Study On Impinging Zone Of Vertical Wall-attached Jets

Good air distribution creates comfortable and healthy environment for indoor occupants and industrial manufacture,and achieve the purpose of saving energy consumption.In order to meet the above requirements,it is necessary to design the indoor air distribution reasonably.Our research group put forward a new air distribution form based on the traditional air distribution—vertical wall-attached jets.The principle is to arrange the air supply inlet on the top of the room,closing to the vertical wall.The jet attaches to the vertical wall under the Coanda effect and Extended Coanda effect.It flows downwards and then impinges the floor,forming an air lake for ventilation.Attachment ventilation has advantages of the flexible air inlet layout,no occupation of occupied zone,high air quality and low energy consumption.Our group has established a relatively complete set of attached jet air supply theory and design system based on years of research.The vertical wall-attached jets can be divided into vertical wall attached zone,impinging zone and horizontal air lake zone.Previous studies on the vertical wall-attached jets mainly focus on the vertical wall attached zone and the horizontal air lake zone,while the air flow characteristics of the impinging zone and its impact on the horizontal air lake still need to be further studied.The impinging region is the key zone where the attached jet separates,deflects and forms an air lake.This article focuses on the jet flow characteristics of the impinging region.In order to explore the air flow characteristics in the impinging region,this paper establishes the mathematical model for predicting the flow characteristics in the impinging region of vertical wall-attached jets based on the theory of fluid mechanics.The effectiveness of the mathematical model is verified through the previous experiments,and makes dimensionless analysis on the main factors such as the air supply speed and air supply height.The main findings are as follows:Firstly,the three significant characteristics of the impingement region are large pressure gradient,corner vortex motion and boundary layer separation,which cause the jet to decelerate,separate,deflect and accelerate when it flows through the impingement zone,and finally form adhesion with the horizontal wall again.Secondly,the definition of separation point was presented and the calculation model of separation point and reattachment point is established.The correlation of separation point position was determined as h/b=11.8（H/b）^2/3（Re）^-1/3 by dimensional analysis and data fitting.The correlation is valid when 0.5<（H/b）^2/3（Re）^-1/3<1.2.The position of reattachment point is confirmed to relate to separation point,which can be expressed as h/b=1.46l/b in the range of（H/b）^2/3（Re）^-1/3 ≤ 0,and h/b=1.58l/b in the range of（H/b）^2/3（Re）^-1/3>0.5.The（H/b）^2/3（Re）^-1/3 is an important parameter that characterizes the attachment characteristics of the attached jet.According to the properties of flow field,vertical wall-attached jets can be divided into three types:incomplete vertical wall-attached jets,fully vertical wall-attached jets,and strong vertical wall-attached jets.In addition,the flow field of vertical wall-attached jet under circular corner is studied.The results show that the arc corner can effectively suppress the jet separation and eliminate the vortex in the impact zone.The jet kinetic energy loss can be reduced by more than 23%after the circular corner with relative dimension R/b=9.The circular corner can extend the range of the horizontal air lake,so as to improve the efficiency of the vertical wall-attached jets.The results show that the Reynolds number Re,the height H/b and the dimensionless gap s/b between the inlet and the wall have little influence on the improvement of the flow field in the impinging region.The key factor is the dimensionless size R/b of the circular corner.Finally,the practical application of arc deflector in vertical wall-attached jets is analyzed,and the deflector form suitable for vertical wall-attached jets is proposed:90 0 Arc shape,dimensionless size R/b=9.