4 research outputs found
Numerical Prediction of Cavitating Vortex Rope in a Draft Tube of a Francis Turbine with Standard and Calibrated Cavitation Model
Transient simulations of flow in a Francis turbine were performed with a goal to
predict pressure pulsation frequencies and amplitudes caused by rotating vortex rope at part
load operating regime. Simulations were done with the SAS SST turbulence model with
curvature correction on basic and refined computational meshes. Without cavitation modelling
too small values of frequency and amplitudes were obtained. With mesh refinement the
calculated amplitudes were a bit closer to the measured values, while the accuracy of predicted
frequency did not improve at all. Agreement between measured and numerical values was
significantly improved when cavitation was included in simulations. In addition, the predicted
value of the dominant frequency was slightly more accurate when, in the Zwart et al. cavitation
model, the default condensation and evaporation model constants were replaced with
previously calibrated ones
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
Optimization of a single-stage double-suction centrifugal pump
In this study, the objective of the optimization of a double-suction pump is the
maximization of its hydraulic efficiency. The optimization is performed, by means of the
modeFRONTIER optimization platform, in steps. At first, by means of a DOE (Design of
Experiments) strategy, the design space is explored, using a parameterized CAD representation
of the pump. Suitable metamodels (surrogates or Response Surfaces), which represent an
economical alternative to the more expensive 3D CFD model, are built and tested. Among
different metamodels, the evolutionary design, radial basis function and the stepwise regression
models seem to be the most promising ones. Finally, the stepwise regression model, trained on
a set of 200 designs and constructed with only five the most influential input design parameters,
was chosen as a potentially applicable metamodel
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-epsilon 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