An Experimental Investigation of Sweeping Mist Jet Film Cooling With Droplet Analysis

Abstract

Abstract. Sweeping jets, generated by fluidic oscillators without moving parts, offer strong potential for gas turbine film cooling by providing wider coverage and more uniform lateral cooling. Furthermore, mist was injected to provide additional cooling enhancement. This article presents an experimental study on utilizing two-phase (air/mist) flow through a row of passive fluidic oscillators in film cooling applications for gas turbine airfoil cooling. The research focused on two main objectives: (a) measuring the potential enhancement of mist film cooling with sweeping jets and (b) analyzing droplet dynamics. Three blowing ratios (BR = 0.66, 1.28, and 2.40) and two mist ratios (MR = 2% and 10%) were studied. Infrared thermography and E-type thermocouples measured wall temperature, while a phase Doppler particle analyzer (PDPA) was employed. The results indicated that a higher mist ratio of 10% provided significantly better film cooling enhancement along the centerline, with a 76% improvement compared to 40% with a lower mist ratio of 2%. The highest droplet concentration was consistently observed near the upper boundary of the distribution (1.5d–2d). Due to centrifugal forces, larger droplets were pushed to the periphery, while smaller droplets remained near the vortex center and evaporated quickly, resulting in significantly lower droplet density than at the top of the periphery vortex, which coincides with the coolant film upper boundary. The mist-sweeping jets achieved approximately 270% enhancement over steady round-hole mist jets, and over 475% over air-steady jets in the region downstream of 10-hole diameter (x > 10d).