The effects of different inlet conditions on the exit flow from a fluidic precessing jet nozzle

The fluidic precessing jet (FPJ) shown in Figure 1 is one of a family of self-excited oscillating jet flows that has found application in reducing Oxides of Nitrogen (NOx) from combustion systems in the high temperature process industries. Its flow field is highly three-dimensional and unsteady, and many aspects of it remain unresolved. Velocity data measured close to the exit plane is presented for a variety of FPJ nozzles with three different inlet conditions, namely a long pipe, a smooth contraction and an orifice. The results indicate that jet inlets which are known to have asymmetrically shedding initial boundary layer, such as that produced by either an orifice or a pipe, trigger jet precession more easily than jet inlets which are known to have symmetrically shedding initial boundary layers. Although the exit flow is dominated by the reliability with which a given configuration generates precession, the three different inlet conditions also produce subtle differences in the exit profiles of mean velocity and turbulence intensity when the flow does precess reliably.