Effects of a Square Groove at the Stagnation Point of a Circular Cylinder on its Near Wake

Öz

In the present study, effects of single longitudinal groove placed at its forward stagnation point on the cylinder wake are investigated. Two different square groove sizes were tested using the particle image velocimetry (PIV) technique and compared with the case of bare cylinder. The cylinders are immersed in a uniform flow field with the Reynolds number, Re=5000. The wakes of these cylinders are evaluated using time-averaged flow data such as vorticity, <ω>, streamline, <Ψ>, components of streamwise, <U/Uo> and transverse, <V/Uo> dimensionless velocity, Reynolds stresses, <u’v’> and turbulent kinetic energy, TKE. In addition, the Strouhal numbers are calculated using frequencies of Karman vortex shedding, which are obtained from single point spectral analysis. It is revealed that the presence of square groove located at forward stagnation point of a circular cylinder has significant effect on the wake formation and turbulence statistics. It is observed that Karman vortex shedding frequency, fk is also influenced on presence of the groove.

Anahtar Kelimeler

• Groove,PIV,Turbulence statistics,Vortex shedding

Durma Noktasına Yerleştirilen Bir Çentiğin Silindirin Ölü Akış Bölgesine Etkileri

Öz

Bu çalışmada, bir dairesel silindirin ön durma noktasına yerleştiriliş tekil eksenel çentiğin silindirin ölü akış bölgesine etkileri araştırılmıştır. İki farklı kare kesitli çentik boyutu parçacık görüntülemeli hız ölçme tekniği ile test edilmiş ve çentik olmayan silindir durumu ile karşılaştırılmışlardır. Silindirler Reynolds sayısı, Re=5000 olan serbest akış bölgesine yerleştirilmişlerdir. Bu silindirlerin ölü akış bölgeleri vortisite, <ω>, akım çizgileri, <Ψ>, akım doğrultusundaki, <U/Uo> ve akıma dik yöndeki, <V/Uo>, boyutsuz hız bileşenleri, Reynolds gerilmeleri, <u’v’>, ve türbülans kinetik enerji, TKE gibi zaman ortalamalı akış verileri ile incelenmişlerdir. Ek olarak, tekil nokta spektral analizinden elde edilen Karman girdap kopma frekansları kullanılarak Strouhal sayıları hesaplanmıştır. Silindirin ön durma noktasına yerleştirilen kare kesitli çentik ölü akış bölgesinin oluşumuna ve türbülans istatistiklerine önemli etkileri olduğu görülmektedir. Çentiğin Karman girdap kopma frekansının, fk üzerinde de etkisi olduğu görülmiştür.

Anahtar Kelimeler

• Çentik,PIV,Türbülans istatistikleri,Girdap kopması

Kaynakça

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