Coriolis and buoyancy effects on heat transfer in viewpoint of field synergy principle and secondary flow intensity for maximization of internal cooling

Abstract

The present investigation emphases on rotation effects on internal cooling of gas turbine blades both numerically and experimentally. The primary motivation behind this work is to investigate the possibility of heat transfer enhancement by dean vortices generated by Coriolis force and U-bend with developing turbulent in the view point of the field synergy principle and secondary flow intensity analysis. A two-passage internal cooling channel model with a 180° U-turn at the hub section is used in the analysis. The flow is radially outward at the first passage of the square channel and then it will be inward at the second passage. The study covers a Reynolds number (Re) of 10,000, Rotation number (Ro) in the range of 0–0.25, and Density Ratios (DR) at the inlet between 0.1–1.5. The numerical results are compared to experimental data from a rotating facility. Results obtained with the basic RANS SST k-ω model are assessed completely as well. A field synergy principle analysis is consistent with the numerical results too. The results state that the secondary flows due to rotation can considerably improve the synergy between the velocity and temperature gradients up to 20%, which is the most fundamental reason why the rotation can enhance the heat transfer. In addition, the Reynolds number and centrifugal buoyancy variations are found to have no remarkable impact on increasing the synergy angle. Moreover, vortices induced by Rotation number and amplified by Reynolds number increase considerable secondary flow intensity which is exactly in compliance with Nusselt number enhancement.