Cooled Silicon Nitride StationaPy Turbine Vane

IO

Risk Reduction

FINAL REPORT

Prepared for Department of the Navy

Office of Naval Research Arlington, VA 22217

Under Contract No. N00014-984-0355

John Holowcak ~

% United b Technologies

Research Center

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1. AGENCY USE ONLY (Leeve Hen&) 2. REPORT DATE

December31,1999

Form Approved REPORT DOCUMENTATION PAGE I OMB No. 0704-0188

3. REPORT TYPE AND DATES COVERED

FinalRep~rt 8/13/98 - 7/13/99 4. TITLE AND SUBTITU

COOLED SILICON MTRIDE STATIONARY TURBINE VANE RISK REDUCTION

6. AUTHOR(S)

John Holowczak

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) United Technologies Corporation

East Hartford, CT 06108 United Technologies Research Center -

9. SPONSORlNG/MONITORlNG AGENCY NAME(S) AND ADDRESS(ES)

Department of the Navy Office of Naval Research klington, VA 222 17

5. FUNDING NUMBERS

NO00 14-98-C-0355

8. PERFORMING ORGANIZATION REPORT NUMBER

R99-6.100.0002-1

10. SPONSORlNG/MONlTORlNG AGENCY REPORT NUMBER

14, SUBJECT TERMS turbine, silicon nitride, cooled ceramic vane, ceramic vane manuf-g,

11. SUPPLEMENTARY NOTES

15. NUMBER OF PAGES

16. PRICE CODE 17

Ea. DISTRIBUTION I AVAILABILITY STATEMENT

18. SECURITY CLASSIFICATION OF ABSTRACT

Unclassified

12b. DISTRIBUTION CODE

20. LIMITATION OF ABSTRACT

SAR

13. ABSTRACT (Maximum 200 wards)

The purpose of this program was to reduce the technical risk factors for demonstration of air cooled silicon nitride turbine vanes. The effort involved vane prototype fkbrication efforts at two U.S. based gas turbine grade silicon nitride component manufacturers. The efficacy of the cooling system was analyzed via a thermal timdtemperature flow test teclmiquie previously at UTRC. By having multiple vendors work on parts fabrication, the chance of program success inmeased, for producing these challenging components. The majority of the effort under this contract focused on developing methods for, and producing the complex thin walled silicon nitride vanes. Components developed underthis program will undergo engine environment testing within N00014-96-2-0014.

17. SECURITY CLASSIFICATION OF REPORT

Unclassified

18. SECURITY CLASSIFICATION OF THIS PAGE

unclassified NSN 7540-01-280-5500

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DISCLAIMER

This repon was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof. nor any of their employees, makes any warranty, express or implied. or assumes any kgal liability or responsibility for the accuracy, completeness, or use- fulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spc- cific commercial product, process, or service by trade name, trademark, manufac- turer, or otherwise dots not ncccssarily constitute or imply its endorstmmt, mrn- mendktion. or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

. .

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

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@ United Techno log ies

Research Center

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R99-6.100.0002-1

(I, Cooled Silicon Nitride Stationary Turbine Vune Risk Reduction

Reported by: I/ John Holowc&k

Approved by:

December 1999

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TABLE OF CONTENTS

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

COOLED SILICON NITRIDE VANE PROTOTYEP FABRICATION.. . . . . . 2

Allied Signal Gel Casting Development ........................... 3

Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Allied Signal Task 2, Core Material Selection ........................ 3

Process using Protoype Cooled FT-8 Vane ........................... Kyocera Industrial Ceramics Corp. Vane Development ....................

Casting Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Cooling Hole Machining Results ................................... Final Grinding Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Kyocera Conclusions and Recommendations .......................... 11

Allied Signul Task I , Electronic Model Translation andMold Tool

Allied Signal Task 3, Demonstrate Feasibility of Net-Shape Forming 4 5

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HEAT TRANSFER BASIC DESIGN VALIDATION ..................... 1 1

LOW TEMPERATURE HEAT TRANSFER TESTING OF CERAMIC VANE FIRST ARTICLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

LOW TEMPERATURE HEAT TRANSFER TESTING OF SECTOR RIG CANDIDATE VANES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

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INTRODUCTION

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Modern stationary gas turbine engines derived fiom aero engine powerplants operate at continuous average turbine inlet temperatures of 1200°C (2200°F) or higher. Due to the radial and circumferential pattern and profile combustion gas temperature differences common in larger turbines, it is not unusual to have gases immediately adjacent to “hot spot” HPT vanes significantly in excess of 1370°C (2500°F). These high gas temperatures require superalloy vanes to be extensively cooled for long term durability. Reductions in the cooling air requirements for vanes and other hot section structures can allow the air to be put to use elsewhere in the engine. For example, the air can be mixed with additional fuel and used to increase the power output of the engine.

