Biomedical subjects

Jianren Fan

Publications and source records attributed to Jianren Fan.

2 recordsLinked to original sources

PubMed2004

Direct numerical simulation of a near-field particle-laden plane turbulent jet.

The present study investigates the gas-particle two-phase flow in the turbulent plane jet by solving the two-dimensional and compressible flow fields numerically using direct-numerical-simulation technique. The flow fields are spatially developing, but we focus our study on the evolution of coherent vortex structures and dispersion patterns of particles in the near field at different Stokes numbers. The initial symmetric mode of flow changes its shape to the asymmetric mode after about three convection periods as the flow moves downstream. The concessive paring processes between two and three vortex structures are observed. The predicted mean velocity profiles show self-similar behavior and coincide well with previous experimental data. The profiles of turbulent intensity and Reynolds shear stress also display self-similar characteristics in the further downstream regions. The local-focusing phenomena of particles occur in the quasicoherent dispersion structure of particles. The higher density distribution at the outer boundary of large-scale vortex structure characterizes the dispersion pattern of particles at the Stokes numbers of order of unity. Furthermore, these particles disperse largely along the lateral direction and show the nonuniform distribution of concentration. For the particles at the Stokes number of 0.01, the dispersion along the lateral direction is considerable due to the small aerodynamics response time, but the particles are distributed evenly in the flow field. Particles at the Stokes numbers of 10 and 50 disperse much less along the lateral direction with the even density distribution. These results support the previous conclusions on the dispersion of particles in the free shear flows.

Journal Article↗

PubMed2003

Modulation on coherent vortex structures by dispersed solid particles in a three-dimensional mixing layer.

Large-scale vortex structures and their effects on the dispersion of particles in turbulent free shear flows are very important in many industrial applications, such as combustion, pollution control, and materials processing. In order to understand large-scale vortex structures and particle dispersion in depth, as well as their interaction effects, a two-way-coupled three-dimensional mixing layer laden with particles at a Stokes number of 5 initially located in the upper half region is studied numerically. A pseudospectral method was used to directly simulate the flow fluid, and the Lagrangian approach was used to trace particles. The concept of computational particles is introduced to vary the mass loading of particles. The momentum coupling effect introduced by a particle approximates to a point force. The simulation results show that coherent structures are still dominant in the mixing layer, but the flow dynamics and particle dispersion are modulated. The length of large-scale vortex structures is shortened and the pairing is delayed. Higher mass loading results in lower energy of the fluid in the phase of Kelvin-Helmholtz rolling up, while in the pairing process of large-scale vortex structures, the energy of the fluid increases as the mass loading increases. Higher mass loading also leads to larger mixed fluid thickness and Reynolds stresses of the flow. In addition, the particle dispersion along the transverse direction differs from that along the spanwise direction, which indicates that the effects of the addition of a particle on the spanwise large-scale vortex structures are different from those on the streamwise large-scale vortex structures.

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