Investigation of penetrative convection in stratified fluids through 3D-PTV

Abstract

Testing existing theories of flow and transport in stably stratified fluids when ''penetrative convection'' occurs requires experimental methods capable of fully three-dimensional descriptions of both the Eulerian velocity field and Lagrangian particle trajectories. Boundary layer experiments utilizing a photogrammetric three-camera three-dimensional Particle Tracking Velocimetry (3D-PTV) technique were performed on a laboratory model which simulated the evolution of the mixing layer in a stably stratified fluid body by heating a tank filled with water from below. A combination of image-and object space-based information was employed to establish the spatio-temporal correspondences between particle positions at consecutive time steps. An appropriate calibration procedure for the stereoscopic system provides the intrinsic and extrinsic parameters of the stereoscopic system to be used for determining the correspondence of points in the object or world reference frame and in the image reference frame. The photogrammetric principles used by 3D-PTV are described. First, the fundamental mathematical model of the collinearity condition and its extensions are explained. Then, the epipolar line intersection method built upon multicamera correspondences (structure-from-stereo) is discussed as well as the procedure of reconstruction of particle trajectories in a single step by conjunctly establishing the spatial and temporal correspondences between particle images. Tests on simulated data were performed as well as experimental data in order to ensure the method's operability and robustness. The reconstructed velocity fields are compared to other laboratory investigations and field data.

Three‐dimensional flow measurements in a static mixer

“…Flow studies using 3‐DPTV are to date restricted to relatively simple flow domains: rectangular tanks; the interior of a cylindrical domain viewed directly through its flat endwalls or indirectly through an enclosing rectangular viewing box . However, static mixers are of far greater geometrical complexity on grounds of the cylindrical boundary and the presence of internal elements.…”

Experimental quantification of turbulence and its applications in the study of multiphase flotation pulps

“…The 2D PTV measures a 2D slice of the flow illuminated by a laser sheet by recording the images of low-density seeding particles and tracks each particle for several frames. In 3D PTV, multiple cameras are used to record images in an illuminated 3D volume to track the flow tracers by using photogrammetry (Dore, et al, 2009). …”

An alternative scaling for unsteady penetrative free convection

“…The experimental effort based on image analysis techniques has mainly consisted on improving illumination conditions as well as time and space resolutions for velocity measurements. The employed optical techniques, namely Feature Tracking (FT) [ Moroni and Cenedese , 2005] and photogrammetric 3D‐Particle Tracking Velocimetry (PTV) [ Dore et al , 2009; Shindler et al , 2010], provided suitable tools for reconstructing longer trajectories (always more than 10 3 trajectories longer than 20 consecutive snapshots) and analyzing images of larger particle density (reliable results for more than 2000 particles in a volume of 0.15 × 0.15 × 0.15 m 3 for 3D‐PTV). Velocity statistics are then more robust than those from 2D tracking techniques more commonly reported in the literature.…”

“…A large amount of investigations have been devoted to the study of the development of the atmospheric CBL, via laboratory experiments, field campaigns, bulk CBL models and numerical simulations. Among the laboratory models, Deardorff and Willis [1985], Hibberd and Sawford [1994], Cenedese and Querzoli [1997], Moroni and Cenedese [2006], Dore et al [2009, 2011] should be mentioned. The characteristics of a shallow dry CBL have been the subject of an extensive field campaign during the International H2O project (IHOP_2002), described by Weckwerth et al [2004].…”

“…A three‐dimensional description of the turbulent structures of the convective boundary layer can be achieved through a fully three dimensional image analysis technique. The three components of velocity can thus be successfully reconstructed in a given volume with high time resolution and sub‐pixel accuracy [ Dore et al , 2009].…”