Optimization of turbulated channels for turbine blades cooling by means of numerical simulation

Rotor blades cooling is one of the most critical aspects to consider for gas turbines. The power generated by the turbine is strongly dependent on the inlet temperature of burned gas. At the same time, increasing gas inlet temperature, it is important to guarantee an efficient cooling system to avoid thermal and mechanical problems at the blades. Turbulated channels represent one of the most used solutions. This method is classified as internal cooling system and uses extracted air from the compressor stage that flows into channels from the lower part of the blade toward the tip, being deflected by ribs. Enhancing turbulence, the presence of ribs improves heat exchange between the coolant and the walls, producing on the other hand an increase of pressure losses and so also of the friction factor. This activity aims to find the optimal configuration of channels, analyzing the impact of geometrical parameters like the rib height to diameter ratio e/D and the rib pitch to height ratio p/e, as well as the influence of Reynolds number on thermal and fluid dynamic performances of the cooling mechanism. After a first theoretical analysis of the most common solutions used, two different rib shapes have been selected: rectangular and semicircular. Computational Fluid Dynamic (CFD) simulations are then performed in the Star CCM+ environment, reproducing experimental results obtained by previous studies to verify the reliability of a numerical approach in the approximation of experimental procedures. Results are verified in terms of Nusselt number and friction factor. After the validation, the analysis focuses on a direct comparison between rectangular and semicircular rib shape, imposing equal boundary conditions and turbulence model and discussing more in detail the thermal and the fluid-dynamic flow fields of the two cases. The final step of the study concerns the direct application of ribs in the cooling channels of an industrial gas turbine rotor blade of the EthosEnergy portfolio 3-D CFD simulations are carried out to reproduce operating conditions of the machine and quantify the efficiency of the cooling system.