Flow measurement methodology for low head and short intake bulb turbines - Iron Gate 2 case

Abstract

Flow measurement of low head turbines, with short intakes like bulb turbines is challenging since there is no “regular” cross-section with fully developed velocity profile. In most situations the flow data during field turbine acceptance tests are obtained using the index method, with flow coefficients transferred from physical model tests done in the laboratory. In the non-standard situations, with adverse flow conditions this may lead to unpredicted flow rate uncertainty. This paper presents the used methodology and results of flow measurement at inlets of two bulb turbines of Hydro Power Plant (HPP) Iron Gate 2 (Danube river). Turbines are Kaplan, with low head (2.5 – 12.5 m), 27 MW and maximal flow rate 420 m3/s. Due to HPP’s disposition the inflow angle (in a “horizontal” plane and in respect to the turbine axis) can be up to 400. Even reverse flow directions in upper regions of cross-section can occur. The movable 14.5x3.1 m steel frame, shaped to minimize flow disturbances was used at the intake of turbine, upstream of the trash rack, to traverse the inflow cross section 14.5x26 m. The 15 spherical 3D electromagnetic velocity meters capable of bi-directional measurements were mounted on the frame, while redundant measurement were made using 2 ADVs. Two measurement strategies were used: incremental with 18 profiles and 10 min averaging time at each profile and continuous using constant lifting speed of 0.05 m/s. Uncertainty assessment procedure yielded discharge measurement uncertainties over 1 % for incremental, and up to 5 % for continuous traversing.