Study On The Natural Ventilation Characteristics Under The Action Of Buoyancy Plumes At Different Vertical Height

Natural ventilation utilizes the pressure difference between indoor and outdoor spaces to achieve natural air flow,which can improve indoor air quality,enhance occupants’ comfort and health,and greatly reduce the frequency of using air conditioning and mechanical ventilation systems,thereby reducing building energy consumption and minimizing the impact on the natural environment.Currently,research on the physical processes of natural ventilation has become increasingly important and has provided an opportunity for the development of natural ventilation.By gaining a deeper understanding of the physical processes related to natural ventilation,such as heat transfer and fluid dynamics,it is possible to provide a reference for the design of sustainable building systems.Therefore,promoting research on natural ventilation plays a crucial role in achieving the dual goals of energy conservation and carbon emission reduction.This paper conducts a study using a combination of theoretical analysis,simulation,and salt water model experiments,focusing on the influence of the size of horizontal openings,buoyancy jet flow relative strength and relative height on flow patterns,thermal stratification positions,and opening flow coefficient,providing a reference for actual natural ventilation design.Firstly,salt water model experiments were conducted on scaled-down building models with horizontal ventilation openings to qualitatively study the natural ventilation flow state under the buoyancy jet flow at different vertical heights.By varying the buoyancy jet flow source strength ratio,height ratio,and opening area size,changes in the height and density distribution of the stratification interface were observed.The results showed that under the action of buoyancy jet flow at different vertical heights,the higher the opening area,the higher the height of the stratification interface and the lower the density at the same steady-state time.When the two buoyancy jet flows at different vertical heights had the same reduced acceleration at the interface I,only two layers of buoyancy fluid were formed inside the model space.When all buoyancy jet flow sources were located at the bottom,the position of the interface between the environmental layer and the buoyancy fluid layer was the lowest.Secondly,a simplified mathematical model that preserves the fundamental physical laws of fluid flow was established based on the different flow states observed in the experiments,and the differences between the experimental results and the predictions of the simplified mathematical model were quantitatively analyzed.In addition,by combining the experimental data,limiting conditions with practical physical significance were summarized and simplified mathematical models were optimized.The results showed that the optimized theoretical model predictions matched the experimental results well.Thirdly,based on the optimized theoretical model and experimental results,the effects of various parameters on the natural ventilation performance were analyzed.The results showed that when all buoyancy plumes were located at the bottom,the position of the interface between the environmental layer and the thermal stratification was the lowest,and the increase in interface height was mainly achieved by increasing the effective opening area of the ventilation opening,which increased with the increase of the opening area.In addition,increasing the relative height of the buoyancy plumes also increased the height of the lowest interface.When the lowest interface coincided with a higher buoyancy plume,the height of the lowest interface reached its maximum.Finally,the classic “emptying filling box” model was extended under the non-Boussinesq approximate,and theoretical analysis of key parameters showed that the discharge coefficient decreases as the plume parameter Γd increases.At the moment when it is close to complete emptying,the interface between the buoyancy fluid layer and the environmental layer rises at a noticeably slower speed.When the thickness of the buoyancy fluid layer drops below the steady-state thickness,overshoot phenomenon is observed,and it oscillates asymptotically around the steady-state value until it stabilizes.