Investigation of Losses Prediction Methods in 1D for Axial Gas Turbines

Abstract: A brief description of the physical flow phenomena in a blade row that creates losses in an axial gas turbine and correlations to estimate these losses in a mean line calculation are given. Investigation and comparison of the loss correlations for 1D mean line calculation between the in-house program (CTC) used at Siemens and loss correlations present in the open literature were made. The investigation is primarily focused on the problems associated with modeling off-design effects on profile and secondary losses, and the effect of tip leakage losses at all loads. For the off-design condition both positive and negative flow incidence were covered with internal tests and numerical 2D investigations. The increase in blade losses at high outlet Mach number and how it is related to the shape of the suction surface for a blade profile was investigated with numerical 2D simulation. The results for the loss models are validated against previous done internal gas turbine test runs at Siemens, external cascade tests and numerical 2D simulations. The overall conclusions are that the in-house program (CTC) shows good prediction ability for the off-design down to the state where the turbine reaches turn-up mode. But some questions about CTC’s distribution between profile and secondary losses are discussed. For the tip leakage loss it was highlighted that CTC shows a somewhat low loss for a constant clearance and also a rather low increase with relative clearance change. A limitation in the prediction ability because the absence of some believed important parameter was also seen and an alternative model was suggested for unshrouded blades. It is clear that there for most blade designs is seen a sudden increase in the blade losses at an outlet Mach number in the region of 0.9. But no obvious relations to which blade parameters that determine the absolute increase were found