Physical Modelling of Turbulent Single- and Multi-phase, Impinging Jets using Particle Image Velocimetry (PIV)

Two-component velocity vector maps of single- and multi-phase turbulent impinging jets were acquired using particle image velocimetry (PIV). Mean and turbulent characteristics were explored with the impingement surface located at three strategic positions; 2 (within the potential core), 6 (just outside the core) and 10 h/d (fully developed jet).
Single-phase trials present the first extensive exploration of all three regions of an impinging jet. As jet height increased, the more advanced the jet expansion, and the centreline mean axial velocity decreased as the jet spread radially with increasing mean radial velocity. An increase in turbulence levels was seen from 2 to 6 h/d as the end of the potential core was exceeded where turbulence from the mixing layer penetrated to the centre, followed by a decrease at 10 h/d as the jet continued to grow before impingement.
A liquid impinging jet laden with 69μm sized glass particles was explored, the particles were found to not follow the turbulent flow. Particle axial velocities were generally smaller than their single-phase counterparts. As the jet height increased the stagnation region broadened, similarly for the single-phase trials. The particles exhibited considerably lower turbulent velocities. The near-field radial wall jet saw the deflection and acceleration to a greater extent for the smallest jet height (2 h/d) than the larger two (6 and 10 h/d). Particle turbulence intensities in the near-field radial wall jet increased as the jet height increased. The particle turbulence was smaller than that of the single-phase, the greatest difference seen for the middle jet height of 6 h/d.
A sensitivity study of particle size effect on a particle-laden turbulent impinging jet with jet-to-plate separation of six diameters has been completed, three particle sizes used; 20, 46 and 69μm. Within the impingement region, the particles do not decelerate as rapidly as the single-phase due to the particle inertia. Turbulent velocities of the particle phases were considerably lower than the single-phase, the turbulent velocity normal to the impingement surface larger than the radial component.
And finally, a preliminary assessment of the feasibility of using fluorescent particle image velocimetry (fPIV) for the purpose of studying turbulence modulation in impinging liquid jets has been undertaken.