Zeeshan Saeed
Ph.D. Candidate
UNH Department of Mechanical Engineering
Friday, May 2, 2025, 3:10 p.m.
Chase 105
Abstract
Flows at the water surface, when thermally scanned, appear striking — rhythmic, convoluted motions folding and fading as they evolve. Yet more striking is what they conceal: two length scales within the same flow, each behaving differently. This talk explores the utility of thermal imagery to uncover patterns within the thermal expressions of a submerged buoyant jet. This sort of flow can be found in the meltwater plumes of marine-terminating glaciers, or industrial outfalls in the ocean. In our idealized experiments, the jet, sourced through a fixed nozzle at constant depth beneath the surface, was tested with varying flow rates. Thermal signatures were captured using a long-wave infrared camera. To filter measurement noise, the noise floor was estimated using the power spectra of the raw thermal images. The images were then reconstructed using orthogonally decomposed modes required to capture the cumulative energy corresponding to the pure part of the measured signal. These de-noised thermal fields were then systematically processed for thermal pattern tracking via a particle image velocimetry (PIV) algorithm to extract free-surface velocity fields. Correlation length scale analysis of the thermal fields revealed a consistent decrease in scalar (temperature)-based integral length scales with increasing source flow rate. In contrast, velocity fields counterintuitively show that momentum-based integral length scales remain “locked” to the flow geometry, independent of the source flow rates. A physical interpretation of these findings is developed by considering: (i) the arrest of vertical motions by inertial effects within the source layer of the free surface interface, diverting flow radially, and (ii) the parallel cascades of thermal and kinetic energy from large scales down to Batchelor and Kolmogorov scales, respectively.
Please note: Images produced by processing data provided by Peter K. Judd (The thermal signature of a submerged jet impacting normal to a free surface.” Journal of Visualization19 (2016): 1-5.).
Bio
Zeeshan is a fifth-year Ph.D. candidate in Mechanical Engineering at UNH, working on the surfacing and mixing dynamics of turbulent buoyant plumes. He received his M.S. degree in Mechanical Engineering from Oklahoma State University in 2019.
