Laboratory e-tutor for Engineering

The laboratory e-tutor is a bespoke collection of self-running presentations in Adobe Communicator on Blackboard, written for the second year thermodynamic and fluid dynamic laboratories. The e-tutor has significantly changed the way laboratories are taught in Engineering by providing a bespoke step by step video guidance to each experiment in the form of an interactive presentation. Building upon the existing LabView computer based data collection and processing, the e-tutor uses the existing PCs attached to each experiment. It enhances the paper instruction sheet that is handed out at the beginning of each laboratory session by providing a multi-media content that enables students to start and run safely through the experiment and data analysis, developing their independent learning and their confidence in performing hands on engineering tasks. Students liked very much the blended learning environment of an e-tutor and a member of staff at hand to ask clarifications if in doubt and embraced the new technology seamlessly. Academic staff are able to focus on stimulating the critical appraisal of the experimental results by the students, which makes laboratories more enjoyable by students and staff

On the generation of the mean velocity profile for turbulent boundary layers with pressure gradient under equilibrium conditions.

The generation of a fully turbulent boundary layer profile is investigated using analytical and numerical methods over the Reynolds number range 422 ≤ Reθ ≤ 31,000. The numerical method uses a new mixing length blending function. The predictions are validated against reference wind tunnel measurements under zero streamwise pressure gradient. The methods are then tested for low and moderate adverse pressure gradients. Comparison against experiment and DNS data show a good predictive ability under zero pressure gradient and moderate adverse pressure gradient, with both methods providing a complete velocity profile through the viscous sub-layer down to the wall. These methods are useful computational fluid dynamic tools for generating an equilibrium thick turbulent boundary layer at the computational domain inflow

Physiological Fontan Procedure

© 2019 Corno, Owen, Cangiani, Hall and Rona. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Objective: The conventional Fontan circulation deviates the superior vena cava (SVC = 1/3 of the systemic venous return) toward the right lung (3/5 of total lung volume) and the inferior vena cava (IVC = 2/3 of the systemic venous return) toward the left lung (2/5 of total lung volume). A “physiological” Fontan deviating the SVC toward the left lung and the IVC toward the right lung was compared with the conventional setting by computational fluid dynamics, studying whether this setting achieves a more favorable hemodynamics than the conventional Fontan circulation. Materials and Methods: An in-silico 3D parametric model of the Fontan procedure was developed using idealized vascular geometries with invariant sizes of SVC, IVC, right pulmonary artery (RPA), and left pulmonary artery (LPA), steady inflow velocities at IVC and SVC, and constant equal outflow pressures at RPA and LPA. These parameters were set to perform finite-volume incompressible steady flow simulations, assuming a single-phase, Newtonian, isothermal, laminar blood flow. Numerically converged finite-volume mass and momentum flow balances determined the inlet pressures and the outflow rates. Numerical closed-path integration of energy fluxes across domain boundaries determined the flow energy loss rate through the Fontan circulation. The comparison evaluated: (1) mean IVC pressure; (2) energy loss rate; (3) kinetic energy maximum value throughout the domain volume. Results: The comparison of the physiological vs. conventional Fontan provided these results: (1) mean IVC pressure 13.9 vs. 14.1 mmHg (= 0.2 mmHg reduction); (2) energy loss rate 5.55 vs. 6.61 mW (= 16% reduction); (3) maximum kinetic energy 283 vs. 396 J/m3 (= 29% reduction). Conclusions: A more physiological flow distribution is accompanied by a reduction of mean IVC pressure and by substantial reductions of energy loss rate and of peak kinetic energy. The potential clinical impact of these hemodynamic changes in reducing the incidence and severity of the adverse long-term effects of the Fontan circulation, in particular liver failure and protein-losing enteropathy, still remains to be assessed and will be the subject of future work

