A STRATEGY FOR CREATING PRISMATIC MESH LAYERS FOR MODELLING FLOW OF THE AHMED BODY USED IN VEHICLE AERODYNAMICS

Year 2022, , 776 - 785, 30.09.2022

Sinan Keiyinci , Mustafa Atakan Akar , Oğuz Baş , Mustafa Özcanlı

https://doi.org/10.21923/jesd.980458

Abstract

In this paper, a mesh generation strategy was investigated on a CFD simulation for Ahmed body which is commonly used in automotive aerodynamics. Generally, in these studies, different kinds of methods can be seen for creating prismatic mesh layers to solve turbulent boundary layers. An insufficient prismatic mesh layer is missing in solving the boundary layer, while the excess of this layer also increases the number of meshes, hence the solution time. In this study, the flow structure of the Ahmed body was studied by using the ANSYS-Fluent™ software at the Reynolds number of Re=2.83×106 depending on the flow rate (u∞=40 m/s) and the body length. The Prismatic mesh layer was generated using mathematical expressions and the results of this mesh were examined both quantitively and qualitatively and further results were evaluated again with a final mesh with a different strategy. To conclude, better results were obtained with developed meshes for modeling the flow profile on the turbulent boundary layer compared to the roughly generated initial mesh. In addition, closer results to the experimental value of CD and CL were obtained at developed meshes compared to the mesh that was roughly applied.

Keywords

CFD, Ahmed Body, Vehicle Aerodynamics, Boundary Layer, Mesh.

TAŞIT AERODİNAMİĞİNDE KULLANILAN AHMED CİSMİNİN AKIŞ MODELİ İÇİN PRİZMATİK AĞ KATMANI OLUŞTURURKEN İZLENECEK STRATEJİ

Abstract

Bu makalede, otomotiv aerodinamiği literatüründe sıklıkla kullanılan Ahmed cismi için bir HAD benzetiminde ağ oluşturma stratejisi üzerine bir çalışma yapılmıştır. Genel olarak bu çalışmalarda, türbülanslı sınır tabaka bölgelerini modellemek için prizmatik ağ katmanı oluştururken farklı yöntemler gözlemlenmektedir. Yetersiz bir prizmatik ağ katmanı sınır tabakasını çözmede eksik kalırken, bu katmanın gereğinden fazla olması ise ağ sayısını, dolayısıyla çözüm sürelerini artırmaktadır. Bu çalışmada, Ahmed cisminin akış yapısı, Ansys-Fluent™ programı ile akış hızına (U∞=40 m/s) ve gövde uzunluğuna bağlı Reynolds sayısı Re=2.83×106 olacak şekilde incelenmiştir. Matematiksel ifadelerden yararlanılarak oluşturulan prizmatik ağ katmanı ve bu ağın sonuçları hem nitel hem de nicel yönden incelenip, farklı bir strateji geliştirilen son bir ağ ile sonuçlar tekrar değerlendirilmiştir. Sonuç olarak, kabaca oluşturulan ilk ağ ile sonradan geliştirilen ağlar arasında, sınır tabakası üzerindeki akış profilini modellemede daha iyi bulgular elde edilmiştir. Ayrıca CD ve CL için deneysel yöntemle elde edilen sonuçlara, geliştirilen ağlarda, kabaca uygulanan ağa göre daha yakın sonuçlar elde edilmiştir.

