Experimental Investigation On Flow And Mixing Characteristics Of Film Flapping Jets

Jets have important application value in equipments such as burners,mixers and reactors.Numerous application practices have shown that the turbulent mixing performance of jets is an important factor affecting combustion efficiency,pollutant emission and reaction rate.Therefore,research on new high-efficiency jets mixing technology has important guiding significance for the development of high-performance marine boiler burners,mixers and other equipments.In this paper,the flow control technology is used to innovatively propose the use of film flapping to improve the mixing performance of the jets with the surrounding stationary fluid.During the experiment,smoke generator,laser,hot wire anemometer and other experimental equipments were used to display the flow field and collect the velocity field data of film flapping jets under different Reynolds number and different film length L.The flow and mixing characteristics of film flapping jets were systematically studied.The main research contents and conclusions of this paper are as follows:(1)Compared with the free jet,the diffusion angle of the jets increases obviously under the action of the film beating,and the obvious pulsation of the film flapping jets can be observed.Furthermore,the experimental results of the velocity decay rate and turbulence of the film flapping jets and the free jet at the centerline and cross section are compared.It is proved that the mixing effect of the film flapping jets on the surrounding stationary fluid is significantly better than that of the free jet.(2)By changing Reynolds number Re and film length L,we find that under the same Reynolds number,the flapping frequency of the film is inversely proportional to the film length.Combining with the motion posture of the film,we find that when the film length reaches 1.5D or more,the flapping effect of the film will present three-dimensional characteristics;furthermore,when the film length is constant,the flapping frequency of the film will gradually increase as the Reynolds number increases.(3)Data acquisition and results analysis of the velocity field of the film flapping jets at different Reynolds numbers and film lengths show that the velocity attenuation rate and turbulence of the film flapping jets increase significantly compared with the free jet,which means that the mixing effect of the film flapping jets on the surrounding stationary fluid around the film flapping jets increases significantly.Further,by comparing the mixing effects of film flapping jets under different film lengths,it is found that the mixing effect of film flapping jets is the most obvious when the film length L=1.25D,which also shows that the effect of film flapping jets does not change linearly with the film length,and this result can provide ideas for subsequent exploration.Therefore,the research on the mixing performance of film flapping jets has important application value for improving the mixing performance of gas boiler burner,mixer and ship air conditioner.By studying the mixing performance of film flapping jets,this paper not only enriches the jets mixing control methods,but also has important application value for the optimization design of green ship technology such as marine boiler burners and mixers.