No abstract

An experimental and theoretical investigation of the flow at the outlet of a Francis

No abstract

No abstract

No abstract

It is well known that the hydro power plants directly influence the habitat and the climate. Still, the hydro power represents a green renewable energy source, not polluting the environment if proper measures are applied. The main objective of the researches in this field is represented by the quality of the water discharged from turbines and especially by the low dissolved oxygen level that may have an unfavorable impact over environment and can endanger the aquatic life. During the summer months, due to the thermal stratification of the dam reservoirs and to the degasification phenomenon resulted when water passes through the turbine, the oxygen level can drop under the minimum limit of 5-6 mg/L, needed for aquatic life. The authors propose the water aeration process optimization, outlining the importance of the aeration "quality" (bubbles dimensions, retention times, pressure drop, geometry and dimensioning of the aeration systems) on the mass transfer process and not the quantity of air injected.

No abstract

The draft tube flow is a two-sided challenge for the operation of a hydraulic turbine. On one side, it is an important component for the performance of low to medium head turbines, where it can provide up to 40% of the extracted energy from the flow. On the other side, being a diffuser with a complex vorticity distribution at the inlet, vortex breakdown instability can occur at part load and generate a corkscrewed precessing vortex that can be associated with cavitation. The cavitating vortex rope, may generate undesired power output fluctuation and/or structural vibration. Therefore, draft tubes are much studied components but hard to tackle both numerically and experimentally. Within the framework of the AxialT project, the flow in the draft tube of a propeller turbine model operating at part load was studied using a combination of two-phase Particle Image Velocimetry (PIV) measurements and Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations. The paper main focus is on the experimental methodology and results. It explains how Particle Image Velocimetry measurements were implemented, validated and post-treated to provide flow measurements in the draft tube cone at part load in the cavitating and non-cavitating regimes. It also describes various image processing techniques used to extract the velocity field around the cavitating vortex rope and to estimate the location of the water-vapour interface of the cavitating region. In the spirit of feeding experimental data to numerical simulations, an analysis of measured velocity profiles just under the runner is presented. Comparison between PIV measurements and preliminary URANS simulations is also illustrated.