Dr. Maarten Vanierschot, Assistant Professor, Mechanical Engineering Technology Cluster TC, campus Group T, KU Leuven, Belgium

Biography: Maarten Vanierschot is an assistant professor at the Mechanical Engineering Technology Cluster TC, campus Group T of KU Leuven. He received a Master’s degree in Electromechanical Engineering from KU Leuven, Belgium in 2002. From 2003 on, he conducted research as a PhD-student at the Division of Applied Mechanics and Energy-conversion on swirling jets and received a PhD in Electromechanical Engineering in 2007. After staying as a postdoc for two more years, in 2009, he became an assistant professor at campus Group T Leuven. He is head of the “Applied Fluid Mechanics and Aero Acoustics” (AFAA) research group and his research interests focus on the measurement and simulation of turbulent flows in general and annular swirling jets in particular.

Research Interest: Fluid mechanics, Turbulent flows, Heat transfer, Experimental flow measurements techniques (LDA, PIV, HWA), Computational Fluid Dynamics, Low order modeling

Speech Title: Coherent Structure Detection in Swirling Jet Combustors Using Unsteady RANS Simulations

Abstract: This paper analyses the capabilities of unsteady Reynolds Averaged Navier Stokes simulations (URANS) to predict the coherent structures found in a swirling jet undergoing vortex breakdown. Recently, tomographic particle image velocimetry experiments of an annular swirling jet at a Reynolds number of 8500 at moderate swirl showed the presence of a double helical structure in the flow field (Vanierschot et al., Physical Review Fluids, 2018). This structure corresponds to the double helix vortex breakdown mode and is rarely observed in turbulent flows. In this study, the same flow topology is simulated using Computational Fluid Dynamics (CFD). Turbulence is modelled using the unsteady RANS methodology with a RNG k-ε turbulence model. The coherent structures in the flow field were analysed using the Spectral Proper Orthogonal decomposition technique. Despite the fact that it is known that steady-state RANS simulations using two-equation isotropic turbulence models have problems in accurately describing swirling flows which are highly anisotropic, this study shows that the unsteady variant was able to predict the large scale flow structures and their associated dynamics reasonable well. In particular, similar to the experiments, a double helical structure was found in the flow field. The structure has windings in the counter-swirl direction and it is wrapped around the central breakdown bubble. To the authors’ knowledge, this study is the first one to show the ability of unsteady RANS to predict not only the presence of the double helix vortex breakdown in the flow field, but also the spatial and temporal structure of it.

Keywords: Unsteady RANS Modelling, Swirling Jets, Double Helix, Vortex Breakdown