Longitudinal Velocity Distribution in Compound Open Channels: Comparison of Different Mathematical Models
Journal Title: International Research Journal of Applied and Basic Sciences - Year 2014, Vol 8, Issue 9
Abstract
Measuring the mean velocity profile through the channel cross section is one of basic issues in hydraulic modeling. In wide open channels, the log law and the log-wake are suitable for describing the velocity profile, but in case of narrow open channel flow, such models deviate from experimental data near the free surface. In such open channels, the three dimensional nature of flow, and transport momentum from the side walls to the central zone, causes the maximum velocity to occur below the water surface producing the velocity-dip-phenomenon. Therefore, developing new relations which is able to show this phenomenon seems to be necessary. Numerous models for determination of velocity profile in narrow open channels have been proposed by many researchers. This study provides a comparison among various existing methods for computing the longitudinal velocity distribution in narrow channels. Four models of velocity distribution were selected such as Yang’s, Bonakdari’s, Absi’s, and Kundu and Ghoshal’s model. To evaluate the accuracy of the models in calculating the velocity profiles, the results of the models were compared to the experimental data obtained from an actual measurement site in narrow sewer. Sewers are designed on the basis of open-channel-flow principles. The results show that all models represent good agreement with the experimental data, however, Absi’s model and Kundu and Ghoshal’s model are more successful in predicting the position of maximum velocity, and provide the least errors in most cases. Also it is concluded that for lower aspect ratios (which makes the condition of narrow channels be satisfied better), the results of the models tend to coincide better with the measured data.
Authors and Affiliations
Negin Binesh| MSc Student, Department of Civil Engineering, Razi University, Kermanshah, Iran, Hossein Bonakdari| Associate Professor, Department of Civil Engineering, Razi University, Kermanshah, Iran, email: bonakdari@yahoo.com
Keywords
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