Technical Field The present invention relates to thermal analysis of turbine components, and, more particularly, to methods and apparatus for predicting thermal performance of turbine components having internal fluid passages, such as an actively cooled turbine blade.

Background A turbine engine, such as one used in an aircraft engine or a turbine- driven electric generator, produces high-energy expanding gas by passing air through a compression stage to a combustion chamber. In the combustion chamber, fuel is burned in the compressed air, to create the high-energy expanding gas. The high-energy expanding gas in turn passes through a turbine stage, and out of the engine. The high-energy expanding gas causes rotation of the turbine stage, and drives the rotation of the compression stage. The two stages share a common shaft on the axis of rotation. The rotating turbine stage can also rotate the shaft to create electrical energy.

The turbine stage comprises one or more turbines. Each turbine comprises a number of spaced-apart turbine blades extending radially from a central turbine ring. The turbine blades have an airfoil profile and are positioned at an angle of attack to the incoming flow of air.

Turbine engine performance is directly related to the level of energy of the expanding gas in the combustion chamber. Consequently, to achieve high energy, the gas is raised to an extremely high temperature by the heat of combustion. Combustion gas temperature of modern turbine engines can exceed the melting temperature of the material of which the turbine blade is made. To prevent the turbine blades from failing, the turbine blades are kept below the melting temperature by the flow of cooling fluid passing through fluid

passages within the internal structures of the turbine blades. This process is referred to as active cooling.

The cooling effect on the turbine blades by the cooling fluid must be carefully balanced with the need to maintain the high energies, and therefore the high temperature, of the combustion gas. To achieve high efficiency, the turbine blades must be cooled enough to keep them from failing, but not cooled enough to significantly lower the temperature of the expanding gas. In practice, the balance between the turbine blade temperature and gas temperature is very narrow to achieve high efficiency and low failure.

The goal of the designer is to produce a uniform thermal profile across the turbine blade outer surface at a low enough temperature to keep the turbine blade from failing, but high enough to maintain good engine efficiency. The fluid passages within the turbine blade are designed considering the heat transfer between the turbine blade and the gas. The design of these fluid passages involves the use of predictive numerical modeling, that is, computer modeling, and prototype testing. Current predictive numerical modeling techniques are tools in the design process, but are not a substitute for prototype testing using actual hardware in an actual turbine engine.

Prototype testing using engine-quality components is an expensive and time consuming process. The process to create a metal turbine component involves creating a metal casting, which is expensive, time consuming and design specific. After casting, the turbine component undergoes an elaborate machining process to remove excess casting material, and create high-tolerance surfaces and features. The turbine component is evaluated for quality to make sure that the turbine component is sound and the fluid passages are free of blockages or malformations. The turbine component then may undergo hardening processes to establish proper material characteristics. The turbine component is incorporated into a test engine and evaluated for performance characteristics.

Test data is taken and evaluated to determine ways in which to improve the cooling efficiency of the fluid channels with an eye toward optimizing the performance of the engine.

The interaction between the engine environment and the efficiency of the fluid passages to thermally manage the turbine component is complex, and requires an iterative process of design and testing to create a new and improved turbine engine. As discussed above, the process is time consuming and expensive, which severely limits the number of iterations that can be economically justified.

Rapid prototyping is a design tool that is being recognized as a valuable asset to design and analysis. Rapid prototyping refers to the process whereas a three-dimensional computer aided drafting (CAD) drawing is used to create a physical manifestation of the component drawn. The rapid prototype components are commonly created out of a polymer material in a process not unlike a printing process. The process can create a physical component in a matter of hours, instead of weeks or months, at a fraction of the cost to make an engine-quality part. Creation of rapid prototype components allows the engineer to hold in her hand what is drawn with the computer, which provides a realistic prospective on a newly created design.

One type of rapid prototype process, among many others, is laser scanning stereo lithography. A three-dimensional CAD drawing of the desired component is converted and broken down into a series of thin planar slices that, when stacked, forms the three-dimensional component. The laser scanning stereo lithography machine uses an ultraviolet beam from a laser, which scans the surface of a liquid photopolymer resin in parallel lines, one layer at a time.

