Numerical Investigation of Impingement Cooling in an Airfoil Leading-Edge Cooling Channel

Technological advancement in gas turbine field demands high temperature gases impacting on the turbine-airfoils in order to increase the thermal efficiency of the associated Brayton cycle. Researchers have been endeavoring to keep the turbine airfoils' surface temperature well below the material-melting point for the past sixty years. Two-pronged approach is often employed to tackle this challenging issue. The first prong to the approach is to develop modern alloys in parallel with the use of ceramic composites to sustain the severe thermal conditions, the other prong is to employ internal and external cooling schemes particularly in the turbine early stages. The presented study embraced an internal impingement cooling in the leading edge as one of the most critical sections of the airfoil using computational fluid dynamics to simulate the actual experimental setup where obtaining important flow features and properties without disturbing the flow field becomes a difficult and costly task. Current experimental setup is a scaled up model of a leading-edge internal concaved surface and its adjacent cavity. Typical cooling flow streams into the model through the inlet ports of the adjacent cavity and consequently impinges on the internal heated surface of the leading edge through a series of identical crossover holes. Four different flow arrangements were tested in addition to five different geometries along with seven different boundary jet Reynolds numbers for each combination of geometry and flow arrangement during the study. This produced 126 numerical tests to be conducted. In order to simulate the flow inside the cavity, a three-dimensional unstructured numerical model of the experimental setup was developed and solved using commercial software packages to comprehensively investigate the behavior of Nusselt number with the variation of Reynolds number, geometry and flow arrangement combined with providing a better flow structure-visualization tool. Results showed a monotonic increase of Nusselt number with increasing Reynolds number, in addition to significant dependency on the axial flow introduced by upstream jets as it drastically diminishes the impingement effect on the target walls.