This paper presents a method for simultaneous measurement of particle position and displacement in depth by depth-from-defocus using time series color images. This method enables us to obtain the particle information for 3D-PIV by using a single color camera. To improve the depth measurement accuracy, three differently blurred images are simultaneously captured as RGB color images and the depth information is estimated from the three images with a neural network considering in-plane position. In performance tests, we numerically and experimentally evaluate the measurement accuracy of particle position and displacement in depth. The results of depth position by neural network show that the RMS error decreases to 65% of that by a calibration line. The results of depth displacement from three color images show that the RMS error decreases to 24% of that from only one color image, corresponding to 9.5% for maximum displacement 2 mm.

  Optical fiber laser induced fluorescence (OFLIF) probe was developed for high spatial resolution and high SN ratio measurement of concentration fluctuation in liquid phase turbulent flows. The advantage of the OFLIF method is the very small path length of incident laser. The calibration curve showed high linearity up to about 30 μmol/L for Rhodamine 6G solution which is about 1,000 times higher than the maximum concentration for conventional LIF method. This enables us to use the fluorescence dye with much higher concentration than conventional LIF method. The OFLIF was applied to concentration measurement in an aqueous axisymmetric turbulent jet. The result showed that the spatial resolution and SN ratio are enough to discuss the spectral shape near Bachelor scale. The measured spectra supported -1 power law predicted by Bachelor and Kraichnan.