3D Modeling of Flow Behind a Heated Backward-Facing Step using 3D Digital Particle Image Velocimetry & Thermometry

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Today's experimental studies of turbulence that use imaging methods, such as Digital Particle Image Velocimetry (DPIV) and Digital Particle Image Thermometry and Velocimetry (DPITV), are huge improvements over previous single-point measurement techniques (e.g. hot-wire anemometry, Laser Doppler Velocimetry (LDV), thermocouples, thermistors, pitot tubes). These new methods allow for simultaneous 2-D measurements of time-evolving temperature and velocity, but inherently cannot address turbulent flows, where 3-D information is absolutely essential. While newly developed 3-D velocity techniques allow for 3-D time-evolving velocity measurements, we have no technique to provide both temperature and velocity in 3-D. The short-term research goal is to develop a novel technique, 3D Defocusing Particle Image Thermometry and Velocimetry (3DDPITV), to simultaneously measure time-evolving temperature and velocity fields within a volume. The long-term research goal is to apply this new technique to study coherent structures, their interactions, and their heat transfer/mixing characteristics in order to develop an understanding of the physics associated with their interactions. In addition, with this gained understanding and with the availability of three-dimensional data fields, subgrid-scale models to be used in LES simulations can be tested and, when appropriate, new models will be proposed. The experiment of choice is the backward-facing step. This flow has the advantage of having areas distinctly different and unique in their flow physics: (1) The separated shear layer is very similar to a mixing layer, thereby providing the opportunity to study the role and effects of coherent structures on mixing and heat transfer across a heated shear layer. (2) The unsteadiness of the shear layer's reattachment will provide an opportunity to study the effects of coherent structures on heat transfer in reattachments problems. (3) The recirculation zone, dominated by convection due to the primary vortex, will provide the opportunity to study heat transfer within recirculating regions, also dominated by coherent structures. (4) The redeveloping boundary layer beyond the reattachment region, dominated by the turbulent heat flux and directly related to the interaction of vortices within the shear layer that impinge upon the wall during reattachment, will provide an opportunity to study developing boundary layers. This research will address broader impacts in three primary areas: integrating education and research, enhancing infrastructure, and promoting benefits to society. The award has been funded by the Thermal Transport and Thermal Processing Program of the Chemical and Transport Systems Division, and it is part of a joint program involving Sandia National Laboratory and the NSF in the area of "Engineering Sciences for Modeling, Simulation, Decision-Making and Emerging Technologies.