Investigation of the flow field of a highly heated jet of air

Abstract

Measurements of mean and fluctuating velocity and temperature and their self-and cross-products to the third-order are presented for a heated axisymmetric air jet. Froude numbers in the range of 3500-13,190, Reynolds numbers in the range of 3470-8500 and non-dimensional streamwise distances, X*, from 0.27 to 1.98 are covered by the data. It was found that turbulence intensity decreases for the heated jet in the region between the inertia dominated and the bouyancy dominated regions which is contrary to findings with helium jets mixing with ambient air to produce density fluctuations. The effects of heating on the turbulent kinetic energy budget and the temperature variance budget show small differences for the inertia dominated region and the intermediate region which help to explain the transition process to the far field plume region. Constants are evaluated for the isotropic eddy diffusivity and generalised gradient hypothesis models as well as the scalar variance model. No significant effect of heating on the dissipation time-scale ratio was found. A novel wire array with an inclined cold wire was used. Measurements obtained with this probe are found to lead to asymmetries in some of the higher -order products. Further investigation suggested that the asymmetries are attributable to an as yet unreported interference effect produced by the leading prong of the inclined temperature wire. The effect may also have implications for inclined velocity wires which contain a temperature component when used in heated flows. © 2002 Elsevier Science Inc. All rights reserved.