We report the construction and use of a vortex reactor which uses a rapidly rotating cylinder to generate Taylor vortices for continuous flow thermal and photochemical reactions. The reactor is designed to operate under conditions required for vortex generation. The flow pattern of the vortices has been represented using computational fluid dynamics, and the presence of the vortices can be easily visualized by observing streams of bubbles within the reactor. This approach presents certain advantages for reactions with added gases. For reactions with oxygen, the reactor offers an alternative to traditional setups as it efficiently draws in air from the lab without the need specifically to pressurize with oxygen. The rapid mixing generated by the vortices enables rapid mass transfer between the gas and the liquid phases allowing for a high efficiency dissolution of gases. The reactor has been applied to several photochemical reactions involving singlet oxygen (1O2) including the photo-oxidations of α-terpinene and furfuryl alcohol and the photodeborylation of phenyl boronic acid. The rotation speed of the cylinder proved to be key for reaction efficiency, and in the operation we found that the uptake of air was highest at 4000 rpm. The reactor has also been successfully applied to the synthesis of artemisinin, a potent antimalarial compound; and this three-step synthesis involving a Schenk-ene reaction with 1O2, Hock cleavage with H+, and an oxidative cyclization cascade with triplet oxygen (3O2), from dihydroartemisinic acid was carried out as a single process in the vortex reactor.

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Thin-film flows encountered in engineering systems such as aeroengine bearing chambers often exhibit capillary waves and occur within a moderate to high Weber number range. Although the depth-averaged simulation of these thin-film flows is computationally efficient relative to traditional VOF methods, numerical challenges remain particularly for solutions involving capillary waves and in the higher Weber number, low surface tension range. A depth-averaged approximation of the Navier-Stokes equations has been used to explore the effect of surface tension, grid resolution and inertia on thin-film rimming solution accuracy and numerical stability. In shock and pooling solutions where capillary ripples are present, solution stability and accuracy are shown to be highly sensitive to surface tension. The common practice in analytical studies of enforcing unphysical low Weber number stability constraints is shown to stabilise the solution by artificially damping capillary oscillations. This approach however although providing stable solutions is shown to adversely affect solution accuracy. An alternative grid resolution based stability criteria is demonstrated and used to obtain numerically stable shock and pooling solutions without recourse to unphysical surface tension values. This allows for the accurate simulation of thin-film flows with capillary waves within the constrained parameter space corresponding to physical material and flow properties. Results obtained using the proposed formulation and solution strategy show good agreement with available experimental data from

a b s t r a c tThe development of a coupled computational fluid-dynamics rigid body (CFD-RBD) model is presented. The RBD model deploys rotational quaternions, which are free from the gimbal lock that is associated with Euler rotational matrix. The quaternion model means that the complex 3D spinning flight modes associated with the flight of plate-type windborne debris can be modelled robustly. This paper attempts to determine the accuracy of the CFD-RBD model by comparing the predicted trajectories from a large number of debris simulations with experimentally derived equations of best fit. Agreement is found to be good and, based on the findings, an alternative form for the dimensionless flight distance is presented, which extends the range of the experimental study to longer flight times.The predictions from the CFD-RBD model are then compared against two quasi-steady analytical debris flight models. The second model is based on modified force and moment coefficients, which are informed by the findings from the CFD-RBD model. For plates that have attained a stable, autorotational flight mode, the CFD-RBD and analytical models are in good agreement. Their predictions differ during the initial stages of flight, where the complex non-linear interactions between the plate and its wake are not captured by the analytical models.

This paper presents a coupled ETFM-VOF framework for the numerical simulation of multi-scale thin liquid films. A depth-averaged Eulerian thin-film model (ETFM) is used to simulate the oil flow in very thin-film regions where film thicknesses are below the grid resolution while elsewhere in the domain where grid resolution is sufficient to resolve the film, a traditional Volume-of-Fluid (VOF) approach is retained. The two approaches are coupled through momentum and mass conserving source terms and a transition criterion is introduced where the total liquid volume fraction in each cell is evaluated and either the ETFM or VOF approach used depending on the sufficiency of the local grid resolution. Using this approach, thin-film flows characterised by multiple film thickness scales may be reliably simulated at a relatively lower computational cost. The model builds upon currently available ETFM and VOF approaches to thin-film modelling and represents a novel approach to the numerical simulation of multiphase flows involving a varying range of film thickness scales in space and time. A numerical test case of the 3D rimming flow inside an idealised aero-engine bearing chamber has been used to demonstrate the approach and comparisons made against high resolution VOF solutions.