Zbornik radova Koridor 10 - Kirilo SaviÄ

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3rd International Scientific and Professional Conference CORRIDOR 10 - a sustainable way of integrations 3. FLOW SIMULATIONS BY FLUENT Flow simulations were made by use of ANSYS Fluent 12.1 software, for half-model train. Flow space around the half-model was discredited by the tetrahedral mesh. Boundary conditions were defined over the boundaries of the numerical flow model. In the near space all over the train body, the appropriate mesh elements were placed in the zone of the boundary layer. Largeness of the boundary layer mesh element was defined upon the condition of y + = 30 for the first mesh element row close to the train body, with adequate 20% mesh element scale increment for every other mesh element row. Number of mesh elements for the train was 5 millions. Numerical flow simulations were performed for train velocities of 180 km/h. Boundary conditions at the flow space input and output, in which simulations were done, were defined by pressures at those actual positions. All other boundary conditions were defined by the flow symmetry. Flow around the train was simulated as steady-state flow of the viscous incompressible fluid. The k – ε Realizable model of turbulence was applied with standard wall functions. The average number of iterations, needed for reaching of the result convergence was about 300 [10,11]. 3.1. Results derived by numerical simulation Figures 6 give the pressure distribution on the train half-model for velocity 50m/s (180km/h). The maximum value of pressure is at the front of the train nose, near the stagnation point. Afterwards stagnation point, the streamlines are accelerating and thus velocity appreciation caused pressure drop. On the left side of the figure 6, on a scale is showing that maximum value of pressure is 1520 Pa. Figure 6: Pressure distribution on the train half-model obtained using Fluent for the speed v=50 m/s Measurements in wind tunnel was obtained non-dimensional pressure coefficient Cp=0,55, which corresponds to the pressure 1680 Pa. The figures show good agreement of the results. 4. CONCLUSIONS Testing of train models in low speed wind tunnel are giving the pressure distribution on the train model and the pressure distribution around the train model in the configuration of single drive on open track. The diagrams of pressure distribution for the points of the front train section and top, in the train’s plane of symmetry and slip angles of = -10 o , 0 o and 10 o , illustrate that the stagnation point in the Belgrade, 2012 225
3rd International Scientific and Professional Conference CORRIDOR 10 - a sustainable way of integrations plane of symmetry is on the spot where Cp has maximum positive value. Flow separation occurs in the spots where the curve of pressure distribution moves away from the abscissa. Measurement results are compared with the results obtained by numerical simulation. The results obtained by flow simulation of the train for velocity 50m/s (180 km/h) using Fluent, show good correspondence with experimental one for scale 1:20. Fluent is advisable for use in aerodynamical research of trains, because of its ability to decrease research costs. At the very beginning of design process, model manufacturing costs are decreased, aerodynamical laboratory costs and human resources costs are decreased as well as research times. Acknowledgments The authors would like to thank the Ministry of Science and Technological Development of Serbia for financial support under the project number TR 35045. Scientific-technological support to enhancing the safety of special road and rail vehicles, 2011-2014. REFERENCES [1] MartyP., AutruffeH., Etudes aerodynamiques instationnaires liees a la circulation des trains a grande vitesse, Revue generale des chemins de fer, 1993. [2] Arth P., Ergebnisbericht zur Untersuchung des sonic boom phanomens auf HGV-strecken, Munchen, 1997. [3] Anderson, J. D., FUNDAMENTALS OF AERODYNAMICS, McGraw-Hill, Inc, 1996. [4] Puharić M., Adamović Ž., ISPITIVANJE BRZIH VLAKOVA U PODZVUČNOM AEROTUNELU, Strojarstvo, ZX470/1339-1343, broj 3., Vol. 50, str 151-160, svibanj-lipanj 2008. [5] LOW SPEED WIND TUNNEL TESTING, Internal edition, Military Technical Institute of Yugoslav Army, September, 1997. [6] Pope, A. WIND-TUNNEL TESTING, John Wiley & Sons, Inc., New York, 1954. [7] Puharić M., Theoretical and experimental research of aerodynamics problems for high-speed trains, M.A. paper, Mechanical Faculty, Belgrade, 2000. [8] Mirjana Puharić, Suzana Linić, Dušan Matić, Vojkan Lučanin, DETERMINATION OF BRAKING FORCE OF AERODYNAMIC BRAKES FOR HIGH SPEED TRAINS, Transaction of Famena, ISSN 1333-1124, UDC 629.4.56, UDC 629.4.077, oktobar 2011., [9] Holmes S., Schroeder M., "Aerodynamic Effects of High-Speed Passenger Trains on Other Trains", DOT/FRA/ORD-01/12, April 2002. Puharić M., Application of aerodynamic tunnels in testing of high-speed trains, cum. Science Technical Inform., 2002. [10] H.K.Veersteg, W. Malalasekera: An Introduction to computational fluid dynamics – The finite volume method, Longman, 1995. [11] J. Blazek: Computational Fluid Dynamics – Principles and Applications, Elsevier, 2001. Belgrade, 2012 226
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