Energy distribution at the draft tube outlet

A thermodynamic measurement of hydraulic efficiency, with special attention to the energy distribution at the outlet cross section of the draft tube, is presented. The measurement was carried out at Bratsberg Power plant in Norway on a Francis turbine with a head of 130 meters. Six temperature probes and six velocity probes were used to measure the energy distribution.. The efficiency was calculated in two different ways, first by using the average, and secondly by using area-weighted velocities and temperatures. These calculations gave two efficiency curves with a difference less than the uncertainty, but more than the repeatability of the measurements. Finally, the hydraulic efficiency was calculated for each measured point, and this gave a good picture of the energy distribution. In addition, a comparison with another measurement, which used the collector method at the outlet of the draft tube, is presented.