Measurement of the flow field induced by a spark plasma using particle image velocimetry

We investigate the local flow field induced by a spark plasma discharge in quiescent air under atmospheric conditions. Particle image velocimetry (PIV) is used to quantify the induced flow field between two conical-shaped electrodes for three different electrode gaps: 8mm, 5mm and 2mm. The results show the existence of three distinct stages of flow. In the first stage of flow, distinct coherent structures are observed near the tips of the electrodes. In the second stage, ambient fluid is entrained along the electrodes to produce axial jets in the electrode gap. The final flow stage is characterized by collision of the jets and decay of vorticity. The flow parameters are all scaled by the induced velocity behind the shock wave produced by the spark and the electrode gap distance. The scaling results in comparable magnitudes of velocity and vorticity induced in the 5mm and 8mm electrode gaps with the onset of each of the flow stages occurring at approximately the same time scale. The magnitude of axial velocity dominates the latter two stages of the flow. Significant correlation is found between circulation and entrainment calculated for the 5mm and 8mm electrode gaps at different time steps, where the decay rates of circulation and that of entrainment are found to be , respectively. The stages of flow development for different electrode gaps at times>100 mu s after the discharge are discussed comprehensively and the choice of scaling based on energy deposited in the electrode gap and gap distance is found to permit direct comparison of the two electrode gaps.Graphical Abstract [GRAPHICS] .