A hybrid RANS model of wing-body junction flow

This is an accepted manuscript of an article published by Elsevier in European Journal of Mechanics B: Fluids on 26/09/2019, available online: https://doi.org/10.1016/j.euromechflu.2019.09.014 The accepted version of the publication may differ from the final published version.The three-dimensional flow separation over the Rood wing-body junction is an exemplar application of separation affecting many important flows in turbomachinery and aerodynamics. Conventional Reynolds Averaged Navier Stokes (RANS) methods struggle to reproduce the complexity of this flow. In this paper, an unconventional use is made of a hybrid Reynolds Averaged Navier Stokes (RANS) model to tackle this challenge. The hybridization technique combines the Menter − − model with the one equation sub-grid-scale (SGS) model by Yoshizawa through a blending function, based on the wall-normal distance. The hybrid RANS turbulence closure captured most of the flow features reported in past experiments with reasonable accuracy. The model captured also the small secondary vortex at the corner ahead of the wing nose and at the trailing edge. This feature is scarcely documented in the literature. The study highlights the importance of the spatial resolution near the wing leading edge, where this localised secondary recirculation was observed by the hybrid RANS model. It also provides evidence on the applicability of the hybrid Menter and Yoshizawa turbulence closure to the wing-body junction flows in aircraft and turbomachines, where the flows are characterised by a substantially time-invariant three-dimensional separation

Numerical investigation of the three-dimensional pressure distribution in Taylor Couette flow

Copyright © 2017 by ASME. An investigation is conducted on the flow in a moderately wide gap between an inner rotating shaft and an outer coaxial fixed tube, with stationary end-walls, by threedimensional Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD), using the realizable k - ϵ model. This approach provides three-dimensional spatial distributions of static and dynamic pressures that are not directly measurable in experiment by conventional nonintrusive optics-based techniques. The nonuniform pressure main features on the axial and meridional planes appear to be driven by the radial momentum equilibrium of the flow, which is characterized by axisymmetric Taylor vortices over the Taylor number range 2.35 × 106 ≤ Ta ≤ 6.47 × 106. Regularly spaced static and dynamic pressure maxima on the stationary cylinder wall follow the axial stacking of the Taylor vortices and line up with the vortex-induced radial outflow documented in previous work. This new detailed understanding has potential for application to the design of a vertical turbine pump head. Aligning the location where the gauge static pressure (GSP) maximum occurs with the central axis of the delivery pipe could improve the head delivery, the pump mechanical efficiency, the system operation, and control costs.Published versio

Local Thermal Non-equilibrium Analysis of Cu-Al2O3 Hybrid ‎Nanofluid Natural Convection in a Partially Layered Porous ‎Enclosure with Wavy Walls

A numerical study is performed to investigate the local thermal non-equilibrium effects on the natural convection in a two-dimensional enclosure with horizontal wavy walls, layered by a porous medium, saturated by Cu-Al2O3/water hybrid nanofluid. It is examined the influence of the nanoparticle volume fraction, varied from 0 to 0.04, the Darcy number (10-5 ≤ Da ≤ 10-2), the modified conductivity ratio (0.1 ≤ ϒ ≤ 1000), the porous layer height (0 ≤ Hp ≤ 1), and the wavy wall wavenumber (1 ≤ N ≤ 5) on natural convection in the enclosure. Predictions of the steady incompressible flow and temperature fields are obtained by the Galerkin finite element method, using the Darcy-Brinkman model in the porous layer. These are validated against previous numerical and experimental studies. By resolving separately the temperature fields of the working fluid and of the porous matrix, the local thermal non-equilibrium model exposed hot and cold spot formation and mitigation mechanisms on the heated and cooled walls. By determining the convection cell strength, the Darcy number is the first rank controlling parameter on the heat transfer performance, followed by N, Hp and γ. The heat transfer rate through the hybrid nanofluid and solid phases is highest when N = 4 at a fixed value of nanoparticle volume fraction

