Simulation of air flow distribution in rooms by a systemic approach.
S. Soares, J.C. Laborde, S. Domenech, P. Floquet, Tracers and tracing methods 2001, 29-31/05/2001, Nancy (France).
In order to achieve a satisfactory level of hygiene and comfort in premises and to assess the pollutant transfers, it is necessary to control the air flow distribution. The research on air distribution in rooms involves full-scale experiments, scale-model experiments and Computational Fluid Dynamics (CFD) tools. An ntermediate approach between predictive numerical simulation and experimental determination of aerodynamic parameters is the systemic approach.
The paper proposed presents the main features of the IDTS code recently developed and based on the principles of the systemic approach. A model is built from a combination of elementary systems representing basic flows as piston, mixing flow, recirculation, short circuiting; each elementary systems is characterized by specific parameters such as the residence time and the
volume of the unitary system. The adjustment of the model is derived from the comparison of the responses to a signal injected into the model with a tracer emission realized in the room inlet; these responses depend on the internal fluid flow pattern. The difficulty consists on finding quickly the adjustment the most representative and the associated parameters. The code IDTS consists on two main subroutines, the functions of which are described: a subroutine in
order to solve the algebra differential equations characterizing the unitary systems, and a subroutine in order to optimize the structural adjusment design satisfying some defined numerical and physical constraints.
Furthermore, the computational tool has been tested from a ventilated laboratory enclosure (40 m 3 volume) where it is possible to obtain different air flow and residence time distributions by changing the blowing and exhaust openings positions. Helium stimulus corresponding to pulse or continuous release is realized in order to characterize the air flow and to reproduce an accidental emission of pollutants. The helium concentrations have been monitored at different points and at the exhaust duct of the test enclosure. The experimental
results are then analysed and compared with the IDTS identifications.
The IDTS code thus constitutes a computer-aided design tool of flow models to improve the knowledge about the gaseous transfers in a ventilated indoor space. So, a preliminary qualification from several experimental data has been achieved and is quite encouraging.
This work has been done in collaboration with the "laboratoire de génie chimique de Toulouse, CNRS, et l'INP-ENSIGC de Toulouse.