An URANS Simulation of the Kelvin-Helmholtz Aerodynamic Effect over the Ahmed Body

Abstract

The reduction of energy consumption of cars is always a significant issue in automotive design. Turbulent flow around a car body is very difficult to simulate accurately due to the complexity of the flow conditions around the body, such as complex flow separation and laminar to turbulent flow transition. In particular, flow over the Ahmed body with a rear angle of 25o is considered a challenging problem for the RANS approach with two-equation turbulence models. In this study, we aim to analyze the Kelvin-Helmholtz instability associated with this flow with a URANS approach. Methodology for utilizing the URANS method is fully discussed. The predicted velocity profiles and drag coefficient are com-pared with experimental results. Three turbulence models, such as the k-ε, k-ω and SST models, are assessed and validated with experimental data. The aim of the study is to evaluate the performance of these models for the study of the Kel-vin-Helmholtz instability over the Ahmed body and for car bodies generally us-ing experimental data for their validations. It is found that the URANS approach with the turbulence models with proper numerical treatment can perform as well as or even better than the LES. And the SST model shows the best performance compared with other turbulence models.

Keywords

• Turbulence Models
• Ahmed Body
• CFD
• LES
• Automotive Aerodynamics
• Car Aerodynamic Design
• URANS
• RANS
• Kelvin- Helmholtz

References

1. Igali, D., Mukhmetov, O., Zhao, Y., Fok, S.C., and The, S.L. 2019. “A comparative analysis of turbulence models for automotive aerodynamic simulation and design.” International Journal of Automotive Technology (accepted for publication).
2. Ahmed, S. R., G Ramm, and G Faltin. 1984. "Some Salient Features Of The Time-Averaged Ground Vehicle Wake."
3. Anatol Roshko. "On the wake and drag of bluff bodies." Journal of the aeronautical sciences 22, no. 2 (1955): 124-132.
4. Argyropoulos, C.D., and N.C. Markatos. 2015. "Recent Advances On The Numerical Modelling Of Turbulent Flows". Applied Mathematical Modelling 39 (2): 693-732. doi:10.1016/j.apm.2014.07.001.
5. Bayraktar, Ilhan. 2001. "Experimental And Computational Investigation Of Ahmed Body For Ground Vehicle Aerodynamics", no. 2001-01-2742.
6. Drazin, P. G. 1993. Meteorology And Numerical Analysis. Cambridge: Cambridge University Press.
7. Gilliéron P and Chometon F. Modelling of stationary three-dimensional separated air flows around an Ahmed reference model. ESAIM: Proceedings 1999; 7: 173–182.
8. Léonard, Thomas, Laurent Y. M. Gicquel, Nicolas Gourdain, and Florent Duchaine. 2014. "Steady/Unsteady Reynolds-Averaged Navier–Stokes And Large Eddy Simulations Of A Turbine Blade At High Subsonic Outlet Mach Number". Journal Of Turbomachinery 137 (4): 041001. doi:10.1115/1.4028493.

9. Marklund, Anders. 2013. "EDITORIAL". Journal Of Scandinavian Cinema 3 (1): 3-5. doi:10.1386/jsca.3.1.3_2.
10. Menter, F. R. 1994. "Two-Equation Eddy-Viscosity Turbulence Models For Engineering Applications". AIAA Journal 32 (8): 1598-1605. doi:10.2514/3.12149. Schwarze, Rüdiger, and Frank Obermeier. 2006. "Performance and Limitations of the Unsteady RANS Approach". PAMM 6 (1): 543-544. doi:10.1002/pamm.200610252. 2018.
11. Cfd.Mace.Manchester.Ac.Uk. http://cfd.mace.manchester.ac.uk/ercoftac/database/cases/case82/Case_data/Ahmed-25-yp000-xz.dat.
12. Serre E, Minguez M, Pasquetti R, et al. 2013. “On simulating the turbulent flow around the Ahmed body: A French–German collaborative evaluation of LES and DES.” Computers & Fluids 78: 10-23.