Computational Analysis of Air/Mist Film Cooling Using a Sweeping Jet Fluidic Oscillator–Part I: Sweeping Air-Only Jet With Detailed Analysis of Vortex Dynamics

Abstract

This two-part paper presents a numerical study to investigate the application of using air/mist sweeping jets in film cooling for protecting turbine airfoils. Part I focuses on validating the computational mode by comparing the thermal-flow and heat transfer behavior between steady and sweeping air-only jets to ensure they are consistent with published information. Part II focuses on the mist behavior and its effect on heat transfer enhancement in the sweeping jet film cooling by adding micro-liquid droplets. An unsteady Reynolds Averaged Navier-Stokes (URANS) simulation accompanied by the k-ω SST turbulence model was used in this study. A comparison is made between steady and sweeping jets at two blowing ratios (BR=1 and 2). The results show that the steady jet provided better film cooling performance along the centerline compared to that of the sweeping jet for both blowing ratios. However, the sweeping jet provided better and more uniform film cooling performance in the spanwise direction. The sweeping jet caused an increase of 9.5% in total pressure losses compared to the steady jet. A detailed analysis is presented to understand the instantaneous vortex dynamics of the sweeping jet that leads to the inward rotating CRVP. The result shows that the pair of counter-rotating vortices is just a time-averaged image of a single vortex sweeping back and forth in the domain; it does not actually exist in real time.