Characterization of Self-Induced oscillating flows by means of optical and sensor measurement methods

Abstract

This paper shows the application of different optical and sensor-based measurement methods to characterize self-induced oscillating flows inside and outside a feedback-free fluidic oscillator. The input pressures considered for the investigation range from 1.0 MPa to 5.0 MPa. Synchronized diagnostic sensors, flow visualisation and flow monitoring were set up to simultaneously acquire a complete description of the oscillator system. Two versions of the fluidic oscillator for the internal visualisation (with internal visual access window) and direct monitoring (with two sensors embedded in the chamber) of oscillating flows were numerically modelled, manufactured and tested. The flow oscillations generation and dynamic activity of vortices inside the oscillator were experimentally and numerically visualised and analysed. The flow fluctuations inside the oscillator were directly measured and the frequency spectra was calculated. The study of the propagation of the sweeping flow out of the oscillator was then tackled by front-light flow illumination and image cross-correlation techniques were used to retrieve the velocity vector field. The dynamic mode decomposition technique was applied to the measured velocity flow field to capture the oscillating flows mode structures and time dynamics. This technique allowed also the computation of the outflow dominant oscillation frequencies, which were compared with results obtained using point monitor frequency calculation and impact pressure measurement techniques. The visualisation and measurements agreed qualitatively and quantitatively with the computational fluid dynamics simulations in all the studied cases. Details of the study are discussed in the paper.