Turbine Discharge Measurement by the Velocity-Area Method

Developing the head-power-discharge relationship for a low-head hydroelectric turbine requires accurate measurements of discharge through the unit. Discharge measurements are commonly determined using some type of velocity-area method. The German (DIN) code is used by many utilities. In this paper a densely spaced array of Ott meter data, collected according to the German code, are used to examine the accuracy of this approach. Field data, obtained near the intake entrance (i.e., stoplog guides) of a low-head hydroelectric generating station, show clearly the complex (i.e., nonfully developed) nature of the horizontal flow. Laboratory testing of a scale model suggest that metering the flow close to the entrance of an intake, according to the German code, where the flow is not yet fully developed, will overestimate the discharge by approximately 3%.