supplying a gas at a known temperature T into the wind tunnel to create an external flow of gas over the external surface of the component in accordance with the predetermined Mach number distribution. The thermal inspection system further includes a thermal monitoring device configured to detect a number of surface temperatures, either directly or indirectly, of the component to generate an external surface temperature distribution for the external surface of the component. The thermal inspection system further includes a processor configured to use the external surface temperature distribution to perform a quality control inspection of the component.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
A thermal inspection system 40 is described with reference to
As indicated, for example, in
The thermal inspection system 40 further includes a thermal monitoring device 24 configured to detect a plurality of surface temperatures, either directly or indirectly, of the component 10 to generate an external surface temperature distribution for the external surface of the component. The term “indirectly” as used herein, should be understood to encompass detecting at least one surface temperature by measuring radiance and performing a necessary conversion or calibration to obtain the temperature. For particular embodiments, the thermal monitoring device 24 comprises an infrared detector 24. Non-limiting examples of infrared detectors include infrared (IR) cameras, actuating pyrometers, and single point pyrometers.
The thermal inspection system 40 further includes a processor 32 configured to use the external surface temperature distribution to perform a quality control inspection of the component 10. The processor 32 is discussed in greater detail below. The quality control inspection may be accomplished, for example, by comparison with a baseline value to determine whether the thermal performance of the component is satisfactory, as discussed below with reference to
For the example arrangement depicted in
For the illustrated example, the thermal inspection system 40 further includes a heat source 26 for heating the gas to the known temperature T prior to supplying the gas into the wind tunnel 20. For certain arrangements, vitiated air (namely air heated by direct combustion) is supplied to the wind tunnel. For other arrangements, non-vitiated air is supplied to the wind tunnel, for example air that is heated by a heat exchanger.
In order to obtain values for the film effectiveness and cooling effectiveness, hot cross-flow and cooling and film flows are required. In particular, the film flow will cover the hot gas path component 10 surface providing the intended protection against the hot flow. For the arrangement shown in
For the configuration shown in
In operation, the temperature distribution for the component is allowed to reach a steady-state recovery temperature distribution, at which point, cooling air is supplied to the component. The internal cooling cools the component, and the film flow provides a cool air buffer against the hotter cross-flow. The resulting component surface temperatures are recorded with the thermal imaging device and used to calculate the film and cooling effectiveness values, respectively. The film effectiveness and cooling effectiveness values can then be compared to expected values from analyses or to a tolerance defined by known thermally good parts.
For particular arrangements, the external surface temperature distribution corresponds to the measured external surface temperature for a number of locations (a few illustrative examples of which are indicated by arrows and reference numeral 14) on the external surface of the component 10. For these arrangements, the processor 32 is configured to use the external surface temperature distribution to determine an overall cooling effectiveness for the component 10 for at least a subset of the locations 14 on the external surface 12 of the component 10. In addition, for the illustrated example, camera control electronics 42 are operatively connected to the imager 24, manipulator 38 and processor 32 to control and automate movement of the imager as well as the collection of images from the imager. In other arrangements, the processor 32 may be configured to control and automate movement of a sensor (not shown) or optical piece (not shown), for example a prism, in order to automate the collection of the thermal inspection data.
The processor is typically capable of capturing an image frame rate of adequate frequency, for example greater than 10 frames per second and typically greater than 15 frames per second, from the imager. It should be noted that the present invention is not limited to any particular processor for performing the processing tasks of the invention. The term “processor,” as that term is used herein, is intended to denote any machine capable of performing the calculations, or computations, necessary to perform the tasks of the invention. The term “processor” is intended to denote any machine that is capable of accepting a structured input and of processing the input in accordance with prescribed rules to produce an output. It should also be noted that the phrase “configured to” as used herein means that the processor is equipped with a combination of hardware and software for performing the tasks of the invention, as will be understood by those skilled in the art.
