Numerical Study of Axial Turbine Flow With Variable Gas Property

Abstract

Aerodynamic performance characteristics and flow details of industrial gas turbines have been evaluated by using a computational fluid dynamics code with a variable gas property model. Systematic simulations have been carried out first to study numerical effects, notably grid resolution and domain size dependency, followed by applications on a warm air turbine rig and an industrial engine. Studies of the turbine rig are focused on the stage performance characteristics and the results agree with the test data fairly well. It is also found that the variable gas property has little influence on the flow half a chord downstream of the rotor trailing edge, where the conditions of the next turbine stage are determined. Further studies on a 3-stage turbine reveal the influence of the variable gas property model. When the gas properties are made constant with respect to the first blade row conditions, the mass flow rate is the same as when using the variable gas property model, however the exit total temperature is over-predicted by about 15 Kelvin. There is also an over-prediction of turbine power output of 0.6%. Simulations using a constant gas property of averaged value or at the last blade row over-predict the mass flow rate by 0.5% and 1% respectively. Downstream on the blade surface and near the exit, they under-predict the temperature and the power output. The predicted efficiency from the various simulations is found to be less influenced than the parameters discussed above, with a difference of about 0.25%. As a conclusion, it is necessary to include the variable gas property effect in 3D calculations of industrial gas turbine flow to achieve an accurate analysis of the flow and performance.