A Computational Investigation of Wall-Film Formation by an Impinging Liquid Jet in Crossflow

Accurate fuel injection modeling remains of critical importance to the simulation of gas turbine engines as the predicted spray structure dictates fuel-air mixing, combustion, and emissions in the combustor. The prefilming airblast atomizer relies on the formation of a thin conical sheet of fuel, which breaks up due to its interaction with the counter-swirling airstreams. Recent x-ray imaging performed at Argonne National Laboratory’s Advanced Photon Source of a prefilming airblast atomizer revealed the formation of a frothy film, which is comprised of both liquid and bubbles. This finding challenges the inherent assumption for existing spray models, which assume that the film is only comprised of liquid fuel, and motivates the detailed investigation of the film formation process. To investigate the physics governing the impingement of a liquid jet in crossflow on a plate, a computational study was carried out. Large Eddy Simulations (LES) coupled with an algebraic volume-of-fluid (VOF) approach were performed to model a liquid water jet interacting with a subsonic crossflow and subsequently impinging on an aluminum plate. For the condition studied, a grid convergence study revealed that a minimum cell size of 25 μm was sufficient to adequately resolve the jet-wall interaction and film formation process, with good agreement with the x-ray measurements. These simulations also predicted the formation of bubbles within the film due to the entrainment of air. The influence of adhesion on the film characteristics and bubble distribution was explored using two different contact angles representing water on polished and unpolished aluminum plates. Although an increase in contact angle was not observed to affect the average film thickness, the lower interfacial tension reduced the number of bubbles that were formed, but increased the average size.