For the embodiment shown in
The overall cooling effectiveness can be viewed as the sum of the film cooling effectiveness, internal cooling effectiveness and thermal conductivity of the component. The overall cooling effectiveness value may be controlled by selectively controlling one or more of these three contributions. For example, if the component is formed from a low thermal conductivity material (for example, using a ceramic or plastic component in the design phase), then the resulting cooling effectiveness would correspond to primarily to the contributions of the film cooling effectiveness and the internal cooling effectiveness. Namely, for this example, the film cooling effectiveness and the internal cooling effectiveness would provide the dominant contribution to the overall cooling effectiveness. Similarly, if the thermal inspection is performed on a test component in the absence of external flow, the resulting cooling effectiveness would correspond primarily to the internal cooling effectiveness and thermal conductivity for the component. In this manner, the thermal inspection system can be used in the design phase to develop improved cooling designs for the components under test.
These examples describe methods of biasing the thermal response of a test component such that one or more of the cooling effectiveness contributors is dominant over the others. By testing at least two, and preferably more than two, variations of the biasing, multiple data sets are obtained from which a regression analysis will determine the correct quantified magnitude of the desired distribution, be that the internal heat transfer coefficients, or the external film effectiveness, or the thermal conductivity contribution to cooling effectiveness. A regression analysis using two or more data sets is required because none of the thermal effectiveness contributors (internal cooling, film cooling, and thermal conduction) can be absolutely and completely eliminated in a test. For example, if the component is tested in the absence of external flow, the film cooling no longer adheres to the component surface and so is almost, but not completely, ineffective. Testing the component with two differing material thermal conductivities then provides two different data sets, one which has stronger conduction effects that the other. The regression analysis then allows determination of the internal cooling effectiveness and the conduction contribution for various material conductivities. If the thermal response is strongly non-linear due to flow or property changes, then more than two data sets will be desired. Another way to achieve similar results is to vary the fluid used as the cooling fluid inside the component and as film cooling, for example, to test the component with air and also with CO2, and/or to vary the temperature of the cooling fluid, and/or the mass flow rate of the coolant. As an example, testing with the external flow over the component can be performed with variations of cooling fluid type, temperature, and flow rate that yield the same film cooling parameters but have differing internal cooling effectiveness. A regression analysis then allows determination of the film cooling effectiveness and the internal cooling effectiveness.
For the example arrangement shown in
For this thermal transient embodiment, the processor 32 may be configured to use the transient thermal response to determine at least one of: a combined thermal response for the component 10, at least one heat transfer coefficient for respective ones of the one or more internal passages 16 in the component, and a flow rate through respective ones of the one or more internal passages 16. As used herein, the term ‘combined thermal response’ reflects all thermal influences for the component 10, including but not limited to all internal cooling, film cooling, and material conduction and thermal diffusivity effects resulting from internal ribs, film holes, internal bumps, crossover holes, and other features. Beneficially, by determining the combined thermal response of all thermal influences in a manufactured part, the present technique can provide an immediate measure of thermal acceptability or rejection for a cooled part, especially for a complex cooled part, such as a turbine airfoil. Further, the term ‘flow rate’ is understood to encompass an actual quantity and a flow rate characteristic such as, but not limited to, a flow coefficient. For certain configurations, the thermal monitoring device 24 is an infrared camera 24 configured to capture multiple images corresponding to a thermal response of the component 10 to the external and coolant flows, where the processor 32 is configured to generate the transient thermal response of the component from the images.
Example heat transfer coefficients {hlmn.} are discussed in commonly assigned, copending U.S. patent application Ser. No. 12/101,285, Bunker et al., “Thermal inspection system and method.” It should be noted that although the thermal monitoring device 24 typically detects a projected surface as a two-dimensional representation, the heat transfer coefficients {hlmn.} correspond to the three-dimensional component. The heat transfer coefficients may be calculated using the techniques described in U.S. patent application Ser. No. 12/101,285 and/or in U.S. Pat. No. 6,804,622, Bunker et al. “Method and Apparatus for Non-destructive Thermal Inspection,” both of which references are hereby incorporated by reference in their entirety. The heat transfer coefficients {hlmn} corresponding to respective locations {l,m,n} within the internal passage can be used to determine at least one of (a) a flow rate through respective ones of the openings for the internal passage(s), and (b) a cross-sectional area for respective ones of the openings for the internal passage(s).
