The first part of this paper analysed the time-averaged flow in a transonic single stage turbine. In this second part, we analyse the three-dimensional unsteady flow and temporal correlations in the rotor frame of reference. Two main conclusions are deduced from the comparison of each correlation. First, all correlations have the same order of magnitude. This is an important conclusion for models that handle the interaction between blade rows, because the temporal correlations are usually neglected. Second, these correlations occur in complementary localizations. In particular, the largest values of spatial deterministic correlations is located between the nozzle trailing edge and the rotor leading edge, as a consequence of nozzle wakes. Conversely, temporal deterministic correlations are located within the rotor blade row. We also establish that entropy accumulations in the stator wake near the end-wall regions generate high fluctuations of the rotor passage vortices. Such a phenomenon may have great repercussions on the radial loss distribution in the stage.

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International audienc

This paper analyses the flow in a transonic turbine stage, using time-dependent numerical results. Unsteady blade-row interaction has repercussions on the time-averaged flow, which are represented by the so-called “deterministic correlations”. These correlations appear in the system of equations governing the time-averaged flow; they can be divided into four types with different physical meanings. Time-dependent results enable direct computation of these correlations in both rotor and stator frames of reference. The computed deterministic correlations are analysed in the paper, in order to bind them to physical phenomena and to evaluate their influence on the time-averaged flow field. This analysis is also intended to help assess the shortcomings of simple mixing-plane methods and more complex approaches using deterministic correlation models. While the first part focuses on one particular type of deterministic correlation, the so-called “spatial correlation”, the second part attempts a more detailed analysis of time-dependent results and gives some clues to the orders of magnitude of the four types of deterministic correlation. The conclusions should be taken with caution; they may partly depend on the present turbine configuration with a specified structure of unsteadiness and on the present turbulence model.