N. Göksu SOYDAN, OĞUZ ŞİMŞEK, M.Sami AKÖZ

Köprü Ayağı Etrafındaki Türbülanslı Akımın Sayısal ve Deneysel Analizi

Dairesel bir köprü ayağı etrafındaki türbülanslı akış alanı, çoklu girdapların oluşumu nedeniyle karmaşık bir yapıya sahiptir. Köprü ayağı etrafında meydana gelen bu karmaşık akım yapısının belirlenmesi, bu tür yapıların tasarımı açısından önem kazanmaktadır. Bu çalışmada köprü ayağı etrafındaki üç boyutlu türbülanslı akımın hız alanı laboratuvar ortamında Lazer Doppler Anemometresi (LDA) ile ölçülmüş ve deney ile aynı koşullardaki akım için temel denklemler, sonlu hacimler yöntemine dayalı ANSYS-Fluent paket programı ile sayısal olarak çözülmüştür. Sayısal modellemede, Standard k-ε, Renormalization Group k-ε ve Realizable k-ε türbülans modeli kullanılmış ve serbest su yüzü profili Akışkan Hacimleri Yöntemi ile hesaplanmıştır. Seçilen ağ yapısının sayısal sonuçlara olan etkisini incelemek için Ağ Yakınsama İndeksi (GCI) kullanılmıştır. Sayısal sonuçlardan elde edilen hız alanı ve su yüzü profilleri deneysel ölçümlerle karşılaştırılmış, Realizable k-ε türbülans modelinin köprü ayağı etrafındaki akım alanını belirlemede diğer modellere göre daha başarılı olduğu tespit edilmiştir.

Anahtar Kelimeler:

Köprü ayağı, LDA, RANS, türbülans modellemesi, VOF

Experimental and Numerical Analysis of Flow around a Circular Bridge Pier

The turbulent ﬂow ﬁeld around a circular pier is complex due to separation and generation of multiple vortices in different structures. This topic has a great interest in engineering applications for the design of the bridges over water. In this study, the velocity field of flow around a circular pier is measured using Laser Doppler Anemometry (LDA). The Basic equations of the problem are solved by ANSYS-Fluent program package based on finite volume method for the flow case having the same experimental conditions. In the numerical simulations, Standard k-ε, Renormalization Group k-ε and Realizable k-ε turbulence closure model are used for the simulation of turbulence, and the flow profile is computed using Volume of Fluid method. Grid Convergence Index (GCI) is performed to examine the effect of the selected grid structure on the numerical results. The computed results for velocities and free surface profiles are compared with measured data. The comparisons of the experimental and numerical results show that Realizable k-ε is more successful turbulence model among the other models in predicting the velocity field and free surface profiles.

Keywords:

