Shao Xue-ming

Interactions between two sedimenting particles with different sizes

An improved implementation of Distributed Lagrange multiplier/fictitious domain method was presented and used to simulate the interactions between two circular particles sedimenting in a two-dimensional channel. The simulation results were verified by comparison with experiments. The results show that the interactions between two particles with different sizes can be described as drafting, kissing, tumbling and separating. Only for small diameter ratio, the two particles will interact undergoing repeated DKT (Drafting,Kissing and Tumbling) process. Otherwise, the two particles will separate after their tumbling. The results also show that, during the interaction process, the motion of the small particle is strongly affected while the large particle is affected slightly.An improved implementation of Distributed Lagrange multiplier/fictitious domain method was presented and used to simulate the interactions between two circular particles sedimenting in a two-dimensional channel. The simulation results were verified by comparison with experiments. The results show that the interactions between two particles with different sizes can be described as drafting, kissing, tumbling and separating. Only for small diameter ratio, the two particles will interact undergoing repeated DKT (Drafting, Kissing and Tumbling) process. Otherwise, the two particles will separate after their tumbling. The results also show that, during the interaction process, the motion of the small particle is strongly affected while the large particle, is affected slightly.

Study on the interaction of sedimenting cylindrical particles in still fluid

The sedimentations of two cylindrical particles in three different initial relative positions are numerically simulated using the lattice Boltzmann method. The movement characteristics and particle interactions during their sedimentation are presented and discussed in detail. The results show that, (i) if the two particles are released parallel but separated horizontally, they push away each other, rotate inwards and separate horizontally as they fall; (ii) if the two particles are released parallel but separated vertically, the sedimentation behavior can be classified into three stages: trailing, tumbling and separating; (iii) if the two particles are released perpendicular but separated vertically, the sedimentation behavior can be characterized as: trailing and rotating, touching and sliding. In order to validate our simulation, experiments were also conducted and the results agree well with the numerical ones.

Sedimentation of a single particle between two parallel walls

The sedimentation of a single circular particle between two parallel walls was studied by means of direct numerical simulation (DNS) and experiment. The improved implementation of distributed Lagrange multiplier/fictitious domain method used in our DNS is a promising new way for simulation of particulate flows. The settling behaviors of the particle are presented ranging in Reynolds number from 0 to about 700, which showed that our results for low Reynolds numbers agreed well with that reported before. Nevertheless, for higher Reynolds numbers our results were different from theirs. The long-term mean equilibrium positions in our results were all on the centerline, but not at off-center position as reported before. In order to validate our simulation, experiments were also conducted. The results showed that the sedimenting behavior simulated in this paper agreed well with our experiment result.The sedimentation of a single circular particle between two parallel walls was studied by means of direct numerical simulation (DNS) and experiment. The improved implementation of distributed Lagrange multiplier/fictitious domain method used in our DNS is a promising new way for simulation of particulate flows. The settling behaviors of the particle are presented ranging in Reynolds number from 0 to about 700, which showed that our results for low Reynolds numbers agreed well with that reported before. Nevertheless, for higher Reynolds numbers our results were different from theirs. The long-term mean equilibrium positions in our results were all on the centerline, but not at off-center position as reported before. In order to validate our simulation, experiments were also conducted. The results showed that the sedimenting behavior simulated in this paper agreed well with our experiment result.

RESEARCH ON PARTICLE DISPERSION IN A PLANE MIXING LAYER WITH COHERENT STRUCTURES

The numerical simulation with two-way coupling was performed in a liquid-particle mixing layer and the corresponding experiment study was made. In the process of vortex rolling up and vortices pairing, the particles with differentSt number have a very different pattern of dispersion. The mean velocity of particle withSt=1 is higher than that of the fluid phase on the low-speed side, and lower than that of the fluid phase on the high-speed side. The RMS of particle approaches that of the fluid phase with decreasing particle St number. The RMS in the transverse direction is smaller than that in the streamwise direction. The velocity fluctuation correlation of particle is smaller than the Reynolds shear stress, the “overshoot” phenomenon that the velocity fluctuation correlation of particle is larger than the Reynolds shear stress does not appear. The larger the St number of particle is, the wider the range of the particle dispersion will be. The computed results are in agreement with the experimental ones.

Wavelet analysis of coherent structures in a three-dimensional mixing layer

Wavelet analysis is applied to the results obtained by the direct numerical simulation of a three-dimensional (3D) mixing layer in order to investigate coherent structures in dimension of scale. First, 3D orthonormal wavelet bases are constructed, and the corresponding decomposition algorithm is developed. Then the Navier-Stokes equations are transformed into the wavelet space and the architecture for multi-scale analysis is established. From this architecture, the coarse field images in different scales are obtained and some local statistical quantities are calculated. The results show that, with the development of a mixing layer, the energy spectrum densities for different wavenumbers increase and the energy is transferred from the average flow to vortex structures in different scales. Due to the non-linear interactions between different scales, cascade processes of energy are very complex. Because vortices always roll and pair at special areas, for a definite scale, the energy is obtained from other scales at some areas while it is transferred to other scales at other areas. In addition, energy dissipation and transfer always occur where an intense interaction between vortices exists.

Research on coherent structures in a mixing layer of the FENE-P polymer solution

The evolution of the coherent structures in a two-dimensional time-developing mixing layer of the FENE-P fluids is examined numerically. By the means of an appropriate filtering for the polymer stress, some characteristics of the coherent structures at high b were obtained, which Azaiez and Homsy did not address. The results indicate that adding polymer to the Newtonian fluids will cause stronger vorticity diffusion, accompanied with weaker fundamental and subharmonical perturbations and slower rotational motion of neighboring vortices during pairing. This effect decreases with the Weissenberg number, but increases with b. In addition, the time when the consecutive rollers are completely coalesced into one delays in the viscoelastic mixing layer compared with the Newtonian one of the same total viscosity.

IBM/ICM method for interactions between moving bodies and free surfaces

The IBM/ICM method is developed to simulate the interactions between moving bodies and free surfaces. This method is a combination of Immersed Boundary Method (IBM) and Interface Capture Method (ICM), inheriting the IBM’s capability of using non-body conformal grids to represent the effect of a moving body in the flow by only adding a pseudo body-force in the right side of Navier-Stokes equations, as well as the capability of ICM, i.e. VOF, to capture the interface between two immiscible fluids. In the current paper, the Lagrange-multiplier based IBM method is employed and the volume of fraction (VOF) is introduced as an indicator function to mark the different fluids. The numerical method is validated by the case of high-speed impact by a horizontal circular cylinder, which exhibits a wide range of dynamical response characteristics, i.e. the formation of a cavity and induced pressure waves in the late stages of the cavity collapse, depending primarily on the projectile’s impact velocity.