Keywords: air curtains, turbulence, hot wire anemometry, CFD, LES, RANS/LES.

Air curtains are generally a set of vertical or horizontal plane jets used as ambient separator. Most of the articles found in the literature about air curtains are based on experimental work. Furthermore, numerical studies have been centred on the analysis of air curtains used in display cabinets, or the discharge jet produced by the air curtain is given as an inlet boundary condition in numerical simulations of adjacent areas presenting different conditions [1]. However, not one of the works is focussed on the detailed study of the discharge plenum of air curtain used in doorways. Thus, the main object of this paper is to study the discharge chamber geometry and the presence of blades for flow orientation at the exit in air curtains mounted above doors. This analysis is carried out in order to understand their influence on the characteristics of the jet produced.

Studies presented are based on the detailed numerical simulation of the air curtain discharge plenum by means of computational fluid dynamics (CFD) using a symmetry-preserving formulation [2]. To solve turbulence, large eddy simulation (LES) [3], and models that combine Reynolds averaged Navier-Stokes simulation (RANS) and LES are selected (hybrid LES/RANS) [4]. The numerical solutions are compared and the influence of the turbulence model used, boundary conditions and computational domain selected are also investigated. It is found that the superimpostion of velocity fluctuations at the inlet slightly affects the predictions at the air curtan discharge region. However, the outlet boundary condition as well as the size of the computational domain considered downstream air curtain discharge, play a more important role.

Moreover, a set of experiments is carried out in order to determine the actual fluid-flow characteristics of the air curtain prototype studied. The technique used for measuring the velocity and turbulent features of flow is hot-wire constant temperature anemometry (HWA). Measurements are done at the exit of the internal fans (plenum inlet) and at the discharge of the air curtain prototype (plenum outlet) analysed. Experiments reveal that the discharge velocity presents an approximate profile and the turbulence intensity is relatively high.

1

H.K. Navaz, D. Dabiri, M. Amin, R. Faramarzi. "Past, Present, and Future Research Toward Air Curtain Performance Optimization", ASHRAE Transactions, 111:1083-1088, 2005.

2

O. Lehmkuhl, C.D. Perez-Segarra, R. Borrell, M. Soria, A. Oliva. "TermoFfluids: A new Parallel unstructured CFD code for the simulation of turbulent industrial problems on low cost PC Cluster", In Proceedings of the Parallel CFD 2007 Conference, pages 1-8, 2007.

3

K. Mahesh, G. Constantinescu, P. Moin. "A Numerical Method for Large-Eddy Simulation in Complex Geometries", Journal of Computational Physics, 197:215-240, 2004. doi:10.1016/j.jcp.2003.11.031

4

P.R. Spalart, S. Deck, M.L. Shur, K.D. Squires, M.K. Strelets, A.Travin. "A New Version of Detached-Eddy Simulation, Resistant to Ambiguous Grid Densities", Theoretical and Computational Fluid Dynamics, 20(2):181-195, 2006. doi:10.1007/s00162-006-0015-0

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