The development of a turbulent jet issuing from an annular source with an open centre

Using particle image velocimetry (PIV) and flow visualisation we investigate the dynamics of a turbulent jet that issues from a thin slot annular source with an open centre - by `thin' we refer to a slot width that is at least an order of magnitude smaller than the diameter of the annulus. For this geometry, entrainment into the near-field region of the jet results in an induced flow in the environment that passes through the open annulus. We explore the streamwise development of the jet towards an approximately self-similar form and identify the key regions of the flow. For the far-field, we show that the flow approximates to a round jet from a circular source and we use our results to estimate the location of the origin for the virtual point source of a round jet that matches the far-field flow produced by an annular source. Finally, we consider some practical implications of our results for inducing air movement in rooms.