Research On Airflow Convergence Mechanism And Distribution Characteristics Under Multi-column Attachment Ventilation Mode

Column attachment ventilation（CAV）is an air supply method that combines the advantages of displacement ventilation and mixing ventilation.In the large-space air distribution,CAV is not delivered to the personnel occupied zone in the form of a single airflow,but in the form of multiple airflow spreading over the ground.At this time,multiple airflows will converge at the same or different development stages,so that the convergence of multiple ground-attached airflows in a large space cannot be simply superimposed as a single-attachment ventilation jet.As a result,the effectiveness of design method based on conventional single-attachment ventilation jets is decreasing.In response to the above problems,this paper summarized the common column layouts,and found that the double-column and three-column layouts can be used as basic research units.Based on this,numerical calculation models and a scaled-down experimental model were respectively established to study on the ground-attached jet convergence under different geometric boundaries and air supply boundaries in the column attachment ventilation mode.The main conclusions are as follows:As for visualization experiment,the"radial"free diffusion movement occurred in the single-column airflow development area of the column attachment air supply mode,while the two-column airflow inhibited this free diffusion movement and became a"seagull-like"diffusion flow.As for geometric boundaries,when the number of air supply columns increases,the airflow pattern between the two columns changes,and a curved,symmetrical arc-shaped airflow and an asymmetric peripheral arc-shaped expanding airflow began to appear.And as the number of air supply columns increases,these two airflows will interact with each other.When there was only a lateral spacing between columns,as the lateral spacing between the columns increased,the converging flow patterns of the ground-attached airflow can be divided into three types,which were fully converging,partially converging,and non-converging.When there are both lateral and horizontal spacing between the columns,the velocity distribution was"M"-shaped,and the axial velocity was concentrated near the columns.As the horizontal spacing increased,the"M"-shaped velocity distribution became less obvious.As for air supply boundaries,with the influence of the air supply velocity,the axial velocity of the three-column and the double-column airflow convergence are basically the same.The general formula of the axial velocity is similar to that of the single-column airflow.According to the different forms of airflow involved in the interaction,the ground-attached airflow with the full-air outlet mode can be divided into the dominant area of collision airflow,the joint dominant area of collision and convergent airflow,and the dominant area of convergent airflow.With the influence of the air supply velocity ratio(r=u₀₂/u₀₁),high air velocity ground-attached jet deflects low air velocity ground-attached jet.The position of the symmetry axis of the double column was not on the geometric symmetry axis of the double column,but was biased to the side of the ground-attached jet where the air supply velocity was low.And the greater the difference between the air supply velocity ratio and 1,the closer the position was,and the greater the position away from the geometric symmetry axis of the double column.In summary,the convergence of multi-column attachment ventilation can be adjusted through the column geometric boundary and air supply boundary of the column attachment ventilation.The findings of this study provide theoretical and methodological support for the effective design and engineering application of double and multi column attachment ventilation jets.