Substitution of monolithic ceramics for thermal barrier coated superalloys have long been viewed as an approach to allowing significantly higher component operating temperatures. They have enjoyed an increasing level of success in small, low pressure ratio turbine engines, including vehicular, expendable, and small stationary turbine engines. As these engines currently operate with uncooled metallic components, substitution of ceramic components allows considerably higher turbine inlet temperatures, resulting in significant increases in specific power output and efficiency.

Large aeroderivative stationary or marine powerplants already have high pressure turbine components that benefit extensively fiom advanced air cooling systems. Uncooled ceramic vanes operating in hot spot locations would have unacceptably high operating temperatures for acceptable long term durability. In order to hamess the higher material operating temperatures of silicon based ceramics, it will be requirement for these types of components to have internal cooling systems.

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Under a DARPA Advanced Materials Partnership program, “Reduced Cost, Improved FOD Resistance, and Improved Attachments for Insertion of Silicon Nitride Turbomachinery Components,” led by Sundstrand Power Systems’, Pratt & Whitney (P&W) and its central R&D facility, United Technologies Research Center (UTRC), are developing an impingement cooled and vented first stage turbine vane in silicon nitride ceramic, for application to the P&WA‘urbo Power and Marine FT8 aeroderivative engine. The FT8, which entered service in 1992, is an industrial derivative of the P&W JT8D aircraft engine. The FT8 has an output of 25 MW with an efficiency of 38.2 % in electrical power generation applications (including generator losses) and has a 39% shaft efficiency. This engine is currently in use for peak power, natural gas pumping, and marine applications worldwide. Y

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Goals for the ceramic vane program include reducing the cooling air required by the first stage vane by approximately 5% of total core flow, while limiting surface material temperatures of the silicon nitride vanes to a level allowing extended operational intervals in field use. The program will culminate in a sector rig cascade test of silicon nitride vanes under temperature, temperature distribution, and pressure conditions identical to those

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’ Administered by Oatice of Naval Research, Contract No. N00014-%-2-0014, Dr. Steven Fishman, monitor.

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encountered in actual FT8 engine operation. This testing is expected to occur during the November 1999 timeframe.

Historically, having only a single manufacturer fabricate silicon nitride turbine parts presents a considerable risk to program success. Ifthe mandacturer chosen does not deliver hardware, then no testing can occur. Similarly, if ceramic components fracture during preliminary testing, due in example to a metal hardware problem, there will not be additional components available for a second build and test. This program addressed this issue by having subcontractors Kywera Industrial Ceramics Corporation (hereafter, KICC) and AlliedSignal Ceramic Components (hereafter, AS-CC) both develop prototype components. KICC's delivered components were deemed adequate for testing within the DARPA program, while AS-CC showed excellent progress in developing gel casting of the hollow airfoil portion of the vanes.

In addition, wall thickness variations may not occur 8s precisely as the current design model has predicted, even though it utilized actual wall thickness variation data taken fiom prototype drain slip cast vanes fabricated by both Kyocera and AlliedSignal. This could present a critical problem if the vane sufface temperatures for the two hot spot vanes exceed their planned 240OOF maximum temperature at the P4 pressure of 265 psi. Testing both the baseline heat transfer design, and the actual prototype vanes, in a low temperature rig/analysis system would be of considerable benefit in assuring that the parts placed in the hot streak region of the combustor have correct heat transfer characteristics.

The program accomplishments in brief were:

1.) ceramic vane prototype fabrication at two of the leading U.S. developers of gas turbine grade silicon nitride

2.) low temperature heat transfer testing of polymeric vane models to assure that the vane cooling system was designed correctly, using a unique UTRC capability

COOLED SILICON " R I D E VANE PROTOTYPE FABRICATION

This Task was conducted under separate subcontracts with Alliedsignal Ceramic Components (AS-CC) and Kyocera Industrial Ceramics Corporation (KICC). The FT8 vane was designed for the drain slip casting forming technique. AlliedSignal elected to focus on utilizing their gel casting approach, and, due to h d i n g constraints, they did not attempt to fabricate the entire vane including platforms. AlliedSignal's efforts focused on production of the airfoil section only, with simplified (flat) outer platforms.