Where the component is to be"printed", the laser hardens the resin at that location. The hardened slice is lowered one layer thickness below the surface of the resin pool and another layer is"printed"until the all of the layers are printed to form the final component. The components produced by these processes can include fine structures and intricate internal features.

Rapid prototype components have been made out of materials that are robust enough to permit some forms of testing, such as fluid flow testing in water and wind tunnels. These materials, though, cannot withstand the thermal and structural environment of the turbine engine, and therefor they have not displaced

the need for engine-quality turbine components and engine testing to evaluate the thermal performance of turbine components.

There remains a need in the art for apparatus and methods for facilitating thermal analysis of turbine components that does not involve the high costs, labor, and time required today.

Brief Description of Drawings Figures 1A-C illustrates a flow diagram of the method in accordance with a number of embodiments of the present invention; Figure 2 illustrates a thermographer comprising a fluid system, a thermal imaging system, and a computer-based control system in accordance with one embodiment of the present invention; Figure 3 illustrates an example of temperature data measured from the above system, in accordance with one embodiment of the present invention; Figure 4 illustrates an example of temperature data measured from the above system, in accordance with one embodiment of the present invention; and Figure 5 illustrates an example computer system suitable for use to perform some or all computations of the present invention.

Description of Embodiments In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention.

Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

Embodiments in accordance with the present invention provide apparatus and methods for determining thermal characteristics of a turbine component incorporating internal fluid passages for thermal management based on the thermal performance of a rapid prototype copy of the turbine component. The embodiments of the apparatus and methods in accordance with the present

invention provide a cost-effective approach for the testing and analysis of turbine component without the need to create engine-quality turbine components for each design.

In accordance with one embodiment of the present invention, a method for predicting the thermal performance of an engine-quality turbine component incorporating a first design of an internal fluid passage is provided. The method includes using thermal performance data of an engine-quality turbine component having a cooling passage of a second design, determining thermal performance data of a rapid prototype copy of the engine-quality turbine component of the second design, and determining thermal performance data of a rapid prototype copy of the turbine component incorporating the proposed first design of the fluid passage. The thermal performance data from the engine-quality second turbine component and its rapid prototype copy are used to create a correlation function that can be used to correlate the thermal performance of the rapid prototype copy of the first turbine component incorporating the proposed first design of the fluid passage with that of a theoretical engine-quality first turbine component incorporating the proposed first design of the fluid passage The thermal performance of one or more designs of turbine components incorporating proposed designs of a fluid passage can be determined from a previously evaluated engine-quality turbine component incorporating a different design of the fluid passages. Once the correlation function has been determined from the previously evaluated engine-quality turbine component and its rapid prototype copy, the need for creating engine-quality turbine components incorporating proposed designs of a fluid passage to provide thermal performance data for those designs is substantially reduced or eliminated. The correlation function enables many proposed designs to be analyzed and/or optimized, without having to fabricate engine-quality turbine components.

Figures 1A-C illustrates a flow diagram of the method in accordance with one embodiment of the present invention. As illustrated in Fig. 1 a, a second design of an internal fluid passage of a second turbine component comprising a first material is supplied with a first fluid at a first temperature over a first predetermined period of time 60. The temperature, including rate of temperature

change, of a first exterior area of a first exterior surface of the second design, during the first predetermined period of time, are measured, recorded, and determined 61. A first temperature data set and a first rate of temperature change data set is then prepared 80.

The second design of the internal fluid passage of the second turbine component comprising a second material is supplied with the first fluid at the first temperature over the first predetermined period of time 64. The temperature, including the rate of temperature change, of a second exterior area of a second exterior surface of the second design, during the first predetermined time period, are measured, recorded, and determined 65. A second temperature data set and a second rate of temperature change data set is then prepared 81.

Next, as illustrated in Fig. 1b, a correlation function based at least in part on a temperature difference between the first and second temperature data set and the difference between the first and second rate of temperature change is determined 84.

A first design of an internal fluid passage of a first turbine component comprising the second material is supplied with the first fluid at the first temperature over the first predetermined period of time 68. The temperature, including the rate of temperature change, of a third exterior area of a third exterior surface of the first design, during the first predetermined time period, are measured, recorded, and determined 69. A third temperature data set and a third rate of temperature change data set is then prepared 83.

