Research On The Secondary Flow In Three-Dimensional Rotating Fluid Based On Lattice Boltzmann Method

Secondary flow phenomena is often involved in nature, industrial and agricultural production and scientific research field, thus has been attracted much attention. Researching on the movement characteristics of secondary flow, which is the frontier and hot topics in computational fluid dynamics, can not only create economic benefits, but also has strong practical value. The behavior mechanism of the secondary flow, which is closely related to the temperature field, the velocity field, the physical parameters and the geometrical parameters of the gas liquid two phases, is integrating with complex flow phenomena of the multidisciplinary cross. At present, the research on the secondary flow is mostly simulated by the traditional method of fluid mechanics. However, the traditional method of fluid mechanics only consider the macro physical quantity of fluid numerical simulation for some simple multiphase flow phenomenon. It can simulate successfully, but it is helpless when simulating the complex multiphase fluid system. Under the different conditions, the complex multi-phase fluid system will generate three issues:dealing with the numerical simulation of the boundary with great difficulty, determining the state equation ambiguously, tracking interface inconveniently and other ones. Different from the traditional method of numerical simulation, in recent years, the lattice Boltzmann method (LBM) has beem rapidly emerging in the field of computational fluid with significant advantage of processing boundary easily and offering program natural parallelism. Lattice Boltzmann method is a mesoscopic model between macro and micro. At the mesoscopic level, LBM is especially suitable for involving complex interface kinetics and phase transformation of the fluid system, which makes the complex fluid system easy to solve the Navier Stokes equations, phase topological deformation processing, and interface reconstruction. Some scholars have used the lattice Boltzmann method to study secondary flow phenomena. But they are_simulating based on single phase LBM model, and can not track a large number of small, scattered interface. Therefore, it is difficult to capture the details of the particle movement, and can not accurately describe the secondary flow phenomenon.Currently, lattice Boltzmann method has been successfully applied into the multiphase flow field of research, and has developed mature multiphase lattice Boltzmann models such as the color gradient model, pseudo potential model, the free energy model, mean field models and so on. They source from different theoretical backgrounds, and each of them have advantages and disadvantages. Our research group directly introduce the non rational force generated by the particles in the interface region from the angle of free energy, and propose a reliable multi phase LB model. Using the multi phase LB model and considering the boundary of wettability, in this paper, we first establish the thermodynamic consistent multiphase LBM secondary flow model,and established model successfully is applied to simulate fluid roation to produce secondary flow phenomena. Combined with Van der Waals state equation and Peng-Robinson state equation, this model is to achieve agitation of different fluids. In this paper, by a series of numerical simulation, we respectively studied the secondary flow vortex intensity which satisfy the above two kinds of state equation of fluid when rotating generated and the affection of the stirring strength and stirring rod distance and the surface wettability of the cylinder wall to the center position. The results obtained are as follows:1.The selection of stirring force should be appropriate. If the stirring force is too small to form a flat, it can not produce the secondary flow.But the stirring force is not better. If the stirring force is too large, it will make the liquid level too concave, and thus do not have the research value. If the stirring force is in the proper range, The relationship between the secondary flow vortex intensity and the stirring force is monotonically increasing.2.The relationship between the secondary flow vortex strength and the surface wettability of the cylinder is that the secondary flow vortex strength intensity firstly increases with the increase of the contact angle of the cylinder side wall. When the contact angle is about 135 degrees, the peak value of the vortex intensity is reached, then the contact angle is decreased.The secondary flow vortex intensity is affected by the influence of the surface wettability of the cylinder. In Peng-Robinson state equation, the secondary flow vortex intensity first slowly decreases with the increase of the contact angle of the cylinder bottom surface. When the contact angle is more than 120 degrees, the contact angle is decreased, and the minimum value of the vortex intensity is reached when the contact angle is 135 degrees, and then the contact angle is increased. The secondary flow vortex of the fluid, which satisfies the der Waals Van state equation, intensity first increases with the increase of the contact angle. When the contact angle is 140 degree, the peak value of the vortex intensity is reached, then the contact angle is decreased.3.With the increase of the distance from the center of the cylinder to the center of the cylinder, the center position of the two vortex is gradually far away from the central axis of the cylinder, and moves toward the outer surface and the outer surface of the cylinder. In addition, under the two intersection, we also found that a pair of symmetric vortex intensity is weak. And small eddy intensity will be affected by the mixing bar to the axis of the D.The above conclusions not only help us to explain the secondary flow related phenomena in the production life, but also is expected to contribute to the research and application of the two flow.