Studies on the Impact of Choice of Gas Models in an Un-Cooled Turbine Stage

CFD analysis has already been established as a preferred way of evaluating turbine stage performance and any incremental increase to it through component design changes. The usually overlooked assumption during a CFD simulation is the choice of gas model. In turbomachinery analysis, for quick assessment of stage performance, modeling the fluid as perfect gas has been yielding fairly reliable results. In general the consideration of real gas effects has been less popular; although they are more realistic. The paper presents the comparison of aero-thermal predictions of an un-cooled turbine stage using ideal and real gas models based on CFD studies only. In addition, the impact of gas models on stage performance predicted using steady state and unsteady CFD analysis is also presented. Based on steady state CFD evaluations, the stage efficiency variation with the change of gas model is less than 0.3% with the real gas effect indicating lower efficiency. However, the unsteady predictions indicate that the time averaged stage efficiency predicted using perfect gas model can be 1% higher than that predicted using real gas model.