Aerodynamic Characteristics of High Speed Train Pantograph with the Optimized Panhead Shape Yeongbin Lee, Joohyun Rho, Minho Kwak, Jaeho Lee, Kyuhong Kim, and Dongho Lee School of Mechanical and Aerospace Engineering Seoul National University, Institute of Advanced Aerospace Technology San 56-1, Shinlim-dong, Gwanak-Gu Seoul, Republic of Korea aerocfd1@snu.ac.kr, http://hypersonic.snu.ac.kr Abstract: - One of the most important reasons which restrict the speed increasing is the limitation of power transmission between the pantograph and the contact lines. It is due to an unexpected aerodynamic characteristics that is vortex shedding behind the pantograph. It causes an acoustic noise and structural vibration. The aerodynamic characteristics as shapes of pantograph are the main issue. For removing those problems, a new pantograph shapes had been proposed for the Korea high speed train. In this research, the optimized shape was selected through the previous research and then alanyzed by experimental test. The pantograph with the optimized panhead shape was compared with the basic pantograph system as the commercial high speed train(ktx-ii) in korea for aerodynamical advantages. The optimized panhead shape showed the increasement of the aerodynamic performance of entire pantograph system on the high speed train. Key-Words: - Aerodynamics, High speed train, Pantograph system, Optimized panhead shape, Wind tunnel experiment 1 Introduction A high speed train (HST) has been rapidly developed all over the world. Researchers realized that one of the most important reasons which restrict the speed increasing of electric locomotives is the capability of power transmission between the pantograph and the contact lines. The Korean high speed train named HEMU-400X is being devleoped for 400 km/h as maximum speed. There are many problems encountered when it runs. The problems are an aerodynamic drag, instability caused by a structural vibration, acoustic noise and so on [1,2]. When vehicles travel at high speed, power transmission is influenced by aerodynamic characteristics of the pantograph. A favorable aerodynamics performance of the pantograph system ensures perfect track capability, the stable contact between of panhead and the contact lines. It can help to reduce an wear and acoustics noise [3,4]. However, it is difficult to prevent the diffusion of such problems, because the pantograph system is located on train roof. Therefore, several researchers have studied the aerodynamic characteristics around the pantograph and made an effort to solve the problems [3,5,6]. General pantograph system is shown in Fig.1 and that is for Korea high speed train(hst-350x). It consists of many subparts and is so complex. Thus, it is so difficult to analyze the aerodynamic characteristics of each subpart and to find what are grave importance.[7] Through the researches, the panhead part was known the most important device to determine the aerodynamic characteristics of high speed pantograph system as shown in table 1. Table 1 Aerodynamic load on pantograph [7] Sub part F x F y F z [kg f ] (1) Lower arm 5.3 0.0 12.5 (2) Strut road 4.2 0.0 7.2 (3) Upper arm 3.2 0.0-9.2 (4) Balance road 0.8 0.0-2.7 (5) Plunger 12.8 0.0 0.0 (6) Panhead 94.5 0.0 13.5 Fig.1 Pantograph system ISSN: 1790-5095 84 ISBN: 978-960-474-106-9
Fig.2 Panhead aerodynamic acoustic noise [8] General panhead shapes are square or circular cylinder. After this blunt body, the flow is separated and/or developed to be turbulent. In some flow condition, the Karman vortex street is founded. This complex flow induces a structural vibration due to an unexpected increasement of lift and drag force. It may causes a damage for the panhead and unstability of the current supply by electric wire. For resolving these problems, an optimized stream lined shape should be needed. And the passive flow control strategy using holes was studied as shown in Fig.2[8,9] In this research, the optimized shape is selected firstly and then analyzed by wind tunnel experiments for investigating an aerodynamic characteristics as the given panhead shapes. The pantograph system with optimized panhead shape compared with basis pantograph system as the KTX-II train(commercial korean high speed train) in the point of aerodynamical advantages. The experimental results showed that the aerodynamic performance of entire pantograph system was increased by the optimized panhead shape increase on high speed train. 2 Experimental model and setup 2.1 Experimental model Robust optimized panhead shapes have been designed by previous researches for favorable aerodynamic characteristics of the pantograph system as shown in Fig. 3 [10]. For optimization of the shape, CFD studies were also conducted by In-house code was 2-D Navier-Stokes solver including Roe s FDS scheme for spatial discretization and LU-SGS with dual time stepping for time integration. All analysis and optimization are carried out with Integrated Super Computing System (ISS) in Tohoku University. Fig.3 Sectional shape of optimized panhead Fig.4 Wind tunnel test model (1/4 scale) Fig.5 Model and DAQ system Two scaled models (1:0.25) were examined to know the performance improvement. One was a basis model as the KTX-II pantograph system which will be served in commercial service. And the other was pantograph with optimized sectionnl shape as shown in right side of Fig. 4. The model height was 275 mm from upper base fairing as shown in left side of Fig 4. Total weight was about 5.5kg and it made of Al alloy and heat treatment iron. 2.2 Experimental Setup The experiments were performed in a closed-type low turbulence wind tunnel in Postech, Korea. The dimension of the closed test section is 1.5 m (height) 1.8 m (width) 4.6 m (length) and the maximum wind speed is about 75m/s with a turbulence intensity being less than 0.2%. The blockage ratio of the experimental model is about 2.5%. The data acquisition program is made use of LABView with multi-purpose DAQ system which has E-6110 board from National Instruments Company as shown in Fig. 5. The aerodynamic forces were measured by 2 axis load cell. The data were measured 18 times which were performed 10 times in preliminary test and 8 times in main test because of hysteresis and accuracy. The experimental Reynolds number range was controlled from 2 10 5 to 6 10 5 and characteristic length was defined the panhead length (145mm). 3 Experimental results These figures show the experimental results of the panhead and the pantograph systems in basis model and the optimized one. As the results of the basis panhead shape and the optimized panhead shape [Fig. 6~9], the ISSN: 1790-5095 85 ISBN: 978-960-474-106-9
