tNNON SOURCES AND ERROR CORRECTION FOR FLOW MEASUREMENT IN OPEN CHANNEL BY ULTRASONIC TRANSIT TIME FLOW METER AND PROPELLER CURRENT METERS

Abstract

Discharge (flow rate) measurement in hydro-power stations is quite complex and demands very accurate methods. For years together the accuracy of flow measurement remained unsatisfying, until the high speed digital age took over the analog methods. The complexity of fluid dynamics with respect to open channel flow influences the measurement of discharge in such channels. The velocity profiles developed in various geometries of open channel are found to be very complex, such that the accurate measurement of these profiles is a tedious and challenging job. Though various correction methods have been tried over the past 20 years, yet the accuracy demands have not been met. The focus of this dissertation work is to investigate the velocity profiles in open channels of various geometries and to develop a mathematical model for these profiles. Flow for various geometries have been modeled and simulated by Computational Fluid Dynamics (CFD) analysis. The flow thus developed is being mimicked by using mathematical expressions (two major expressions- one for horizontal and other for vertical) with 10 control parameters. These parameters accounts for various factors in real situations such as side wall, bed friction, air friction and the geometry of the channel. Prior to the modeling, validation of CFD has been done by comparing the modeling results with site data (measurement done by Acoustic Doppler Current Profiler). Thus in this work an effort has been made to reveal the complex profiles of open channel flow for various conditions, the complexity of which is a major source of error for discharge measurement. An attempt has also been made to generalize these profiles using mathematical models. Subsequently, various error sources involved in the discharge measurement using propeller current meters and Ultrasonic Transit Time Flow meters (UTTF) have been identified. Later part of the work is dedicated to uncertainty analysis. The numerical integration error, which is a major source of error in discharge calculation, is analytically investigated for the simulated profiles, for both propeller current meters and UTTF. iv