Validation of the Immersed Mesh Block (IMB) Approach Against a Cooled Transonic Turbine Stage

Due to difficulties associated with directly meshing and solving cooled turbine geometries, evaluation of cooling designs at an early design stage is not practical. This results in a severely disjointed aerodynamic and heat transfer design process and affects turbine optimisation. In order to reduce the time cost of evaluating cooled geometries, the Immersed Mesh Block (IMB) approach was previously proposed. The IMB is an independent, high density cooling hole mesh that can be mapped to the surface of a turbine and solved with two-way coupling within hours, thus allowing cooling holes to be consistently and reliably modelled at an early design stage. The main focus of this paper is to validate the IMB approach by comparing its results of a cooled transonic NGV against experimental data. Prior to this, a series of mesh dependency tests are conducted on the base solver for a turbine stage. These highlight the need for greater rigour in mesh generation for RANS predictions of heat transfer over aerodynamics. The effect of mesh density on cooling hole predictions is then considered; a range of meshes are employed to model a row of holes on a flat plate. Hence the need for high resolution meshes for cooled geometries is emphasised. Subsequently, it is demonstrated that grid dependency studies of cooling holes on the turbine surface can easily be conducted with the IMB approach. Finally, the IMB method is validated by comparison of its results to experimental data for a cooled turbine stage. The results show that the IMB predicted Nusselt number distribution agrees well with experimental data.