Experimental Study of Standard Aeration Efficiency in a Bubble Column

Water aeration is a major feature in many industrial applications, for example, hydraulic turbines, fish farms, water treatment, and so on. A key consideration is the efficiency of the aeration itself, that is, the effectiveness of the transfer of oxygen from air to water in relation to the energy consumed by injection. In this chapter, several configurations of the aerator are analyzed for overall efficiency optimization. Two different parameters are investigated (the arrangement of aeration apertures and aperture diameters between 0.2 and 1.6 mm) using aerators with perforated metal plates and, for comparison, ceramic and fritted (sintered) glass plates. For the arrangement of the apertures on the perforated metal plates, bubble coalescence and contraction coefficients are measured. Each configuration’s results (Kla, SOTR, SAE) are compared and analyzed

Analysis of the Cavitating Draft Tube Vortex in a Francis Turbine Using Particle Image Velocimetry Measurements in Two-Phase Flow

Partial flow rate operation of hydroturbines with constant pitch blades causes complex unstable cavitating flow in the diffuser cone. A particle image velocimetry (PIV) system allows investigating the flow velocity field in the case of a developing cavitation vortex, the so-called vortex rope, at the outlet of a Francis turbine runner. The synchronization of the PIV flow survey with the rope precession allows applying the ensemble averaging by phase technique to extract both the periodic velocity components and the rope shape. The influence of the turbine setting evel on the volume of the cavity rope and its centerline is investigated, providing a physical knowledge about the hydrodynamic complex phenomena involved in the development of the cavitation rope in Francis turbine operating regimes

Experimental setup to study two phase flows for environmental applications

The air water mix is a major concern for the environmental application. This paper proposes an experimental method to accede simultaneously at the water flow velocity field and at the void fraction. Instantaneous and mean fields, as well as the evolution with the flow parameters variation are obtained in cavitation or aerated flows. This method allows a good accuracy for the flow velocity fields (2%) and void (vapours or air) contours (4%)

Analysis of the Swirling Flow Downstream a Francis Turbine Runner

An experimental and theoretical investigation of the flow at the outlet of a Francis turbine runner is carried out in order to elucidate the causes of a sudden drop in the draft tube pressure recovery coefficient at a discharge near the best efficiency operating point. Laser Doppler anemometry velocity measurements were performed for both axial and circumferential velocity components at the runner outlet. A suitable analytical representation of the swirling flow has been developed taking the discharge coefficient as independent variable. It is found that the investigated mean swirling flow can be accurately represented as a superposition of three distinct vortices. An eigenvalue analysis of the linearized equation for steady, axisymmetric, and inviscid swirling flow reveals that the swirl reaches a critical state precisely (within 1.3%) at the discharge where the sudden variation in draft tube pressure recovery is observed. This is very useful for turbine design and optimization, where a suitable runner geometry should avoid such critical swirl configuration within the normal operating range

Experimental Study and Numerical Simulation of the Flindt Draft Tube Rotating Vortex

The dynamics of the rotating vortex taking place in the discharge ring of a Francis turbine for partial flow rate operating conditions and cavitation free conditions is studied by carrying out both experimental flow survey and numerical simulations. 2D laser Doppler velocimetry, 3D particle image velocimetry, and unsteady wall pressure measurements are performs to investigate thoroughly the velocity and pressure fields in the discharge ring and to give access to the vortex dynamics. Unsteady RANS simulation are performed and compared to the experimental results. The computing flow domain includes the rotating runner and the elbow draft tube. The mesh size of 500,000 nodes for the 17 flow passages of the runner and 420,000 nodes for the draft tube is optimized to achieve reasonable CPU time for a good representation of the studied phenomena. The comparisons between the detailed experimental flow field and the CFD solution yield to a very good validation of the modeling of the draft tube rotating vortex and, then, validate the presented approach for industrial purpose applications

Numerical Simulation and Analysis of Swirling Flow in the Draft Tube Cone of a Francis Turbine

The paper presents numerical investigations of decelerated swirling flows specific to hydraulic turbines draft tube cone, within the framework of axisymmetric flow models. First, we investigate the behaviour of a Burgers vortex in a diffuser as the swirl intensity is increased. We show that first a steady vortex breakdown occurs, with a central stagnation region, then the flow becomes highly unsteady with vortex rings convected downstream. Our main result proves that the vortex breakdown and the unsteadiness can be removed by slighlty altering the inlet axial velocity profile. A rather weak water jet injected at the axis in the inlet section, recovers a steady breakdown-free flow configuration. Second, we validate and assess the accuracy of the turbulent axisymmetric flow model in comparison with velocity and turbulent kinetic energy measurements in a model Francis turbine draft tube cone

Experimental Analysis of Rotor-Stator interaction in a Pump-Turbine

An exhaustive experimental exploration of the flow and pressure fields between runner and guide-vanes, of a pump-turbine, is performed using LDV, PIV and an unsteady 5 sensors probe. Measurements for design and off-design conditions, have been analyzed in both turbine and pump operation modes. For the pump operating regime, one of the investigated operating points is in the instability zone of the characteristic. This study case was used for CFD validations in the Thematic Network on Quality and Trust in the industrial applications of CFD: QNET-CFD AC6-04 test case