DOI:
https://doi.org/10.64539/sjer.v2i1.2026.353Keywords:
Mesh Independence, Reynolds-Number Sensitivity, Automotive Aerodynamics, Crosswind Flow, y⁺ Wall TreatmentAbstract
Aerodynamic prediction for full scale passenger vehicles relies on the use of mesh resolutions which accurately represent boundary layer evolution and wake dynamics while maintaining reasonable computational expense. To verify the drag prediction for two production-derived vehicle geometries (Notchback and Hatchback) simulated at 15° steady state crosswind using incompressible RANS with SST k−ω turbulence models, the verification process consisted of a systematic set of five progressively refined polyhedral meshes (1.5 million cells - 7.2 million cells) created using a controlled refinement template to maintain consistent near-wall treatment within all five meshes. The drag results showed significant improvement from the coarsest mesh to the finest mesh (≈ 14% improvement for Notchback ≈ 12% improvement for Hatchback) and then clearly exhibited asymptotic results as evidenced by the difference between M4 and M5 decreasing to less than approximately 1.5%, indicating that M4 provides mesh-independent accuracy with over 20% less computational cost than M5. Furthermore, a Reynolds number sweep across the range of representative full-scale Reynolds number values demonstrated that drag is effectively insensitive to Reynolds number once the fully turbulent regime is reached and wake structures between the Notchback and Hatchback. Through this analysis it has been determined that targeted refinement strategies around A-pillar and rear-end separation zones and the near wake will provide the greatest accuracy and cost-effective use of computational resources as compared to uniform global densification, thus providing a validated mesh resolution strategy for using RANS simulations to predict drag for full scale passenger cars under steady state conditions.
References
[1] J. H. Ferziger, M. Perić, and R. L. Street, Computational Methods for Fluid Dynamics. Springer, 2019. https://doi.org/10.1007/978-3-319-99693-6.
[2] S. B. Pope, Turbulent Flows. Cambridge Univ. Press, 2000. https://doi.org/10.1016/S0010-2180(01)00244-9.
[3] T. Cebeci, Analysis of Turbulent Flows: With Computer Programs. Springer, 2009. https://books.google.co.id/books?id=UX_hXE4luVMC.
[4] M. A. A. Al-Maghrebi et al., “Aerodynamic design and performance evolution of notchback vehicles,” Eur. J. Appl. Sci., Eng. Technol., vol. 3, no. 5, pp. 78–87, 2025, https://doi.org/10.59324/ejaset.2025.3(5).06.
[5] J. Hüttenrauch, “The second generation of the VW Polo BlueMotion,” ATZ Worldw., vol. 112, pp. 16–23, Feb. 2010, https://doi.org/10.1007/BF03225112.
[6] C. Repmann and M. Hähnel, “The aerodynamics development of the new Volkswagen Polo,” in Progress in Vehicle Aerodynamics and Thermal Management (FKFS 2017), J. Wiedemann, Ed. Cham, Switzerland: Springer, 2018, pp. 160–167, https://doi.org/10.1007/978-3-319-67822-1_10.
[7] A. Kazi, P. Acharya, A. Patil, and A. Noraje, “Effect of spoiler design on hatchback car,” Int. J. Mod. Trends Eng. Res., vol. 3, no. 9, pp. 192–200, 2016. https://scispace.com/pdf/effect-of-spoiler-design-on-hatchback-car-539a43rt0h.pdf.
[8] O. Čavoj, O. Blaťák, P. Hejtmánek, and J. Vančura, “Vehicle ride height change due to radial expansion of tires,” Mach. Dyn. Diagn., 2015, https://doi.org/10.1515/mecdc-2015-0008.
[9] B. N. Zakher, M. Elhadary, M. A. El-Gohary, and I. M. El Fahham, “Comparison between experimental life road simulation and computational fluid dynamics and fluid structure interaction for sedan car,” CFD Lett., vol. 14, no. 2, pp. 81–97, 2022, https://doi.org/10.37934/cfdl.14.2.8197.
[10] L. Jiang, H. Liu, G. Chai, G. Jiang, and W. Lin, “Effect of automotive headlamp modeling on automotive aerodynamic drag,” in Proc. 2008 9th Int. Conf. Computer-Aided Industrial Design and Conceptual Design (CAIDCD), Kunming, China, Nov. 2008, pp. 588–593, https://doi.org/10.1109/CAIDCD.2008.4730637.
[11] F. R. Menter, “Two-equation eddy-viscosity turbulence models for engineering applications,” AIAA J., vol. 32, no. 8, pp. 1598–1605, 1994. https://doi.org/10.2514/3.12149.
[12] P. J. Roache, Verification and Validation in Computational Science and Engineering. Hermosa Publishers, 1998. https://lccn.loc.gov/98096214.
[13] B. C. Ismail et al, “Procedure for estimation and reporting of uncertainty due to discretization in CFD applications,” J. Fluids Eng., vol. 130, no. 7, p. 078001, 2008. https://doi.org/10.1115/1.2960953.
[14] A. N. N. Azman, K. Venkatason, and S. Sivaguru, “Mesh convergence analysis on the aerodynamic performance of a sedan vehicle,” J. Eng. Technol. Appl. Phys., vol. 7, no. 1, pp. 85–95, 2025. https://doi.org/10.33093/jetap.2025.7.1.14.
[15] A. Ghavidel, M. Rashki, H. G. Arab, and M. A. Moghaddam, “Reliability mesh convergence analysis by introducing expanded control variates,” Front. Struct. Civ. Eng., vol. 14, no. 4, pp. 1012–1023, 2020. https://doi.org/10.1007/s11709-020-0631-6.
