CFD分析基础边界条件和湍流.pptVIP

In discussing this slide, please remember that there is a tutorial for each of the models mentioned above. General introduction that Fluent CFD software contains a variety of state-of-the-art turbulence modeling options; however, successful predictions of turbulent flows will only result from turbulence modeling decisions based on sound engineering judgement. In this lecture we will identify the issues which must be considered, discuss the turbulence modeling options available in Fluent CFD software, and describe how an engineer should decide how to model turbulent flows. Point out that the governing equations for turbulence are well-known and are the non-linear, unsteady three-dimensional Navier-Stokes equations. Useful to think of the instantaneous velocity in terms of a mean velocity with random fluctuations superimposed. Not only are there fluctuations in velocity but also in pressure, temperature, and scalar variables. The ability to predict the mixing resulting from turbulence is important in a large number of applications. Although governing equations for turbulence are well-known, and even with todays supercomputers, we are only able to solve simple low-Re turbulent flows with DNS and we must find another approach to solve real engineering problems. The RSM attempts to more mechanistically account for the various physical phenomena that contribute to the behavior of the turbulent stresses. The convective and generation/destruction terms are computed directly while the pressure-strain, potentially anisotropic dissipation, and turbulent diffusion terms need to modeled to provide closure. In addtion to the mean momentum equations and pressure equation, the RSM model solves 6 transport equations for the Reynolds stresses and one transport equation for the dissipation rate. Velocity contours show flow acceleration due to boundary layer displacement on side walls. Temperature contours show thermal boundary layer growth as well as contours within insulat