Research On The Characteristics Of Excited Acoustic Field And Spray Based On Karman Vortex Street

Research on impacts of vortex shedding on the thermoacoustic oscillation and spray characteristics in the presence of acoustic field were firstly reviewed. Then test principles and methods involved in this paper were introduced in detail, so were the dynamic pressure measurement system and PDA system.An experimental setup including a long straight square tube was firstly built to investigate the effect of different vortex frequencies and shedding positions on the features of one-dimensional acoustic field excited by vortex shedding which is Karman vortex street generated by flow around a bluff body here in cold condition using the dynamic pressure measurement system and FFT method. Results show that acoustic field excited by vortex shedding consists of acoustic waves with various frequencies and amplitudes. Excited frequency and amplitude of acoustic wave is related to vortex frequency and shedding position. Moreover, excited acoustic wave showed the feature of pure standing wave only under certain vortex frequency.Then the experimental setup was transformed to investigate independent and combined impacts of Karman vortex street and acoustic oscillation on the spray characteristics using the PDA system. The excited acoustic field here is to simulate the fluctuating pressure field of thermoacoustic oscillation. Results show that acoustic oscillation can increase spray droplet velocity and reduce droplet size. Vortex can significantly affect spray development, spray droplet velocity and its distribution; however its effect on spray droplet size is more complicated.Vortex enhanced by acoustic oscillation further affect spray droplet velocity, but its effect on spray droplet size basically remains the same as before.These experimental conclusions provide basics and references for further study of the excitation process of vortex shedding on thermoacoustic instability, and lay foundation for further investigations about characteristics of spray and its combustion in the presence of thermoacoustic instability in industrial burners, which will help to make use of spray to control thermoacoustic instability.