Loss Audit of a Turbine Stage

Abstract

In order to achieve high aerodynamic efficiency of a turbine stage, it is crucial to identify the source of aerodynamic losses and understand the associated loss generation mechanisms. This helps a turbine designer to maximize the performance of the turbine stage. It is well known that aerodynamic losses include profile, endwall, cooling/mixing loss, leakage, and trailing edge loss components. However, it is not a trivial task to separate one from the others because different loss sources occur concurrently and they interact with each other in a machine. Consequently, designers tend to rely on various empirical correlations to get an approximate estimate of each aerodynamic loss contribution. In this study, a systematic loss audit of an uncooled turbine stage has been undertaken by conducting a series of numerical experiments. By comparing entropy growth across the turbine stage, aerodynamic losses are broken down within the stator, rotor, and interblade row gap. Furthermore, losses across each blade row are broken down into profile, leakage, endwall, and trailing edge losses. The effect of unsteady interaction due to the relative motion of the stator and the rotor was also identified. For the examined turbine stage, trailing edge losses of the rotor were dominated, contributing to more than a third of the total aerodynamic loss. The profile loss across the stator and the rotor, unsteady loss between the stator and the rotor, and the stator endwall loss were also identified to be the significant loss sources for this turbine stage. The design implications of the findings are discussed.