Experimental investigation on flow characteristics of compressible oscillating jet

Abstract

An experimental study was performed to investigate the characteristics of a self-sustained oscillating jet emitted from a double feedback channel fluidic oscillator under high pressure inlet conditions. The working fluid was N2 gas from a portable liquid nitrogen tank. The pressure, temperature, and flow rate were measured, and z-type schlieren visualization was performed to study the high-frequency oscillating jet at nozzle pressure ratios (NPRs) of 4-16. A proper orthogonal decomposition (POD) technique was performed on schlieren images, and a Fast Fourier transform was performed on time coefficients of POD modes to calculate the frequency of oscillations. The results show that for the examined NPRs, the frequency of the oscillating jet is independent of the pressure and flow rate, which contrasts with previous studies. However, the flow behavior varies when changing the NPR. The frequency did not increase with increasing supply pressure. In order to find the main reason for the fixed frequency, a second-order mass spring system was assumed. An equation is also proposed for obtaining the resonance frequency of the double feedback fluidic oscillator.