AEROENGINE HIGH PRESSURE TURBINE BLADE COOLING SYSTEM CONCEPT

Transcription

1 Proceedings of ASME Turbo Expo 2013: Turbine Technical Conference and Exposition GT2013 June 3-7, 2013, San Antonio, Texas, USA GT AEROENGINE HIGH PRESSURE TURBINE BLADE COOLING SYSTEM CONCEPT S. Riznyk, A. Artushenko SE IVCHENKO-PROGRESS 2, Ivanova str, Zaporozhye 69068, Ukraine tel. (0612)656295, fax (0612)654697, ABSTRACT Aeroengine high-pressure turbine (HPT) is the key engine component. HPT must withstand high inlet temperatures and mechanical loads providing necessary level of efficiency. To achieve these objectives effective and complex blade cooling systems (internal convective and film cooling) are used in HPT design. Methodology of effective HPT blade cooling system design, numerical and experimental investigations are described in the article. Different HPT cooling systems are considered: internal convective serpentine schemes with ribs in channels and wall-cooled system. Two types of film cooling channels (round and shaped) are used in HPT blade cooling systems design. The role of thermal barrier coating is described. Experimental test rig was designed and manufactured to define the heat transfer coefficients and hydraulic parameters for HPT blade with wall-cooled system cooling channels. The results obtained on this test rig were used to determine boundary conditions and temperature fields in advanced HPT blade with wall-cooled cooling system. Numerical and experimental results obtained in HPT blade cooling system research are presented in the article. NOMENCLATURE d - impingement cooling hole diameter, mm; B - channel width, mm; H - channel height, mm; S -spacing of cooling holes, mm; P -pressure, kg/cm 2 ; T - temperature, K; Re - Reynolds number; Nu - Nusselt number; Tg - gas temperature; Tc - cooling air temperature; Tm - metal temperature; Θ - blade cooling effectiveness. Abbreviations: HPC - high-pressure compressor; HPT - high-pressure turbine; CFD - computational fluid dynamics; TBC Thermal barrier coating; SE - State Enterprise; UDF unducted fan; TET - Turbine Entry Temperature (inlet rotor gas temperature). 1 Copyright 2013 by ASME

2 INTRODUCTION SE Ivchenko-Progress has gained great experience in creating high-temperature HPT both for aircraft (airplane and helicopter) engines and for the industrial gas turbine engines with various HPT blade cooling systems for the level of TET up to K. Cooling systems of different types are used to ensure reliable operation of the turbine at high inlet gas temperature (Fig.1). Blade cooling effectiveness (defined as: Θ=(Tg-Tm)/(Tg-Tc)) depends on cooling system scheme and cooling air flow amount (Fig.2a,b). In effectivness definition Tg is relative gas temperature at the turbine middle section inlet, Tc is cooling air at the blade cooling system inlet and Tm is bulk metal temperature of the blade middle section. Figure 2b- SE Ivchenko-Progress aeroengine HPT cooling blades effectiveness INVESTIGATION OF TURBINE BLADE COOLING SYSTEM DESIGN Numerical investigations Theoretical investigation of hydraulic characteristics, temperature distributions, boundary conditions estimations are necessary for the blade cooling design. One of the most perspective methods for solving HPT blade temperature distribution problem is using 3-D N-S CFD [5] calculations of the thermal state of cooled blades in twoside conjugate formulation for the gas flow in interblade channels and for the air flow in Figure 1- SE Ivchenko-Progress aeroengine HPT cooling blades Figure 2a- SE Ivchenko-Progress aeroengine HPT cooling blades 2 Copyright 2013 by ASME

3 Figure 3- Results of small aeroengine HPT cooling blades thermal calculations cooling channels with ribs inside the channels. Results of this calculation are shown in the Fig.3,here is a comparison with experimental data obtained during engine tests (Fig. 4a). The accurate prediction of the thermal state of cooled turbine blade is one of the most challenging tasks for the designers of modern gas turbines. Therefore, an essential aspect in turbine designing is the experimental verification of the aerodynamic and thermal models on special experimental facilities and on the engine. Experimental investigations Figure 4a- Preparation of HPT blade Radius 79.5 mm Despite the fact that the precision and complexity of the thermal calculations increase, experimental studies are a necessary part of the turbine cooling system design. The experiments were performed on the engines and test rigs using a variety of measurement technologies (thermopaints, thermocouples, thermal crystals). Metal temperatures in the points on blades surfaces, cooling system parameters (pressures and temperatures) are obtained. For example, in small aeroengine HPT blades (Fig. 4a) outer surface thermal crystals (0,2-0,3 mm size) incorporated blades were installed in engine and tested at engine Take Off rate. Then, after the engine disassembly, thermal crystals were extracted, characteristics of the crystal lattice were transcribed in temperature values (Fig. 4a, b). Figure 4b- Gas and metal temperature distributions in small aeroengine HPT blade 3 Copyright 2013 by ASME

