Моделирање и нумеричке симулације вихорних струјања

Abstract

Вихорна струјања су веома присутна у техничкој пракси...

Swirling flows are very common in technical practice. Flows in turbomachinery and rotating systems, flows in pipelines after local resistances, flows of air in cyclones and combustion chambers are just few examples of swirling flows in technical practice. Turbulence structure in swirling flows are highly inhomogeneous and anisotropic. In most cases turbulent models based on Boussinesq, linear eddy viscosity assumption, give poor results. That is specially pronounced in case of Rankine type profile for circumferential velocity. Reynolds stress models give better results in prediction of swirling flows, but their usage in complex geometries are very demanding from the viewpoint of solution convergence and time of calculation. In this thesis main accent of research is on numerical simulations of swirling flows by use of various turbulent models, and on theoretical analysis of the models and numerical methods which are used for computations. An open-source software OpenFOAM was used for all computations. Due to openness of the OpenFOAM code, it’s possible to analyze the way of implementation of various mathematical models. Based on the code analysis, Speziale-Sarkar-Gatski (SSG) Reynolds stress model was implemented in OpenFOAM code. Also, some additional postprocessing tools and applications were created and implemented in the code. Two problems are considered: axisymmetric swirl flow in long circular pipe with Rankine profile of circumferential velocity, and three-dimensional swirl flow in the pipe behind axial fan. In first problem, swirl generator wasn’t considered, and experimental results in one cross-section were used as boundary condition at the inlet. As a validation tool for numerical computations, experimental results in other cross-sections were used. Several turbulent models were tested on this problem. From class of two equation models k-", RNG k-", Launder-Sharma k-" and k-! SST models were used, while from Reynolds stress models class Launder-Reece-Rodi (LRR), Launder-Gibson (LG) and SSG model were used. It was shown that all two-equation models give poor results, both for profiles of mean velocities, and for turbulent kinetic energy. Reynolds stress models give better results for mean velocity profiles...