Steady and unsteady CFD simulations of the Turbine-99 Draft Tube using CFX-5 and STREAM

Abstract

The numerical prediction of the flow field in a hydraulic turbine draft tube is very challenging due to its complex flow properties and has already been studied in detail in two former ERCOFTAC Turbine-99 workshops. In this third workshop yet another step to determine the state of the art techniques in draft tube flow simulation are taken. Three cases were suggested in the workshop, wherein we have contributed to the first two cases (Case 1 respectively Case 2) in this paper using the CFD codes CFX-5 and Loci-STREAM. For the first case (steady calculation), the turbulence is modeled with the standard k-ε model and Menter's BSL and SST k-ω models, whereas for the second case (unsteady calculation), we use the SST based DES turbulence model. Results from these simulations show that both codes predict about the same main flow structures although significant differences in detailed flow fields are noticed between the two codes and between applied turbulence models.Godkänd; 2005; 20070109 (ysko