Showing 2 results for Boundary Layer
H. Afzalimehr, M. Heidarpour, S. H. Farshi,
Volume 7, Issue 1 (4-2003)
Abstract
In this study, two data ranges of uniform flow (bulk parameters) and non-uniform flow (local parameters) are employed to investigate resistance to flow and the factors affecting it using velocity distribution of boundary layer theory.
The results indicate that the cross-section form factor or adjustment roughness coefficient of logarithmic law can not improve the prediction of flow resistance. On the other hand, it is possible to ameliorate the prediction of resistance to flow by application of the Froude number and the Shields parameter along with the integration constant of the logarithmic velocity distribution. Also, there is no improvement in flow resistance prediction by taking into account power equations. On the other hand, the application of boundary-layer characteristics such as displacement thickness and momentum thickness in velocity profile can remove the risk of spurious correlation. Based on the measured velocity profiles for non-uniform flow in Gamasiab river, a new flow resistance equation is suggested in which the following bulk parameters are considered: flow depth, maximal velocity at the water surface, and friction slope.
H. Afzalimehr, M. Heidarpour, S. H. Farshi,
Volume 10, Issue 1 (4-2006)
Abstract
Suitable stable channel design and optimization of river geometry can reduce cost of projects. The regime theory provides the possibility of empirical and semi-empirical investigations of stable channel design in which erosion and sediment transport are in equilibrium. The objective of this research is an investigation and a comparison of the influence of uniform and non-uniform flows on the prediction of stable channel characteristics. The following empirical and semi-empirical (extremal hypothesis) equations were selected to study the effect of uniform flow: Lacey, Chital, Kondap and Garde, and Chang. Using 24 regime channels in USA, the statistical and graphical approaches were applied to compare and to evaluate the power of prediction of the selected equations. In order to investigate the effect of non-uniform flow structure on the stable channel characteristics, 21 measured velocity profiles in Gamasiab River were applied. Using the boundary-layer theory, shear velocity was computed for each profile. Accordingly, the estimated Shields parameter using the boundary-layer approach is the most effective parameter on the regime channel prediction. Simultaneous application of the non-uniform flow effect and the boundary-layer theory not only remove the risk of spurious correlation but also improve the estimation of stable channel characteristics.
