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

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

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.

Keywords:

Ahmed body, Drag coefficient, Shape modification, Turbulence model,

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