Synergy principle and its application of endwall loss analyses in the turbine stator

The endwall flow significantly impacts the turbine performance behavior, and it is necessary to investigate the development of endwall secondary vortices and relevant losses. Inspired by the field synergy principle, the synergy between the velocity and the pressure gradient established by the three-dimensional mechanical energy conservation equation is innovatively applied to the endwall loss analysis in the stator of an axial-inflow turbine. In terms of the synergy equation, the loss is not only related to the viscous dissipation, but also the included angle (or the synergy angle) between the velocity vector and the pressure gradient vector. The physical content of the synergy angle suggests that the larger synergy angle is (i.e., the worse synergy), the higher losses should be. This conclusion has been validated by present numerical results, and an apparent positive correlation between the synergy angle and the losses could be perceived under time-averaged and transient conditions. The worse synergy could be observed at the passage rear part and the wake, where complex passage vortices and local separation exist. In these regions, the local velocity vector is not aligned with the bulk pressure gradient of the mainstream. Hence, the synergy angle has a marked rise, corresponding to the local high losses.