It is assumed that the second design of the internal fluid passage of the second turbine component comprising the first material is supplied with the same thermal stress as the second design of the internal fluid passage of the second turbine component comprising the second material.

As illustrated in Fig. 1 c, a distance between the third exterior area of the third exterior surface and the corresponding internal area of the internal surface of the first design of the internal fluid passage of the first turbine component, a first material heat capacity value, and a second material heat capacity value and second material thermal conductivity value are provided 85.

Therefore, the rate of temperature change of a theoretical fourth exterior area of a fourth exterior surface, wherein a first design of an internal fluid passage of a first turbine component comprising the first material supplied with the first fluid at the first temperature over the first predetermined period of time, is calculated using the following equation 86: dT4 dT3 Cp. first dt Cp. second j Cp. second d t-w. -second L J where: dT4/dt is fourth rate of temperature change; the subscript 3 denotes the third rate of temperature change; t is time; w is the wall thickness at the area; Cp. second is the second material heat capacity; ksecond is the second material thermal conductivity; and Cp. first is the first material heat capacity.

The correlation function is applied to the third temperature data set to determine the temperature of the theoretical fourth exterior area of the fourth exterior surface, wherein the first design of the internal fluid passage of the first turbine component comprising the first material is supplied with the first fluid at the first temperature over the first predetermined period of time 87.

In accordance with another embodiment of the present invention, as illustrated in Fig. 1a, the second design of the internal fluid passage of the second turbine component comprising the first material is further supplied with a second fluid at a second temperature different than the first temperature over a second predetermined period of time 62. The temperature, including the rate of temperature change, of the first exterior area of the first exterior surface, during the second predetermined time period, are measured, recorded, and determined 63. The first temperature data set and the first rate of temperature change data set is then enhanced with this additional data, 80.

The second design of the internal fluid passage of the second turbine component comprising the second material is further supplied with the second fluid at the second temperature different than the first temperature over the second predetermined period of time 66. The temperature, including the rate of temperature change, of the second exterior area of the second exterior surface, during the second predetermined time period, are measured, recorded, and determined 67. The second temperature data set and second rate of temperature change data set is then enhanced with this additional data 81.

Next, as illustrated in Fig. 1 b, the correlation function based at least in part on a temperature difference between the first and second temperature data set, and the difference between the first and second rate of temperature change, is again determined 84.

The first design of the internal fluid passage of the first turbine component comprising the second material is further supplied with the second fluid at the second temperature different than the first temperature over the second predetermined period of time 70. The temperature, including the rate of temperature change, of a third exterior area of a third exterior surface, during the second predetermined time period are measured, recorded, and determined 71.

The third temperature data set and the third rate of temperature change data set is then enhanced with this additional data 83.

Then, as illustrated in Fig. 1c, the rate of temperature change of a theoretical fourth exterior area of a fourth exterior surface wherein a first design of an internal fluid passage of a first turbine component comprising the first material supplied with the first fluid at the first temperature over the first and second predetermined periods of time is calculated as described above 87.

In accordance with an embodiment of the present invention, a thermographer is provided that is adapted to thermally stress a component having an internal fluid passage, such as a cooling passage of a turbine component, to perform the earlier described measurements and determinations of the thermal properties of the various turbine components of various designs and various materials, under dynamic thermal loading conditions of various fluids, temperatures and time periods. More specifically, in use, the thermographer

causes a fluid of predetermined temperature to pass through the internal fluid passage. The surface temperature of the component is measured and recorded using an appropriate device, such as, but not limited to, a thermal imaging system. The resulting data, in one embodiment, are used to quantify the component's internal heat transfer coefficient.

