Gemi Pervanelerinde Kavitasyon Kaynaklı Gürültü ve Farklı İz Alanlarının Pervane Performansına Etkisinin İncelenmesi

Gemi pervanelerinde, pervaneye gelen akım alanının ünifom olmaması (iz dağılımının düzensiz olması) ve pervane kanatlarında oluşması muhtemel olan kavitasyon olgusunun meydana istenmeyen etkiler (performans kaybı, erozyon, titreşim, gürültü ) meydana getirebilmektedir. Özellikle, pervane kanatları üzerinde oluşan tabaka kavitasyonu büyüklüğünün periyodik olarak değişmesi, daimi olmayan pervane kuvvetlerine ve titreşime, su altında ve gemi bünyesinde ise gürültü oluşumuna sebebiyet vermektedir. Bu çalışmada, geometrisi belli olan ve verilen çalışma koşulları altında kavitasyon gösteren bir gemi pervanesinin tabaka kavitasyonu kaynaklı gürültü tahmini öngörülmüştür. Ayrıca beş farklı gemi arkası iz dağılımının, ele alınan pervanenin performansına, pervane kanadının bir tam devrindeki itme değerlerine ve pervane tarafından gemi üzerindeki bir noktada oluşturulan basınç değişimlerine olan etkisi karakteristiklerinden biri olan çalıklık değeri değiştirilerek (iki farklı çalıklık açısı), bu özelliğin kavitasyon kaynaklı gürültü üzerine olan etkisi parametrik olarak analiz edilmiştir. Aynı zamanda sadece orjinal olan pervane, performans açısından incelenmiştir. Yapılan hesaplamalarda, kaldırıcı yüzey teorisine (lifting surface method) dayalı olan ve gürültü öngörüsü için geliştirilmiş Brown yöntemini kullanan sayısal bir yöntemden yararlanılmıştır. Elde edilen gürültü seviyeleri literatürde yer alan diğer gürültü öngörü yaklaşımları ile karşılaştırılmıştır. İz dağılımının düzensiz olduğu durumlarda çalıklığın etkin bir özellik olarak öne çıktığı görülmüş ve bu çalışma koşullarındaki pervanenin çalıklığı arttırılarak, titreşim ve gürültünün önemli seviyelerde azaltılabileceği sonucuna varılmıştır.

Investigation of Cavitation Induced Noise and Effects on Performance of Different Wake Fields in Marine Propellers

The fact that the inflow to the marine propeller is not uniform and cavitation phenomenon which is likely to develop on propeller blades may lead to undesirable effects (performance loss, erosion, vibration, and noise) with respect to hydrodynamic performance. Particularly, periodically changing of the sheet cavitation size on the propeller blades leads to unsteady propeller force, vibration, underwater radiated noise as well as noise in the ship. In this study, prediction of sheet cavitation induced noise of a marine propeller whose geometry and wake distribution are known, were examined. Cavitation was present in all given operating conditions. Further investigations were carried out for the target propeller to observe the effect of five different wake distributions on propeller performance, thrust values on the propeller blade for one rotation, and changing of propeller induced pressure pulse at a point on the hull. By changing skew value (two different skew angle), which is one of the geometric characteristics of original propeller, the effect on the cavitation induced noise was analyzed parametrically. The current study includes a discussion for only the original propeller in terms of performance (thrust, torque and efficiency). A numerical approach, based on Brown's method and lifting surface method, was used to predict noise calculations. Noise levels obtained from calculations were compared to the other noise predictions in literature. It can be seen that skew has an effect in cases where the inflow is non-uniform. It can be concluded that vibration and noise levels can be reduced significantly by increasing the skew value of the propeller in these operating conditions.

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