Nonlinear Dynamic Aalysis of Natural Ventilation in a Two-Zone Building: Part B—CFD Simulations

Abstract

Computational fluid dynamics (CFD) is a widely accepted design and analysis tool for building ventilation. This paper presents a simple method using commercial CFD software to obtain the solution multiplicity characteristics of laminar and turbulent indoor airflows. The method is known as the two-way continuation simulation, which has been developed for identifying multiple solutions in computational fluid dynamics. We consider airflows in a simple two-zone building with four openings, where one of the zones has a constant heat source, modeling the heat or pollutant generation and spread in buildings governed by natural stack forces. Using the new two-way continuation simulation method, we describe the flow variation and physical mechanisms at different heights in the two zones for different Rayleigh numbers. The results show that two steady solutions with the same boundary conditions and building geometry can be obtained step-by-step in the simulation process. Flow multiplicity can also be found as the height ratio of the two zones increases or decreases. As an important physical parameter, the Rayleigh number can also have some significant influences on the flow bifurcation or variation. Compared with conventional CFD simulation, the two-way continuation simulation method can effectively identify the possible existence of multiple solutions of indoor airflows and pollutant spread with different initial conditions. One shortcoming of the two-way method is that it cannot identify unstable solutions.