Figure 2 illustrates a thermographer comprising a fluid system 30, a thermal imaging system 21, and a computer-based control system 1, in accordance with one embodiment of the present invention. The fluid system 30 comprises a pressurized fluid vessel 3, a first fluid supply line 4 and a second fluid supply line 16 both in fluid communication with the fluid vessel 3, and a test fixture 18. The first fluid supply line 32 comprises a first vessel fluid line 4 in fluid communication with the vessel 3, a first control valve 8 in fluid communication with the first vessel fluid line 4, a first valve fluid line 10 in fluid communication with the first control valve 8, a first heat exchanger 12 in fluid communication with the first valve fluid line 10, a first heat exchanger fluid line 16 in fluid communication with the first heat exchanger 12, with the test fixture 18 in fluid communication with the first heat exchanger fluid line 16.

Similarly, the second fluid supply line 34 comprises a second vessel fluid line 5 in fluid communication with the vessel 3, a second control valve 9 in fluid communication with the second vessel fluid line 5, a second valve fluid line 11 in fluid communication with the second control valve 9, a second heat exchanger 13 in fluid communication with the second valve fluid line 11, a second heat exchanger fluid line 17 in fluid communication with the second heat exchanger 13, with the test fixture 18 in fluid communication with the second heat exchanger fluid line 17.

The thermal imaging system 21 comprises components, such as, but not limited to, one or more infrared cameras, adapted to visualize and measure the dynamic surface temperature encountered during the evaluation.

The computer-based control system 1 comprises a central processing unit, with corresponding data lines in electrical communication with the various components of the thermographer 30. The control system 1 is adapted to control and record the fluid pressure within the vessel 3 through the pressure vessel data

line 2; control the first and second heat exchangers 12,13 to control and record the temperature of the fluid through the first and second heat exchanger data lines 14,15, respectively; control the first and second control valves 8,9 to regulate the flow of fluid to the test fixture 18 through first and second control valve data lines 6,7, respectively; and control and record data from the thermal imaging system 21 through the thermal imaging system data line 20.

The control system 1 is adapted to communicate a signal through the first valve data line 6 to control the first control valve 8 to regulate the release of a predetermined amount of fluid from the pressurized fluid vessel 3 through the first vessel fluid line 4. The fluid passes through the first control valve 8 and the first valve fluid line 10 to the first heat exchanger 12. The first heat exchanger 12 is adapted to provide the fluid with a predetermined temperature controlled by the control system 1 via the first heat exchanger data line 14. The first heat exchanger 12 is adapted to heat the fluid to an elevated temperature, such as, but not limited to, 450 C, and supply the test fixture 18 with the fluid through the first heat exchanger fluid line 16.

The control system 1 is adapted to communicate a signal through the second valve data line 7 to control the second control valve 9 to regulate the release of a predetermined amount of fluid from the pressurized fluid vessel 3 through the second vessel fluid line 5. The fluid passes through the second control valve 9 and the second valve fluid line 11 to the second heat exchanger 13. The second heat exchanger 13 is adapted, to provide the fluid with a predetermined temperature controlled by the control system 1 via the second heat exchanger data line 15. The second heat exchanger 13 is adapted to provide the fluid with a desired temperature, and supply the test fixture 18 with the fluid through the second heat exchanger fluid line 17.

In accordance with an embodiment of the method of the present invention, the thermographer 30 is used to test and record thermal performance data of an actively cooled component, such as a turbine blade, having an internal fluid passage. An actively cooled component 19 is mounted on the test fixture 18 such that the internal fluid passage 56 within the component 19 is in fluid communication with the fluid supplied by the first heat exchanger fluid line 16 as

well as the second heat exchanger fluid line 17. The actively cooled component 19 is mounted such that the surface of interest is in view of the IR camera 21.

The control system 1 controls and records the fluid pressure in the pressurized vessel 3 and communicates a signal to open the first control valve 8.

The fluid passes through the first control valve 8 and through the first control valve fluid line 10 to the first heat exchanger 12. The first heat exchanger 12 provides a hot fluid having a predetermined temperature, which is supplied to the internal fluid passage 56 of the component 19.

After the component 19 reaches a steady-state thermal condition from the hot fluid from the first heat exchanger 12, the control system 1 communicates a signal to close the first control valve 8 and open the second control valve 9. Fluid passes from the vessel 3 through the second control valve 9 and through the second control valve fluid line 11 to the second heat exchanger 13. The second heat exchanger 13 provides a cold fluid with a predetermined temperature lower than that of the hot fluid provided by the first heat exchanger 13, such as, but not limited to, a temperature 50 C lower. The cold fluid is supplied to the internal fluid passage 56 of the component 19.

