Shock-cell noise investigation on a subsonic/supersonic coaxial jet
Date: Thursday 02 March 2017 to Thursday 02 March 2017
Location : von Karman Institute for Fluid Dynamics, Sint-Genesius-Rode (near Brussels), Belgium
PhD Thesis of Daniel Guariglia
Defended on 22 February 2017 at the Università degli studi di Roma "La Sapienza"
To commission the facility, several test campaigns on a supersonic single stream jet were conducted using PIV in synchronous with microphones mounted on a polar antenna. Multiple screech harmonics and subharmonics tones have been documented, showing a directivity pattern similarly to the supersonic broadband noise (BBSAN).
Turbulence integral length scales have been computed using correlation functions. The average of Reynolds shear stress fields shows the presence of lobes in the jet near field which are the trace of a standing wave caused by the screech.
Following the commissioning, the coaxial jet has been investigated. Multiple combinations of pressure conditions for the primary and secondary flows have been tested. Acoustic measurements have been performed in synchronous with the PIV, which has been applied for the first time in the literature on a supersonic coaxial flow.
A simple method to infer the screeching dynamics from the spatial correlation functions was proposed. The correlation suggests the presence of a pulsation (or breathing) motion of the internal jet, which is cause/effect of the screech. A second screech mode was also retrieved from acoustic data, for which, the correlation functions suggest the presence of a sinusoidal motion of the internal jet.