Numerical investigation on the effect of rotation and holes arrangement in cold bridge type impingement cooling systems

This work presents the results of a numerical analysis performed on a gas turbine leading edge cooling system. The investigation was carried out in order to provide a detailed interpretation of the outcomes of a parallel experimental campaign. The cooling geometry consists of a cold bridge type impingement system: a radial channel feeds an array of holes, which in turn generate impingement jets cooling down the inner side of the leading edge surface. Coolant is extracted by five rows of holes, replicating film cooling and showerhead systems. Two impingement geometries were considered, presenting different holes arrangements and diameters but sharing the same overall passage area, in order to highlight the effect of different coolant distributions inside the leading edge cavity. For both geometries a single test point was investigated in static and rotating conditions, with an equivalent slot Reynolds number of around 8200 and feeding conditions corresponding to the midspan radial section of the blade. Both steady RANS approach and Scale Adaptive Simulation (SAS) were tested. Due to the strong unsteadiness of the flow field, the latter proved to be superior: as a consequence, SAS approach was adopted to study every case. A fairly good agreement was observed between the measured and computed heat transfer distributions, which allowed to exploit the numerical results to get a detailed description of the phenomena associated with the different cases. Results reveal that the two holes arrangements lead to strongly different heat transfer patterns, related to the specific flow phenomena occurring inside the leading edge cavity and to the mutual influence of the various system features. Rotational effects also appear to interact with the supply condition, altering the jet lateral spreading and the overall heat transfer performance.