Modelling for fluid flow with Linear Characteristics in Rectangular Open-Channel

Abstract

Discharge measurement in an open channel within a pre-fixed degree of accuracy with least compromise on the head of flowing liquid is a challenging task. Sharp crested and broad crested weirs have been tried and investigated to the maximum extent and have not been popularly used in the field due to its intrusive nature which reduces the fluid head. Further, discharge measuring flumes like Venturi-flume, Standing-wave-flume have been successfully used with least disturbance in flow. However, the accuracy of flow depends on the fabrication. In addition, the change in bed levels may also induce slight changes in streamline flow inducing increased resistance to flow. Even a slight error in the fabrication to the designed profiles may induce large errors. Further, use of monograms or charts or computations with equations is mandatory to obtain the instant discharge in the flume at any instant. The discharge-depth relationships in regular channels have been rarely investigated to make it more useful flow measuring devices.

The authors, for the first time, have proposed a theoretical and experimental investigations for the flow in open rectangular channel and it is found that it is possible to get a near linear depth-discharge relationship. In this paper, the flow parameters are determined through a new general optimisation procedure presented. It is found that the near linear depth-discharge relationship is valid from Y_A(b) to Y_B(b), within a deviation of ±2 percent error, where b is the half base width of the channel. The proposed linear equation is given by

The significance of proposed research is that, the shift is from measurement of discharge through computations to direct reading of the discharge with a calibrated piezometer. Further, the medium of discharge conveyance, rectangular channel itself is used as a flow measuring device. Auto recordings can also be done using sensors or float devices, avoiding human interference.