Turbulent heat transfer and friction in a segmental channel that simulates leading-edge cooling channels of modern turbine blades

Abstract

Experiments are conducted to study the effects of channel geometry and asymmetric heating on the heat transfer and friction characteristics of turbulent flows in leading edge cooling channels in stator blades of gas turbines. The leading edge cooling channels are modeled as straight segmental channels with 90' rib turbulators on the curved wall only. The ribs are square in cross section and have a height-to-hydraulic diameter ratio of 0.0625. The rib array has a pitch-to-height ratio of 10. Steady state heat transfer experiments for three channel cross sections, ribbed curved wall-to-smooth flat wall heat flux ratio of 0.0, 1.0, 2.0, 4.0, 6.0, and infinity, and mass flow rates corresponding to Reynolds numbers between 10 000 and 70 000 are conducted to determine the streamwise distributions of the regionally-averaged heat transfer coefficient on both the rib-roughened curved wall and the smooth flat wall. Local heat transfer maps are also obtained from transient experiments using thermochromic liquid crystals at Reynolds numbers of approximately 35 000. The overall ribbed curved wall Nusselt number, normalized with the corresponding Nusselt number for fully developed turbulent flow through a tube, increases slightly with increasing heat flux ratio and is only mildly dependent on the channel cross-sectional shape. The smooth flat wall Nusselt number ratio decreases with increasing heat flux ratio and, in general the results indicate that the effect of wall heat flux ratio gradually reduces with increasing Reynolds number. The overall Nusselt number ratio and relative thermal performance for the curved wall and smooth wall on all three test sections can be predicted with a simple power function of the Reynolds number. In addition, the transient results indicate that there is substantial streamwise and spanwise variations of heat transfer between the ribs on the curved wall.