Unsteady aspects of multi-interacting swirlers using POD analysis

Twin annular premixed swirler known as TAPS by GE has provided an effective solution to generate low NOx combustion by implementing both diffusion and premixed flames. The fuel injector is less susceptible to combustion instabilities owing to its central diffusion flame and eco-friendly due to its radial premixed swirler. To this extent, 2D PIV experiment was conducted on three newly designed triple swirlers to measure their corresponding velocity fields. The swirlers were designed in a way that the inner and intermediate swirlers are axial type, counter-rotating and remained unchanged with three different radial type outer swirlers. The design characteristic swirl numbers of the outer swirlers were 0.5, 1.0 and 1.5, to impose low, medium and intense swirling motion, respectively. The main objective of the current study is to investigate the interaction of the shear layers emerging from the outer swirler with the both inner and intermediate. Air is used as working fluid and experiments were done in confined condition. The study of the mean flow field indicated that the outer swirler dominates the flow field and defines the behavior of the main features such as swirling jet angle, the resultant inner recirculation zone, and the wall stagnation points. Proper Orthogonal Decomposition (POD) analysis showed a wide range of low-frequency modes spread over the entire domain and stated the domination of the outer swirling flow. It was found that an increase in the intensity of the outer swirler contributes to an intensified interaction with the model chamber walls highlighting the significance of the confinement ratio in higher swirl numbers.