Author(s): S. Samuel Li
Linked Author(s): S. Samuel Li
Keywords: Shallow mixing layer Coherent structures Mixing width Smoothed particle hydrodynamics
Abstract: Shallow mixing layer is a prevalent phenomenon of flow that occurs in a shallow confluence when two inflow streams of different bulk velocities meet and interact. This interaction gives immediate rise to unsteady wakes from where the streams initially coincide. The wakes culminate downstream along the interface between the streams and the resultant flow instability transforms them into coherent structures. The coherent structures feature an organised component of vorticity over their spatial extension. This study investigates the flow characteristics of a shallow mixing layer at different velocity ratios (Vr = 1.15,1. 5 and 3) of two parallel streams. The smoothed Particle Hydrodynamics (SPH) method is utilised to simulate the shallow mixing layer. The SPH results are compared with experimental data and empirical relations. A velocity deficit due to the presence of the wake region produced by a splitter plate can be seen from the three cases of Vr values. However, for large velocity ratio (Vr = 3), velocity gradients dominate the velocity deficit area. The SPH results suggest that setting the initial width of the shallow mixing layer to the depth of flow will overestimate the mixing width using the empirical relations. The SPH simulation produces new insights into the pairing process of eddies in the mixing region. This study discusses the effect of core distance and average vorticity of the neighbouring eddies on the pairing process. The Okubo-Weiss parameter is suitable for distinguishing between the near-field and far-field regions of mixing.
Year: 2025