Coherent Structures in a Jet Indicating Edgetone Oscillation (2nd Report, Eduction of Coherent Structures by Using Low Pressure Region and Velocity Gradient Tensor)

Abstract

Coherent vortical structures in a high-Reynolds number turbulent jet indicating edgetone oscillations were extracted from velocity and pressure data. Three quantities were chosen as candidate indicators of the coherent structures : (i) phase-averaged vorticity, (ii) phase-averaged pressure, and (iii) the phase-averaged velocity gradient tensor. All these quantities worked well in extracting coherent structures in a test case of a low-Reynolds number wake of a cylinder. However, when applied to the high-Reynolds number edgetone flow, (ii) and (iii) indicated much better performance than (i), since (i) was affected by the background time-averaged vorticity field. The advection of the coherent structures was well captured by using (ii) and (iii).