Effect of Surface Roughness and Inlet Turbulence Intensity on a Turbine Nozzle Guide Vane External Heat Transfer: Experimental Investigation on a Literature Test Case

Surface roughness is well known to significantly influence turbine aerodynamics and heat transfer; different studies have been undertaken in the last decades, in order to precisely characterize its effects and pursue a reliable and unified computational fluid dynamics modeling approach. Despite the effort, further research is still required to completely fulfill the goal, due to the complexity of the considered environment, with many other aspects and flow characteristics factoring into the final behavior. In this work, an experimental campaign was carried out to evaluate the heat transfer coefficient on a linear nozzle guide vane geometry. The adopted geometry has been developed and tested, at different inlet turbulence intensity, Reynolds and Mach number, at Von Kármán Institute. The results achieved on a test article with smooth surface were made available. In the present work, the effect of increased turbulence level and surface roughness was taken into account, respectively, using passive grids and conditioning the test sample surface finishing. Experiments were conducted using a transient technique by measuring the surface temperature evolution by IR thermography. The collected results integrate the existing database available in the open literature in order to support development and benchmarking of numerical approaches aimed at a reliable characterization of these aspects.