Effects of Chevron Exit on Impinging Synthetic Jets

The behaviour of a chevron syntethic jet in impinging configuration is experimentally investigated by using Stereoscopic Particle Image Velocimetry at Reynolds number equals to 4500, dimensionless stroke length (i.e. nverse of Strouhal number) equals to 28 and at a nozzle-to-plate distance of 2 diameters. The effect of the presence of the impinging plate on the flow field organisation is discussed. The characterisation of the flow field evolution on the impingement plate is studied. Then, a complete three-dimensional reconstruction of the entire flow field at the phases, chosen by analysing the results obtained through the previous analysis, is carried out. Three phases are reconstructed corresponding to three synthetic jet conditions: approaching vortex, impinging vortex and flow developing on the plate. The chevron synthetic jet is characterised by two main features: the cross-shaped exit leads to the acceleration of the fluid, thus to a larger impinging velocity; second one, the presence of streamwise structures are responsible forthe generation of preferential paths along which the turbulent wall jet develops modelling the convecting primary coherent vortex structure in a hexagonal shape.