[16] N. Ashton, P. Unterlechner, and T. Blacha, “Assessing the sensitivity of hybrid RANS-LES simulations to mesh resolution, numerical schemes and turbulence modelling within an industrial CFD process,” SAE Tech. Paper 2018-01-0709, 2018. https://doi.org/10.4271/2018-01-0709.
[17] C. Zhang, C. P. Bounds, L. Foster, and M. Uddin, “Turbulence modeling effects on the CFD predictions of flow over a detailed full-scale sedan vehicle,” Fluids, vol. 4, no. 3, p. 148, 2019. https://doi.org/10.3390/fluids4030148.
[18] E. Guilmineau, “Numerical simulations of flow around a realistic generic car model,” SAE Int. J. Passeng. Cars–Mech. Syst., vol. 7, pp. 646–653, 2014. https://doi.org/10.4271/2014-01-0607.
[19] M. N. F. Kamal et al., “A review of aerodynamics influence on various car model geometry through CFD techniques,” J. Adv. Res. Fluid Mech. Therm. Sci., vol. 88, no. 1, pp. 109–125, 2021. https://doi.org/10.37934/arfmts.88.1.109125.
[20] M. G. Connolly, A. Ivankovic, and M. J. O’Rourke, “Drag reduction technology and devices for road vehicles – a comprehensive review,” Heliyon, vol. 10, no. 13, p. e33757, 2024. https://doi.org/10.1016/j.heliyon.2024.e33757.
[21] S. Sarkar, K. Thummar, N. Shah, and V. Vagrecha, “A review paper on aerodynamic drag reduction and CFD analysis of vehicles,” Proc. A Rev. Paper Aerodyn. Drag Reduct. CFD Anal. Vehicles, pp. 231–235, 2019. https://doi.org/10.13140/RG.2.2.31506.91849.
[22] R. F. Soares, “Drag of road cars: cost-effective CFD setup, proposal of an aerodynamic concept and case studies,” 2015. https://doi.org/10.14393/ufu.di.2015.352.
[23] C. W. Hirt and B. D. Nichols, “Volume of fluid (VOF) method for the dynamics of free boundaries,” J. Comput. Phys., vol. 39, no. 1, pp. 201–225, 1981. https://doi.org/10.1016/0021-9991(81)90145-5.
[24] M. Schlipf, A. Tismer, and S. Riedelbauch, “On the application of hybrid meshes in hydraulic machinery CFD simulations,” IOP Conf. Ser.: Earth Environ. Sci., vol. 49, p. 062013, 2016. https://doi.org/10.1088/1755-1315/49/6/062013.
[25] V. Kausalyah et al., “Optimisation of vehicle front-end geometry for adult and pediatric pedestrian protection,” Int. J. Crashworthiness, vol. 19, no. 2, pp. 153–160, 2014. https://doi.org/10.1080/13588265.2013.879506.
[26] M. Braza, P. Chassaing, and H. H. Minh, “Numerical study and physical analysis of the pressure and velocity fields in the near wake of a circular cylinder,” J. Fluid Mech., vol. 165, pp. 79–130, 1986. https://doi.org/10.1017/S0022112086003014.
[27] Y. Wang, C. Wu, G. Tan, and Y. Deng, “Reduction in the aerodynamic drag around a generic vehicle by using a non-smooth surface,” J. Automob. Eng., vol. 231, no. 1, pp. 130–144, 2017. https://doi.org/10.1177/0954407016636970.
[28] M. N. Sudin, M.A. Abdullah, S. A. Shamsuddin, F. R. Ramli, and M. M. Tahir, “Review of research on aerodynamic drag reduction methods,” Int. J. Mech. Mechatronics Eng. (IJMME-IJENS), vol. 14, no. 2, 2014. https://eprints.utem.edu.my/id/eprint/12204/1/145302-6868-IJMME-IJENS.pdf.
[29] K. Nisugi, T. Hayase, and A. Shirai, “Fundamental study of aerodynamic reduction for vehicle with feedback flow control,” JSME Int. J., Ser. B, vol. 47, no. 3, 2004. https://doi.org/10.1299/jsmeb.47.584.
[30] F. Mariani, C. Pogianni, F. Risi, and L. Scappaticci, “Formula SAE racing car: Experimental and numerical analysis of the external aerodynamics,” in 69th Conf. Italian Thermal Machines Eng. Assoc. (ATI 2014), 2014. https://doi.org/10.1016/j.egypro.2015.12.111.
[31] A. Javed, K. Djijdeli, and J. T. Xing, “A coupled meshfree-mesh-based solution scheme on hybrid grid for flow-induced vibrations,” Acta Mech., vol. 227, no. 8, pp. 2245–2274, 2016. https://doi.org/10.1007/s00707-016-1614-5.
[32] N. R. Morgan and J. I. Waltz, “3D level set methods for evolving fronts on tetrahedral meshes with adaptive mesh refinement,” J. Comput. Phys., vol. 336, pp. 492–512, 2017. https://doi.org/10.1016/j.jcp.2017.02.030.
[33] M. Alam, K. Walters, and D. Thompson, “A transition-sensitive hybrid RANS/LES modeling methodology for CFD applications,” in 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Grapevine, TX, USA, 2013, p. 995. https://doi.org/10.2514/6.2013-995.
[34] S. Jakirlic, L. Kutej, B. Basara, and C. Tropea, “Computational study of the aerodynamics of a realistic car model by means of RANS and hybrid RANS/LES approaches,” SAE Int. J. Passeng. Cars – Mech. Syst., vol. 7, no. 2, pp. 559–574, 2014. https://doi.org/10.4271/2014-01-0594.
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Copyright (c) 2025 Mohammed Almaghrebi, Ahmed Atta Elhussein Ali
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