Ahmed modelinin sürükleme katsayısını azaltmak için şekil modifikasyonu ve türbülans modelinin belirlenmesi

Yıl 2021, , 824 - 832, 27.07.2021

Ahmet Şumnu

https://doi.org/10.28948/ngumuh.879584

Cited By: 3

Öz

Bu çalışmada, uygun türbülans modelini belirlemek ve şekil modifikasyonu yaparak sürükleme katsayısını azaltmak için jenerik otomobil modeli olan Ahmed modelinin aerodinamik analizi yapılmıştır. Bu amaçla, Hesaplamalı Akışkanlar Dinamiği (HAD) analizi, Spalart-Allmaras, (Shear Stress Transport) SST k-omega, Standard k-epsilon, Realizable k-epsilon, (Re-Normalization Group) RNG k-epsilon türbülans modelleri olmak üzere beş farklı türbülans modelleri kullanılarak gerçekleştirildi. Sonuçlar literatürde bulunan deneysel verilerle karşılaştırıldı. RNG k-epsilon türbülans modelinin diğer modellere göre daha üstün performans gösterdiği gözlemlendi. Sürükleme katsayısını düşürmek için birinci modifikasyonda modelin üst yan bölgeleri 25 mm sabit yarıçap uygulanarak yuvarlatılmıştır. Pürüzsüz yüzey, aerodinamik açıdan yüksek performans sağlayabilir. HAD çözümü değiştirilen model için tekrarlandı ve sonuç, sürükleme katsayısı değerinin yaklaşık % 6 oranında azaldığını göstermektedir. Ayrıca gövdenin her iki üst ve arka alt tarafı sabit yarıçap ile yuvarlatılmış ve gövdenin arka taraflarına da 50 mm pah uygulanarak ikinci modifikasyon yapılmıştır. Ancak, sürükleme katsayısı azalma seviyesi, ilk değiştirilen modelle yaklaşık olarak aynıdır. Basınç katsayısı konturları ve hız akış çizgileri, sonuçları göstermek üzere sunulmuştur.

Anahtar Kelimeler

Ahmed modeli, Sürükleme katsayısı, Şekil modifikasyonu, Türbülans model

Shape modification of Ahmed body to reduce drag coefficient and determination of turbulence model

Öz

In this study, the aerodynamic analysis of Ahmed body which is generic automobile model is performed to determine convenient turbulence model and reduce drag coefficient by modifying shape of model. For this purpose, Computational Fluid Dynamics (CFD) analysis is carried out using different turbulence models that are Spalart-Allmaras, (Shear Stress Transport) SST k-ω, Standard k-ε, Realizable k-ε, (Re-Normalisation Group) RNG k-ε turbulence models. The results are compared with experimental data that is available in literature. The results show that RNG k-ε turbulence model gives superior performance when compared with other models. In order to reduce drag coefficient, the upper region of sides of model is rounded by applying fixed blend radius with 25 mm. The smooth surface can provide high performance in point of aerodynamics. CFD solution is then repeated for the modified model and the result show that drag coefficient value reduces about 6%. In addition, the second modification is performed by applying fixed blend radius with rounded both upper sides and rear underside of body and chamfer with 50 mm is also applied to rear sides of body. However, drag coefficient reduction level is approximately same with first modified model. The pressure coefficient contours and velocity streamlines are presented to show results for baseline and modified bodies.

