Self-Preserving Properties of Unsteady Round Nonbuoyant Turbulent Starting Jets and Puffs in Still Fluids

The self-preserving properties of round nonbuoyant turbulent starting jets, puffs and interrupted jets were studied experimentally and theoretically for flows in still and unstratified environments. The experiments involved dye-containing fresh water sources injected into still fresh water within a large fresh water tank with images of the flows obtained using a video camera. Near-source behavior varied significantly with source properties but self-preserving behavior was observed at distances greater than 20–30 source diameters from the source. Within the self-preserving region, normalized streamwise and radial penetration distances varied as functions of time, in accord with requirements for self-preservation, to the following powers: 1/2 for starting nonbuoyant jets and 1/4 for nonbuoyant puffs. Effects of injected fluid quantity for puffs were reflected by the location of the virtual origin which was independent of injected fluid volume for small volumes but became proportional to injected fluid volume for large volumes typical of interrupted jets.