Turbine Blade Internal Cooling: Trailing Edge, Coolant-Passage Entry, Bend Effect and Improvement in Thermal Performance

Abstract

Efficient cooling of gas turbine blade is imperative for safe operation of the gas turbine engine at high temperatures. In the present work, two converging lattice structures suitable for trailing edge applications are tested and their performance is compared with a conventional pin-fin configuration. Another constant cross section lattice structure is tested to see the cooling efficiency of lattice channels with different number of sub-channels. Converging lattice structures show higher heat transfer enhancement and comparable or higher thermal performance than traditional pin-fin cooling used in gas turbine trailing edge. The highest pressure drop incurred in a multi-pass channel is at the bend region. A turbine designer always desires to reduce the pressure drop in the bend region without reducing the heat transfer in that region. A total of nine different bend geometries are studied numerically and their performance is compared with a baseline U-bend geometry. Modifications for the bend geometry are made along the channel divider wall and at the endwall of the 180 degree bend. From the numerical study, two geometries (symmetrical bulb and bulb-bow combination) are down selected for experimental study with the goal of improving the Thermal Performance Factor (TPF) in the coolant channel. Different shapes and arrangements of rib turbulators were studied over the last few decades to enhance local turbulence close to the hot gas turbine blade wall and promote secondary flow close to the wall. A combination of angled grooves and angled ribs are used to find the heat transfer and pressure drop across the channel and compare their performance with standard ribbed channel. A 1:4 Aspect Ratio (AR) two-pass cooling channel is tested with three different entrance geometries under stationary conditions. It is seen that the presence of the complex entrance geometries changes the heat transfer enhancement profile at the inlet of the test section significantly when compared to a fully developed entrance. Numerical simulations are done in rotating condition to see the complex interaction of the entrance geometry driven flow and rotation induced flow.