An experimental analysis of the Precessing Vortex Core (PVC) instability in a free swirling jet of air at ambient pressure and temperature was performed by means of Time Resolved Particle Image Velocimetry (PIV). Axial and tangential velocity components have been measured in a plane located just above the nozzle exit and perpendicular to the axis of the swirl jet. The instantaneous unconditional acquired velocity maps have been phase averaged by means of a post processing technique. The center of the main vortex has been identified on both phase averaged and instantaneous velocity maps by means of a vortex identification procedure. The latter procedure is based on the velocity inversion points method. Results from phase averaged maps evidenced that vortex center travel along an approximately circular trajectory centered on the nozzle axis. On the other side its instantaneous position estimated from instantaneous velocity maps result to be quite scattered around the circular trajectory. The final objectives of the work are to clarify the flowfield structure in the presence of the PVC instability and to improve understanding of the interaction between PVC and the flow turbulence.
Analysis of Precessing Vortex Core (PVC) phenomena by post-processing of unconditional TR-PIV measurements
COZZI, FABIO;MALAVASI, STEFANO;COGHE, ALDO SEBASTIANO
2008-01-01
Abstract
An experimental analysis of the Precessing Vortex Core (PVC) instability in a free swirling jet of air at ambient pressure and temperature was performed by means of Time Resolved Particle Image Velocimetry (PIV). Axial and tangential velocity components have been measured in a plane located just above the nozzle exit and perpendicular to the axis of the swirl jet. The instantaneous unconditional acquired velocity maps have been phase averaged by means of a post processing technique. The center of the main vortex has been identified on both phase averaged and instantaneous velocity maps by means of a vortex identification procedure. The latter procedure is based on the velocity inversion points method. Results from phase averaged maps evidenced that vortex center travel along an approximately circular trajectory centered on the nozzle axis. On the other side its instantaneous position estimated from instantaneous velocity maps result to be quite scattered around the circular trajectory. The final objectives of the work are to clarify the flowfield structure in the presence of the PVC instability and to improve understanding of the interaction between PVC and the flow turbulence.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