The cold fluid acts as a"cold"source, which cools the component 19 from the previously heated state. After the component 19 reaches a steady-state thermal condition from the cold fluid from the second heat exchanger 13, the control system 1 communicates a signal to close the second control valve 9, completing a cycle of the test.

During the test cycle, the control system 1 sends a signal via the thermal imaging system data line 20 to the thermal imaging system 21 to control the IR camera 22. The IR camera 22 detects and records thermal images, or surface temperature profile maps, at predetermined times during the cool-down phase of the test cycle, to record the change in temperature of the surface of interest on the component 19. The IR camera 22 collects the data and communicates the information via the thermal imaging system data line 20 to the control system 1 for recording and processing.

Figure 3 illustrates an example of temperature data measured from the above system, in accordance with one embodiment of the present invention.

Trace 25 is the temperature of an exterior area of an exterior surface of a second design of an internal fluid passage of a turbine component comprising a second material, such as material used to produce rapid prototype components. Trace 26 is the temperature of the exterior area of the exterior surface of the second design of the internal fluid passage of the turbine component comprising a first material, such as a metal using in engine-quality turbine components. From this data, the rate of temperature change for the turbine component with the second design of an internal fluid passage for both materials can be determined, and a correlation function can be derived.

Figure 4 illustrates an example of temperature data measured from the above system, in accordance with one embodiment of the present invention.

Trace 27 is the temperature of the exterior area of the exterior surface of a first design of an internal fluid passage of the turbine component comprising the second material, such as material used to produce rapid prototype components.

From this data, the rate of temperature change for the turbine component for the second material can be determined. Using the above equation and the rate of temperature change for the turbine component for the second material, the rate of temperature change for the turbine component for the first material can be determined.

The correlation function can be applied to the rate of temperature change for the turbine component for the second material to determine the temperature trace 28, and therefore the thermal performance, of the exterior area of the exterior surface of the first design of the internal fluid passage of the turbine component comprising a first material, such as a theoretical metal engine-quality turbine component.

Figure 5 illustrates an example computer system suitable for use to practice the present invention, in accordance with one embodiment. As shown, computer system 600 includes one or more processors 602, and system memory 604. Additionally, computer system 600 includes mass storage devices 606 (such as diskette, hard drive, CDROM and so forth), input/output devices 608 (such as keyboard, cursor control and so forth) and communication interfaces 610 (such as network interface cards, modems and so forth). The elements are

coupled to each other via system bus 612, which represents one or more buses.

In the case of multiple buses, they are bridged by one or more bus bridges (not shown).

Each of these elements performs its conventional functions known in the art. In particular, system memory 604 and mass storage 606 may employed to store a working copy and a permanent copy of the programming instructions implementing the computational logic 622 to practice the present invention.

Computational logic 622 may be implemented in assembler instructions supported by processor (s) 602 or high level languages, such as C, that can be compiled into such instructions. The permanent copy of the programming instructions may be loaded into mass storage 606 in the factory, or in the field, through e. g. a distribution medium (not shown) or through communication interface 610 (from a distribution server (not shown)).

The constitution of these elements 602-612 are known, and accordingly will not be further described.

In embodiments in accordance with the present invention, performance of a turbine component of a particular material with a particular internal passage design may be analyzed and predicted.

It is understood that embodiments of the present invention may be practiced using a number of techniques for determining the surface temperature of the component. It is further understood that embodiments of the present invention may be practiced using a number of techniques for determining the internal heat transfer coefficient of the component.

Variations of embodiments in accordance with the present invention achieve the same or similar result for the purpose of thermally stressing a turbine component via hot and cold fluids, internal or internal and external flow, and recording the temperature at the surface using a thermal imaging system for the purpose of evaluating actively cooled components to quantify the internal heat transfer coefficients.

Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent

implementations calculated to achieve the same purposes may be substituted for the specific embodiment shown and described without departing from the scope of the present invention.

Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.