A Three-Dimensional Particle Tracking Velocimetry System for the Evaluation of Large Eddy Simulation Turbulence Models

The necessity for evaluating the accuracy and characteristics of new Large-Eddy Simulation (LES) turbulence models in modern fluid mechanics research has inspired the development of a Three-Dimensional Particle Tracking Velocimetry (3DPTV) system capable of producing 3-Dimension 3-Component (3D3C) velocity vector fields. The system is based on the triangulation method of particle location and utilizes an optical system comprised of three 4008 x 2672 charge-coupled devices (CCDs), three 120mm lenses, and a water-filled prism. The tracer particles used in the system were <5microm TiO2 and were illuminated using a 532 nm Nd:YAG dual pulsed laser. The system was configured to study a backward-facing step flow in a 6" x 12" water tunnel due to this flow's consistency in separation and unsteady, turbulent characteristics. The experimental flow had a freestream velocity of 22 cm/s, a Reynolds number based on the step height of 6274, and a Taylor-microscale Reynolds number of approximately 130. Data from this flow was used in a priori testing of various LES models including the Smagorinsky, Similarity, Mixed, Dynamic, Coherent Structures, and Stretched Vortex Models. The system is preferable to Direct Numerical Simulation (DNS) for such testing in that it is capable of acquiring data at a resolution adequate for a priori testing without the computational restrictions for high Reynolds numbers. In the present configuration, the system is capable of achieving a Taylor-microscale Reynolds number of 214, but with an increase to the CCD resolution of the system, a Taylor-microscale Reynolds number of nearly 400 would be attainable.