Abstract
Turbulent fluid flow and heat transfer in a simulated rotating two-pass internal coolant passage of a turbine blade were investigated experimentally by using Laser-Doppler velocimetry (LDV), thermocouple couple (TC), and transient liquid crystal thermometry (TLCT) systems. Geometrically, the coolant passages have a square cross-section. The Reynolds numbers (Re) and rotation number (Ro) were 1.0□104 ~ 1.4□104 and 0 ~ 0.20 for the LDV and TLCT experiments. The TLCT experiments under rotating condition were performed for the first time in open literature. The TC experiments had extensive parametric ranges of Re = 5.0□103 ~ 5.0□104 and Ro = 0 ~ 0.44. The stationary case was first selected to study the typical flow characteristics of a 180-deg sharp turning duct. It is found that the three-dimensional flows are characterized by the upstream and downstream extents of the sharp-turn effects on the main flow profiles, curvature induced Dean vortices inside the turn, turning geometry-induced separating bubble immediately downstream of the turn, and the resultant double-peak mean velocity profiles in the second pass. Results of rotating duct flows show that duct rotation increases linearly the skewness of mean velocity profiles and magnitude of secondary-flow velocity, and nonlinearly the turbulent kinetic energy. These trends are quantified by simple correlations. The global increases in above-mentioned thermal-fluids parameters due to rotation contribute to the overall heat transfer enhancement around the 180-deg sharp turn. As the rotation number is increased from 0, the curvature induced symmetric Dean-type vortices in the mid-turn is gradually dominated by a single vortex, and most of which impinges directly on the outer part of leading wall to enhance the heat transfer rate in the vicinity and influence the downstream flow characteristics in the second pass. Highly spanwise variations of both the fluid flow and heat transfer results in the first and second passes due to rotation are found and quantified for the first time. A critical rotation number, 0.10 □ Rocritical □ 0.15, is identified such that below which, rotation has no prominent effect on the regional averaged Nusselt number ratios in the regions after the 180-deg sharp turn. For both the stationary and rotating ducts, the direction and strength of the secondary flow with respect to the wall are found to be the most important fluid dynamic factors affecting the local heat transfer rate distributions, followed by the convective mean velocity, and last the turbulent kinetic energy.