Author(s): Mauricio Romero, Jose Junji Ota, Tobias Bleninger, Paulo Henrique Cabral Dettmer, Marcelo Luiz Noriller, Guilherme Moreira Grossi
Keywords: Ejection effect; Low-head hydropower plant; Lateral conduits; Submerged condition; Gain of head;
Abstract: The aim of the present research is to assess the ejection effect in a low-head hydropower plant with lateral conduits. The study includes six geometrical variants, under submerged downstream condition using 1:70 scale model tests. The model test results are compared to theoretical equations from the scientific literature, and new equations are proposed to assess ejection effects. All variants consist of three vertical Kaplan turbines, four lateral bottom conduits, a ramp and two lateral piers towards the main channel. Steady water discharges through the turbines and lateral conduits, as well as flow elevations upstream and downstream the plant, were calibrated by means of 82 model tests under submerged downstream condition. Pressure heights at the bottom of the turbine draft tube outlets were measured using 10 piezometers to assess the total ejection and the gain of head due to the turbines. Theoretical models of Slisskii (1953) and Krei (1920) produced effective ejection results for the initial geometrical configuration of the plant. Equations of Bernoulli and Conservation of Momentum were applied when the geometrical variants of the plant became too complex. The calibrated equations produced remarkably consistent results for the effective ejection assessment from 360 hypothetical flow scenarios. Results showed that the effective ejection is more sensitive to geometrical variations of the plant for a shallower submerged condition of the structure. Such differences in between scenarios are somehow reduced for deeper submergences.