Cavitation is undesirable phenomena and more prone in reaction turbines. It is one of the challenges in any hydro power plant which cause vibration, degradation of performance and the damage to the hydraulic turbine components. Under the present study, an attempt has been made to carry out a numerical analysis to investigate the cavitation effect in a Francis turbine. Three dimensional numerical study approach of unsteady and SST turbulence model are considered for the numerical analysis under multiphase flow such as cavitating flow. The performance parameters and cavitating flow under different operating conditions have been predicted using commercial CFX code. Three different operating conditions under cavitation and without cavitation with part load and overload conditions of the turbine for a plant sigma factor are investigated. The results are presented in the form of efficiency, pressure fluctuation, vortex rope and vapor volume fraction.It has been observed that variation in efficiency and vapor volume fraction is found to be nominal between cavitation and without cavitation conditions at rated discharge and rated head. turbine efficiency loss and vapor bubbles formation towards suction side of the runner blade are found to be maximum under overload condition. However, the pressure pulsation has been found maximum under part load condition in the draft tube. The simulation results are found to be in good agreement with model test results for efficiency. The locations of cavitating zone observed well with the result of previous studies.

Overall turbine analysis requires large CPU time and computer memory, even in the present days. As a result, choosing an appropriate computational domain accompanied by a suitable boundary condition can dramatically reduce the time cost of computations. This work compares different geometries for numerical investigation of the 3D flow in the runner of a Francis turbine, and presents an optimum geometry with least computational effort and desirable numerical accuracy. The numerical results are validated with a GAMM Francis turbine runner, which was used as a test case (GAMM workshop on 3D computation of incompressible internal flows, 1989) in which the geometry and detailed best efficiency measurements were publically accessible. In this simulation, the flow is assumed to be steady and the inlet boundary condition is prescribed using experimental data. The effect of turbulence is considered by the k-e model. The present investigation demonstrates that consideration of 2-blade geometry with periodic boundary conditions is the best choice of computational domain. By 1-blade geometry, convergence of the numerical simulation is not appropriate, whereas 13-blade geometry leads to a coarse grid that can increase inaccuracy and computational cost. Finally, this paper presents a qualitative survey to forecast cavitation region inception which correlates satisfactorily with experimental observations.

Cavitation in hydraulic installations is still a major concern when it comes to producing electricity. We are aware of the danger of cavitation and the damage it can cause. We have carried out a study of the behavior of the Francis de song lou lou turbines in operation, their areas of application and their various modes of degradation. The first step was to identify the nature of cavitation during operation. We used the three-dimensional Naviers Stokes equations. The pressure and velocity fields obtained are examined to observe the various fluctuations that disrupt the correct operation of the turbine, and consequently reduce production efficiency. The characteristics of the turbine at the Song Loulou hydroelectric power station in Cameroon were used. The results obtained, compared with those in the literature, are satisfactory. This modelling is an effective tool for detecting the presence of cavitation in the Francis turbine

The hydraulic turbines, especially Francis turbines, frequently run at part load (PL) conditions to meet the dynamic energy needs. The flow field at the runner exit changes significantly with a change in the operating point. At PL, flow instabilities such as the Rotating Vortex Rope (RVR) form in the draft tube of the Francis turbine. The present paper compares the features of the velocity and vorticity field of the Francis turbine draft tube at the best efficiency point (BEP) and PL operations using the Proper Orthogonal Decomposition (POD) of the 2D-PIV data. The POD analysis decomposes the flow field into coherent and incoherent structures describing the spatiotemporal behavior of the flow field. A visual representation of the coherent structures and the turbulent length scales in the flow field is extracted and analyzed for BEP and PL, respectively. The study highlights the salient features of the draft tube flow field, which differentiate the BEP and PL operation. The fast Fourier transform of the temporal coefficients confirms the presence of RVR frequency (0.29 times the runner frequency) at PL. The phase portraits of different modes elucidate the relationship between different harmonics of the RVR frequency at PL.

The blade vortex evaluation in Francis turbine under deep part load conditions generates severe pressure ‎fluctuations in the runner. The complex flow in a model turbine is numerically investigated based on a ‎modified Partially Averaged Navier-Stokes method. The main emphasis is focused on revealing the ‎correlation mechanism of blade vortex evolution and energy production. The results indicate that the ‎modified PANS method shows significant advantages in hydro turbine’s simulation than the traditional ‎RANS method. At deep part load conditions, the vorticity formed at the leading edge of the suction ‎surface and the trailing edge of the pressure surface in the blade channels. The stretching term provides ‎the most vorticity increments while the dilation term inhibiting part which only provides a decrement of ‎the vorticity evolution. Based on the entropy production theory, the total entropy production distribution ‎is consisting with the distribution of vorticity. At deep part load condition, direct dissipation and turbulent ‎dissipation provide the most entropy, while at part load condition the proportion of these two-part ‎decreased‎.