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Kyocera used drain slip casting, and was able to deliver 5 candidate vanes for sector rig testing. Initial efforts utilized a UTRC developed laser bisque machining process for fabricating the tapered trailing edge vents. However, during sintering of trial components significant cracking was observed in the trailing edges. The cracking was attributed to differential sintering shrinkage caused by condensation of silica containing matter during the

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laser machining process. To acquire hardware for testing, the trailing edge was clipped back and circular holes were machined in using more conventional bisque drilling techniques, as detailed below.

AlliedSignal Gel Castinn Develoument

The feasibility of fabricating net-shaped hollow vanes by the gelcasting method was demonstrated. Gelcasting is a net shape forming process that reduces or eliminates costly machining of components and facilitates fabrication of complex shaped components, such as the UTRC FT-8 Cooled Industrial Turbine Vane. Under this phase of development, AS-CC fabricated prototype FT-8 vanes with hollow airfoils and unfinished platforms. Under the next phase AS-CC will deliver FT-8 vanes for high-temperature testing, complete with finished platforms and cooling channels from the airfoil’s core to its trailing edge.

Gelcasting molds must be fabricated of material that does not react with the gel slurry, has adequate thermal conductivity to properly initiate the gelation, and is sufficiently rigid to ensure dimensional control. Metals such as aluminum or steel are ideal mold materials and so are commonly used. The typical gelcasting mold is designed such that the mold sections can be pulled away from, or out of, the gelcast part. Upon analysis of the FT8 cooled vane, it was determined that neither aluminum nor steel mold cores could be pulled successhlly from the casting. Thus work performed under this program focused on demonstrating that the hollow vane could be fabricated by gelcasting using atypical mold materials. Results of AlliedSignal’s subtasks are summarized below;

AlliedSignal Task I , Electronic M&l Translation ami Mold Tool Design:

AS-CC translated and analyzed UTRC’s electronic model of the FT-8 vane, determining that a mold core made of typical materials (Le., aluminum or steel) could not be pulled successfully from the casting. A gelcasting mold tool was conceptualized under this task, forming the basis for the mold that was fabricated under Task 3 (below).

AlliedSignal Task 2, Core Material Selection:

A list of twelve materials and nine coating systems with potential for successhl core forming and removal fiom complex-shaped hollow airfoils was generated. This list was reduced to the top six candidates, by weighing the known advantages and disadvantages of each material. Among the criteria used to select the top potential materials were: compatibility with gelcasting slurry (if known), characteristics at gelation temperature, cost per use, ability and/or need to coat, and dimensional capability.

The six materials were tested in gelcasting experiments using simple shaped molds (i.e., blocks) such that at least one surface of the gelled part was in contact with the potential core material. The core material was coated if necessary before gelcasting. The gelcast blocks were thermally processed through sintering, and the surfaces were visually inspected at each processing step. Of the six materials screened, two materidcoating systems displayed the greatest potential, and were selected for additional evaluation in Task 3.

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AlliedSignal Task 3, Demonstrate Feasibility of Net-Shape Forming Process using Prototype Cooled FT-8 Vane:

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The first items to be accomplished under this task were completion of the mold designs and fabrication of the mold tools for forming the prototype FT-8 vanes. Two mold tools were designed and fabricated, one for the core and another for gelcasting. The two most promising materials were used to form cores for the prototype vanes. An effective gelcasting procedure was developed using the new molds with one of the two core materials, as shown in Figure 1,

In all, eleven prototype vanes were gelcast and thermally processed through sintering to reach 111 density. One of the two core materidcoating systems selected for the vane casting experiments clearly performed best. Distortion during sintering was minimal, as illustrated in Figure 2, where the vane on the left is green and the vane on the right is sintered to full density.

Figure 1. The two green (as-cast) vanes illustrate that prototype FT-8 vanes can be successllly formed by gelcasting.

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Y Figure 2. Uniform shrinkage, minimal distortion is observed after green gelcast prototype FT-8 vanes have been M y densified.

