The velocity and temperature measurements of a heated jet issuing from a square nozzle into stagnant ambient air are presented. Measurements were accomplished by means of single hot-wire, single cold-wire, x-wire and three-wire (a cold wire in front of an x wire) probes. The result showed that the jet initial boundary layer was laminar. Mean velocity and temperature reached the self-preservation immediately after the jet potential core. Based on the decay of the local maximum velocity and temperature, as well as the spreading of velocity and temperature half-width, the interaction region was determined to be We. It was found that the Reynolds normal stress, Reynolds shear stress, and heat flux achieved a self-preservation state at x = 20De, 30De, and 35De, respectively. The turbulent Prandtl number, which was determined based on the Reynolds shear stress and heat flux, kept approximately constant from the jet centerline until the half-width of the jet and increased thereafter in the outer jet. This finding suggested that some inaccuracies might have incurred in the computation fluid mechanics results by assuming a constant turbulent Prandtl number in the similarity solution of the jet. Last, comparison of velocity half-width along the y and w axes, as well as the measurements of mean velocity contours at various streamwise locations, indicated that there was an axis switching in the present square jet, although more experimental evidence would be required.
|Publication status||Published - 2004|