Scale effect of micro ribs on the turbulent transport in an internal cooling channel

This is the authors' abstract. We don't add key points for this paper.

Owing to the limited supply and pressure margin in the air system, a cooling technique providing efficient heat transfer with lower flow loss is highly desirable for gas turbine blades. Microscale ribs have promised to be a potential cooling candidate. In this work, large eddy simulations are implemented to reveal the scale effect of micro ribs on the near-wall turbulent transport in a cooling channel. Considering a mechanistic study and practical applications, both single-rib and rib-array arrangements are studied with a wide range of dimensionless viscous-scaled rib heights involving the entire boundary layer. The results indicate that the rib-induced destruction and regeneration of coherent structures are, respectively, responsible for the weakened momentum transport and enhanced heat transport in the near-wall region. Using tiny ribs, regenerated quasi-streamwise vortices are mainly located in the buffer layer. The resulting turbulence burst greatly enhances wall heat transfer while keeping a lower flow loss due to the weak form drag. Regenerated hairpin vortices using tall ribs are activated in the log-law layer and intensively interact with mainstream. Along with improved wall heat transfer, the significant form drag results in a remarkably high flow loss. Accordingly, heat transfer and flow loss show different dependencies on the rib height, which contributes to an optimum height interval of ribs (e+ = 20–40) located in the high buffer and low log-law layer for maximizing the overall performance. Furthermore, for the rib-array scheme, adequate inter-rib spacing is essential to achieve turbulence regeneration for enhancing near-wall heat transport.