Modeling of turbulence in stirred vessels using （建模的动荡在搅拌容器中使用）.pdf

Modeling of turbulence in stirred vessels using large eddy simulation André Bakker (presenter), Kumar Dhanasekharan, Ahmad Haidari, and Sung-Eun Kim Fluent Inc. Presented at CHISA 2002 August 25-29, Prague, Czech Republic © André Bakker (2002) 1 © Fluent Inc. (2002) Introduction • Nature of turbulence: – High Reynolds numbers, chaotic flow, dissipative, diffusive, vortex stretching, energy spectrum. • Objective of turbulence modeling. • Prediction methods and large eddy simulation models. • Multiple hydrofoil impeller system example. • Glass lined vessel example. • When to use LES. 2 Turbulence: high Reynolds numbers Turbulent flows always occur at high Reynolds numbers. They are caused by the complex interaction between the viscous terms and the inertia terms in the momentum equations. Turbulent, high Reynolds number jet Laminar, low Reynolds number free stream flow 3 Turbulent flows are chaotic One characteristic of turbulent flows is their irregularity or randomness. A full deterministic approach is very difficult. Turbulent flows are usually described statistically. Turbulent flows are always chaotic. But not all chaotic flows are turbulent. 4 Turbulence: diffusivity The diffusivity of turbulence causes rapid mixing and increased rates of momentum, heat, and mass transfer. A f