Large-Eddy Simulations of Wind-Driven Cross Ventilation, Part1: Validation and Sensitivity Study

Abstract

Natural ventilation is gaining popularity in response to an increasing demand for a sustainable and healthy built environment, but the design of a naturally ventilated building can be challenging due to the inherent variability in the operating conditions that determine the natural ventilation flow. Large-eddy simulations (LES) have significant potential as an analysis method for natural ventilation flow, since they can provide an accurate prediction of turbulent flow at any location in the computational domain. However, the simulations can be computationally expensive, and few validation and sensitivity studies with respect to simulation parameters such as grid resolution and boundary conditions have been reported. The objectives of this study are to validate LES of wind-driven cross-ventilation and to quantify the sensitivity of the solution to the grid resolution and the inflow boundary conditions. We perform LES for an isolated building with two openings, using three different grid resolutions and two different inflow conditions with varying turbulence intensities. Predictions of the ventilation rate are compared to a reference wind-tunnel experiment available from literature, and we also quantify the age of air and ventilation efficiency. For the cross-ventilation case modeled in this paper, the prediction of the mean ventilation flow rate is very robust, showing negligible sensitivity to the grid resolution or the inflow characteristics with the maximum error of 1.9 and 1.3% for each sensitivity study. However, a sufficiently fine grid resolution is required to obtain accurate predictions of the detailed flow pattern and the age of air as they show comparably larger errors of 10 and 20% in the grid sensitivity study, and the standard deviation of the instantaneous ventilation rate is affected by the turbulence in the inflow condition with showing 44% difference.

Large-Eddy Simulations of Wind-Driven Cross Ventilation, Part 2: Comparison of Ventilation Performance Under Different Ventilation Configurations

“…This section first provides a summary of the simulation set-up presented in Part 1 of this study (Hwang and Gorlé, 2022), including the governing equations and discretization methods, the computational domain and mesh, the boundary conditions, and the quantities of interest. Subsequently, we introduce the additional ventilation configurations that are considered in this paper.…”

“…This section briefly summarizes the inflow and boundary conditions, which are identical to those used for the simulations in Part I of this study (Hwang and Gorlé, 2022). For the inflow condition, we combine a divergence-free of a digital filter method (Xie and Castro, 2008;Kim et al, 2013) with a gradient-based optimization technique to obtain the desired turbulence characteristics at the building location (Lamberti et al, 2018).…”

Large-eddy simulations to define building-specific similarity relationships for natural ventilation flow rates

“…The first challenge is the validation of CFD predictions of the complex flow phenomena that occur during combined buoyancy- and wind-driven natural ventilation in an urban environment. To date, validation of CFD results for natural ventilation has primarily focused on wind-driven ventilation processes, considering both small-scale (Adachi, Ikegaya, Satonaka, & Hagishima, 2020; Hirose, Ikegaya, Hagishima, & Tanimoto, 2021; Hu, Ohba, & Yoshie, 2008; Hwang & Gorlé, 2022a, 2022b; Murakami, Ikegaya, Hagishima, & Tanimoto, 2018; Ramponi & Blocken, 2012; Shirzadi, Tominaga, & Mirzaei, 2020; Tominaga & Blocken, 2016; van Hooff, Blocken, & Tominaga, 2017) and full-scale (Jiang & Chen, 2002; King et al., 2017; Larsen, Nikolopoulos, Nikolopoulos, Strotos, & Nikas, 2011) experiments. Buoyancy-driven ventilation has received comparatively less attention, possibly because the flow is more challenging to model.…”