Experiments And Data Processing For Turbulent Flows Using Eulerian And Lagrangian Techniques
In the study of turbulent flows, two reference frames exist in which fluid properties can be measured: a frame fixed in space, the Eulerian viewpoint, or a frame moving with the particle trajectory, the Lagrangian viewpoint. Turbulence research has been advanced primarily on experiments conducted using Eulerian techniques, but the developing Lagrangian methods are needed in order to determine the full acceleration, its temporal and spatial variation, of fluid particles. This research looks at two different problems involving turbulence: a turbulent boundary layer evolving beneath a turbulent free stream and the Lagrangian tracking of particles in turbulent flows. The results of Eulerian measurements of a turbulent boundary layer evolving beneath free-stream turbulence using hot-wire anemometry are reported. The flat-plate boundary layer was created on a glass plate in a low-speed wind tunnel and freestream turbulence was generated by an active grid. Systematic variation of the freestream conditions from very low turbulence (0.25% turbulence intensity) to high turbulence (10.5% intensity) showed effects well within the boundary layer. The freestream Reynolds number based on the Taylor micro-scale varied between 20 and 550; the boundary-layer momentum-thickness Reynolds number varied from 550 to almost 3,000. At high turbulence intensities, the effects of the free-stream turbulence extend deep into the boundary layer: affecting especially the velocity variances and the energy spectra. The energy spectra display a double-peak, for both near-laminar and turbulent free-streams. At very-low free-stream turbulence intensities, the two peaks represent the inner and outer scales of the turbulent boundary layer. With higher intensity free-stream turbulence present, the energy associated with the free-stream peak dominates the outer peak of the boundary layer. A detailed description of the Lagrangian particle tracking framework used in experiments at Cornell University is presented. The theory and detailed instructions on the implementation of Lagrangian particle tracking are included. Camera calibration, both from a mask of points and using found particle data output from the tracking code from actual experiments (dynamic calibration) is described. The code used to conduct the analysis of particle image data obtained from the cameras is presented in detail. The code performs three main steps: 1) particle center finding, 2) stereomatching (determining particle 3D coordinates, if more than one camera is used), and 3) tracking particles through the time-series of images to construct trajectories. Each of these steps is conducted by a function called by the controller program. The controller program takes information such as the camera image filenames, the number of movies to be processed, the location and name of the calibration parameters file, and image intensity threshold values and outputs the reconstructed particle trajectory information in a data file. In order to assist future users of the code, the details of the original code and all edits made by the author have been included.
dissertation or thesis