Dragica Jošt

Numerical simulation of flow in a high head Francis turbine with prediction of efficiency, rotor stator interaction and vortex structures in the draft tube

The paper presents numerical simulations of flow in a model of a high head Francis turbine and comparison of results to the measurements. Numerical simulations were done by two CFD (Computational Fluid Dynamics) codes, Ansys CFX and OpenFOAM. Steady-state simulations were performed by k- and SST model, while for transient simulations the SAS SST ZLES model was used. With proper grid refinement in distributor and runner and with taking into account losses in labyrinth seals very accurate prediction of torque on the shaft, head and efficiency was obtained. Calculated axial and circumferential velocity components on two planes in the draft tube matched well with experimental results.

Numerical Prediction of Efficiency, Cavitation and Unsteady Phenomena in Water Turbines

The paper presents numerical analysis of the flow in all types of water turbines. Analysis was performed by ANSYS CFX-11.0 computer code. A detailed analysis of complete radial and axial turbine is presented. On the basis of numerical results efficiency and cavitation are predicted and compared to the measured results obtained on test rigs in Turboinstitut. The paper presents also numerical analysis of the flow in a two jet Pelton turbine. The analysis was divided into two parts. At first a steady state analysis of the flow in the piping system with the jets at the outlet was performed. The second step was unsteady analysis of the runner with jets. The casing was not included in the domain of calculation. The predicted efficiency is compared to the measured values.Copyright

Model and Prototype Draft Tube Pressure Pulsations

All producers of Francis turbines daily meet the problem of draft tube vortex appearance and its consequences [1,2,3,4]. Limitations in turbine operation because of the vortex appearance and undesirable consequences on hydraulic system are sufficient reason for its intensive researching. According to such unpleasant and sometimes only hard soluble consequences on the prototypes, the research is directed to model tests and numerical flow analysis with the aim to predict consequences on prototype.

Numerical Flow Analysis of a Kaplan Turbine

This paper details the numerical analysis of the flow in a Kaplan turbine, The purpose of the research is related to the refurbishment of two hydropower plants on the Drava River in Slovenia. This project was begun at the beginning of 1994 and is now nearly finished.

Decoupled CFD-based optimization of efficiency and cavitation performance of a double-suction pump

In this study the impeller geometry of a double-suction pump ensuring the best performances in terms of hydraulic efficiency and reluctance of cavitation is determined using an optimization strategy, which was driven by means of the modeFRONTIER optimization platform. The different impeller shapes (designs) are modified according to the optimization parameters and tested with a computational fluid dynamics (CFD) software, namely ANSYS CFX. The simulations are performed using a decoupled approach, where only the impeller domain region is numerically investigated for computational convenience. The flow losses in the volute are estimated on the base of the velocity distribution at the impeller outlet. The best designs are then validated considering the computationally more expensive full geometry CFD model. The overall results show that the proposed approach is suitable for quick impeller shape optimization.

Numerical predictions of the turbulent cavitating flow around a marine propeller and an axial turbine

The numerical predictions of cavitating flow around a marine propeller working in non-uniform inflow and an axial turbine are presented. The cavitating flow is modelled using the homogeneous (mixture) model. Time-dependent simulations are performed for the marine propeller case using OpenFOAM. Three calibrated mass transfer models are alternatively used to model the mass transfer rate due to cavitation and the two-equation SST (Shear Stress Transport) turbulence model is employed to close the system of the governing equations. The predictions of the cavitating flow in an axial turbine are carried out with ANSYS-CFX, where only the native mass transfer model with tuned parameters is used. Steady-state simulations are performed in combination with the SST turbulence model, while time-dependent results are obtained with the more advanced SAS (Scale Adaptive Simulation) SST model. The numerical results agree well with the available experimental measurements, and the simulations performed with the three different calibrated mass transfer models are close to each other for the propeller flow. Regarding the axial turbine the effect of the cavitation on the machine efficiency is well reproduced only by the time dependent simulations.

Numerical investigation of the flow in axial water turbines and marine propellers with scale-resolving simulations

The accurate prediction of the performances of axial water turbines and naval propellers is a challenging task, of great practical relevance. In this paper a numerical prediction strategy, based on the combination of a trusted CFD solver and a calibrated mass transfer model, is applied to the turbulent flow in axial turbines and around a model scale naval propeller, under non-cavitating and cavitating conditions. Some selected results for axial water turbines and a marine propeller, and in particular the advantages, in terms of accuracy and fidelity, of ScaleResolving Simulations (SRS), like SAS (Scale Adaptive Simulation) and Zonal-LES (ZLES) compared to standard RANS approaches, are presented. Efficiency prediction for a Kaplan and a bulb turbine was significantly improved by use of the SAS SST model in combination with the ZLES in the draft tube. Size of cavitation cavity and sigma break curve for Kaplan turbine were successfully predicted with SAS model in combination with robust high resolution scheme, while for mass transfer the Zwart model with calibrated constants were used. The results obtained for a marine propeller in non-uniform inflow, under cavitating conditions, compare well with available experimental measurements, and proved that a mass transfer model, previously calibrated for RANS (Reynolds Averaged Navier Stokes), can be successfully applied also within the SRS approaches.