Experimental investigation of the influence of Reynolds number and buoyancy on the flow development of a plane jet in the transitional regime

Heated horizontal plane jets find wide applications in engineering appliances such as air curtains and discharge of industrial effluents. In the present study, experimental investigations are conducted on a heated horizontal plane jet with the Reynolds numbers in the transitional regime, using a hotwire anemometer. In the far to very far-field (20 < x/d < 100) centreline velocity decay and jet spread increases faster with the decrease of Reynolds number. This is because, with the increase of Reynolds number, the turbulent kinetic energy is distributed on a broadband of scales. As a result, larger scales, which are responsible for increased entrainment, get weaker. The shifting of the centre plane generally occurs in the far region for low Reynolds number jets. A comparison with the result of an isothermal jet at similar Reynolds numbers from the literature at identical conditions shows that the turbulence intensity is decreased due to heating. Centreline velocity decays slowly and half-width increases marginally for a heated jet when compared with an isothermal jet. The effect of heating is prominent for low Re jets. Spectral development shows a delayed transition due to heating. Probability density function plots reveal lack of equilibrium and presence of large-scale eddies in the flow field.