Çarpan osilasyonlu jetlerde osilasyon karakteristiklerinin ve çarpma mesafesinin akış ve ısı transferine etkilerinin sayısal olarak incelenmesi

Bu çalışmada, birbirine paralel olarak yerleştirilmiş, iki yatay sonsuz levha arasına püskürtülen bir jet ele alınmıştır. Üst levhada bulunan dikdörtgen bir lüleden osilasyonlu bir hava jeti, sıcak alt levhaya çarptırılmıştır. Jetin lüleden çıkış hızı, zamana bağlı olarak sinüs eğrisi şeklinde periyodik olarak değişmektedir. Kontrol hacmi metodu ve SIMPLE algoritması kullanılarak bir bilgisayar programı geliştirilmiştir. Levhalar arası mesafenin lüle genişliğine oranının (H/W), jet hızının salınım genliğinin ve frekansının, akış ve ısı transferine etkileri incelenmiştir. Yapılan simülasyonlar, levhalar arası mesafe arttıkça, durma noktası Nusselt sayısının azaldığını, ancak H/W oranının 2’den büyük değerlerinde Nusselt sayısındaki değişimin çok az olduğunu göstermiştir. Durma noktası Nusselt sayısının, H/W oranının küçük değerlerinde, kararlı jet Nusselt sayısına çok yakın olduğu; H/W oranının 1,5’den büyük olduğu durumlarda ise osilasyonlu jet Nusselt sayısının, kararlı jet Nusselt sayısından daha büyük olduğu görülmüştür.

Numerical analysis of effects of the oscillation characteristics and the nozzle to plate distance on the flow and heat transfer in oscillating impinging jets

In this study, a sinusoidally oscillating jet injected through a rectangular slot between two infinite horizontal plates was considered. Bottom plate was kept at constant temperature and the top plate was insulated. The oscillating air jet, issued from a rectangular slot on the top plate was impinged on the bottom hot plate. A computer program was developed by using the control volume technique and SIMPLE algorithm. Using this computer program, flow and heat transfer characteristics of the jet flow were numerically analyzed. The effects of the H/W, oscillation amplitude and oscillation frequency on the flow and heat transfer were investigated. It was observed that the stagnation point Nusselt number decreases with the increasing H/W ratio, but variation in the Nusselt number for H/W greater than 2 is very small. It is also observed that the oscillation of jet has no effect on stagnation Nusselt number when H/W is approximately less than 1.5. However, at the cases when H/W is greater than 1.5 the oscillating increases the Nusselt number with respect to the Nusselt number of a steady jet.

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