4 Theoretical investigations To provide reliable turbine blade operation with the required lifetime investigation project was started. The objective of this project is to design aeroengine HPT cooling system to withstand blade inlet gas temperature level TET approx K with minimal cooling airflow amount. HPT blade of real engine (UDF engine with TET=1720K) was taken as a base design (Fig.7). It is a convective multipass with film cooling monocrystal blade. Different advanced HPT internal convective serpentine cooling systems with ribs in channels are designed and investigated. Two types of film cooling channels (round and shaped) are used in HPT blade. The boundary conditions data are very important, so, additionally, inlet air flow temperature and gas temperature near the blade surface must be measured as it is shown in Fig.5. Figure 5- Gas temperature measurements for HPT blade Figure 7- Base design of aeroengine HPT blade The obtained blade temperature numerical model, verified by experiments, is used for cooling system optimisation and blade lifetime calculations. But the most important criteria for blade cooling system design is real experience of HPT blade long time operation on the aeroengine operating conditions in real environment conditions (Fig.6). The thermal barrier coating (Fig.8) advantages were investigated numerically and experimentally. Figure 8- Aeroengine HPT blade with modified film cooling and TBC Besides typical HPT blade cooling systems advanced HPT blade wall-cooled system was investigated and was compared with typical system by criteria of effectiveness and weight. In advanced HPT blade wall-cooled system special types of cooling channels are used. Experimental test rig was designed and manufactured to define the heat transfer coefficients and hydraulic parameters for such type of blade wall-cooled cooling channels. The results obtained on this test rig were used to determine metal temperature fields in prospective HPT blade with wall-cooled system. Main results of these investigations are presented in Fig. 9 and Table 1. Figure 6- HPT blade after long time operation on the D18T aeroengine operating conditions Experimental and numerical results, experience of HPT blade long time operation on the aeroengine operating conditions provide motivation for searching new ideas in creation of a favorable temperature state of HPT blade. ADVANCED HPT BLADE COOLING SYSTEM INVESTIGATIONS 4 Copyright 2013 by ASME

5 A B C Figure 9. Aeroengine HPT blades: A-base design, B- Modification 1, modified blade with shaped film cooling holes, C- Modification 2, wall-cooled design Table 1 Blade Mean Section Base Modification 1 cation 2 Modifi- Leading Edge, С Trailing Edge, С Bulk Metal, С As the table shows, the modification 1 of the blade with modified shaped film cooling holes has an average temperature of the middle section 23 C lower than the blade with base design at the same air cooling flow. Modification 2, wall-cooled system blades has an average temperature of the middle section 68 C lower than the blade with base design, but air flow increased by 0.77%. The use of TBC with 0.14 mm thickness and a thermal conductivity 2.8 W/(m K) leads to the decrease in the average temperature of the blade cross section for C for all presented cooling blades. The results of presented investigation show, that one of the most challenging cooling system for the engines with gas temperature at HPT rotor blade inlet TET = K is a wallcooled system ( penetrating cooling ). SE Ivchenko-Progress has designed an original wall-cooled system [3,4] used for rotor blade with penetrating cooling system. Blade profile cross-sections for both - internal convective serpentine film cooling and wallcooled system are shown in Fig.10. Wallcooled system blade temperature distribution is presented in Fig. 11. Figure 10- HPT blade profile cross-sections with internal convective multipass serpentine film cooling and wall-cooled system (Modification 2a) Figure 11- Modification 2a, SE Ivchenko- Progress temperatures of wall-cooled blade original design (TET = 1745 К) Experimental investigation of wall-cooled system ( penetrating cooling ) heat transfer In SE Ivchenko-Progress blade with wallcooled system an air is delivered to inside wall channels on the blade suction side through channels located in blade root. Then the air through the holes is delivered to central cavities from which through other holes it passes to the channels located inside the blade pressure side wall. And after that through the holes for 5 Copyright 2013 by ASME

