Computational Examination of Unsteady Cavitating Flow Characteristics on a 2D NACA66 Profile by Utilizing OpenFOAM®

Öz

The complexity of the flow mechanism is one of the crucial problems in cavitation. In this present study, detailed computational examinations of cavitating flow around a NACA66 hydrofoil were performed by using OpenFOAM® software. Dynamic and unsteady behaviours of cavitating flow were solved utilizing the k-ω SST turbulence model. Schnerr-Sauer cavitation model was used for the calculations. Numerical simulations were performed for 6° and 8° angle of attack with different cavitation numbers and the outlet pressure conditions, the cases are called “Case 1” and “Case 2” respectively. The results were compared with the studies performed by Leroux et. al. Oscillation cycles and flow characteristics were obtained successfully in both cases. The mechanism called the re-entrant jet was shown to be primarily responsible for cavitation break-off in two cases. This mechanism consists of two steps: 1) an interplay between the re-entrant flow and the cavity contact surface in the occlusion region, resulting in recurrent secondary cloud shedding until the primary cloud detachment, and 2) a shock wave triggered by the primary cloud collapsing, which affects the development of the remnant cavity. The main contribution of this study is to examine the impact of using the k-ω SST turbulence model with the Schnerr-Sauer cavitation model on predicting flow characteristics such as cavitation dynamics, pressure distribution and cavity form. Acceptable accuracy has been observed for pressure fluctuations and cavitation dynamics.

Anahtar Kelimeler

• cavitation
• cavitation break-off
• k-ω SST model
• NACA66 hydrofoil
• OpenFOAM®

Kararsız Kavitasyonlu Akış Karakteristiklerinin 2 Boyutlu Bir NACA66 Profili Üzerinde OpenFOAM® Kullanılarak Sayısal Olarak İncelenmesi

Öz

Akış mekanizmasının karmaşıklığı, kavitasyondaki en önemli problemlerden biridir. Bu çalışmada, OpenFOAM® yazılımı kullanılarak bir NACA66 hidrofili etrafındaki kavitasyonlu akışın ayrıntılı sayısal incelemeleri yapılmıştır. Kavitasyonlu akışın dinamik ve kararsız davranışları, k-ω SST türbülans modeli kullanılarak çözülmüştür. Hesaplamalar için Schnerr-Sauer kavitasyon modeli kullanılmıştır. Sırasıyla “Durum 1” ve “Durum 2” olarak adlandırılan çıkış basıncı koşullarına paralel olarak farklı kavitasyon sayılarına sahip iki farklı 6° ve 8° hücum açısı için sayısal simülasyonlar yapılmıştır. Sonuçlar, Leroux çalışmasının deneysel ve sayısal sonuçlarıyla karşılaştırılmıştır. Leroux deneylerine kıyasla her iki durumda da salınım döngüleri ve akış özellikleri başarılı bir şekilde elde edildi. Yeniden giren jet olarak adlandırılan mekanizmanın, iki durumda da kavitasyon kopmasından birincil olarak sorumlu olduğu gösterildi. Bu mekanizma iki adımdan oluşur: 1) ana bulut ayrılmasına kadar tekrarlı ikincil bulut dökülmesiyle sonuçlanan, yeniden giriş akışı ile kavitasyon arayüzü arasındaki, kapanma bölgesindeki bir etkileşim ve 2) ana bulutun çökmesi tarafından tetiklenen kalan kavitasyonun gelişimini etkileyen bir şok dalgası şeklindedir. Bu çalışmanın ana katkısı, Schnerr-Sauer kavitasyon modeli ile k-ω SST türbülans modelinin kullanılmasının kavitasyon dinamikleri, basınç dağılımı ve kavitasyon formu gibi akış özelliklerinin tahmin edilmesi üzerindeki etkisini incelemektir. Basınç dalgalanmaları ve kavitasyon dinamikleri için kabul edilebilir doğruluk gözlemlenmiştir.

Anahtar Kelimeler

• kavitasyon
• kavitasyon kopması
• k-ω SST model
• NACA66 hidrofil
• OpenFOAM®

Kaynakça

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