While in general shrinkage during sintering is uniform, some distortion along the airfoils’ trailing edge was observed. The cause was traced to the de-molding procedure, which will be revised accordingly to prevent similar distortion in fbture FT-8 vane castings. A sintered vane was delivered to UTRC to demonstrate the state of gelcast processing (note: heat treatment crystallization was not performed on the vane delivered to UTRC).

The results fiom the prototype FT-8 cooled vane program demonstrated the feasibility of the net-shape forming concept. Further work is warranted, to fabricate FT-8 vanes with finished platfoxms and cooling channels firom the core to the airfoil trailing edge, for testing in the UTRC engine rig at elevated temperatures and pressures.

Kvocera Industrial Ceramics COT. Vane Development

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The objective of this effort was to examine potential fabrication methods for fabricating individual, cooled, Si3N4 vane segments for use in the P&W FT8 industrial turbine engine. The vanes were to include an internal cavity in the airfoil for a cooling baffle, and trailing edge slots to provide an exit for the cooling air and additional trailing edge cooling. Initially, Kyocera’s participation was to focus on the hollow vane structure, while UTRC would perform the slot machining. However, KICC was also to consider methods to provide the vent slots.

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KICC was initially to provide one as-sintered vane to UTRC for initial heat transfer testing. Subsequently, KICC was to provide approximately 7 parts for potential sector rig testing. The parts would approximate the dimensions of the part print on a best effort basis, as limited by the duration and funding of the program. The parts would include grinding of selected features of the platform attachment surfaces. The quantity of deliverables would be a function of the products of the mold, and yield.

The vanes were fdnicated from Kyocera’s SN282 silicon nitride utilizing drain Casting and plaster molds. The hollow interior of the airfoil was achieved by partially casting the vane against the mold walls and draining the mold prior to complete solidification. Simultaneously, the thicker, solid portions of the plaiform were also cast in the same casting process. A particular challenge was to obtain a 3 mm thin wall in the hollow airfoil location, while also achieving up to approximately 10 mm of thickness in the platform.

After casting and drymg, the vane segments were partially fired to a bisque state. In this condition, the vanes achieved a significant handing strength, but were capable of being machined using conventional machining methods. Vanes in this condition were hitially provided to UTRC for trailing edge vent hole machining. The vent holes were of an oval, tapered configuration, suitable for laser machining. However, the laser approach resulted in crack around the holes, as will be discussed. As an alternate approach, KICC subsequently machined round TE holes using conventional carbide drills. This approach proved successll, but the round holes would adversely affect the cooling of the “E?. To compensate for the cooling loss, UTRC requested that a portion of the trailing edge also be removed during the bisque machining operation.

After bisque machining, the vanes were fully sintered and final machined. Only selected portions of the non-gas path Surfaces of the vane platforms were machined to mate with support stnrctures of UTRC’s FT8 sector burner rig.

Casting Results

Parts were cast in an interactive manner, modiwng the mold fill, draining, and timing to achieve the desired part. The first castings were made to determine casting rate, and to evaluate the process capability to achieve the different section thicknesses, the thin, uniform walls, a smooth interior cavity, and the extra stock to accoMmodate machining attachment features. Initial parts were sectioned to reveal the results of the process. The first parts contained thick walls, and /or incomplete solidification of the vane platform portions, as shown in Figure 3a Cracking at the platform edge also occurred occasionally. Improvements to the process provided more uniform parts, and complete casting, as shown in Figure 3b.

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Figure 3 Initial casting, a) with non uniform wall thickness, and Cavities, and b) improved casting.

Successive casting trials resulted in a process capable of providing the desired vane casting, as shown in Figure 4. Completed parts were bisque fired as planned.

Figure 4. Completed, as cast vanes.

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Cooling Hole Machining Results

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Two, as-cast and bisque fued airfoil sections (without the platforms), and seventeen full as-cast and bisque fired parts were provided to UTRC for laser machining process development. After processing at UTRC, successfblly completed or trial parts were returned to KICC for sintering. Initial returned laser machined parts contained the desired oblong and tapered shape, but also exhibited non-uniform machining, rough edges, debris in the passages, and cracking. The sintered parts exhibited additional cracking, as illustrated in Figure 5a. UTRC subsequently modified its process to achieve improved results on full vane segments. However, these parts also exhibited cracking around the holes after the sintering process, as shown in Figure 5b. UTRC also cut back the trailing edge in an attempt to eliminate the cracking, however, this did not prevent the occurrence, Figure 6.