6 film cooling the air flows out to the turbine duct. Investigations of heat transfer on all channel surfaces with wall-cooled system are presented in [2]. Work was fulfilled for blade cooling system proposed by Dailey [1]. In this [2] work heat transfer coefficients on all surfaces are presented for the Reynolds Number calculated using holes diameter for impingement cooling (Re = 41170). Also geometrical characteristics of a test sample were provided in the article [2] in dimensionless form: B/d=7.5; H/d=1.25; S/d=4. Injecting holes were arranged in two rows ±1.9d away from the channel axial line. Holes at channel outlet were 30 inclined. The distance between holes was 5,475d. Tests were executed for Re numbers: In or studies of the advanced HPT blade cooling system the results presented in [3] can not be used because of: - there is no geometrical similarity between studied wall-cooled system channel [2] and SE Ivchenko-Progress blade wall-cooled system channel; - discrepancy of Re numbers in fulfilled tests [2] and Re numbers in SE Ivchenko-Progress blade; - in the work [2] criteria dependences for Nusselt number calculation were not specified. The goal of the current experimental work is a heat transfer investigation in wall-cooled system channel. This channel has geometry and operational conditions similar to the channel of the blade designed by SE Ivchenko-Progress. Experimental facility Electrometric method was selected for heat transfer investigations in wall-cooled system channel. Copper plates with embedded thermocouples along the test plate were used. The copper strips were heated with electric heaters to provide a locally constant heat flux. The measured wall temperatures were considered as averaged, as copper is an excellent conductor of heat. The local heat flux is known from the energy supplied to the copper plate. Experimental facility is an open-ended air contour that consists of experimental sector, shut-off-and-regulating accessories, flow-measuring apparatus, air filter, direct current power supply 8301 HD and ТЕС 5010, thermocouples, cold junction AD 592, measuring and computing complex MIC-400D. Experimental sector of the facility is shown in Fig. 12. The photo of the front plate is shown in Fig. 13. Figure 12 Experimental sector of the facility 6 Copyright 2013 by ASME

7 Figure 13 Front plate Experimental sector consists of a case that is made from plexiglas with 10 mm thickness. In this plexiglas case a working section is installed. On the outer side the case is tightly covered by plastic foam plates (with 20 mm thickness) for additional heat insulation. The investigated channel with 22 mm length is formed in working section. The shape of its cross-section is oval with the width B=35.4 mm and height H=20.5 mm. Front and back surfaces of this channel are flat, but top and bottom ones are curvilinear with mm radius. The investigated channel is formed by four copper plates. Each plate is 226 mm long, with 1.5 mm thickness and 22.4 mm width. To improve the glue adhesion copper plates were nickel-plated. For the purpose of exclusion of heat leakage from one plate to another balsa tapes (1.1 mm thickness) were placed between the plates. Balsa tapes were smoothed out aflush with internal surface of a channel. Along the full length of each plate from the side of heat insulation electrical heaters were fastened with the help of BK-9 glue. Heaters are chrome-nickel tapes (0.05 mm thickness) with 2.5 mm width on the back plate and 3.5 mm on the front, top and bottom plates. On each copper plate two chrome-nickel tapes (connected sequentially by copper bridge on a plate edge) are fastened. For each of four copper plates, different dc power supply was used. Six cable chromel-alumel thermocouples (1mm diameter) were soldered in copper plates. End surfaces of thermocouples were placed aflush with internal surface of the channel. Each cooper plate after fastening of thermocouples and heaters was glued to a balsa lath (12 17mm thickness) that served as heat insulation. Front and back laths were glued to glass-fibre plastic plates with 3 mm thickness. For air temperature measuring two cable chromel-alumel thermocouples (1 mm diameter) were installed at the air inlet to the receiver of experimental sector and at the air outlet from the facility. In the back plate on the symmetry axis five holes (diameter d=10.5 mm) were evenly perforated (pitch S= 45 mm). The main purpose of these holes is a stream inleakage of the air on the front plate. In the direction of the air flow, at first in the plexiglass, holes (20 mm long) have the diameter of 20 mm and then in glassfibre plastic plate, wooden lath and copper plate (whole length is mm) these holes have the diameter of 10.5 mm. At the inlet (in glass-fibre plastic plate) and at outlet (in copper plate) holes (10.5 mm diameter) were made with fillets (2.5 mm and 0.5 mm for inlet and outlet respectively). The front plate has six holes for air outflow from the channel. The diameter of four central holes is 8 mm with pitch between them equaling to 45 mm and the diameter of two last holes is 5.6 mm (the distance from these end-holes to the nearest hole with 8 mm diameter is 36 mm). All these holes are located on the plate axis of symmetry and four central holes are chequerwise placed relative to the holes for stream inleakage of air. To prevent heat leakage from front copper plate through the holes for air outflow, holes in copper plate were made with diameter that is 2 mm bigger than aforesaid diameters. Balsa pieces were mounted in these holes and then the holes were perforated with aforesaid diameters. The cooling air with indoor temperature fed to the internal cavity of experimental facility, goes through the grid and enters the receiver. From the receiver through five holes for stream inleakage the air gets to the investigated channel, where it cools four copper plates and through six holes in the front plate flows out to the atmosphere. Experimental technique Experiments were conducted when the temperature of all four copper plates was 50±1 С. This temperature was provided by 7 Copyright 2013 by ASME

