Detailed Studies on the Flow Field and Heat Transfer Characteristics Inside a Realistic Serpentine Cooling Channel With a S-Shaped Inlet

Abstract

Accurate temperature prediction of turbine blades for gas turbine is very important to assure the life-span of the blade under a hostile hot gas environment and intense centrifugal force. Therefore, there have been a number of studies carried out to clarify the cooling performance of serpentine cooling channel inside a turbine blade for gas turbine, however, it remains to be quite difficult to make an accurate numerical prediction of the performance. Apart from the effects of disk rotation as well as large temperature gradient near the wall, such a poor predictability can be attributed to the complicated vortical motions caused by the rib-roughened cooling channel whose cross-sectional shape varies along the channel and by the existence of u-bends. Furthermore, since the cooling channel inside a real turbine blade usually has a curved or S-shaped inlet, which may induce flow separation as well as swirl developed in the inlet, it can be imagined that the flow and heat transfer inside the cooling channel is likely to become much more complicated than that with a straight inlet. Despite this situation, only few studies are made in order to examine the flow and heat transfer characteristics inside the cooling channel with s-shaped inlet. Accordingly, this study aims at detailed experimental and numerical investigations on the flow and heat transfer characteristics of a realistic serpentine rib-roughened cooling channel with an s-shaped inlet, which is modeled from an actual HP turbine blade for gas turbine. This study employs a transient TLC (Thermochromic Liquid Crystal) technique to measure the heat transfer characteristics, along with the flow visualization on the inner surface of the channel using oil mixed with titanium powder. Note that a special focus in this flow visualization is placed on the area of s-shaped inlet. As for the flow measurement, 2D-PIV (Particle Image Velocimetry) method is used to understand time-dependent vortical structures of the flow field that can have significant impacts on the heat transfer. RANS-based numerical simulation is also executed to predict the heat transfer distribution on the inner surface of the cooling channel.