Figure 5. a) Initial, and b) improved laser machined passages, as sintered. b>

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Figure 6. Laser machined cooling passages on cut back trailing edge, as sintered.

Subsequently, additional castings were fabricated, and KICC performed the hole machining using conventional carbide drilling. The resultant holes were round rather than oblong. Thus, to compensate for the change in heat transfer characteristics during burner rig testing, UTRC temporarily modified the design by cutting back the trailing edge, as shown in Figure 7. This design change provided a flat, but abrupt trailing edge that also simplified the drilling operation. Parts were cast, bisque machined and fired to provide the desired results, as shown in Figure 8.

Final Grinding Results

Six parts were final ground on the platfonn edges and attachment surfaces for delivery to UTRC. During final grinding, two parts exhibited a break through from the outer platform to the vane cavity at the leading andor trailing edge, as shown in Figure 9. These parts, however, were judged acceptable by UTRC for initial evaluations.

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Y Figure 9. Completed FT8 vaue segments, also illustrating the breaktbrough into cooling cavity.

Kyocera Conclusions and Recommendations

Hollow FT8 vane segments were successfully cast, and the process of introducing trailing edge cooling passages was demonstrated. However, additional casting development is recommended to improve the casting yield, eliminate the platform to cavity breakthrough, and to achieve the desire TFi cooling passage shape and taper without the need for cutting back the trailing edge. KICC believes that the casting yield and control can be achieved through modifications to the plaster mold design, and further casting process improvements. Furthermore, the desired trailing edge hole configuration is feasible by CNC machining, or by casting them in place. KICC recommends that the FT8 fabrication effort be continued to achieve these objectives.

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HEAT TRANSFER BASIC DESIGN VALIDATION

The purpose of this task was to experimentally verify, at low temperature, the heat transfer performance of the FT8 cooled silicon nitride vane, designed under a previous Cooperative Agreement (NOOO14-96-2-0014, funded by DARPA). Within this task, stereolithography was used to fabricate a FT8 vane model. The model was fitted with a metallic baffle, and mounted in RTV rubber end caps for testing in UTRC’s Thermal Imaging Inspection facility.

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The facility uses warm compressed air, supplied to the internal cooling system of the vane, to gradually warm the vane in an environment where there is no external Bow. By observing the outside vane with cameras, and observing the time taken to reach certain temperatures, the internal cooling system geometry can be verified. Thermal paint is used on the vane exterior to provide accurate temperature readings. The technique was developed prior to the start of this contract.

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The other major effort under this Task was to develop a computer model for analyzing the timehemperature data generated by this inspection, and relating it back to the high temperature heat transfer analysis performed during design of the vane. In this fashion, the accuracy of the vane impingement cooling system can be experimentally verified. UTRC subcontracted this portion of the effort to Computer Aided Engineering Associates (Woodbury, CT), as they were very familiar with the vane design, having performed the original high temperature heat transfer analysis under the prior Cooperative Agreement.

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To minimize the cost of the data analysis model, only the data from the hot streak (center of vane span) was utilized. It was extruded in space to create a reasonable facsimile of the full airfoil. Using this approach, the 2D transient heat transfer analysis system for the vane has been completely developed, including automatic reading of EXCEL boundary condition data and including modeling of core shift. The automated procedure developed can run the ceramic vane transient heat transfer analysis and plothecord for each point on the external surface the time required to reach a specified target temperature. This result was to be used to directly correlate with the test data. The predicted temperature at various locations on the stereolithographic vane, as a function of time of exposure to warm compressed air, is shown in Figure 10 below.

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Vane Transient Heat Transfer Analysis Results Time To Reach Trip Temperature On Surface

Case 1, SLA Vane

I Case 1 Condlflons:

SLAVane (Lucite properties) h-inl based on fkw parameter

TJnt = 150 F

SucionSide 4 hSSlJr3side -

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4.0 3.0 -20 -1 .o 0.0 1 .o 2.0 3.0 Dlstance On Surface From Stagnation Polnt (Inch)

Figure 10. Predicted time to reach temperature at various locations on tereolithographic test vane.

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Cooling effectiveness tests were completed to assess the internal cooling design of the FT8 Ceramic vane. The purpose of the test was to identify internal cooling design deficiencies which could jeopardize the hot test. A flow bench was used for conducting the test. An SLA model was fabricated fiom the product definition design. A metal core identical to that used in the hot test was also used to insure similar internal cooling flow features. A transient, thermal test technique developed at PW and UTRC was used to assess the vane cooling design.

