Velocity and turbulence distribution in two phase air-water flows on stepped floodway channels

Subject Areas : Farm water management with the aim of improving irrigation management indicators

Mohammad Reza Beheshti ¹ , Amir Khosrojerdi ² , Hossein Sedghi ³ , Seyed Mahmud Borghei ⁴

1 - PhD student, Department of Water Science and Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
2 - Assistant professor, Department of Water Science and Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
3 - Professor, Department of Water Science and Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
4 - Professor, Civil Engineering Department, Sharif University of Technology, Tehran, Iran

Received: 2012-08-10 Accepted : 2012-12-20 Published : 2013-03-12

Keywords: conductivity probe, inception point, stepped floodway channel, turbulence intensity,

Abstract :

Soil conservation against flood erosion is very important for optimal use of soil and water resources. Stepped floodway channels are one of the essential structural approaches for soil protection against flood flows in high slope lands at urban areas. In these channels flows are characterized by intense turbulence and strong flow aeration, but most studies did not investigate the turbulence characteristics. In this study, highly turbulent airwater flows skimming down a large-size stepped chute were systematically investigated. An experimental study of detailed air-water flow properties measurements were introduced in different types of flow regimes on a stepped channel (θ = 21.8º, h=0.04m, l=0.10m) model to investigate the location and the flow depth at inception point of air entrainment and velocity profiles distributions. Detailed velocity and turbulence intensity measurements in flow direction were performed by use of a phase detection conductivity probe which was designed, developed and calibrated by writers. The results showed that the turbulence characteristics vary in different regions. The study showed further that the turbulence intensity increases rapidly close to the step bottom at the viscous sub layer and maximized for 0.4≤ y/dc ≤ 0.5 at intermediate region then decreases gradually in the upper region. It is hypothesized that the high turbulence levels in the intermediate region were caused by the continuous deformations and modification of the air-water interfacial structure.