A LABORATORY SCALE INVESTIGATION OF MANNING ROUGHNESS COEFFICIENT IN OPEN CHANNEL BED WITH DIFFERENT GRAIN SIZE AND SLOPES

Abstract

Efforts for getting the maximum efficiency from the existing water resources and to implement new projects are getting more attention these days. Determining the flow resistance for the project design and control process in open channels requires sophisticated applications. It is usually essential to be aware of the characteristics of the channel and flow to determine the hydraulic roughness, which represents the resistance of the flow. Hence, empirical calculation and evaluation of the hydraulic roughness will support future design and planning processes. In this study, four different particle sizes (d50= 28mm, 17.5mm, 4mm, and 1.75mm) that were fixed on blocks were used. These particle sizes were then used as the bed covering together with, three different horizontal bed slopes, and flow rates in the experiments to determine the associated Manning roughness, n. During the experiment, Froude number values were examined and it was determined that, in 32 experiments the flow regime can be considered as subcritical. Alternatively, the Lotter method was used to confirm the roughness values obtained by the Manning equation. It was concluded that the roughness values obtained by the selected methods have good concordance with each other.

Keywords

• Roughness coefficient
• Open channel flows
• Manning
• Grain diameter

Farklı Taban Dane Çapı ve Eğimlere Sahip Açık Kanallarda Manning Pürüzlülük Katsayısının İncelenmesi

Abstract

Mevcut bulunan su kaynaklarından maksimum verimi alabilmek ve yeni projeleri hayata geçirmek amacıyla yapılan çalışmalar gün geçtikçe artmaktadır. Açık kanallarda proje tasarım ve kontrol etme sürecinde akış direncini belirlemek oldukça karmaşık bir süreci gerektirir. Akışa karşı direnci temsil eden hidrolik pürüzlülüğü hesaplayabilmek için kanal ve akışın karakteristiklerini bilmek şarttır. Hidrolik pürüzlülüğün ampirik olarak hesaplanması ve değerlendirilmesi ilerde yapılacak tasarım ve planlama süreçlerine destek olacaktır. Bu çalışmada aynı boyutta bloklara yerleştirilen dört farklı dane çapına sahip agrega kullanılmıştır (d50= 28mm, 17.5mm, 4mm ve 1.75mm) Deneylerde n, pürüzlülük katsayısının farklı zemin numuneleri kullanılarak üç farklı eğim ve debide oluşan farklılıklar gözlenmiştir. Deney süresince Froude sayısı değerleri incelenmiş ve 32 adet deneyin nehir rejiminde devam ettiği görülmüştür. Alternatif olarak, Manning denklemi ile elde edilen pürüzlülük değerlerini doğrulamak adına Lotter yöntemi kullanılmıştır ve seçilen yöntemlerle elde edilen pürüzlülük değerlerinin birbiri ile iyi uyum gösterdiği sonucuna varılmıştır.

Keywords

• Pürüzlülük katsayısı
• Açık kanal akımları
• Manning
• Dane çapı

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