Zeeshan Saeed
Ph.D. Candidate
UNH Department of Mechanical Engineering
Friday, March 27, 2026, 3:10pm
Chase 105
Abstract
Free-surface flows offer a window for the development of remote sensing tools to replace hazardous in-situ, subsurface measurements. This work experimentally investigates the sensitivity of free surface features to sub-surface and source conditions using thermal imagery. High-fidelity free-surface thermal fields were obtained covering a range of source-based Reynolds numbers ($600 < Re (= U_0 D/\nu) < 10200$), and free-surface locations ($35 < h/D < 65$) (where $\nu$ is the kinematic viscosity of water with bulk velocity U0 at a jet orifice of fixed diameter D, separated from the free surface by distance h). To filter measurement noise, raw images were reconstructed using orthogonally decomposed modes corresponding to the noise-free part of the signal estimated via power spectra. These de-noised thermal fields were systematically processed for thermal pattern tracking using a particle image velocimetry algorithm to access the mean and turbulent velocity fields. A bi-directional correlation analysis of the thermal scales (radial and angular) revealed their sensitivity to source momentum flux (parametrized by Re) and source-surface separation h; while the former decreased the angular thermal scales by amplifying free surface-induced shear, the latter increased the radial scales by allowing more room for the jet to spread laterally. For velocity fields, increasing Re at a fixed h amplified the mean and turbulent motions, while increasing h at a fixed Re weakened these motions and spread them over larger radial distances. Additionally, the mean flow profiles, when rescaled using appropriate velocity and length scales, collapsed onto a self-similar curve. Consistent with the obtained self-similar profile, asymptotic analysis predicts motion increasing linearly near the center of the flow field and decaying inversely far from it. While the linear behavior originates from a geometry-enforced balance between angular and radial turbulent velocity fluctuations, the inverse decay originates from the turbulent redistribution of the radial advection of mean radial momentum. Self-similar profiles imply that free surface interfacial processes are passive; they do not impose any additional characteristic scales and represent the adjusted continuation of the self-similar impinging flow as it is redirected along the free surface plane. Therefore, the scales yielding self-similar profiles act as surrogates for estimating sub-surface flow and its TE properties, facilitating the development of remotely observable flow metrics for geophysical and engineering applications.
Bio
Zeeshan is a 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.