Bridge pier, LDA, RANS, turbulence modeling, VOF,

PDF

___

[1] Yanmaz, A.M., "Köprü Hidroliği", ODTÜ Geliştirme Vakfı Yayıncılık ve İletişim A.Ş., ANKARA, (2002).
[2] Richardson, J.E. and Panchang, V.G., "Three-dimensional simulation of scour-inducing flow at bridge piers", Journal of Hydraulic Engineering, 124(5): 530-540, (1998).
[3] Melville, B.W. and Coleman, S.E., "Bridge scour", Water Resources Publication, Colorado, U.S.A.,(2000).
[4] Kirkil, G., Constantinescu, G. and Ettema, R., "Detached eddy simulation investigation of turbulence at a circular pier with scour hole", Journal of Hydraulic Engineering, 135(11): 888-901, (2009).
[5] Huang, W., Yang, Q. and Xiao, H., 2009. "CFD modeling of scale effects on turbulence flow and scour around bridge piers", Computers & Fluids, 38(5): 1050-1058, (2009).
[6] Salaheldin, T.M., Imran, J. and Chaudhry, M.H., "Numerical modeling of three-dimensional flow field around circular piers", Journal of Hydraulic Engineering, 130(2): 91-100, (2004).
[7] Duan, J.G., "Two-dimensional model simulation of flow field around bridge piers", Impacts of Global Climate Change: 1-12, (2005). [8] Melville, B.W., "Local scour at bridge sites", researchspace@auckland, (1975).
[9] Yanmaz, A.M. and Altinbilek, H.D., "Study of time-depenbent local scour around bridge piers", Journal of Hydraulic Engineering, 117(10): 1247-1268, (1991).
[10] Ali, K. H. and Karim, O., "Simulation of flow around piers", Journal of Hydraulic Research, 40(2): 161-174, (2002).
[11] Smith, H.D. and Foster, D.L., "Modeling of flow around a cylinder over a scoured bed", Journal of Waterway, Port, Coastal, and Ocean Engineering, 131(1): 14-24, (2005).
[12] Jensen, B., Sumer, B., Jensen, H. and Fredsoe, J., "Flow around and forces on a pipeline near a scoured bed in steady current", Journal of Offshore Mechanics and Arctic Engineering, 112(3): 206-213, (1990).
[13] Fayyadh, M., Akib, S., Othman, I. and Razak, H.A., "Experimental investigation and finite element modelling of the effects of flow velocities on a skewed integral bridge", Simulation Modelling Practice and Theory, 19(9): 1795-1810, (2011).
[14] Zhu, Z. and Liu, Z., "CFD prediction of local scour hole around bridge piers", Journal of Central South University, 19: 273-281, (2012).
[15] Demirci, M., Kocaman, S. and Varlı, B., "Farklı geometrilerdeki köprü kenar ayakları etrafındaki hız dağılımının sayısal incelenmesi", Erciyes Üniversitesi Fen Bilimleri Enstitüsü Dergisi, 28(3): 161-173, (2012).
[16] Afzal, M.S., Bihs, H., Kamath, A. and Arntsen, Ø.A., "Three-dimensional numerical modeling of pier scour under current and waves using level-set method", Journal of Offshore Mechanics and Arctic Engineering, 137(3): 032001, (2015).
[17] Zhang, K., Katsuchi, H., Zhou, D., Yamada, H. and Han, Z., "Numerical study on the effect of shape modification to the flow around circular cylinders", Journal of Wind Engineering and Industrial Aerodynamics, 152: 23-40, (2016).
[18] Launder, B.E. and Spalding, D.B., "Lectures in Mathematical Models of Turbulence", Academic Press, London, (1972).
[19] Yakhot, V. and Orszag, S.A., "Renormalization-Group Analysis of Turbulence", Physical Review Letters, 57(14): 1722-1724, (1986).
[20] Yakhot, V., Orszag, S.A., Thangam, S., Gatski, T.B. and Speziale, C.G., "Development of Turbulence Models for Shear Flows by a Double Expansion Technique", Physics of Fluids a-Fluid Dynamics, 4(7): 1510-1520, (1992).
[21] Shih, T.H., Liou, W.W., Shabbir, A., Yang, Z.G. and Zhu, J., "A New Kappa-Epsilon Eddy Viscosity Model for High Reynolds-Number Turbulent Flows", Computers & Fluids, 24(3): 227-238, (1995).
[22] Hirt, C.W. and Nichols, B.D., "Volume of Fluid (VOF) Method for the Dynamics of Free Boundaries", Journal of Computational Physics, 39(1): 201-225, (1981).
[23] ANSYS, "Fluent Theory Guide", ANSYS Inc. USA, (2012).
[24] Patankar, S.V. and Spalding, D.B., "A calculation procedure for heat, mass and momentum transfer in three-dimensional parabolic flows", International Journal of Heat and Mass Transfer, 15(10): 1787-1806, (1972).
[25] Chen, H. and Patel, V., "Near-wall turbulence models for complex flows including separation", AIAA Journal, 26(6): 641-648, (1988).
[26] Çelik, I.B., Ghia, U., Roache, P.J. and Freitas, C.J., "Procedure for Estimation and Reporting of Uncertainty Due to Discretization in CFD Applications", Journal of Fluids Engineering-Transactions of the ASME, 130(7), (2008).
[27] Roache, P.J., "Verification of codes and calculations", AIAA Journal, 36(5): 696-702, (1998).