Effects of velocity ratio and inflow pulsations on the flow in a T-junction by Large Eddy Simulation

Abstract

Large Eddy Simulations (LES) of the flow in a T-junction are performed and analyzed in terms of mixing quality, secondary structures and flow modes. Different mass flow ratios between the two inlet branches are applied and strong pulsating inflow conditions are considered in order to simulate engine-like conditions. The mixing quality is assessed by using several mixing parameters. For steady inflow conditions, it is found that the mixing quality depends on the mass flow ratio. For cases where the branch jet impinges on the opposite pipe wall, the largest turbulence intensities and mixing qualities are observed. Furthermore, the distribution of the mean concentration is dependent on the evolution of secondary structures, which also depend on the mass flow ratio. Flow pulsations are found to affect the mixing quality depending on the pulsation frequency. The spatial mixing quality is not necessarily enhanced by the pulsations. The flow structures are attributed to a Kelvin–Helmholtz instability due to the strong shear layer and vortex shedding past the branch jet. The normalized frequency of the vortex shedding is dependent on the mass flow ratio. Dynamical Mode Decomposition (DMD) is applied in order to investigate the spatial shapes of the flow modes. It is found that DMD is able to capture the vortex shedding mechanism even for the pulsating cases.