Lagrangian visualization of turbulent field by using correlation technique

To investigate the evolving process of the large structures in turbulence, imageprocessing technique for traversing camera at mean flow velocity along the axis of the flow was developed by using cross-correlation technique and applied to the axisymmetric jet. In order to obtain a complete velocity profiles, a traversing unit for CCD was controlled by a personal computer to synchronize its traversing rate with the mean flow. Video signals from the CCD were recorded continuously on VTR with two binary barcode; one for identify the video field, the other for specify the camera position and the traversing rate. From recorded images, the cross-correlation technique was employed to obtain two-dimensional velocity distributions. From successive maps of instantaneous velocity and vorticity distribution, the motion of large eddies (vortex pairing, entrainment) can be dynamically revealed which was unable to measure by fixed camera measuring techniques.