Bir ters-basamak üzerindeki engellerin etrafındaki akışın sayısal olarak incelenmesi

Öz

Bu çalışmada, bir ters-basamak üzerine konumlandırılmış kare, daire ve eşkenar üçgen kesitli prizmatik engellerin akım alanı üzerindeki etkileri sayısal olarak incelenmiştir. Türbülanslı, üç-boyutlu, daimi ve sıkıştırılamaz olarak kabul edilen akış, modifiye k-omega türbülans modeli kullanılarak çözülmüştür. Elde edilen sonuçlar, boyutsuz sürtünme ve boyutsuz basınç katsayıları ile boyutsuz ayrılmış akış bölgesi cinsinden sunulmuşlardır. Çalışmada engellerin geometrik şekillerinin dışında, yüksekliklerinin (h) ilgili değişkenler üzerindeki etkileri basamak yüksekliği (H) ile boyutsuzlaştırılarak H/h=0,125; 0.25; 0,5 ve 1 için sunulmuştur. Üzerinde engel bulunmayan ters-basamak için elde edilen sayısal sonuçlar, Driver and Seegmiller, 1985`in deneysel verileri ile karşılaştırılarak sayısal modelin doğruluğu gösterilmiştir. Üzerinde engel olmayan ters-basamak üzerindeki akış göz önüne alındığında, sadece engellerin varlıklarının değil, aynı zamanda kesit şekillerinin de sürtünme katsayısı, basınç katsayısı ve boyutsuz ayrılmış akış bölgesi uzunluğu üzerinde etkilerinin olduğu görülmüştür. Ters-basamak üzerine konulmuş engellerin kesit geometrisi fark etmeksizin herhangi bir engelin varlığının, ayrılmış akış bölgesi uzunluğunu artırdığı, ancak en uzun bölgeye, eşkenar üçgen kesitli prizma kullanıldığında ulaşıldığı saptanmıştır. Engel yüksekliğinin ayrılmış akış bölgesi üzerindeki etkisinin H/h=0,25 ten sonra oldukça düşük olduğu belirlenmiştir.

Anahtar Kelimeler

• Ters-basamak
• ayrılma
• türbülans
• hesaplamalı akışkanlar dinamiği

Öz

In the present study, the effects of the square, circular and equilateral triangular cross-sectional obstacles placed on a backward-facing step on the flow-field were investigated numerically. Assumed to be fully turbulent, three-dimensional, steady and incompressible flow was solved by modified k-omega turbulence model. Obtained results were exhibited in terms of non-dimensional friction and non-dimensional pressure coefficients in addition to non-dimensional reattachment length. Apart from the geometric shapes of the obstacles, the influence of their heights (h) on the relevant parameters were presented for H/h=0.125, 0.25, 0.5 and 1 by dimensionalizing with the step height (H). Results obtained for the backward-facing step without any obstacles were compared with the experimental data of Driver and Seegmiller, 1985 to show the accuracy of the model. It was shown that in comparison with the step without the obstacles, not only the existence of the obstacles but their cross-sectional shapes also affect friction and pressure coefficients and the reattachment length. Regardless of the cross-sectional geometry of the obstacles, it was detected that the existence of the obstacles increases the length of the recirculation, however, the longest regions were obtained when an equilateral triangular cross-sectional one was used. It was revealed that the effect of the height of the obstacle on the detached flow region is quite low for H/h=0.25.

Anahtar Kelimeler

• Backward-facing step
• separation
• turbulence
• obstacle
• recirculation

Kaynakça

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