FARKLI GÖZENEKLİLİK VE AÇI DEĞERLERİNE SAHİP GEÇİRGEN AYIRICI PLAKA İLE DAİRESEL BİR SİLİNDİRİN AKIŞ KONTROLÜ

Öz

Titreşim ve akustik gürültü veya rezonans gibi iz akışının olumsuz etkilerini ortadan kaldırmak için batık gövdelerin akış kontrolü kapsamlı bir şekilde incelenmiştir. Isı eşanjör boruları, enerji nakil hatları, egzoz bacaları, köprüler, radyo teleskoplar, enerji hatları, açık deniz sondaj kuleleri vb. birçok mühendislik uygulamalarında kullanılan, silindir gövdenin iz akışını kontrol etmek için çeşitli art iz konumuna geçirgen bir ayırıcı plaka yerleştirilmiştir. Tüm deneyler, Çukurova Üniversitesi Akışkanlar Mekaniği Laboratuvarı'ndaki büyük ölçekli bir kapalı devre su kanalında, PIV kullanılarak, silindir çapına (D) bağlı olarak Re=5000'de gerçekleştirilmiştir. Dört farklı ayırıcı plaka açısı (θ =0°; 15°; 30°; 45°), üç farklı gözeneklilik (ε=0.30; 0.50; 0.70) incelenmiştir. Ayırıcı plakaların geçirgenliği (ε) plaka üzerindeki toplam delik alanının, plaka toplam alanına oranı olarak belirlenmiştir. Tüm değişkenler silindir çapına (D) bölünerek boyutsuzlaştırılmış ve * indisi ile gösterilmiştir. Ayırıcı plaka uzunluğu da deney sırasında ls*=1 olarak sabit tutulmuştur. Ayırıcı plaka ile silindir arasındaki mesafe, ayırıcı plakanın art iz eksenine göre açısı değişken olduğundan sabit değildir. Bunun üstesinden gelebilmek için silindir ile ayırıcı plaka dönme ekseni arasındaki mesafe ele alınmış ve ** indisi ile gösterilmiştir. Ayırıcı plaka orta noktası ile silindir (lg**) arasındaki boşluk, deneyler boyunca lg**=1.5 olarak sabit tutulmuştur. Plakalar döndürüldüğünde akışa paralel kesit azalmakta, bu da sınır tabakalar arasındaki etkileşimi artırmaktadır. Geçirgen ayırıcı plakalar, silindir etrafındaki akışta oluşan sınır tabakaların etkileşimini engellediğinden, sınır katmanların etkileşiminin arttığı ardıl bölgelerde geçirgen ayırıcı plakaların etkisi artmaktadır. Böylece dalgalanmalar azalmakta ve silindirin akış aşağısında daha kararlı bir iz akışı oluşmaktadır. Ayırıcı plaka açısının artmasıyla çevrinti oluşumunun geciktiği gözlenmiştir. Bu çalışmada ayırıcı plaka açısının etkisi ve plaka geçirgenliğinin etkisi net bir şekilde gözlemlenmiştir.

Anahtar Kelimeler

• PIV
• Akış Kontrol
• Silindir
• Ayırıcı plaka
• Geçirgen plaka

FLOW CONTROL OF A CIRCULAR CYLINDER BY PERMEABLE SPLITTER PLATE WITH DIFFERENT POROSITIES AND ANGLE VALUES

Öz

Flow control of bluff bodies has been studied extensively to eliminate adverse effects of wake flow such as vibration and acoustic noise or resonance. The circular cylinder has been studied as the bluff body since it is basic geometry and has been used in engineering applications such as heat exchanger tubes, power transmission lines, chimney stacks, bridges, radio telescopes, power lines, offshore drilling rigs etc. In this study, a permeable splitter plate was located at various downstream locations to control the wake flow of the cylinder. All experiments were carried out in a large-scale closed-loop water channel in the Fluid Mechanics Laboratory at Cukurova University. PIV was used to measure the instantaneous velocity vector field in the wake region of the cylinder at Reynolds number Re=5000, which is based on the cylinder diameter, D. Four different splitter plate angle values (θ =0°; 15°; 30°; 45°), three different porosity values (ε=0.30; 0.50; 0.70) were investigated. The porosity (ε) of the separator plates is defined as the ratio of the total hole area to the plate surface area. All lengths are nondimensionalized by dividing by the cylinder diameter and shown with the * index. The splitter plate length kept to constant during the experiment as ls*=1. The distance between the leading edge of the splitter plate and the cylinder (lg*) is variable due to the rotation of the separator plate at certain angles in the flow direction. To overcome this, the distance between the splitter plate rotation axis and the cylinder was taken as a parameter and shown with the **. The gap between splitter plate midpoint and cylinder (lg**) kept to constant during the experiments as lg**=1.5. When the plates are rotated, the cross-section parallel to the flow decreases, which increases the interaction between the boundary layers. Since the permeable separator plates prevent the interaction of the boundary layers formed in the flow around the cylinder, the effect of the permeable separator plates increases in the downstream regions where the interaction of the boundary layers increases. Thus, the fluctuations are reduced, and a more stabilized trail flow occurs downstream of the cylinder. It was observed that the vortex formation was delayed with the increase of the separator plate angle. In this study, the effect of the separator plate angle and the effect of the plate permeability were clearly observed.

Anahtar Kelimeler

• PIV
• Flow Control
• Cylinder
• Separator plate
• Permeable plate

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