| As a mechanical cooling equipment with low energy consumption and high efficiency,ceiling fans can effectively promote indoor air circulation,improve the air velocity around the human body,strengthen the convective heat transfer,improve the thermal comfort of human body.At present,the researches on ceiling fans mainly focus on the velocity distribution in the airflow core area of the ceiling fan flow field and the velocity influence on human comfort.Few people study the airflow characteristics in the wall jet zone outside the airflow core area.However,in actual use,most indoor areas are outside the airflow core area of the ceiling fan.At the same time,the popular HVLS(High Volume Low Speed)fan overturns people’s traditional ideas in recent years.The main feature of the fan is that the wind speed is not high in the airflow core area,while in the wall jet area,compared with the traditional ceiling fan,it can form thicker and more uniform air flow within the range of human activities.People can also feel the soft and comfortable wind formed by the ceiling fan outside the range of the airflow core area.Therefore,this paper takes the flow field of HVLS fan as the starting point to study the airflow distribution characteristics in the wall jet zone of the ceiling fan flow field.The flow field formed by ceiling fan is a special impinging jet.Firstly,this paper summarizes the airflow characteristics and rules in different zones of impinging jet,and makes a comparative analysis with the airflow characteristics of ceiling fan,so as to provide a theoretical basis for further research on the airflow laws in the wall jet zone of ceiling fan flow field.Secondly,the impinging jet and ceiling fan flow field were numerically simulated by Fluent,and the accuracy of the numerical model was verified by comparing with the experimental measurement results.Then the velocity distribution of the traditional ceiling fan flow field and the HVLS fan flow field is measured,and the experimental conditions of the ceiling fan flow field are obtained,so as to make experimental preparation for further verifying the accuracy of the theoretical formula.Finally,the simulation results of impinging jet and ceiling fan flow field in different working conditions were compared and analyzed,the theoretical formula was revised,the flow law of ceiling fan flow field was summarized,and the velocity distribution of traditional ceiling fan flow field and HVLS fan flow field in the wall jet zone was predicted.As for the study on the velocity distribution in the wall jet zone of impinging jet under different outlet conditions,the simulation results between impinging jet under different working conditions and between impinging jet and ceiling fan flow field in the wall jet zone are mainly compared and analyzed.Then,the calculation formula of the peak velocity and characteristic thickness of impinging jet is revised to apply to the ceiling fan flow field.The simulation results show whether the outlet flow is uniform or rotating.It has no obvious effect on the dimensionless velocity distribution in the wall jet zone.It is also shown that When the ceiling fan operates under the influence of the limit of the far wall and ceiling,the dimensionless velocity distributions at different radial distances in the wall jet zone show a good self-similarity,which is consistent with the impinging jet.For this case,the dimensionless velocity distributions in the wall jet zone can be predicted by Glauert wall jet theory.As for the study on the velocity distribution in the wall jet zone of the ceiling fan flow field under different room sizes,the simulation results of the distance between the ceiling fan center and the wall(L),the distance between the ceiling fan and the ceiling(C)and the installation height of the ceiling fan(H′)are mainly compared and analyzed,and the velocity distribution in the wall jet zone of the ceiling fan flow field under different changing conditions are summarized.When C is greater than 0.5 D′(D′is the diameter of the ceiling fan),and L is greater than 3 D′,the revised peak velocity formula can be used to predict.When C is greater than 0.5 D′ and L is greater than 4 D′,the revised characteristic thickness formula can be used to predict.When C is greater than D′,L is greater than 6 D′,and H′ is greater than 2 D′,the Glauert wall jet theory can be used to predict the dimensionless velocity distribution in the wall jet zone.Then,the revised formula was used to predict the velocity distribution in the wall jet zone of the traditional ceiling fan flow field,and the dimensionless velocity distribution of Glauert wall jet theory was corrected by Gaussian error function to reduce the velocity prediction error in the area above the characteristic thickness.Finally,the revised formula is used to accurately predict the velocity distribution and effective coverage of 1.5 times fan diameter in the wall jet zone of HVLS fan flow field.In practical engineering,after simple measurement according to different room conditions,the revised formula can be used to predict the velocity distribution in the wall jet zone of ceiling fan,which can provide reference for engineering design and engineering installation. |
PDF Full Text Request