Spray response on a model prefilmer under unsteady airflows of various frequencies

Abstract

An appealing concept for jet engine combustors is the Lean Premixed Prevaporized (LPP) combustor, which operates at high pressures. The low NOx emissions achieved by lean combustion are one of the targets for modern aircraft engines. However, these types of combustors can introduce thermoacoustic instabilities that can potentially damage the engine and reduce its lifespan. Since the potential instabilities on the fuel spray characteristics, i.e. the spray mass flux, can affect the flame stability, the need arises to investigate the spray response under an unsteady airflow. For this study, a model prefilmer was experimentally investigated to produce a two-dimensional droplet flow without swirl flow. An acoustic forcing in the range of 100–500 Hz was introduced into the airflow, characterized by a hot wire Constant Temperature Anemometry (CTA) setup. Droplet characteristics, namely the droplet diameter distribution and velocity, were determined using a Phase Doppler Anemometry (PDA) setup, while the acquired data were phase-averaged in one period of the airflow oscillation. The influence of the excitation frequency and the air-to-liquid ratio (ALR) on the spray was studied: the spray responded to the acoustic excitation and therefore critical performance parameters, such as the spray mass flux, oscillated indicating potential problems regarding the flame stability.

Analysis of the thermo-acoustic response of an aero-engine injector using compressible LES

“…Another possible source of deviation that is not accounted for in the present LES is the possible influence of acoustic excitation on the spray characteristics. In particular, the airblast atomization process assisted by the shear caused by can be affected by acoustic fluctuations (Christou et al, 2022;Ahn et al, 2018). Under such circumstances, the frequency response of the atomizer would be manifested as equivalence ratio fluctuations and have an influence on the overall spectrum of the flame response.…”