Analysis of fluctuating characteristics of wind-induced airflow through a single opening using LES modeling and the tracer gas technique

• LES modeling and tracer gas decay method are used to predict ventilation rate.
• Instantaneous velocity and pressure fields around a single opening are analyzed.
• Transient single-sided ventilation rates under five wind directions are analyzed.
• Dominant ventilation mechanisms for different wind directions are discussed.
• Effect of time interval on the prediction of mean ventilation rate is examined.

The turbulent nature of wind significantly complicates the airflow-exchange process at single openings that function as both inlets and outlets simultaneously. For such flow problems, describing the ventilation rate using a constant value is insufficient if the fluctuating intensity is too large. This paper uses a large eddy simulation (LES) model combined with the tracer gas concentration decay method to investigate fluctuating ventilation characteristics through a single opening under various approaching wind directions. The numerical method is validated against a field measurement of single-sided ventilation rates. Results show that wind direction (which characterizes the external airflow pattern) greatly influences the airflow exchange at a single opening. The ventilation rate is relatively steady for a windward opening and shows more unsteadiness for a lateral and a leeward opening. The airflow-exchange process is mainly driven by the mean flow at the windward opening and is dominated by the turbulent flow at the lateral opening. The findings from this study imply that the turbulence-induced component of single-sided ventilation rates should always be considered, especially for non-windward openings.