Direct Numerical Simulation Of Gas-Solid Two-Phase Plane Mixing Layer

A computational study of spatially evolving two-dimensional plane mixing layer has been performed using direct numerical simulation(DNS). Up to now, studies about plane mixng layer using large eddy simulation(LES) are prolific. However, numerical studies of spatially evolving plane mixing layer using DNS are considerably few.Based on the thoroughly review and summary in the research status of two phase turbulent structures in mixing layer near thirty years, the thesis is initiated the study of the two-dimensional particle laden plane mixing layer flow by DNS and experimental verification. It is yielded some creative achievements with important theoretical significance and engineering application value.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 plane mixng layer 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 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 plane mixing layers.First, we simulate the time-evolving flow structures in spatially evolving plane mixing layer in the inflow without forcing and the dispersion rules of particles of typical sizes in this field. there are two types of computational condition. One is the initial longitudinal velocity ratioU1/U2= 2:1, Reynolds number based on the initial longitudinal velocity difference U1-U2= U and the initial momentum thickness is 176; the other one is U1/U2 = 5:1 ,Reynolds number based on U and 0 is 664. The computational results expose a spatially evolving vorticity field, 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 plane mixing layer. 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 flow field statistical results, the mean longitudinal velocity U compares well with the experimental data. U does not reach the self-similar state until The mean profiles of Reynolds stresses bear some specialty, i.e. the longitudinal fluctuations intensity shows a double hump characteristic. The longitudinal fluctuation intensity at the centerline no longer shows a strong growth downsteam, which is resulted from vortexes' pairingprocess. The characteristic of curves of Reynolds stressU is the same as this in the experiment, at the same time, the greater width and greater highness of the two-dimensional plane mixing layer, when compared with experimental data in the figure, which was seen in the lateral Reynolds stress profile, because of the absence of bypass effects of the spanwise component.The second part of this dissertation is the DNS study of a two-dimensional gas-solid two-phase plane mixing layer in the inflow with forcing. The effects of inflow forcing on two-dimensional plane mixing layer has been importantly studies. Because of inflow forcing on the mixing layer, vortexes are more quickly rolled up, moreover, the positions of rolling-up vortexes shift upsteam. At the same time, inflow disturbance inhibit the the pairing process of spanwise vortexes. In the study of this dissertation we capture precisely the phenomena w...