Tek Fanlı Karayolu Tünellerinde Kavis Geometrisinin Taşıt Egzozundan Yayılan Karbondioksit Dağılımları Üzerindeki Etkisinin İncelenmesi

Öz

Bu çalışmada, karayolları tünellerinde taşıtların egzozlarından yayılan kirletici gazlardan karbondioksitin tünel içerisindeki dağılımları deneysel ve sayısal olarak incelenmiştir. İlk önce Trabzon ili Ortahisar ilçesinde bulunan Akyazı Tüneli’nde karbondioksit ölçümleri gerçekleştirilmiştir. Daha sonra ise, karayolları tünellerinde biriken karbondioksitin fan etkisiyle dağılımları sayısal olarak incelenmiştir. Tünel içerisinde taşıtların olmadığı ve tünel girişinden 100 m ileride tünel tavanına yakın bir konuma yerleştirilmiş tek fan durumu için, 500 m uzunluğundaki iki şeritli düz bir tünel ve R=950 m ve R=1900 m yarıçap değerlerine sahip iki çemberin 500 m uzunluğundaki yay parçalarıyla oluşan iki farklı kavise sahip iki şeritli iki tünel içerisindeki üç boyutlu akış alanları zaman bağımlı olarak Standart k-ε türbülans modeli ile çözülmüştür. Tünel içerisindeki karbondioksit düzeylerinin çalışan fan etkisiyle zamana göre değişimlerinin incelendiği çalışmada, başlangıçtaki karbondioksit seviyesi 25000 ppm olarak dikkate alınmıştır. Zaman adımı 1 dakika seçilerek 60 dakikalık çözümler gerçekleştirilmiştir. Ağdan bağımsız çözümler, düz tünelde 8,5 milyon ve kavisli tünellerde 16 milyon ağ yoğunluğu değerlerinde sağlanmıştır. Fan itme kuvvetinin 950 N olduğu çalışmada, fan çalışma süresinin sonunda tünel içerisindeki hız ve karbondioksit değerleri grafiklere yansıtılmıştır. Kavis etkisi nedeniyle, karbondioksit değerleri tünel kesitinin dış bükey tarafındaki sol bölgesinde düşük, iç bükey tarafındaki sağ bölgesinde büyük olmaktadır. Tünel hacmi içerisinde karbondioksit seviyelerindeki azalmada kavis yarıçapındaki değişim etkili olmamakta, hem düz tünelde hem de kavisli tünellerde 60 dakika sonunda karbondioksit seviyeleri yaklaşık 5000 ppm düzeyine düşmektedir. Sayısal çalışmada kullanılan Standart k-ε modeli ile elde edilen sonuçlar deneysel verilerle iyi bir uyum göstermektedir.

Anahtar Kelimeler

• Fan itme kuvveti
• Karbondioksit dağılımı
• Düz tünel
• Kavisli tünel
• Standart k-ε türbülans modeli

Investigation of the Effect of Curve Geometry on Carbon Dioxide Distributions Emitted from Vehicle Exhausts in Single-Fan Road Tunnels

Öz

In this study, the distributions of carbon dioxide, one of the pollutant gases emitted from vehicle exhausts in road tunnels, were investigated experimentally and numerically. Initially, carbon dioxide measurements were conducted in the Akyazı Tunnel located in the Ortahisar district of Trabzon province. Subsequently, the fan-induced distributions of carbon dioxide accumulated in road tunnels were numerically investigated. For the case of a single fan positioned near the tunnel ceiling 100 m ahead of the tunnel entrance, with no vehicles present in the tunnel, the three-dimensional flow fields within two-lane tunnels, one consisting of a 500 m long straight tunnel and two different curves formed by 500 m long arc segments of two circles with radii R=950 m and R=1900 m, were solved time-dependently using the Standard k-ε turbulence model. In the study, which examined the time-dependent changes in carbon dioxide levels inside the tunnel under the effect of the operating fan, the initial carbon dioxide level was considered to be 25000 ppm. Solutions were performed for 60 minutes with a time step of              1 minute. Grid independence was achieved at mesh densities of 8.5 million for the straight tunnel and 16 million for the curved tunnels. In the study, where the fan thrust force was 950 N, the velocity and carbon dioxide values inside the tunnel at the end of the fan operating time were reflected in the graphs. Due to the curvature effect, carbon dioxide values are low in the left region on the convex side of the tunnel cross-section and high in the right region on the concave side. Changes in the radius of curvature do not affect the decrease in carbon dioxide levels within the tunnel volume; in both straight and curved tunnels, carbon dioxide levels drop to approximately         5000 ppm after 60 minutes. The results obtained using the Standard k-ε model in numerical study showed good agreement with the experimental data.

Anahtar Kelimeler

• Fan thrust force
• Carbon dioxide distribution
• Straight tunnel
• Curved tunnel
• Standard k-ε turbulence model

Kaynakça

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