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Abstrakt

The collision of plane jets between ceiling-mounted active chilled beams is studied in the present paper. Draught problems are often caused by the deflection of an attached ceiling jet downwards into the occupied zone. As computational fluid dynamics is utilized, a correct simulation of these jets is important for the estimation of thermal comfort. RANS (Reynolds-averaged Navier-Stokes) simulations tend to overestimate the maximum flow velocities and the thermal discomfort in the occupied zone. In order to improve the prediction, LES (large-eddy simulation) models are studied in comparison with RANS using different turbulence models. Subgrid-scale turbulence modeling is based on dynamic Smagorinsky or turbulence kinetic energy equation models. The desirable symmetric flow state was found to be negatively stable with LES when applying non-turbulent inlet boundary conditions. As a remedy, turbulent time-dependent flow distributions are applied. Simulations are made using the OpenFOAM 1.5 -code. The beams were installed in a laboratory test room and the flow pattern between the units was measured for validation. The flow pattern after the collision of the jets was found to be fluctuating.

Referanser

[1] Brockmann T., Method of Large Eddy Simulation Applied to Recirculating Ventilation Flow in a Room, Master\'s thesis, Department of Applied Mechanics, Espoo, 2009

[2] Germano.M, Piomelli U., Moin P., and Cabot W.H., Large Eddy Simulation: A Dynamic Subgrid-scale Eddy Viscosity Model, Physics of Fluids, Vol. 7, pp-1760-1765, 1991.

[3] Lilly D.K., A Proposed Modication of the Germano Subgrid-scale Closure Method, Physics of Fluids, Vol. 4, pp.633-635, 1992.

[4] Piomelli U. and Liu J. Large-eddy simulation of rotating channel ows using a localized dynamic model. Physics of Fluids, Vol. 7, pp. 839-848, April 1995.

[5] OpenFOAM 1.5 source code, OpenCFD, 2008.





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