8 power supplies regulation. The air temperature at the experimental sector inlet depends on test conditions and varies in range of 13 С 19 С. After stabilizing the copper plates temperature and electric power, heat leakages for each plate were measured (as leakages in that case one can understand the loss of electric power provided to each plate without feeding of cooling air). In some cases heat leakages were measured at the end of the working day. After defining the heat leakages the experimental facility was tested with different mass flow rates of cooling air. Temperatures, mass flow rates and powers, as a rule, were measured twice under each operational condition: at first after stabilization of copper plates temperature (when temperature change during five minutes is not more than 0.2 С) second time is 5 10 minutes after the first measurement. It was required to hold the same mass flow rate and constant electric powers during the period of time between measurements. As a rule initially tests with increasing of air mass flow rate were carried out at first and only after that tests with decreasing of flow rate. Thus for each mass flow rate results of four measurements of temperatures, flow rates and powers were obtained. Results of experiments Experimentally obtained dependence between Nusselt number and Reynolds number for front, back and side walls of the channel with penetrating cooling is shown in Fig. 14. Diameter of impingement holes of air and air parameters at the channel inlet were used for the calculation of Nusselt number and Reynolds number. To define Nusselt numbers experimentally obtained heat leakages were subtracted from measured electric power (that provided to each copper plate). Also for the back plate heat leakages to the central part of impingement holes were subtracted. Heat leakages to the central part of the holes for stream inleakage of air were defined by calculation. According to the obtained results that are shown in Fig. 14 we can draw following conclusions: the growth of Reynolds number causes increasing of Nusselt number for all surfaces; exponents at different Reynolds numbers for different surfaces and channels are: 0.56 for the front wall, 0.75 for the side walls, 0.83 for the back wall; with constant Reynolds number the maximum Nusselt number is obtained for the front plate and minimum for the back plate; the difference between maximum Nusselt number and minimum reduces when Reynolds number increases. Nusselt numbers for bottom and top side walls are the same. - front plate - side plate (top) - side plate (bottom) - back plate Figure 14 Dependence between Nusselt number and Reynolds number (B/d=3.37, H/d=1.95, S/d=4.29) 8 Copyright 2013 by ASME

9 It is estimated that the maximum possible inaccuracy in measuring of Nusselt number is not higher than 10 % for the front and side walls and not higher than 14 % for the back surface. The experimentally investigated heat transfer coefficients in a wall-cooled channels (that has geometry and operational conditions similar to the channel of the blade designed by SE Ivchenko-Progress ) were used as boundary conditions for advanced HPT blade cooling system design (Fig. 10). SUMMARY AND CONCLUSIONS A brief introduction to the history of SE Ivchenko-Progress turbine blade cooling system design is presented. The methodology of numerical and experimental blade cooling systems investigations is described. Original wall-cooled blade was designed, numerical investigations were fullfiled, experimental test rig provided the necessary data for heat transfer coefficient calculations ACKNOWLEDGMENTS The authors express thanks to SE Ivchenko-Progress engineers Yakushev Yu.V., Boris S.B., Karpenko A.M. for their support in the present work. REFERENCES 1. Dr.G.Dailey, Aero-Thermal Performance of Internal Cooling Systems in Turbomachines, Von Karman Institute for Fluid Dynamics Lecture Series VKI-LS Gillespie D.R.H, Son C.M, Ireland P.T, Dailey G.M. The Development and Validation of Simple Empirical Models of Impingement Cooling from Full Surface Heat Transfer Coefficient Distributions. Paper presented at the RTO AVT Symposium on Advanced Flow Management: Part B Heat Transfer and Cooling in Propulsion and Power Systems, held in Leon, Norway, 7-11 May 2001, and published in RTO-MP-069(I). 3. Ukrainian patent Turbine Cooling Blade UA U, registered г. 4. Russian patent Turbine Cooling Blade RU U1, registered г. 5.ANSYS CFX User s Guide, Release ANSYS, Inc., 2007 ANSYS CFX Tutorials, Release ANSYS, Inc., Copyright 2013 by ASME

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