Anahtar Kelimeler

Ahmed body, Drag coefficient, Shape modification, Turbulence model

Kaynakça

• S. R. Ahmed, G. Ramm, and G. Faltin, Some salient features of the time-averaged ground vehicle wake. SAE Transactions, 473-50, 1984. https://doi.org/ 10.4271/840300
• S. R. Ahmed, Wake structure of typical automobile shapes. Transaction of the ASME, 162-169, 1981. https://doi.org/10.1115/1.3240767
• S. R. Ahmed, Influence of base slant on the wake structure and drag of road vehicles. Journal of Fluid Engineering, 429-434, 1983. https://doi.org/10.1115/ 1.3241024
• R. S. Khan, and S. Umale, CFD aerodynamic analysis of Ahmed body. International Journal of Engineering Trends and Technology, 18(7), 301-308, 2014. doi:10.14445/22315381/IJETT-V18P262
• C. A. Gilkeson, V. V. Toropov, H. M. Thompson, M. C. T. Wilson, N. A. Foxley, and P. H. Gaskell, Dealing with numerical noise in CFD-based design optimization. Computers and Fluids, 94, 84-97, 2014. https://doi.org/10.1016/j.compfluid.2014.02.004
• W. Meile, G. Brenn, A. Reppenhagen, B. Lechner, and A. Fuchs, Experiments and numerical simulations on the aerodynamics of the Ahmed body. CFD letters, 3(1), 32-39, 2011.
• J. Östh, B. R. Noack, S. Krajnović, D. Barros, and J. Borée, On the need for a nonlinear subscale turbulence term in POD models as exemplified for a high-Reynolds-number flow over an Ahmed body. Journal of Fluid Mechanics, 747, 518-544, 2014. https://doi. org/10.1017/jfm.2014.168
• R. Volpe, P. Devinant, and A. Kourta, Experimental characterization of the unsteady natural wake of the full-scale square back Ahmed body: Flow bi-stability and spectral analysis. Experiments in Fluids, 56(5), 99, 2015. https://doi.org/10.1007/s00348-015-1972-0
• V. K. Yakkundi, and S. S. Mantha, CFD Analysis of flow over car variants and validation with Ahmed body. CURIE Journal, 3(1), 2010.
• S. Thabet, and T. H. Thabit, CFD simulation of the air flow around a car model (Ahmed body). International Journal of Scientific and Research Publications, 8(7), 517-525, 2018. http://dx.doi.org/10.29322/IJSRP. 8.7.2018.p7979
• T. Tunay, E. Firat, and B. Sahin, Experimental investigation of the flow around a simplified ground vehicle under effects of the steady crosswind. International Journal of Heat and Fluid Flow, 71, 137-152, 2018. https://doi.org/10.1016/j.ijheatfluidflow. 2018.03.020
• T. Tunay, L. Drugge, and C. J. O’Reilly, On coupling methods used to simulate the dynamic characteristics of heavy ground vehicles subjected to crosswind. Journal of Wind Engineering and Industrial Aerodynamics, 201, 104194, 2020. https://doi.org/10.1016/j.jweia. 2020.104194
• T. Tunay, B. Sahin, and V. Ozbolat, Effects of rear slant angles on the flow characteristics of Ahmed body. Experimental Thermal and Fluid Science, 57, 165-176, 2014. https://doi.org/10.1016/j.expthermflusci.2014. 04.016
• B. Zafer, and F. Haskaraman, Önden ve yanal rüzgar şartı altında Ahmed cisminin sayısal incelenmesi. Journal of the Faculty of Engineering and Architecture of Gazi University, 32(1), 2017. https://doi.org/ 10.17341/gazimmfd.300613
• F. J. Bello-Millan, T. Mäkelä, L. Parras, C. Del Pino, and C. Ferrera, Experimental study on Ahmed's body drag coefficient for different yaw angles. Journal of Wind Engineering and Industrial Aerodynamics, 157, 140-144, 2016. https://doi.org/10.1016/j.jweia.2016. 08.005
• C. Chovet, M. Feingesicht, B. Plumjeau, M. Lippert, L. Keirsbulck, F. Kerhervé, and J. M. Foucaut, Sliding mode control applied to a square-back Ahmed body. European Journal of Mechanics-B/Fluids, 81, 151-164, 2020. https://doi.org/10.1016/j.euromechflu.2019. 07.010
• H. Park, J. H. Cho, J. Lee, D. H. Lee, and K. H. Kim, Aerodynamic drag reduction of Ahmed model using synthetic jet array. SAE International Journal of Passenger Cars-Mechanical Systems, 6(2013-01-0095), 1-6, 2013. https://doi.org/10.4271/2013-01-0095
• S. Banga, M. Zunaid, N. A. Ansari, S. Sharma, and R. S. Dungriyal, CFD simulation of flow around external vehicle: Ahmed body. IOSR Journal of Mechanical and Civil Engineering, 12(4), 87-94, 2015. http://dx.doi.org/10.9790/1684-12438794
• P. R. Spalart, and S. R. Allmaras, A one-equation turbulence model for aerodynamic flows, AIAA, 92-0439, 1992. https://doi.org/10.2514/6.1992-439
• F. R. Menter, Two-equation eddy-viscosity turbulence models for engineering applications, AIAA journal, 32, 1598-1605, 1994. https://doi.org/10.2514/3.12149
• B. E. Launder, and B. I. Sharma, Application of the energy-dissipation model of turbulence to the calculation of flow near a spinning disc. Letters in heat and mass transfer, 1(2), 131-137, 1974. https://doi.org/ 10.1016/0094-4548(74)90150-7
• B. E. Launder, and D. B. Spalding, The numerical computation of turbulent flows. Numerical prediction of flow, heat transfer, turbulence and combustion 96-116, 1983. https://doi.org/10.1016/B978-0-08-030937-8.50016-7
• Fluent, A.N.S.Y.S. ANSYS Fluent 12.0 Theory Guide. ANSYS Inc., Canonsburg, PA. 2009.
• D. C. Wilcox, Turbulence modeling for CFD. Vol. 2, 103-217, 1998. La Canada, CA: DCW industries.
• V. Yakhot, S. A. Orszag, S. Thangam, T. B. Gatski, and C. G. Speziale, Development of turbulence models for shear flows by a double expansion technique. Physics of Fluids A: Fluid Dynamics, 4(7), 1510-1520, 1992. https://doi.org/10.1063/1.858424
• C. Hinterberger, M. Garcia-Villalba, and W. Rodi, Large eddy simulation of flow around the Ahmed body. The aerodynamics of heavy vehicles: trucks, buses, and trains, 77-87, 2004. Springer, Berlin, Heidelberg.