The test was conducted using a transient, thermal test technique. The flow bench consists of a regulated, high-pressure air supply, an air heating assembly, and a model support furture. The tests are conducted by flowing air at the desired flow parameter through the heater to warm all the components to steady state temperatures. Typically, the model airfoil is initially at room temperature, -7OF, while the heated air is sufficient to cause a color change to the thermo- chromatic paint applied to the model. Airfoil surface temperatures are monitored with a video camera and recorder.

Monitoring the inlet temperature of the coolant during the test and noting when particular areas of the airfoil surface change color (i.e temperature), permits the operator to determine the external cooling effectiveness of the internal cooling design. Effectiveness patterns can be used to determine where over- or under-cooling is occurring within the airfoil. Quantitative cooling information can be obtained when the measured effectiveness results from the transient tests are combined with FEA models of the airfoil being tested.

Images from one of these tests are provided in Figures 11 through 14. The images are in the order they were acquired on the video recordings. Pressure si& results are shown. The times shown with the figures refer to the number of seconds from the time the heated air is diverted through the model. The color change of the liquid crystal coating with increasing temperature is characterized by a the change fiom the black background to red, yellow, green, and then blue. The blue color starts about 2F after the start of the red color. The results are interpreted knowing that regions of greater cooling effectiveness will turn color (i.e. change temperature) more rapidly.

The figures show that the passages feeding the trailing edge slot are the first to turn, implying the greatest cooling effectiveness is in the trailing edge. This is likely to be generally true but must be tempered with the knowledge that wall thickness also plays a part (i.e. thinner walls will also change color sooner). The second image at 40 seconds clearly shows the effectiveness of several vertical rows of impingement holes of the core in the midchord location of the airfoil pressure side. The third image shows a coalescing of the cooling effects of the trailing edge feed passages and the pressure side rows of impingement holes. The last image at 125 seconds shows that most of the airfoil is now changed except for the leading edge region and a small region near the bottom of the image (in this case the vane tip) at about 75 percent chord. The sequence of images indicates that the highest effectiveness is at the pressure side trailing edge followed by the pressure side, core-driven internal impingement region.

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The conclusion fiom the cooling effectiveness tests is that there is good and fairly even coverage of cooling over most of the airfoil except for the leading edge region. For this region it appears that additional impingement cooling holes andor rows might be necessary to maintain airfoil temperatures and life.

Figure 1 1. Pressure side of FT8 vane 25 seconds after start of heat transfer test. Thermal paint is just beginning to change color near trailing edge discharge.

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Figure 12. Pressure side of W8 vane 40 seconds after start of heat transfer test. Cooling of the mid-span via impingement is noted.

Figure 13. Pressure side of FT8 vane 60 seconds after start of heat transfer test. Trailing edge and main airfoil cooled areas are coalescing.

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Figure 14. Pressure side of FT8 vane 125 seconds after start of heat transfer test. Note that leading edge has not yet changed color at a longer tie interval than predicted by the data shown in Figure 11.

LOW TEMPERATURE HEAT TRANSFER TESTING OF CERAMIC VANE FIRST ARTICLE

The purpose of this task was to pefiorm low tempera- heat transfer analysis on the first silicon nitride vane produced under Task 1. The analysis was to be identical to what was used for the stereolithographic (plastic) vane in Task 2 above. Ongoing problems with fabricating the trailing edge portion of the silicon nitride vanes prevented this task tiom being completed.

LOW TEMPERATURE HEAT TRANSFER TESTING OF SECTOR RIG CANDIDATE VANES

The purpose of this Task was to evaluate various rig test candidate silicon nitride vanes generated in Task 1, utilizing the same technique utilized in Tasks 2 and 3. Ongoing problems with fabricating the trailing edge portion of thevanes prevented this task fiom being performed.

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ACKNOWLEDGEMENTS

The author would like to thank Joel Wagner and Deborah Haas for performing the low temperature heat transfer experiments. The author would also like to acknowledge Dr. Steve Fishman, program monitor, as well as the funding for this effort provided by the U.S. Department of Energy, United Technologies Corporation, Kyocera Industrial Ceramics Corp., and AlliedSignal Ceramic Components.

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