TEK ÜÇGEN SİLİNDİRDEN TÜMLEŞİK ZORLANMIŞ VE DOĞAL TAŞINIM

Öz

Eşkenar üçgen silindir etrafında kararsız laminer sınırlı/sınırsız akışkan akışı ve tümleşik (doğal ve zorlanmış) taşınımla ısı transferi sayısal olarak incelenmiştir. Sayısal model, BR=0.5, 0.25, 0.2, 0.1, 0.05 ve 0.0333 blokaj oranlarına ve Reynolds sayılarının 100 ile 200 arasında değiştiği iki boyutlu bir alandır. Çalışma akışkanı sudur (Pr=7). Termal kaldırma kuvvetininin destek olma ve buna karşı çıkma etkileri, Boussinesq yaklaşımı kullanılarak Navier-Stokes denklemlerine dahil edilmiştir. Doğal taşınımın göreceli bir ölçüsü olan Richardson sayısı 2≥Ri≥-2 aralığında değişmiştir. Yönetici denklemler, taşınım terimlerinin ayrıklaştırılması için second order upwind şeması ile Sonlu Hacim Yöntemi kullanılarak çözülmüş ve hız-basınç bağlantısı için SIMPLE algoritması kullanılmıştır. Blokaj oranının ortalama sürükleme katsayısı, ortalama rms kaldırma katsayısı, Strouhal sayısı ve ortalama Nusselt sayısı üzerindeki etkisine ilişkin elde edilen sonuçlar çalışmada sunulmuştur. Eş girdap ve boyutsuz eş sıcaklık eğrileri altta yatan fiziksel mekanizmaları yorumlamak ve anlamak için oluşturulmuştur. Sonuçlar Richardson ve Reynolds sayılarına ek olarak blokaj oranının kanalda girdap dağılımında etkili olduğunu ortaya koymaktadır. Azalan blokaj oranı ile silindir arkasında oluşan girdapların kanala yayıldığı tespit edilmiştir. Özellikle yüksek Reynolds sayılarında hem sürükleme katsayısı hem de ortalama Nusselt sayısı blokaj oranından önemli ölçüde etkilendiği görülmüştür. Ri=0’da BR=0.25 için sürükleme katsayısı BR=0.05 durumuyla karşılaştırıldığında Re=100 ve 200’de sırasıyla yaklaşık %9 ve %29 daha yüksek çıkmıştır. BR<0.1 için Ri=0 ve -2’ye kıyasla termal kuvveti destekleyici durumda (Ri=2) kanal arkası çift girdap oluşumu yerini tekli girdaplara bırakmıştır. Ayrıca akış özellikleri ve ısı transferi için faydalı korelasyonlar, elde edilen veriler kullanılarak türetilmiştir.

Anahtar Kelimeler

• Isı transferi
• Sınırlı akış
• Tümleşik taşınım
• Eşkenar üçgen silindir
• Korelasyonlar

COMBINED FORCED AND NATURAL CONVECTION FROM A SINGLE TRIANGULAR CYLINDER

Öz

Unsteady laminar confined and unconfined fluid flow and mixed (forced and free) convection heat transfer around equilateral triangular cylinders are investigated numerically. The computation model is a two-dimensional domain with blockage ratios of BR=0.5, 0.25, 0.2, 0.1, 0.05, and 0.0333, with the Reynolds numbers ranging from 100 to 200. The working fluid is water (Pr = 7). The effects of aiding and opposing thermal buoyancy are incorporated into the Navier-Stokes equations using the Boussinesq approximation. The Richardson number, which is a relative measure of free convection, is varied in the range -2 ≤ Ri ≤ 2. The governing equations are solved by using the Finite Volume Method with a second-order upwind scheme used for differencing of the convection terms, and the SIMPLE algorithm is used for the velocity-pressure coupling. A discussion of the effect of the blockage ratio on the mean drag, mean rms lift coefficients, the Strouhal number, and the mean Nusselt number is also presented. The iso-vorticity contours and dimensionless temperature field are generated to interpret and understand the underlying physical mechanisms. The results reveal that, in addition to the Richardson and Reynolds numbers, the blockage rate is effective in the vortex distribution in the channel. It has been determined that the vortices formed behind the cylinder spread to the channel with a decreasing blockage rate. Especially at high Reynolds numbers, both the drag coefficient and the mean Nusselt number are significantly affected by the blockage ratio. For Ri=0, the drag coefficients for BR=0.25 in comparison to the BR=0.05 case are about 9% and 29% larger for Re= 100 and 200, respectively. For BR<0.1, two-column vortex formation at the back of the cylinder gave way to single vortexes in the aiding thermal buoyancy condition (Ri=2) compared to Ri=0 and -2. Also, useful correlations for flow characteristics and heat transfer are derived using the computed data.

Anahtar Kelimeler

• Heat transfer
• Confined flow
• Mixed convection
• Equilateral triangle cylinder
• Correlations

Kaynakça

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