Heat transfer technology for internal passages of air-cooled blades for heavy-duty gas turbines.

The present review paper, although far from being complete, aims to give an overview about the present state of the art in the field of heat transfer technology for internal cooling of gas turbine blades. After showing some typical modern cooled blades, the different methods to enhance heat transfer in the internal passages of air-cooled blades are discussed. The complicated flows occurring in bends are described in detail, because of their increasing importance for modern cooling designs. A short review about testing of cooling design elements is given, showing the interaction of the different cooling features as well. The special focus of the present review has been put on the cooling of blades for heavy-duty gas turbines, which show several differences compared to aero-engine blades.

Prediction of pressure loss and heat transfer in internal cooling passages.

This paper reports CFD-simulations of the turbulent flow, pressure loss and heat transfer occurring in ribbed passages. The channel section is rectangular, with an aspect ratio of 2.04. Ribs are square cross-section, their height is 10% of the channel height, and their inclination is varied from 90 degrees to 33 degrees. Reynolds number is 30,000. Three turbulence models (k-epsilon wall functions and 2-layer, V2F) are used and compared to the experimental data of Cho et al. All three models accurately predict the pressure losses due to the ribs and the qualitative heat transfer distribution on the ribbed wall. However, only the V2F model can accurately reproduce the absolute heat transfer levels, this at all inclination angles. The correlation developed by Han and co-workers for smaller rib-heights under-predicts the friction factor and wall heat transfer level on the current configuration. This shows the danger of using a correlation outside of its application range.