Progress in PIV-PTV methods: application to concentration measurements

The purpose of this work is to discuss the ability to simultaneously measure the concentration of dispersed particle and the velocity field. It is basically an extension of particle imaging methods (such as PIV or PTV). These methods experienced major developments during this last decade and became nowadays very common instruments. Such combined tool would be valuable for investigating the distribution of droplet in combustion, the dispersion of pollutant gas or other similar applications. The main idea consists to use all the information available on the image to measure the concentration. Image processing provides an instantaneous velocity field for each couple of images and analyzing the spatial distribution of the particle images gives simultaneously a concentration field. A method based on particle counting is investigated and characterized. It is showed that trade-off has to be made between the accuracy and the spatial resolution. Systematic tests on synthetic images and real images showed that the tool has a non-linear response. Nevertheless, the mean measurements present self-similar profile and a correction is possible if experimental parameter such as particle image diameter are determined. The instantaneous measurements are more delicate. They present scatter due to the performances of identification algorithm and due to the error made on the particle position