Numerical Study On Flow Characteristics Of Self-excited Sweeping Jet

With the deepening of jet research,the application potential of self-excited jet oscillator in fluid machinery,aviation and other fields has been gradually discovered,and it has technical advantages in friction drag reduction,air noise reduction and microbubble formation.Due to the high complexity of the internal and external flow fields of the self-excited jet oscillator,it is difficult to accurately measure the key data using experimental methods.Especially for the flow analysis of the jet oscillator with different structures under different working conditions,a systematic research system has not yet been formed.The simulation method can make reasonable predictions for the experiment.In this paper,Fluent pre-processing software is used to build geometric models and Fluent mesh is used to divide structural meshes.By means of grid independence verification,Strouhal number（S_r）verification and comparison with the conclusions reported in the literature,it is concluded that the calculation results and the model are reliable.Finally,using the numerical simulation method,the SST k-ωturbulence model is selected to analyze the flow characteristics and key variables of the incompressible fluid in the jet oscillator.The research on the following contents has been carried out concretely.The aspect ratio n of the jet oscillator and the exit angleθare two key structural parameters that affect the sweeping jet.The difference between the aspect ratio and the exit angle will affect the calculation results of the self-excited oscillating jet.This paper discusses the velocity field and pressure field of the jet oscillator under different aspect ratio n and outlet angleθ,and obtains the flow characteristics of the internal and external flow fields.At the same time,it analyzes the oscillator structure with different n andθunder different inlet flow rate V_inlet.The variation law of the oscillation frequency f,the sweep angleφ,the turbulent kinetic energy k along the way,the vortex area S in the cavity and the vortex area S_out in the outer sweeping area.The results show that the oscillation frequency f of the jet oscillator is independent of the type of fluid,and within the allowable range of the structure,when the inlet velocity V_inlet increases,the sweep angleφincreases and the oscillation frequency f increases linearly.The maximum instantaneous velocity and the minimum instantaneous pressure at any point in the cavity appear at the same time.When the aspect ratio n increases,the oscillation frequency f and its peak value increase,the main jet produces secondary oscillation in the chammber,the radial outflow velocity increases,the pressure inside the throat decreases,the sweep angleφincreases,and the radial turbulent kinetic energy k rises,the vortex area of the internal main vortex S and the outer sweep area S_out increases.When the outlet angleθincreases,the effective sweeping area of the external flow field increases,f and its peak value gradually decrease to a critical value,the radial outflow velocity increases,and the internal pressure of the throat remains unchanged,the radial turbulent kinetic energy k increases under high Reynolds number Re conditions,the area of the vortex in the outer sweeping area S_out is basically unchanged.