Impact of multiscale flow structures on mixing and losses in turbine blade tip region

Multiscale mixing of the turbine blade tip leakage and mainstream flows causes considerable aerodynamic loss. Understanding it is crucial to correctly estimating the mixing loss and thus improving the turbine's performance. The multiscale mixing phenomenon in a typical high-pressure turbine rotor flow was studied in this work. The contributions of various scale flows to entropy production and mixing properties were identified. The corresponding physical mechanisms at different scales were explored. It is shown that the large-scale and time-averaged flow contributions to mixing are significant, accounting for approximately 37.1 % and 25 % of the total. Time-averaged and large-scale flows cause the majority of the fluid deformation of the material surface, while meso- and small-scale flows just generate finer deformations. It raises the area stretch coefficient and the virtual concentration gradient. Thus, mixing is enhanced. Furthermore, time-averaged and large-scale flows account for the majority of the losses in the upstream and downstream regions of the blade tip respectively, accounting for approximately 53.8 % and 33.5 % of the total. The sheet-like structures—rather than the tip leaking vortex—are the primary source of the loss. High-dissipation regions are produced by the sheet-like structures via the pressure Hessian term and the self-amplification terms.