On the dynamics of jets and branched fluidic networks
Jan Siemen Smink is a PhD student in the Department of Engineering Fluid Dynamics. (Co)Promotors are prof.dr.ir. C.H. Venner and dr.ir. C.W. Visser from the Faculty of Engineering Technology and dr. S.G. Huisman from the Faculty of Science & Technology.
Fluid jets are encountered everywhere, from the kitchen tap and water fountains to engineering systems such as water jet cutting techniques and fuel injection. The dynamics of jets has been studied for centuries, because of the ubiquity and broad applicability of jets. For many applications, having multiple jets in parallel configuration is important for e.g., increasing the mass throughput, or improving the mixing behaviour of jets with the medium in which they are injected. An approach to facilitate the parallelisation of jets is by using branched fluidic networks, where one main channel branches out into smaller channels to distribute the fluid towards multiple nozzles or orifices. Biological systems such as the bronchial trees of the lungs and vascular networks gave inspiration for the desired engineering networks, but how could the optimal network geometry be obtained for laminar and turbulent flow of different fluid models?
In this thesis, the dynamics of jets and their parallelisation via branched fluidic networks are discussed. The first part explains the optimisation of branched fluidic networks for laminar flow of non-Newtonian fluids, resulting in the optimal network geometry. It was found that the optimisation condition Q ∝ R3 does not only hold for Newtonian, but also for non-Newtonian fluids. When generalising the optimisation theory to turbulent flow of non-Newtonian fluids in rough-wall channels, the optimisation condition changes to Q ∝ Rx with x having a lower value than 3. The second part discusses the dynamics of a solidifying gravity-stretched liquid jet. The diameter of the yielding solid fibre is systematically modelled and measured, resulting in predictable fibre geometries for the production of (micro)fibres. The third part discusses dual injection of sonic jets into a supersonic cross-flow, both experimental and numerical, which is a model problem for fuel injection into the combustion chamber of a high-speed vehicle. The maximum penetration of the jets into the cross-flow – important for mixing air with fuel – depending on the relative jet strength and spacing between the two jets is found and discussed. Altogether, this thesis highlights the breadth and wealth of fluid dynamics of jet flow and branched fluidic networks.
