Experimental Study On The Airflow Characteristics Of The Interaction Between Nozzle Jets And Plumes Formed By Interior Heat Sources In Large Spaces Based On Two-dimensional Particle Image Velocimetry(2D-PIV)

How to quantitatively describe the complex airflows in large space buildings,in order to optimize the stratified air-conditioning airflow distribution and create the comfortable interior thermal environment,which is essential and urgent for indoor environment studies.This paper is based on the airflow distribution of the sidewall nozzle air supply for large spaces,focusing on the mixed motion characteristics between jets and plumes in the actual large space buildings.An advanced experimental measurement platform was built to conduct experimental research and theoretical analysis on multiple time-averaged flow fields reflecting the mixed motion between jets and plumes in the laboratory,which provides reference value for practical application of ventilation design and pollution control for nozzle jet air supply in large spaces.In addition,the transient flow characteristics and turbulence structures of a single thermal plume were excavated,which provides experimental data and theoretical support for the comparison and verification of non-steady-state numerical simulation.The main contributions and innovations are as follows:(1)Relying on the thermal environment simulation experiment platform that can realize multi-condition simulation and thermal boundary control,a large-size and high-power 2D-PIV system was built.With the slider system and synchronous control system,the accurate measurement of the complex flow field in the enthalpy-difference chamber was realized.The image stitching technology was used to realize the global flow field presentation with flexible indoor area,clear flow field structure,rich flow information and high spatial resolution.(2)Through large-scale image stitching technology,the high-resolution global flow field data of mixed motion between non-isothermal jets and thermal plumes was obtained.The influence of heat source parameters on the overall airflow motion characteristics in the enthalpy-difference chamber was explored,mainly including the velocity and vorticity distribution in the cross section,the trajectory and velocity attenuation of the jet,and the velocity profiles of two typical heights.Multi-chamber theory was applied to calculate and analyze the effective energy consumption of jets.The above parameters can provide a reference for optimizing the ventilation design of nozzle air supply in large spaces.(3)Based on the continuous snapshot measurement of the instantaneous plume fields,the evolution processes of the instantaneous velocity and vorticity of the plume in a non-ventilated environment were revealed.The distribution and generation of plume vortex structures were analyzed,and the transient flow characteristics of plume at different heights were summarized.The dominant coherent structures of the instantaneous plume fields and the distribution of turbulent kinetic energy at each level were analyzed.The above analysis provides a new idea for the comparative verification of non-steady-state numerical simulation.The research mainly led to following conclusions:(1)There was a wide range of air circulation in the middle of the scale enthalpy-difference chamber.The existence of the thermal plume would limit the development of the jet structure to a certain extent,squeezing the free shear layer of the jet.The dimensionless velocity attenuation along the jet can be divided into free jet area and buoyant plume area.In free jet zone,the velocity attenuation was consistent with the traditional non-isothermal jet theory,while in buoyant plume region,the velocity attenuation obviously became faster,negatively correlated with A_r.(2)The plume structures consisted of a series of rising vortices.The plume vortexes showed unstable self-oscillation.The turbulent kinetic energy was transferred from the large vortex to the small one,which was in line with the theory of energy cascade.The fluctuation periods of Plume Zones 1-3 were estimated to be 1-2 s,3-4 s,and 4-6 s,respectively.The dominant coherent structures of the plume consisted of two vortices in opposite directions.The plume vortex center corresponded to the maximum turbulent kinetic energy.The low-level turbulent structure reflected the highly random nature of the instantaneous plume fields.