Computational Analysis of Air/Mist Film Cooling Using A Sweeping Jet Fluidic Oscillator–Part II: Sweeping Mist Jets

Abstract

An ongoing research effort has been conducted for years to investigate the feasibility of mixing the air with mist (micron-level water droplets) to enhance heat transfer. It becomes very interesting to investigate how these tiny droplets behave in conjunction with the periodic sweeping jets. Will they move synchronously with the fluid or asynchronously with a phase lag? How would the interaction between the droplets and the sweeping jets affect the film cooling effectiveness? To answer these questions, Part II of this paper specifically focuses on investigating the droplet dynamics and thermoflow behavior of droplet evaporation on film cooling effectiveness in a sweeping jet. An unsteady Reynolds Averaged Navier–Stokes simulation accompanied by the k–ω shear stress transport turbulence model is used in this study. The multiphase computational fluid dynamics model employs an Eulerian–Lagrangian approach. The Eulerian method is used for the continuous phase including air and water vapor and the Lagrangian method in terms of the discrete phase model is used to simulate the dispersed phase (e.g., liquid droplets) in a continuous phase (e.g., air). A mist ratio of 10% with a droplet size of 10 μm was used in this study. The results show that, for a blowing ratio of 1, using mist provides better film cooling performance with an average enhancement of 50–90% in comparison to that without mist. Using a mist ratio of 10% could save approximately 50% of the cooling air. It is observed that the liquid droplets mostly follow the main sweeping flow and its vortical structure and horseshoe vortices, but with a phase lag between the droplets and the main sweeping jet. This phase lag further enhances both temporal and spatial film cooling surface protection during the sweeping motion.