A PIV Study of Flow Dynamics in a Cold-Flow Replica of a Swirl Stabilized Plasma Torch

Experimental flow field measurements are required for validation and uncertainty quantification in the development of a multi-physics simulation of an inductively coupled plasma torch. For this purpose, an optically-accessible torch replica has been built and PIV measurements are being made on the cold flow field, which is present prior to plasma ignition. The replica consists of a tube that is approximately 250 mm in length with a 56 mm inner diameter. The flow is injected tangentially at the bottom of the tube through four 1.44 mm² jets, each of which has a jet Reynolds number of 9000, which gives a swirl number of S = 4.3. The flow exits through a 30mm diameter nozzle into the room. Both two-dimensional three velocity component (2D-3C) measurements at low repetition rate and time-resolved 2D two-component (2D-2C) PIV velocity fields are presented. The 2D-3C measurements are made along the full length of the replica torch body and show a complex swirl dominated flow that exhibits vortex breakdown within the tube. The average axial velocity profile is axisymmetric and exhibits two closely spaced and interacting shear layers, separating regions of reversing flow directions. The complexity of the flow is further illustrated in the nozzle exit region, where the flow direction reverses around the centerline, and gas is sucked back into the tube. Time-resolved 2D-2C PIV is used to investigate the unsteady flow dynamics of this swirling and shearing flow further.