Two-fluid LES and RANS modeling of sudden-expansion gas-particle flows

- A two-phase SGS energy equation model for two-fluid LES is proposed.
- The LES instantaneous results show detailed gas and particle flow structures.
- The RANS-USM modeling cannot give the detailed flow structures.
- 2-D LES results are better than the RANS-USM modeling results.

Sudden-expansion gas-particle flows are widely encountered in fluid and thermal engineering and are typical cases for basic studies. Both two-fluid large-eddy simulation (LES) and Reynolds averaged Navier-Stokes (RANS) modeling using a unified second-order (USM) two-phase turbulence model are studied in this paper. The advantage of LES is showing the detailed flow structures and improving the simulation results. For LES most of investigators adopt Eulerian-Lagrangian (E-L) LES approach, in which the widely used are Smagorinsky eddy-viscosity model, Germano dynamic eddy-viscosity model and Kim's SGS energy equation model for single-phase flows and there are no particle SGS stress models. Some researchers proposed gas-phase SGS stress models accounting for the effect of particles in E-L LES. A few investigators proposed particle SGS stress models for two-fluid LES of gas-particle flows, however the particle SGS stress models are simply imitated from the gas SGS stress model, and the interaction between gas and particle SGS stresses is not taken into account. In this paper a kgs-kps-kpgs two-phase SGS stress model for two-fluid LES of gas-particle flows is proposed to simulate sudden-expansion gas-particle flows. Simultaneously, The USM-RANS modeling was made for sudden-expansion gas-particle flows. Also, measurements were made to validate both LES and RANS modeling results. It is shown that LES can reveal the detailed flow structures and surely in most regions of the flow field make some improvements over the USM-RANS modeling.

LES-predicted two-phase instantaneous streamlines.252