Direct Numerical Simulation Of Gas-Solid Two-Phase Plane Turbulent Jets

The free shear layer is a typical flow phenomenon which includes transition and turbulence. The plane jet is a type of free shear flow more complicated than the plane mixing layer. Up to now, studies about round and rectangular jets are prolific. However, numerical studies of plane jets, especially the DNS (Direct Numerical Simulation) data which bear profound significances on turbulence research, are considerably few. To the author's knowledge, this dissertation is a rather early study of DNS on gas-solid two-phase plane turbulent jets in mainland.The solving object is a set of governing equations of a flow field with weak compressibility. We also simulate the dispersion characteristic and concentration field of solid particles of various typical sizes in the jet field with one-way coupling method. The numerical schemes of DNS are based on finite difference methods. The fourth-order compact difference schemes with high resolution are applied to discretize the space derivatives, and a low-storage fourth-order explicit Runge-Kutta scheme is used in time marching. We use non-physical exit zones (PML buffer zones) together with Thompson's Non-Reflecting Boundary Conditions to set the boundary schemes. The Characteristic Inflow Boundary Conditions are used at the inflow boundary. We also set the pressure correction term at the outflow boundary. The detailed flow structures uncovered in the numerical results have proven the validity of the above designed numerical methods in DNS of free jets.First, we simulate the time-evolving flow structures in tow-dimensional weak-shearing free jets and the dispersion rules of particles of typical sizes in this field. The computational results expose a vorticity field with a fully symmetrical mode about the jet centerline, in which we capture precisely the rolling-up of spanwise vortexes, the pairing of two vortexes, and the special mixing progress of three vortexes appearing in the weak-shearing free jets. If just judging from the phenomena, we can divide linearly three vortexes' mixing into two consecutive two vortexes' pairing. The vortex thickness after two vortexes' pairing is two times of that of a single vortex kernel, and extends to three time of one vortex's thickness after three vortexes mix. In the statistical results, the mean longitudinal velocity U compares well with the experimental data. U does not reach the self-similar state until x/h=11.5. The mean profiles of Reynolds stresses bear prodigious specialty, i.e. the lateral fluctuations at the centerline are inhibjied strongly and the longitudinal oneshave the tendency of growing continuously, which is induced by the special symmetrical vorticity field.The second part of this dissertation is the DNS study of a two-dimensional gas-solid two-phase strong-shearing plane turbulent jet. Because the symmetrical mode of two free shear layers in the jet is destroyed at x/h=6.0, the vortex street develops in non-symmetrical (sinuous) modes downstream of this station. The typical coherent large scale structures include the single spanwise vortex, the pairing vortexes with same signs, which are similar to the structures in the weak-shearing jet, and the vortex pair composed of two vortexes with opposite signs. The mean velocities compare rather well with the experimental and numerical results of predecessors. The staring points of U exhibiting self-similarity and the symmetrical mode of the vortex street being destroyed almost overlap, both at x/h=6.0. The mean lateral velocity V needs much longer streamwise journey to reach its self-similar state. In this paper, about at the downstream location of x/h=11.5, we can deem that V have got to the self-similar state. Both the linear relationship between the jet half-width δu and the streamwise coordinate x and the predicted inverse-squared relationship between the mean centerline velocity excess and x compare well with the experimental results. The differences only exist in the virtual origin values, which is reasonable due to the unpredictable factors in various n...