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THE TURBULENT/NON-TURBULENT INTERFACE OF A COOLED JET

Jerry Westerweel
Laboratory for Aero- and Hydrodynamics, Delft University of Technology, Leeghwaterstraat 21, 2628 CA Delft, The Netherlands

A. Petracci
Laboratory for Aero & Hydrodynamics, Delft University of Technology Leeghwaterstraat 21, 2628 CA Delft, Netherlands

Rene Delfos
Laboratory for Aero & Hydrodynamics, Delft University of Technology Leeghwaterstraat 21, 2628 CA Delft, Netherlands

Julian C. R. Hunt
Laboratory for Aero & Hydrodynamics, Delft University of Technology Leeghwaterstraat 21, 2628 CA Delft, Netherlands

Abstract

The turbulent/non-turbulent interface of a jet is characterized by sharp jumps ('discontinuities') in the conditional flow statistics relative to the interface. Experiments were carried out to measure the conditional flow statistics for a cooled jet. These experiments are complementary to the experiments reported by Westerweel et al. (2005) on a Re=2000 jet, where the thermal diffusivity is intermediate the diffusivity of momentum and the diffusivity of mass. The experimental method is a combined LIF/PIV method, where a temperature-sensitive fluorescent dye (rhodamine 6G) is used to measure the instantaneous temperature fluctuations. The results show that the cooled jet can be considered to behave like a self-similar jet without any buoyance effects. The detection of the interface is based on the instantaneous turbulent kinetic energy, and provides a reliable means to detect the interface. Conditional flow statistics reveal the superlayer jump in the conditional vorticity and in the temperature.