Marco Tulio C. Faria

Influence of Mechanical Draft Tube Fish Barrier on the Hydraulic Thrust of Small Francis Turbines

Environmental regulations have required from hydroelectric power plants more effective means of restricting the access of fish into the draft tube of hydraulic turbines. The decline of fish populations on rivers used for electricity generation has motivated the installation of mechanical gates as fish barriers on the tailrace pipe of hydroelectric power plants as a technical solution to preserve aquatic wild life. However, variations in the flow conditions through the turbine runner may modify the performance characteristics of turbines, thus affecting their capacity for electricity production. This note presents an experimental study of the influence of draft tube gates on the hydraulic forces acting on Francis turbines. A Francis turbine test bench was specially designed to allow this investigation. Measurements of the hydraulic thrust in relation to the level of flow restriction at the draft tube exit indicate that the mechanical gates excessively increase the axial load on the runner shaft, which may shorten the hydrogenerator unit life.

Analysis of the hydraulic behavior of a vertical slot fishway in two slopes

ABSTRACT Several fish transposition systems (MTP´s) have been employed to allow the fish upstream migration through river dams for spawning. The design of MTP´s of the type of vertical slot fishways requires not only the analysis of the pool hydraulic behavior to evaluate the velocity fields, the energy dissipation levels, and the Reynolds shear stress distributions, but also the study of biological characteristics of aquatic species impacted by the river dams. However, these parameters are not evaluated together, and some of them are valued at the average of the tank. This work deals with an analysis of the main hydraulic characteristics of a slot vertical fishway at two channel slopes, 6% and 12%. The hydraulic characteristic graphs obtained in this work show that a slope of 6% is preferable for the design of this kind of fishway, since the associated velocity magnitudes fits better to the ideal conditions for the safe fish passage. The slope of 12% creates restrictions in terms of the available area for fish passage due to power dissipation and shear stresses conditions.

Reduced hydraulic model of Forquilha IV tailings dam

This paper presents the development of a reduced hydraulic model (RHM) for the outflow operating system at the Forquilha IV (scale 1:10) tailings dam, owned by Vale S.A. The studies were performed by Centro de Pesquisas Hidraulicas e Recursos Hidricos (CPH) of Universidade Federal de Minas Gerais (UFMG) and the company Vogbr Recursos Hidricos & Geotecnia Ltda. We present here a brief description of the model construction and the test battery set for the structure’s hydraulic analysis. RHM involves the hillside culvert, the dissipation box and the exit to the restitution tunnel. The RHM project represents an essential step in the first analysis of the hydraulic behavior of the prototype, considering the designed flood station (ten thousand-year flood flow), as well as the analysis of its operation with more frequent flows.

Acoustic Emission Tests in the Monitoring of Cavitation Erosion in Hydraulic Turbines

This work presents an experimental study about the application of acoustic emission (AE) techniques in the monitoring of cavitation erosion mass loss in small Francis turbines. A vertical Francis turbine test bench is specially devised to perform some experiments designed to evaluate the influence of small surface mass losses on turbine blades in the acoustic emission signals. An AE wideband transducer is employed in the test bench instrumentation system. In order to evaluate the AE levels associated with the turbine erosion stages, a small defect is introduced into the turbine runner. This defect is intended to simulate a small mass loss in the turbine runner. The measurements of the AE signals are performed in the Turbine Francis model at two situations: 1) turbine without defect, which means that the runner blades are free of apparent geometric imperfections; 2) turbine with defect, which is represented by a small hole drilled into a runner blade. The AE transducer is installed on the turbine draft tube and the AE measurements are performed at several operating conditions. The preliminary results obtained for the AE amplitude in this investigation show that the small defect introduced into a runner blade causes variations in the AE levels measured in the experiments, confirming that there is a large potential for the application of AE monitoring techniques in the accurate evaluation of cavitation wear on hydraulic turbines in field.Copyright

Computational analysis of coned-face spiral groove gas seals using the finite element method

In this work, an efficient finite element procedure for high speed thin gas film lubrication problems, which is based on the Galerkin weighted residual method with high order shape functions, is employed to analyze the effects of the face coning on spiral groove face seal performance. Opening force, dynamic force coefficients and leakage flow are determined for different face seal coning angles and operating conditions. Finite element predictions bring some insights into the influence of the face coning on gas-lubricated spiral groove face seal performance characteristics at high speeds.