For example, and as discussed in U.S. patent application Ser. No. 12/101,285, once the heat transfer coefficients {hlmn} are known, the following equation can be solved to determine either the flow rate through respective ones of the opening(s) for the internal passage(s) or (b) the cross-sectional area for respective ones of the opening(s) for the internal passage(s):
h=(k/D)CRemPrn, Eq. 1
where k is the thermal conductivity of the fluid, D is the hydraulic diameter of the connecting orifice, Re is the Reynolds number, and Pr is the Prandtl number. C, m and n are correlation constants. Equation 1 applies to a very large range of flow situations applicable to internal flows, whether compressible or incompressible. For any particular inspection geometry case, the correlation constants are known from prior research and testing, such as that performed in the design and development of the nominal part. To determine the cross-sectional area for one of the openings for the internal passages, Equation 1 is solved for D. If the hydraulic diameter of the orifice(s) is known, for example determined by x-ray imaging, then Equation 1 is solved for the Reynolds number, which provides the flow rate through the orifice. If the hydraulic diameter, or area, is not known, but the inspection is for a single orifice only, then Equation 1 is solved for the hydraulic diameter D. If the hydraulic diameter(s) is not known, and there are multiple orifices, then Equation 1 is solved for the average hydraulic diameter of the group of orifices. Alternately in this latter case, multiple inspections may be executed with various flow rates. Although the various hydraulic diameters will not change between inspections, the heat transfer coefficients will change. A regression analysis can then be used to determine the individual hydraulic diameters and flow rates knowing that the form and fit of Equation 1 remains unchanged.
In addition, the processor 32 may be further configured to compare at least one of the flow rate, the at least one heat transfer coefficient, and the combined thermal response of at least a portion of the component to at least one baseline value to determine whether a thermal performance of the component is satisfactory. In this manner, the quality control inspection of the component may be accomplished. Non-limiting examples of the baseline values include one or more local values, mean value of a group of local values and a standard deviation of a group of local values. There are various stages at which the baseline values may be defined. In one embodiment, measurements performed on components 10 in a “new” and an optimal condition prior to any degradation effects form a baseline for subsequent measurements performed. In another embodiment, the baseline values are obtained by performing a transient thermal analysis prior to installation of the component 10 on a turbine engine, for example, by performing multiple bench tests on the component 10. In yet another embodiment, the baseline values are redefined by obtaining and analyzing measurements taken during any point in-service; such a redefined baseline would act as a comparison data for subsequent measurements going forward in time.
In addition and as noted above, the thermal inspection system 40 may further include a display 36 for displaying a result of the comparison with the baseline value.
A thermal inspection method is described with reference to
According to more particular embodiments, the thermal inspection method may optionally include at step 46, forming a cascade in the wind tunnel to facilitate generating the external flow of gas over the external surface of the component in accordance with the predetermined Mach number distribution.
As indicated in
For the particular embodiment illustrated in
For the particular embodiment illustrated in
For the particular embodiment shown in
For the particular embodiment shown in
For the particular embodiment shown in
Beneficially, the thermal inspection method and system of the invention can be used to perform quantitative assessment of production airfoils and other hot gas path components. Further, the above described thermal inspection process can be performed at a variety of manufacturing stages. For example, the inspection can be performed at the initial manufacturing stage and can also be applied to components that have gone through a repair process. In addition, the inspection can be performed for components prior to repair, in order to determine whether repair is needed. For turbine components, the inspection can be performed after investment casting and prior to final machining. The inspection can also be performed after final machining. Further, the inspection can be performed after film holes are formed (post-casting process) and before or after coatings are applied. Moreover, the thermal inspection method and system of the invention can be used to measure thermal performance on test airfoils to screen turbine airfoil cooling designs.
Although only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
