FLOW MEASUREMENT IN TRAPEZOIDAL OPEN CHANNELS WITH, PROFILER AND PROPELLER CURRENT METERS

Abstract

Discharge measurement in a hydropower station is the most difficult and complex problem as it demands accuracy in measurement. For years the accuracy of flow measurement remained unsatisfying, until the high speed digital age took over the analog methods. An accurate measurement of water discharge rate using flow measurement devices can be ensured only by applying flow measurement devices correctly, which in turn requires the knowledge of the flow profile in the water channel. The velocity profiles developed in various geometries of trapezoidal open channel are found to be so complex, that the accurate measurement of these profiles is a tedious and challenging job. Though various flow measurement methods have been tried over the past 20 years, yet the accuracy demand has not been met so far. In this dissertation work, a comparison of recently developed open channel flow measurement instrument Horizontal-Acoustic Doppler Current Profiler (H-ADCP) and traditional instrument Propeller Current Meter (PCM) have been done for three small hydro power stations in Punjab (India), the comparison reveals satisfactory performance of H-ADCP. Effort has been made to investigate the velocity profile for various trapezoidal geometries of open channels. Flow in nine geometrically different open channels has been simulated by using Computational Fluid Dynamic (CFD), and from simulated open channels data, average velocity has been computed and compared to evaluate the accuracy of. discharge measurement. Efforts have also been made to investigate the effect of -different values of power law exponent and cubic spline interpolation schemes on accuracy of discharge computation. Accuracy of average width discharge computational method has been compared for three simulated trapezoidal open channels. Prior to trapezoidal open channel simulation work, validation of CFD has been done by comparing the simulated results with field-measured data obtained with H-ADCP and PCM. Two rectangular open channels have been simulated by CFD analysis and discussed effect of aspect ratio on velocity profile of rectangular open channel. Simulated velocity profile has been compared for logarithmic law, power law, and parabolic law. iv