Experimental Study Of Jet Impingement Based On A Sweeping Jet

Impinging jet can significantly increase the heat transfer rate in the impact region,and has been widely used in various applications such as gas turbines,aircraft de-icing and metallurgy.However,when using a traditional steady jet for impingement,the efficiency of the jet is not high due to the limited impact area of the jet.Generated by a fluidic oscillator,sweeping jet is a new type of jet that is temporally continuous but spatially oscillating,which can greatly expand the spatial range of the impinging jet and improve the heat transfer efficiency.In this thesis,particle image velocimetry(PIV)technology was used to experimentally study the flow characteristics of a sweeping jet and its performance when used as an impinging jet.Firstly,a Stereo-PIV experiment was performed with a sweeping jet,and the three-dimensional characteristics of its flow field were studied.On the cross-sectional plane,a pair of counter-rotating vortices was found to develop with the switching of sweeping jet.Then the sweeping jet is applied to impinge on a cylinder.The flow field characterized by the interactions between the jet and the cylindrical surface under different conditions were obtained.At the low Reynolds number case where Re=3.3×10~3,the spreading angle of the oscillating jet was 30°;at a higher Reynolds number 10×10~3,the spreading angle was expanded to 80°.Steady jet impingement experiment was conducted to compare with the sweeping jet.It was found that the steady jet impinged about 5%of the cylinder,while the sweeping jet impingement could cover up to 50%of the cylinder.Compared with steady jet,the higher velocity and turbulence induced by sweeping jet also added to a stronger impingement.Finally,a novel design of master-slave jet actuator that features an adjustable spreading angle sweeping jet to suit different application scenarios was proposed and verified by impingement experiments with cylinders of different diameters.In the process of analyzing experimental data,if traditional methods were used to sample signals based on several locations in the flow field,effective phase information cannot be obtained due to the instability of the sweeping jet.To counter this challenge,phase averaging and proper orthogonal decomposition techniques were used for data processing,and a phase identification method utilizing the POD temporal parameters was proposed to realize the recognition of the flow patterns.