CFD Simulation of the Submerged Cofferdams Effect on the Operation of the Future Tocoma Hydroelectric Power Plant

Abstract

The Tocoma hydroelectric power plant, currently under construction, is located on the lower basin of the Caroni River in Bolivar State in Venezuela. This power plant will have 10 Kaplan turbines in its powerhouse that will generate approximately 2160 MW of hydroelectric power. During its construction, two cofferdams designated “A” and “B” will be built and afterwards will remain submerged. The main purpose of this experimental-numerical study is to analyze the possible future hydrodynamic effects of these structures on the operation of the Kaplan turbines. The presence of the submerged cofferdams could originate tridimensional hydrodynamic behaviors that could produce energy looses and operational and functional problems to the turbines. Two mathematical steady state single phase models using Computational Fluid Dynamics (CFD) Techniques and applying the commercial software ANSYS-CFX were developed. The first model represented the hydroelectric power plant reservoir that was quantitatively and qualitatively calibrated with a Froude Similarity 1:80 Scale Physical Model. Hydrodynamic flow patterns near to the intakes were found in the first model. Those patterns showed a non-uniform velocity profile in the unit’s intakes nearest to cofferdam “B”. The second mathematical model represented the study of the intake, the semi-spiral case and the Kaplan turbine. This model considers the non-uniform velocity profile that was found in the first model as an inlet boundary condition. Two methodologies were used to develop this model: one using two simulations with two overlapping physical domains, and the other one using the whole geometry. It was found that using overlapping domains in order to reduce the computational cost of the total simulation is a good way to obtain physical results with fair accuracy. The general results reported that the velocity profile at the intake of the powerhouse does not produce any stationary non uniform behavior on the velocity and pressure profiles in the unit compared to the uniform velocity profile case. This result could be an indicator that the non uniform condition at the intake of the Kaplan Turbines at Tocoma will not affect the normal operation conditions of the unit.