Keywords

HAD, Ahmed Cismi, Taşıt Aerodinamiği, Sınır Tabakası, Çözüm Ağı

References

• Ahmed, S. R., Ramm, G., & Faltin, G. (1984). Some Salient Features Of The Tme-Average d Ground Vehicle. SAE Technical Paper Series, (840300).
• Aljure, D. E., Calafell, J., Baez, A., & Oliva, A. (2018). Flow over a realistic car model: Wall modeled large eddy simulations assessment and unsteady effects. Journal of Wind Engineering and Industrial Aerodynamics, 174(December 2017), 225–240. https://doi.org/10.1016/j.jweia.2017.12.027
• Balafas, G. (2014). Polyhedral Mesh Generation for CFD-Analysis of Complex Structures (Technical University of Munich). Retrieved from http://www.cie.bgu.tum.de/publications/masterthesis/2014_Balafas.pdf
• Bayındrılı, C., Çelik, M., & Demiralp, M. (2018). Bir Otobüs Modeli Etrafındaki Akış Yapısının CFD Yöntemi İle İncelenmesi ve Sürükleme Kuvvetinin Pasif Akış Kontrol Yöntemi İle İyileştirilmesi. Journal of Polytechnic, 0900(4), 785–795. https://doi.org/10.2339/politeknik.403993
• Cengel, Y., & Cimbala, J. (2006). Fluid Mechamics: Fundamentals and Application. McGraw-Hill, 342.
• Guilmineau, E., Deng, G. B., Leroyer, A., Queutey, P., Visonneau, M., & Wackers, J. (2018). Assessment of hybrid RANS-LES formulations for flow simulation around the Ahmed body. Computers and Fluids, 176, 302–319. https://doi.org/10.1016/j.compfluid.2017.01.005
• Huminic, A., & Huminic, G. (2017). Aerodynamic Study of A Generic Car Model with Wheels and Underbody Diffuser. International Journal of Automotive Technology, 18(2), 397–404. https://doi.org/10.1007/s12239
• Josefsson, E., Hagvall, R., Urquhart, M., & Sebben, S. (2018). Numerical Analysis of Aerodynamic Impact on Passenger Vehicles during Cornering. SAE Technical Papers, 2018-May(May). https://doi.org/10.4271/2018-37-0014
• Lanfrit, M. (2005). Best practice guidelines for handling Automotive External Aerodynamics with FLUENT. Fluent, 2, 1–14.
• Launder, B. E., & Spalding, D. B. (1974). The numerical computation of turbulent flows. Computer Methods in Applied Mechanics and Engineering, 3(2), 269–289. https://doi.org/10.1016/0045-7825(74)90029-2
• Le Good, G. M., & Garry, K. P. (2004). On the use of reference models in automotive aerodynamics. SAE Technical Papers, 2004(724). https://doi.org/10.4271/2004-01-1308
• Meile, W., Brenn, G., Reppenhagen, A., Lechner, B., & Fuchs, A. (2011). Experiments and numerical simulations on the aerodynamics of the ahmed body. CFD Letters, 3(1), 32–38.
• Menter, F. (1992). Improved two-equation k-omega turbulence models for aerodynamic flows. NASA Technical Memorandum, (103978), 1–31.
• Mohammadikalakoo, B., Schito, P., & Mani, M. (2020). Passive flow control on Ahmed body by rear linking tunnels. Journal of Wind Engineering and Industrial Aerodynamics, 205(June), 104330. https://doi.org/10.1016/j.jweia.2020.104330
• Morel, T. (1978). Aerodynamic drag of bluff body shapes characteristic of hatch-back cars. SAE Technical Papers, 1270–1279. https://doi.org/10.4271/780267
• Orszag, S. A. (1970). Analytical theories of turbulence. Journal of Fluid Mechanics, 41(2), 363–386. https://doi.org/10.1017/S0022112070000642
• Palin, R., Johnston, V., Johnson, S., D’Hooge, A., Duncan, B., & Gargoloff, J. I. (2012). The aerodynamic development of the Tesla model S-part 1: Overview. SAE Technical Papers. https://doi.org/10.4271/2012-01-0177
• Schlichting, H., & Gersten, K. (2016). Boundary-Layer Theory. In Boundary-Layer Theory. https://doi.org/10.1007/978-3-662-52919-5
• Shih, T.-H., Povinelli, L. A., Liu, N.-S., Potapczuk, M. G., & Lumley, J. L. (1999). A Generalized Wall Function. National Aeronautics and Space Administration, (July), 1–20. https://doi.org/19990081113
• Şimşek, O. (2020). Üstten Akişli Kapak Akiminin Sayisal Modellemesi̇. Mühendislik Bilimleri ve Tasarım Dergisi, 8(3), 808–819. https://doi.org/10.21923/jesd.752914
• Soares, R. F., & De Souza, J. L. F. (2015a). Influence of CFD Setup and Brief Analysis of Flow Over a 3D Realistic Car Model. SAE Technical Paper Series.
• Soares, R. F., & De Souza, J. L. F. (2015b). Tailpipe Position over a Realistic 3D Road Car Model: The Effect on Drag Coefficient Copyright. SAE Technical Paper Series.
• Tunay, T., Yaniktepe, B., & Sahin, B. (2016). Computational and experimental investigations of the vortical flow structures in the near wake region downstream of the Ahmed vehicle model. Journal of Wind Engineering and Industrial Aerodynamics, 159(January), 48–64. https://doi.org/10.1016/j.jweia.2016.10.006
• Vino, G., Watkins, S., Mousley, P., Watmuff, J., & Prasad, S. (2005). Flow structures in the near-wake of the Ahmed model. Journal of Fluids and Structures, 20(5), 673–695. https://doi.org/10.1016/j.jfluidstructs.2005.03.006
• Wang, Y., Wu, C., Tan, G., & Deng, Y. (2017). Reduction in the aerodynamic drag around a generic vehicle by using a non-smooth surface. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 231(1), 130–144. https://doi.org/10.1177/0954407016636970
• Yang, Y., Zhang, D., & Liu, Z. (2018). Optimization and design method for a rough rear surface on the notchback MIRA model. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 232(10), 1297–1309. https://doi.org/10.1177/0954407017728840
• Yılmaz, N., & Çiçek, İ. (2017). Standart Test Pervanesi Anali̇zleri̇ ile Hesaplamalı Akişkanlar Di̇nami̇ği̇ Anali̇z Altyapisinin Doğrulanmasi. Mühendislik Bilimleri ve Tasarım Dergisi, 6(4), 681–690. https://doi.org/10.21923/jesd.400115
• Zafer, B., & Haskaraman, F. (2017). Önden ve yanal rüzgar şarti altinda Ahmed cisminin sayisal incelenmesi. Journal of the Faculty of Engineering and Architecture of Gazi University, 32(1), 237–251. https://doi.org/10.17341/gazimmfd.300613
• Zhang, C., Bounds, C. P., Foster, L., & Uddin, M. (2019). Turbulence modeling effects on the CFD predictions of flow over a detailed full-scale sedan vehicle. Fluids, 4(3), 1–28. https://doi.org/10.3390/fluids4030148