Lobed grilles for high mixing ventilation – An experimental analysis in a full scale model room

In the present study it is shown that jet flows from innovative rectangular air diffusion grilles with lobed ailerons ensure higher mixing in a room than baseline jets from classical rectangular air diffusion grilles with straight ailerons. The experimental approach uses time resolved and classical large scale PIV measurements. The estimated entrainment in the case of the jet issued from the grille with lobed ailerons is found to be greater than in the case of the standard grille with straight ailerons. This way, lobed ailerons might be a solution for the optimization of air diffusion grilles in order to insure more uniform flows and to reduce thermal discomfort and draught sensation. An analysis of the phenomena being at the origin of this performance is proposed. The jet issued from an elementary slot with lobed geometry is compared to the linear slot jet. Based on the elementary slot jets analysis, it is shown that the vortical dynamics in the lobed flow is complex and is governed by large streamwise structures generated by the lobed nozzle lip. This explains the recorded performance in terms of induction and mixing. The special geometry of the lobed grille was not found to generate supplementary noise as the sound pressure levels were recorded for both grilles for different discharge flow rates. Pressure losses were also found to have similar values for both grilles.