ECMO for COVID-19 patients in Europe and Israel

Since March 15th, 2020, 177 centres from Europe and Israel have joined the study, routinely reporting on the ECMO support they provide to COVID-19 patients. The mean annual number of cases treated with ECMO in the participating centres before the pandemic (2019) was 55. The number of COVID-19 patients has increased rapidly each week reaching 1531 treated patients as of September 14th. The greatest number of cases has been reported from France (n = 385), UK (n = 193), Germany (n = 176), Spain (n = 166), and Italy (n = 136) .The mean age of treated patients was 52.6 years (range 16–80), 79% were male. The ECMO configuration used was VV in 91% of cases, VA in 5% and other in 4%. The mean PaO2 before ECMO implantation was 65 mmHg. The mean duration of ECMO support thus far has been 18 days and the mean ICU length of stay of these patients was 33 days. As of the 14th September, overall 841 patients have been weaned from ECMO support, 601 died during ECMO support, 71 died after withdrawal of ECMO, 79 are still receiving ECMO support and for 10 patients status n.a. . Our preliminary data suggest that patients placed on ECMO with severe refractory respiratory or cardiac failure secondary to COVID-19 have a reasonable (55%) chance of survival. Further extensive data analysis is expected to provide invaluable information on the demographics, severity of illness, indications and different ECMO management strategies in these patients

The acoustic resonance of cylindrical cavities

The grazing flow past a cylindrical surface cut-out can develop instabilities that adversely affect the aerodynamic performance of airframe, automotive, and railway components. Such instabilities can be either fluid dynamic, hydroelastic or flow-resonant, depending on whether aeroelastic or acoustic effects contribute to the flow unsteadiness. The flow past the surface cut-out, or cavity, separates at the upstream edge, forming a shear layer, as shown in figure 1. Provided the cavity streamwise length to depth ratio (L/D) is low, typically L/D ≤ 6, the shear layer spans across the cavity opening and reattaches on the downstream wall, forming an `open' cavity flow. For a given inflow condition and geometry, a cavity fluid dynamic instability can manifest itself as limit cycle modes spanning a specific frequency range. The presence of acoustic or aeroelastic resonant modes in an open cavity over the same frequency range can play an important role in mode selection and in phase-locking the feed-back process. An analytical model for the small amplitude acoustic perturbations inside an enclosure with rigid walls is developed from classical linerized acoustics. The method is applied to a L/D = 0.714 cylindrical geometry and the normalized mode shapes and frequencies of the first six standing wave modes are given. The results are used to diagnose whether, at a free stream Mach number M[subscript ∞] = 0.235, coupling is likely to occur between the first two Rossiter modes and the acoustic standing waves, which may lead to a reinforcement of the flow instability. At the selected test conditions, the method indicates that the second Rossiter mode can couple with the first axial acoustic mode, also known as the organ-pipe mode or the quarter-wavelength mode. The parametrized analytical solutions developed in this study enable the aero-acoustic engineer to diagnose whether coupling between a given fluid dynamic instability and acoustic resonance is likely to affect a cylindrical cavity component

Control of transonic cavity flow instability by streamwise air injection

A time-dependent numerical model of a turbulent Mach 1.5 flow over a rectangular cavity has been developed, to investigate suppression strategies for its natural self-sustained instability. This instability adversely affects the cavity form drag, it produces large-amplitude pressure oscillations in the enclosure and it is a source of far-field acoustic radiation. To suppress the natural flow instability, the leading edge of the two-dimensional cavity model is fitted with a simulated air jet that discharges in the downstream direction. The jet mass flow rate and nozzle depth are adjusted to attenuate the instability while minimising the control mass flow rate. The numerical predictions indicate that, at the selected inflow conditions, the configurations with the deepest nozzle (0.75 of the cavity depth) give the most attenuation of the modelled instability, which is dominated by the cavity second mode. The jet affects both the unsteady pressure field and the vorticity distribution inside the enclosure, which are, together, key determinants of the cavity leading instability mode amplitude. The unsteadiness of the pressure field is reduced by the lifting of the cavity shear layer at the rear end above the trailing edge. This disrupts the formation of upstream travelling feed-back pressure waves and the generation of far-field noise. The deep nozzle also promotes a downstream bulk flow in the enclosure, running from the upstream vertical wall to the downstream one. This flow attenuates the large-scale clockwise recirculation that is present in the unsuppressed cavity flow. The same flow alters the top shear layer vorticity thickness and probably affects the convective growth of the shear layer cavity second mode