Abstract

The aerodynamic design of a turbine stage starts with a mean line aerodynamic calculation that gives the stage main geometric features. A key element in that calculation is the aerodynamic loss system. The AMDCKO (Ainley and Mathieson, Dunham and Came, and Kacker and Okapuu) loss system, after being tested on hundreds of modern axial turbines over a wide design point operating range, was found lacking in its ability to predict reasonably well the aerodynamic turbine efficiency at higher than optimum reaction. Based on a better understanding of the loss mechanisms at high Mach number at blade exit and given a good base of test data, modifications are made to the trailing edge loss, tip-clearance loss and secondary loss models to reflect recent design practices. The modified AMDCKO loss system is validated against the known efficiencies of 46 turbine stages of varied engine applications. It is believed that this new model improves significantly the predictive capability of the mean line design program and provides a better assessment of compressibility effect on the different loss components.