Numerical Prediction Of Torque On Guide Vanes In A Reversible Pump-Turbine Turbine and pump mode operation
The paper presents the numerical flow analysis of the torque on guide vanes pivots in reversible pump-turbine (PT) in turbine and pump mode operation. Flow conditions in a typical PT often point out the importance of the unsteadiness of the flow, first of all because of its instability caused by the viscous effects – the boundary layer separation, vortex spreading and the influence between rotating and non-rotating parts. The detailed analysis of the time dependent distribution of torque on guide vanes is presented. The numerical analysis was performed for complete pump-turbine with various turbulence models. The numerical results were compared with the experimental results. Keywords—water turbine, reversible pumpturbine, CFD, guide vanes, dynamic chyracteristics
Development and Application of SST-SAS Turbulence Model in the DESIDER Project
The paper reports on the current state of the SST-based Scale-Adaptive Simulation model (SST-SAS model), and summarises the validation activity performed with this model in the course of the DESIDER project. The turbulence-resolving capability of the SST-SAS model has been validated with the official project test cases, covering both the underlying generic flows as well as practical aerodynamic applications. Among the latter ones are also the two aero-acoustic test cases of industrial interest. The paper includes a brief description of the current state of the SST-SAS model, as well as the illustrating test case results. Potentials of the SAS approach are briefly discussed, as well as its position amongst the other transient simulation methods.
Improved two-equation k-omega turbulence models for aerodynamic flows
Two new versions of the k-omega two-equation turbulence model will be presented. The new Baseline (BSL) model is designed to give results similar to those of the original k-omega model of Wilcox, but without its strong dependency on arbitrary freestream values. The BSL model is identical to the Wilcox model in the inner 50 percent of the boundary-layer but changes gradually to the high Reynolds number Jones-Launder k-epsilon model (in a k-omega formulation) towards the boundary-layer edge. The new model is also virtually identical to the Jones-Lauder model for free shear layers. The second version of the model is called Shear-Stress Transport (SST) model. It is based on the BSL model, but has the additional ability to account for the transport of the principal shear stress in adverse pressure gradient boundary-layers. The model is based on Bradshaw's assumption that the principal shear stress is proportional to the turbulent kinetic energy, which is introduced into the definition of the eddy-viscosity. Both models are tested for a large number of different flowfields. The results of the BSL model are similar to those of the original k-omega model, but without the undesirable freestream dependency. The predictions of the SST model are also independent of the freestream values and show excellent agreement with experimental data for adverse pressure gradient boundary-layer flows.