Effect of nozzle geometry and semi-confinement on the potential core of a turbulent axisymmetric free jet

The effects of nozzle geometry and confinement on the potential core and subsequent axial development of a turbulent axisymmetric air jet at a Reynolds number of 22 500 have been studied Four jet exit conditions, namely, flat and fully developed velocity profiles for unconfined and semi-confined cases were investigated. Mean velocity and turbulence profiles were measured using laser-Doppler anemometry. Liquid crystal thermography used in steady state enabled optimal nozzle to plate spacing to be established for maximum heat transfer. Preliminary results presented here indicate that the length of the potential core is greater for the fully developed jet exit profile and is further extended by semi-confinement. The semi-confinement reduces the stagnation point heat transfer by up to ten per cent.