Investigation of End-Wall Film Cooling Configuration Performances in a Linear Cascade

An end-wall cooling geometry with both fan-shaped and cylindrical holes is tested. The test case is composed by a linear cascade with cylindrical blades, the cooling holes disposed over eight rows. Each row is disposed along iso-Mach lines to ensure same blowing conditions for each hole of the row. Fan-shaped and cylindrical holes groups are fed by separated plenums to achieve different blowing ratio for each group. Nevertheless in the present study all holes were fed with same condition. Three tests are carried out with different blowing ratios and performances in terms of adiabatic effectiveness are investigated. To perform the simulations a hybrid unstructured mesh formed by about 4 millions elements is used, with most of them placed in the end-wall region. Attention is paid in the discretization of the platform, because the evaluation of heat transfer is important to evaluate performances of platform-cooling. The code used is HybFlow, an in-house code developed at Energy Engineering Department "Sergio Stecco", which can resolve both structured and unstructured mesh using a finite volume up-wind TVD approach. For modelling turbulence the two equations k-ω model proposed by Wilcox is used. Results show very different behaviour for every blowing ratio, due to the different interaction between cooling flow and main flow. This is a consequence of major or minor momentum associated with cooling fluxes and consequently their ability to resist secondary flows as the passage vortex. Fan-shaped holes show best behaviour at the lowest BR, while at the highest BRs the pre-throat region of end-wall were not sufficiently covered because cooling flow lifts off from the surface. Instead of this, the post-throat region shows best performances at highest values of BR, where flows from cylindrical holes can resist to end-wall secondary flows and fluxes come from fan-shaped holes reattach the platform.