Flow Structure and Noise Characteristics in Underexpanded Starting Jet
High-speed jets have been widely used in material cutting,surface cleaning and rocket launching.Steady free jet has been widely studied,but transient jet has not received the same attention,so the underexpanded starting jet is the main concern.The large eddy simulation of supersonic underexpanded free jet with nozzle pressure ratio of 2.7 is carried out.The transient flow characteristics are in good agreement with the experimental results.When the jet just ejects from the nozzle,the whole flow field is axisymmetric,and after jet stabilizes,the whole flow field is asymmetric.By analyzing the evolution of vortex structure,the reason why the downstream of jet becomes asymmetric is given.Using the dynamic mode decomposition method,the changes of screech frequency and screech mode during the starting process are studied for the first time.
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