Fig.6 Basis panhead drag (forward direction) Fig.10 Basis pantograph bidirectional mean drag Fig.7 Optimized panhead drag (forward direction) Fig.11 Optimized pantograph bidirectional mean drag Fig.8 Basis panhead lift (forward direction) Fig.12 Basis pantograph bidirectional mean lift Fig.9 Optimized panhead lift (forward direction) Fig.13 Optimized pantograph bidirectional mean lift ISSN: 1790-5095 86 ISBN: 978-960-474-106-9
Fig.14 Mean drag distribution (forward direction) Fig.15 Mean drag distribution (backward direction) Fig.16 Mean lift distribution (forward direction) Fig.17 Mean lift distribution (backward direction) optimized panhead shape has lower drag and lift than basis shape. The basis panhead shape is the parallel square cylinder. Because of blunt body shape, it makes the larger vortex shedding from the panhead. It caused the unsteady lift force fluctuation, the structural instability and severe acoustic noise. Contrary to the basis shape, the optimized panhead shape showed to prevent the large vortex shedding. The optimized shape reduced the drag about 40% and maximum amplitude of lift about 25% than basis panhead shape. In addition, the flow diection effect was studied because a train would move bidirectionally. As the flow direction is backward shown in [Fig. 10~13], the mean drag and lift force value(averaged for eight test cases) measured similar to forward flow case when panhead was basis shape. This result arise from the non-directional shape of the square cylinder. In case of the optimized panhead shape, mean drag force measured lower than the basis panhead shape in backward flow. But, the mean lift is higher. It is disadvantage for streamlined body shape. The leading edge of the optimized shape showed good aerodynamic performance for any angles of attack. But, sharp trailing edge is not good. That is to say, the optimized panhead shape has the weakness when the pantograph system is in the backward flow. However, it will not be important issue because the korean high speed train use only forward direction because of using intensify the push-pull type. From the present results of the mean drag and lift force distribution as flow direction [Fig.14~17], the panhead shape effect has over half porting of whole drag and lift production. The present work showed that an important key to make a decision the aerodynamic performance because the pantograph system is consisted of various parts. Therefore, the efficient way to design a whole pantograph system is optimized a panhead shape. 4 Conclusion The experiments were performed to know aerodynamic characteristics of pantograph system using wind tunnel. The optimized panhead shape is chosen through reviewing the previous research results. Then the aerodynamic characteristics of pantograph with the optimized panhead shape was compared with basis pantograph system for performance advantage of commercial high speed train. From this work, the panhead shape was important on whole performance of the pantograph system. Considring flow conditions, the optimized panhead shape showed the low mean drag and lift force than basis panhead shape. Therefore the optimized panhead shape ISSN: 1790-5095 87 ISBN: 978-960-474-106-9
increases the aerodynamic performance of entire pantograph system on the high speed train. Acknowledgements: This work was supported by the BK 21 Project, GCOE, NSL(S10801000121-08A0100-12110) and Railroad Technology Development Program. References: [1] Hisung Lee, Dae-seop Moon, 2005, Next Generation of Korea Train Express (KTX): Prospect and Strategies, Proceedings of the Eastern Asia Society for Transportation Studies, Vol. 5, pp. 255-262. [2] Joseph A. Schetz, 2001, Aerodynamics of High-Speed Trains, Annual meeting. Rev. Fluid Mech., Vol. 33, pp. 371-414. [3] T.Kitagawa, K. Nagakura, 2000, Aerodynamic Noise Generated by Shinkansen Cars, J of Sound and Vibration, Vol. 231(3), pp. 913-924. [4] T. Yoon, S. Lee, 2001, Efficient prediction methods for the micro-pressure wave from a high speed train, J. Acoust. Soc. Am., Vol. 110(5), pp. 2379-2389. [5] B Schulte-Werning, 2003, Research of European railway operators to reduce the environmental impact of high-speed trains, Proc. Instn Mech. Engrs, Vol 217. Part F: J. Rail and Rapid Transit. pp. 249-257. [6] Jaeho Hwang, Dongho Lee, 2001, Investigation on Severe Aerodynamic Load Condition about Pantograph, KSME conference paper, pp. 1-6. [7] K. R. Chung, S.H. Park, 2001, Structural Design Verification and Design Optimization of Pantograph for Korean Very High Speed Train, KSNVE conference paper. pp. 1229-1234. [8] Mitsuru Ikeda, Takehisa Takaishi, 2004, Perforated Pantograph Horn Aeolian Tone Suppression Mechanism, QR of RTRI, Vol. 45, No. 3, pp. 169-174. [9] T. Takashi, M. Miyazawa and C. Kato, 2007, A computational method of evaluating noncompact sound based on vortex sound theory. J. Acoust. Soc. Am. Vol. 121(3), pp. 1353-1361. [10] Joohyun Rho, Shinkyu Jeong, Dongho Lee, 2007, Robust Design Optimization of the Pantograph Panhead Shape on high Speed Train, KSME conference paper, Vol. 10, pp. 1-4. ISSN: 1790-5095 88 ISBN: 978-960-474-106-9