A laboratory experiment of shear-induced natural ventilation

When the wind direction is parallel to the opening façade, the wind shear near the building opening generates turbulence and entrains air across the opening. This kind of shear-induced ventilation cannot be predicted by the orifice equation because the time-averaged pressure difference across the opening is close to zero. This study uses wind tunnel experiments and the tracer gas decay method to investigate the ventilation rate of shear-induced ventilation. The influences of opening area A, external wind speed U and wind direction on the ventilation rates Q, of single-sided and two-sided openings are systemically examined. The experimental results indicate that the dimensionless ventilation rate, Q* = Q/UA, of shear-induced ventilation is independent of the wind speed and opening area, and the value of Q* of two-sided openings is larger than that of a single-sided opening. In addition, a cosine law was used to predict the ventilation rate of building with two-sided openings under various wind directions, and the results are compared with the prediction of the multizone ventilation model COMIS.

► The dimensionless ventilation rates of shear ventilation for single and two-sided openings are independent of the opening area A and external wind speed U.
► The dimensionless ventilation rate of two-sided openings is larger than that of a single opening for shear ventilation.
► A cosine law was used to predict the ventilation rate of building with two-sided openings under various wind directions.