Large eddy simulation of optimized air curtain separation via secondary co-flowing jets

Unconditioned air infiltration through frequently used entrance doors can degrade building energy performance, indoor air quality, and thermal comfort. Air curtains mitigate these effects and are also critical in smoke and dust control, cleanrooms, and cold rooms. Their performance is commonly expressed as separation efficiency, which depends on jet dynamics and entrainment. While most studies consider single-jet air curtains, this work investigates secondary co-flowing jets as a design strategy to reduce entrainment and enhance separation efficiency. Large eddy simulations (LES), validated against a dedicated particle image velocimetry (PIV) dataset of plane turbulent impinging co-flowing jets, assess the influence of key jet parameters: velocity ratio (R), secondary-jet width (W_s), and inter-jet spacing (d). The results indicate that incorporating secondary jets under suitable discharge conditions increases infiltration-based separation efficiency by up to 5.4% without compromising the combined infiltration–exfiltration metric; the latter can also improve by up to 3%. Given baseline efficiencies of 86.2 % (infiltration) and 78.7% (combined) for an optimized single-jet curtain, these gains are significant.