Large eddy simulation of a swirling kerosene spray flame: A proper orthogonal decomposition and wavelet transform analysis on the flow structure and hydroxyl species field

Abstract

The combustion performance can be promoted by the shear layer, recirculation zones, and precessing vortex cores in the swirling flow field. The swirling flow promotes the mixing between air and fuel, but may also jeopardize the combustion stability. In order to study the interaction between the swirling flow structure and the combustion reaction, large eddy simulation (LES) is employed to simulate the turbulent combustion process of a typical swirling kerosene spray burner. A flamelet generated manifold (FGM) chemistry table built with three-component surrogate kerosene skeletal mechanism is coupled with LES to describe the combustion reaction. The FGM-LES approach is validated by comparing the velocity and temperature statistics against the experimental data. The obtained instantaneous LES snapshots of the kerosene flame are then analyzed using proper orthogonal decomposition (POD) and wavelet transform to investigate the time–frequency characteristics. The influence of swirling flow structures on the combustion reaction field is discussed. The results show that the first POD mode with the highest energy contribution is characterized by a low-frequency signal at 2.46 Hz. The second and third modes correspond to the double helix structure in the flow field, while the fourth and fifth modes correspond to the large vortex core structure in the central recirculation zone. The signals of combustion intermediate product hydroxyl species show higher amplitudes near the 78.62 Hz associated with the second and third modes, suggesting the two modes have a significant influence on the turbulent combustion characteristics of the swirling kerosene spray flame.