Heat Transfer in Turbine Blade Cooling System: A Numerical Investigation of Recessed Endwalls in Ribbed Cooling Channel

Modern gas turbines demand effective cooling methods to manage high -temperature inlet gases (up to 2000oK) and protect turbine components. One crucial cooling technique involves casting ribs on the pressure and suction sides of cooling serpentine passages. These ribs generate vortices that enhance heat transfer via turbulence promotion. Typically, cooling cascades feature two types of ribs: straight ribs, which offer a more uniform flow but lower heat transfer, and inclined ribs, known for higher turbulence and superior heat transfer capabilities. In the context of turbine blades, inclined ribs introduce a unique characteristic: secondary flow, which substantially contributes to heat transfer through turbulence promotion. This study explores three geometries of recessed endwalls for these ribs using Reynolds-averaged-Navier-Stokes (RANS) equations coupled with a k-omega turbulence model to assess heat transfer characteristics. These endwalls variations aim to preserve and amplify the secondary flow between the casted ribs. The results at Re = 19683 demonstrate increased heat transfer in channels with these new designs. Specifically, the growth of 9.3%, 12.1%, and 14.4% in the Nusselt number is discovered for the reference triangular, curved, and trapezoidal endwall designs, respectively. This augmentation in secondary flow is accompanied by an increase in pressure loss. Consequently, the Heat Transfer Efficiency Index (HTEI) of the channels increases by 5.2%, 7.0%, and 8.3% with the new designs compared to the flat endwall at Re = 19683. Furthermore, when varying the height of the recessions, it becomes evident that the secondary flow intensifies with increased height. However, the expansion of friction factors somewhat offsets the substantial Nusselt number increase. This leads to a 27.0%, 32.7%, and 31.4% HTEI increase at Re = 6844 for the triangular, curved, and trapezoidal endwall designs, respectively. At Re = 19683, these figures are 13.5%, 18.7%, and 18.1%. These findings underscore the potential for significant enhancements in heat transfer by optimizing endwall designs, which can alter the vortex systems within the channel.