Effect of Turning Vane on Tip Wall Heat Transfer in a Rotating Two-Pass Rectangular Channel

During gas turbine operation, the blade tip region experiences high thermal load. Adequate cooling near the tip is necessary to reduce thermal stresses and extend blade lifespan. This study examined heat transfer distribution on the tip wall of internal cooling channels through experimental measurement and numerical simulation. A two-pass rectangular channel with an aspect ratio (AR) of 1:4 and a hydraulic diameter of 25.6 mm was used. In the 180° turn region, both full turning vanes and slotted turning vanes were installed to minimize pressure loss while maintaining favorable heat transfer distribution. Thermochromic liquid crystals thermography and stroboscopic photography were employed in the experiment to obtain heat transfer distribution on the tip wall. The Reynolds number ranged from 10,000 to 30,000, while the rotation number ranged from 0 to 0.53. To increase rotation number, internal channel pressure was increased while keeping Reynolds number constant in order to decrease flow velocity. In the numerical study, ANSYS-Fluent R19.2 software was used for predicting flow field using a transition SST turbulence model with air as working fluid. The slotted turning vanes allowed flow impingement on the tip wall resulting in a higher heat transfer rate compared to cases with full turning vanes (10% higher). Both cases with turning vanes showed lower pressure drop and reduced heat transfer magnitude compared to smooth cases without turning vanes. Generally, rotation had less effect on tip wall heat transfer for cases with turning vanes due to reduction of rotation-induced secondary flow by these vane structures. The effect of channel orientation was less significant for cases with turning vanes compared to those without them.