Particle-laden swirling flow

Application Challenge AC3-12 © copyright ERCOFTAC 2024

Key Fluid Physics

The introduced swirling flows are highly turbulent and as known, the turbulence structure is strongly anisotropic. Moreover, the flow is characterized by a central recirculation region and a flow separation in the pipe expansion. Mostly such kind of flows is not stationary, but exhibits some fluctuations of the vortex core (precessing). This effect also influences the particle behaviour which is manifested in the formation of particle ropes. These are caused by slight fluctuations of the particle-laden primary jet induced by the vortex precession. Eventually these ropes move spirally along the test section wall downward. As a consequence of the locally high particle concentration two-way coupling effects and also inter-particle collisions might become of importance.

Application Uncertainties

The flow geometry is relatively simple and can be accurately specified and discretised. The inlet conditions were measured 3 mm downstream the exit of the inlet tubes so that the variation of the flow during the first 3 mm (i.e. from the exact geometrical exit) can be neglected. In previous calculations, as shown above, the particle size across the central tube inlet was specified according to that provided in Fig. 2 (i.e. no variation). The first measured profile reveals that a spatial variation of the particle size distribution at the exit can be neglected. Possibly however, the mean velocity and the rms values for the different particle size classes might be slightly different. It should be also kept in mind that the measurements were only done for one profile across the test section. Hence any asymmetries of the flow could bias the results.