Farklı Ağ Elemanı Boyutlarının ve Türbülans Modellerinin Düz Levha Sürtünme Direnci Üzerindeki Etkisinin Sayısal Olarak İncelenmesi

Öz

Geminin hız gereksinimini karşılayacak makine gücünü belirlemek için gemi direncinin doğru bir şekilde tahmin edilmesinde kullanılan model deneyleri yönteminde model deneylerinin sonuçları ölçeklendirilerek modelden gemiye aktarılır ve gemi direnci belirlenir. Bu aktarımda uygulanan işlem adımlarında düz bir levhanın sürtünme direncinin belirlenmesi önemli bir rol oynamaktadır. Bu çalışmada iki boyutta düz bir levha üzerindeki akış 7 farklı Reynolds sayısı aralığında hesaplamalı akışkanlar dinamiği kullanılarak standart k-ε (gelişmiş duvar yaklaşımı ile) ve SST k-ω türbülans modelleri ile analiz edilmiştir. Analizler neticesinde yerel ve toplam sürtünme katsayıları ampirik bağıntılarla karşılaştırılmış, farklı ağ boyutlarının sayısal çözümler üzerinde etkisi incelenmiş ve türbülans modelleri karşılaştırılmıştır. Öncelikle akış yönünde eleman sayısı ve ilk ağ elemanın duvardan olan mesafesinin değiştirildiği ağ yapıları oluşturulmuştur. Bu ağ yapılarının seçilen türbülans modellerinde sürtünme direnç katsayıları ile olan ilişkisini belirleyebilmek için en düşük ve en yüksek hızda analizler gerçekleştirilmiştir. Analizler neticesinde akış yönündeki eleman sayısının toplam direnç katsayısı üzerinde etkisinin çok az olduğu görülmüştür. Buna karşın ilk ağ elemanın duvardan olan mesafesi özellikle düşük Reynolds sayısında gerçekleştirilen analizlerde etkilidir. En düşük ve en yüksek hızlarda gerçekleştirilen analizlerde yerel sürtünme direnç katsayısı eğrisinin ampirik bağıntılarla olan uyumlu olduğu ağ yapısında tüm hızlar için analizler gerçekleştirilmiştir. Sonuç olarak toplam sürtünme direnç katsayısı ve maksimum sınır tabaka kalınlıkları SST k-ω türbülans modeline göre standart k-ε (gelişmiş duvar yaklaşımı ile) türbülans modelinde daha büyük çıkmaktadır.

Anahtar Kelimeler

• Düz levha
• sürtünme direnci
• hesaplamalı akışkanlar dinamiği
• ağ yapısı

Numerical Investigation of the Effect of Different Grid Element Sizes and Turbulence Models on the Friction Resistance of Flat Plates

Abstract

In the model testing method, the results of the model testing are scaled and transferred from the model to the ship, and the ship resistance is determined to accurately estimate the resistance of the ship to determine the engine power that meets the speed requirement of the ship. The evaluation of the frictional resistance of a flat plate is critical to the process steps used in this transfer. In this study, the flow on a flat plate is analyzed in two dimensions using computational fluid dynamics in the 7 different Reynolds numbers with standard k-ε (with an enhanced wall treatment) and SST k-ω turbulence models. As a result of the analyzes, local and total friction coefficients are compared with empirical relationships, the effect of different grid sizes on numerical solutions is investigated and turbulence models are compared. In the first step, structures are developed where the number of elements in the flow direction and the distance of the first grid element from the wall are modified. The lowest and highest velocity analysis is performed to determine the relationship of these grid structures to the resistance coefficients in the selected turbulence models. The analysis shows that the number of elements in the flow direction has little impact on the total resistance coefficient. However, the distance from the wall of the first grid element is particularly effective in analyzing the low Reynolds number. Analyzes are performed for all velocities in the grid structure where the local frictional resistance coefficient curve is compatible with empirical correlations in the analyzes performed at the lowest and highest velocities. As a result, the total frictional drag coefficient and maximum boundary layer thicknesses are larger in the standard k-ε turbulence model (with an enhanced wall treatment) than in the SST k-ω turbulence model.

Keywords

• Flat plate
• friction resistance
• computational fluid dynamics
• grid structure

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