An Air Curtain Along a Wall With High Inlet Turbulence

Abstract

A downward blowing isothermal wall jet at moderate Reynolds numbers (1,500 to 8,500) with significant inflow turbulence (ca. 6%) was investigated. The flow configuration is an idealization of the air curtains of refrigerated display cases. Flow visualization using particle seeding was employed to identify the flow field eddy dynamics. Particle Image Velocimetry was used to examine the velocity fields in terms of mean and fluctuating values. These diagnostics showed that the air curtain entrainment was dominated by a large variety of eddies that engulfed ambient air into the air curtain. The velocity fields generally showed linear spreading, significant deceleration and high turbulence levels (ca. 25%). It was observed that the air curtain dynamics, velocity fields and growth were not significantly sensitive to Reynolds number variation between Re=3,800 and Re=8,500. However, at low air velocities (Re=1,500), the curtain was found to detach, leading to a large air curtain thickness and high curtain entrainment.

Air curtain performance: Introducing the adapted separation efficiency

“…The vortex method is used to generate random time-dependent fluctuations of the velocity at the inlet. Turbulence intensity is specified as TI = 6% (as a typical value for ACs [74]) along with a turbulence length scale l = 4.26 mm, which is based on the spacing of the discharge flow rectifier of a commercial AC [78]. The air flow rate supplied by the AC at the discharge is equal to the rate extracted by the AC (recirculation), hence consistent with mass conservation.…”

Air curtains of open refrigerated display cases revisited: a new technique for infiltration rate measurements

“…They have also mentioned that certain operating conditions can result in improved performance of an air curtain [12,13]. Field et al [14,15] studied circulating air curtains of a display case by the PIV visualization. For better understanding of the buoyancy effect, a flat vertical wall was installed in front of the shelves.…”

Numerical Modeling of Doorway Flow Induced by an Air Curtain

“…[3][4][5][6][7][8][9][10] They are also popular for isolating refrigerated display cases in supermarkets. [11][12][13][14][15][16] Other special uses of air curtains include prevention of smoke propagation, 17 reduction of fire oxygenation, 18,19 and contaminant or biological control. [20][21][22][23][24][25][26][27][28][29] Recently, air curtains have been suggested for use in explosive detection portals (EDPs), where a large airflow is used to dislodge particles from a human subject for testing for explosive traces.…”