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Liu, Athena

University of British Columbia

This research studies the impingement of a free surface Newtonian liquid jet on a dry solid moving wall using theoretical, numerical and experimental methods. The study focus mainly on the parameter range of jet Reynolds numbers 100< Reⱼ <1000 and the wall-to-jet velocity ratios 0.04<uw/vⱼ <30, where the effect of surface tension is negligible, and the major impingement regimes are splash and deposition, although cases with a wider parameter range are probed through CFD or experiments to identify the limit of the proposed theory. First, the 2D (slot or planar) jet impingement problem is explored. A regime diagram based on Reⱼ and uw/vⱼ is established using CFD, and four regimes are identified: splash, steady deposition with a heel, steady deposition with a heel with bumps, and unsteady deposition. A semi-empirical model based on the boundary layer theory and the Karman-Pohlhausen averaging scheme is developed to describe the flow of the steady heel regime. The model provides full solutions for the interface profile, boundary layer thickness, and the velocity field for a given the parameter setting of Reⱼ and uw/vⱼ, and the model predictions agree well with CFD. A second model using the time-dependent boundary-layer equations is developed to rationalize the spreading dynamics of the shallow film, which provides explanations on why the steady state disappears when uw/vⱼ < 2 or when uw/vⱼ is too large. Then, the study advances to the 3D (circular) jet impingement problem. Experiments are conducted using a custom apparatus with high speed imaging technique that map out the regime diagram based on Reⱼ and uw/vⱼ and measure the geometry of the impinging jet. The experiments are complemented with numerical simulations, which reveal the anatomy of the spreading film (lamella) and aid the development of a theoretical model. The model predicts the dimensions of the lamella (the length of the upstream heel and the width of the downstream lamella), and that the shape takes a universal form when scaled by one of these distances. These predictions agree well with the experiments and simulations provided that a lamella exists.

Text

2022-12-06

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/83358

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/