Swirl, confinement and nozzle effects on confined turbulent flow

Predictions of swirl, confinement and nozzle effects on confined turbulent flow are exhibited and compared with five-hole pitot-probe time-mean velocity measurements. Two sets of computations are given, one using the standard k-epsilon turbulence model and the other using a C sub mu formulation model deduced from recent six-orientation single-wire hot-wire measurements. Results confirm that the accuracy of the latter model is superior. To highlight the effects of confinement and exit nozzle area on this flow, three expansion ratios and two contraction ratios are used. Predictions are given for a full range of swirl strengths using measured inlet conditions for axial, radial and swirl velocity profiles. The predicted velocity profiles illustrate the large-scale effects of inlet swirl on flowfields. It appears that a strong contraction nozzle has a pronounced effect, on swirl flow cases, with discouragement of central recirculation zones, and forward flow in highly swirled vortex core regions. The expansion ratio value has large-scale effects on the size and location of the recirculation zones.