| Due to the complexity of the internal flow system in the impinging flow field,the linear control,prediction and analysis of the basic characteristics of the flow field are very difficult.Based on the development of non-linear analysis methods and feature information extraction technology,for the study of non-linear behavior in impinging stream mixer,it not only provides a new technical means,but also has great significance for improving impinging stream theory.This paper focuses on the application of Planar Laser Induced Fluorescence(PLIF)technology to measure the concentration field in a two-component layered impinging stream mixer.With the help of the Hilbert-Huang Transform(HHT)method,The implicit information in the concentration signal is extracted and the nonlinear characteristic parameters are defined to characterize the flow characteristics of the mixer,in order to enrich the description of the concentration field of the impinging stream mixer.The specific research work is as follows:In the experiment,the concentration field of the two-component layered impinging stream mixer was measured using PLIF technology.The Empirical Mode Decomposition(EMD)was used to "screen" the concentration signal,and the concentration signal was decomposed into a series of Intrinsic Mode Functions(IMF1 to IMFn),and then the Intrinsic Mode Functions was used as Hilbert transform to obtain the three-dimensional spectrum of the time-energy-frequency distribution of the signal,which is the Hilbert spectrum.The results show that the local energy and instantaneous frequency derived from IMF can present the time-frequency-energy distribution of a complete signal,which is ideal for nonlinear and non-stationary signal analysis.The Hilbert spectrum and Marginal spectrum were obtained by performing Hilbert-Huang transform on the IMF components after EMD.The analysis of the experimental results shows that the concentration signal in the two-component layered impinging stream mixer has a large energy value in the low frequency region and concentrated characteristics,while the energy value in the high frequency region is relatively small and scattered;The Hilbert spectrum and the Marginal spectrum of concentration signals under different operating conditions were compared and studied.It can be found that the continuous increase of the nozzle diameter D and the nozzle spacing L have a certain effect on the change of the concentration signal energy,which shows a trend of increasing first and then decreasing,and the energy peaks at D=10mm and L=3D respectively;while the jet Reynolds number Re continuously changes,the energy of the concentration signal increaseswith the increase of Re.Correspondingly,the variation law of concentration amplitude expressed by the Marginal spectrum also supports this conclusion,and further shows that based on the selection of the appropriate nozzle specifications,appropriately increasing the jet Reynolds number can increase the fluid contact area,effectively promote the mixing of materials,and increase the response effectiveness.In addition,the Hilbert spectrum and the Marginal spectrum at different axial X positions were investigated.It was found that the axial X position kept away from the impinging center,and the concentration signal energy increased first and then decreased,which further verifies the basic principle of the impinging stream.Under different operating conditions,by quantitatively analyzing the IMF energy distribution and its transition in each frequency band of the concentration signal,the energy characteristic value was used to describe the flow pattern change law of the two-component layered impinging stream mixer,and the mixer was divided from the center of the impiging along the radial direction Y into the axial impinging zone,a vortex zone,and a radial impinging zone.It directly reveals the internal law between the concentration signal energy distribution and fluid flow pattern,and provides a powerful quantitative basis for the identification of impinging steam pattern. |
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