Simultaneous, two-camera, 2D gas-phase temperature and velocity measurements by thermographic particle image velocimetry with ZnO tracers

This work presents simultaneous 2D temperature and velocity measurements on a heated jet using two non-intensified cameras to realize thermographic PIV. In contrast to previous studies which use separate PIV cameras and LIP cameras, the present experiment uses only a double-pulsed UV laser and two low-speed CCD cameras running in double-frame mode, greatly simplifying the setup. The intensity ratio is calculated based on the image pair recorded at two spectral lines for thermography, while the cross-correlation is performed over the two consecutive frames for PIV. A method is proposed to correct for the effects of non-uniform spatial distribution of laser fluence on the intensity ratio, by including the laser fluence into the calibration function. The laser sheet energy profiles are measured and the intensity ratio is translated into temperature according to the local laser fluence and two-colour ratio. The temperature accuracy using this technique is estimated as 3 K at 410 K, by comparing the mean temperature field with the result provided by a thermocouple. Simultaneous 2D temperature and velocity fields are presented for a simple heated jet, demonstrating the expected similarities. The demonstration shows the potential of thermographic PIV in the investigation fundamental problems on turbulent flows, and shows that the technique can be improved through the availability of a dual-cavity UV laser.