INVESTIGATION ON CIRCULAR AND CHEVRON IMPINGING JETS BY IR THERMOGRAPHY AND TIME-RESOLVED TOMOGRAPHIC PIV

This paper describes an experimental investigation on impinging jets issued through a circular and a chevron nozzle by means of IR thermography and time-resolved tomographic particle image velocimetry. Measurements are performed at Reynolds number of 5000, based on the flow rate and on the nozzle diameter D. Time-resolved tomographic experiments are performed at kilo-hertz repetition rate in a tailored water jet facility where a plate is placed 4 D off the nozzle. The measurements are done at the nozzle exit in a cylindrical volume with a diameter of 4.5 D and an axial length of 4 D. Time-averaged heat transfer measurements of the convective heat transfer on the plate are performed by means of IR thernnography with the heated-thin-foil heat transfer sensor for nozzle-to-plate distances ranging from 2 D to 10 D. Heat transfer measurements are shown in terms of Nusselt number (Nu) maps. The instantaneous three-dimensional organization of coherent structures is described for both the configurations. The heat transfer performances of the chevron jet are compared with those of the circular one, analyzing the influence of the nozzle-to-plate distance on the distribution of Nu. The most relevant issues for the chevron jet and the relation between the flow organization and the heat transfer are investigated.