Thierry Maître

Flow Analysis Inside a Pelton Turbine Bucket

The aim of this work is to provide a detailed experimental and numerical analysis of the flow in a fixed bucket of a Pelton turbine. The head, jet incidence, and flow rate have been varied to cover a wide range of the turbine functioning points. The experimental analysis provides measurements of pressure and torque as well as flow visualization. The numerical analysis is performed with the FLUENT code using the two-phase flow volume of fluid method. The results present a good consistency with experimental data. In particular, the pressure distribution is very well predicted for the whole range of the studied parameters. A detailed analysis of torque and thrust allows evaluating the losses due to the edge and the cutout of the bucket. These results give insight into the benefit we can expect of steady flow calculations through the optimization process of the design of Pelton turbines.

Numerical and experimental analysis of a darrieus-type cross flow water turbine in bare and shrouded configurations

The aim of this paper is to present the results of the analysis of a Darrieus-type cross flow water turbine in bare and shrouded configurations. Numerical results are compared to experimental data and differences found in values are also highlighted. The benefit of the introduction of a channelling device, which generates an efficiency increment factor varying from 2 to 5, depending on the configuration, is discussed.

3D RANS modeling of a cross-flow water turbine

This paper presents several aspects of the URANS numerical modeling of a three-straight-bladed cross flow turbine. In a first part, a 2D analysis is presented as a reference configuration. The near wall grid is refined until the solution stabilizes. Calculations are performed for three tip speed ratios to cover the three classical regions: primary effects, transition, and secondary effects. Three-dimensional modeling uses 3D grids obtained by translating the 2D one in the span direction. A simplified version considers only the 3 straight blades though the complete version takes all the geometric parts into account: blades, arms, shaft, and hub. The mean and instantaneous power coefficients, obtained with the 2D and 3D grids, are compared to those given by the hydrodynamic LEGI tunnel on a small-scale model. Experimental uncertainties are also carefully quantified for these quantities. It is shown that the 3D modeling improves significantly the power predictions. The main loss regions are the blade tips and the spoke-arm attachments where horseshoe vortices take place. The power distribution along the span is strongly affected by these two zones. The analysis of the vorticity field highlights large 3D vortex structures shed by the blades and convicted inside the turbine.

Modeling the Unsteady Cavitating Flow in a Cross-Flow Water Turbine

The noncavitating and cavitating flows over a cross-flow water turbine are simulated by using an unsteady Navier-Stokes formulation. For the cavitating flow case, a homogeneous mixture with a varying density is considered and one additional transport equation is explicitly solved in time for the liquid volume fraction. The instantaneous rate of vapor production and absorption appearing as a source term is governed by a hydrodynamic model based on a simplified bubble dynamic equation. The spatial discretization is achieved by a 2D multiblock technique consisting of fixed and rotating blocks, which were especially adapted for Darrieus geometry. Several test cases corresponding to experiments performed on fixed and rotating blades are selected to compare the numerical results with experimental data. Finally, a calculation of a monobladed cavitating cross-flow turbine is presented. The effect of cavitation on the dynamic stall phenomenon and on the turbine performance is analyzed. In particular, it is shown that cavitation earlier reveals the stall phenomenon on the blades and magnifies the size of the shedding vortex structures in the turbine. [DOI: 10.1115/1.4001966].

Cavitating Behaviour Analysis of Darrieus-Type Cross Flow Water Turbines

The aim of this paper is to study the cavitating behaviour of bare Darrieus-type turbines. For that, the RANS code CAVKA, has been used. Under non-cavitating conditions, the power coefficient and the thrusts calculated with CAVKA are compared to experimental values obtained in the LEGI hydrodynamic tunnel. Under cavitating conditions, for several cavitation numbers, the numerical power coefficients and vapour structures are compared to experimental ones. Different blade profiles and camber lines are also studied for non-cavitating and cavitating conditions.