13 results found
Calmet H, Bertomeu PF, McIntyre C, et al., 2022, Computational modelling of an aerosol extraction device for use in COVID-19 surgical tracheotomy, Journal of Aerosol Science, Vol: 159, ISSN: 0021-8502
In view of the ongoing COVID-19 pandemic and its effects on global health, understanding and accurately modelling the propagation of human biological aerosols has become crucial. Worldwide, health professionals have been one of the most affected demographics, representing approximately 20% of all cases in Spain, 10% in Italy and 4% in China and US. Methods to contain and remove potentially infected aerosols during Aerosol Generating Procedures (AGPs) near source offer advantages in reducing the contamination of protective clothing and the surrounding theatre equipment and space. In this work we describe the application of computational fluid dynamics in assessing the performance of a prototype extraction hood as a means to contain a high speed aerosol jet. Whilst the particular prototype device is intended to be used during tracheotomies, which are increasingly common in the wake of COVID-19, the underlying physics can be adapted to design similar machines for other AGPs. Computational modelling aspect of this study was largely carried out by Barcelona Supercomputing Center using the high performance computational mechanics code Alya. Based on the high fidelity LES coupled with Lagrangian frameworks the results demonstrate high containment efficiency of generated particles is feasible with achievable air extraction rates.
Basley J, Gouder K, Morrison JF, 2022, MIXING AND LARGE-SCALE MODULATION OF A TURBULENT BOUNDARY LAYER PERTURBED BY AN EFFUSION FILM
The large-scale modulation of an effusion film injected into a high Reynolds-number boundary layer is investigated for a wide range of film-velocity to freestream-velocity ratios. Particle Image Velocimetry (PIV), visualisations and hot-wire measurements are used to characterise the momentum effects underlying the mixing of the effusion film. For this experiment, the geometry of a turbine blade is idealised in a large-scale facility with a canonical upstream boundary layer where the effusion film and the boundary layer are isothermal. Spectral analysis shows that the injection of the effusion film first promotes near-wall turbulence until the film breaks away from the surface when the velocity ratio reaches a critical value. For higher velocity ratios, large-scale motions from the incoming boundary layer no longer penetrate the sublayer. The associated spectral signature is accompanied by enhanced inter-scale exchanges, as shown by the skewness of the streamwise velocity component and the amplitude modulation coefficients. Use of seeding in the film flow enables the estimation of the concentration of injected fluid in the laser sheet. Joint momentum-concentration data show that the mixing of the film is strongly modulated by the large-scale motions of the turbulent boundary layer, although in different ways depending on the velocity ratio. For very low velocity ratios, large-scale motions are largely unaffected by the film. They encompass the boundary layer down to the injected sublayer and modulate locally the concentration of injected film. For higher velocity ratios, mixing intensifies as the effusion film is injected with momentum and reaches further from the wall. As a result, the concentration of injected fluid in the near-wall region is remotely, yet more intensively modulated by the large-scale motions above the sublayer.
Buscariolo FF, Hoessler J, Moxey D, et al., 2019, Spectral/hp element simulation of flow past a Formula One front wing: validation against experiments, Publisher: arXiv
Emerging commercial and academic tools are regularly being applied to thedesign of road and race cars, but there currently are no well-establishedbenchmark cases to study the aerodynamics of race car wings in ground effect.In this paper we propose a new test case, with a relatively complex geometry,supported by the availability of CAD model and experimental results. We referto the test case as the Imperial Front Wing, originally based on the front wingand endplate design of the McLaren 17D race car. A comparison of differentresolutions of a high fidelity spectral/hp element simulation usingunder-resolved DNS/implicit LES approach with fourth and fifth polynomial orderis presented. The results demonstrate good correlation to both the wall-boundedstreaklines obtained by oil flow visualization and experimental PIV results,correctly predicting key characteristics of the time-averaged flow structures,namely intensity, contours and locations. This study highlights the resolutionrequirements in capturing salient flow features arising from this type ofchallenging geometry, providing an interesting test case for both traditionaland emerging high-fidelity simulations.
Gouder KA, Naguib AM, Lavoie PL, et al., 2017, Control of boundary layer streaks induced by freestream turbulence using plasma actuators, 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017
Copyright © 2016 Zakon Group LLC. Previously, a systematic series of investigations, such as those of Hanson et al. (2010), Hanson et al. (2014) and Bade et al. (2016) were carried out aimed at assessing the capability of plasma-actuator-based Feedforward-Feedback control system to weaken streaks that were artificially induced into a Blasius boundary layer using dynamic roughness elements. In contrast, the current work builds on these previous works and drives towards the delay of bypass boundary layer transition, where in the presence of a freestream flow with turbulence intensity exceeding approximately 1%, streaks form naturally and stochastically in the underlying boundary layer. For the freestream velocity of the current experiment, turbulent spot formations were first observed at a streamwise location x ≈ 350 mm from the leading edge. Upstream of this location, the naturally-occurring high and low-speed streaks exhibit linear transient growth. Two wall-shear-stress sensors - one feed-forward (FF) and one feedback (FB) - and two plasma actuators capable of producing positive and negative wall-normal forcing to oppose high and low-speed streaks respectively were placed in the linear growth region. The output from the FF sensor was used in conjunction with single-point Linear Stochastic Estimation (LSE) and actuator-flow identified response models in order to generate a counter-disturbance, which, at the (downstream) FB sensor location, was equal in magnitude but opposite in sign to the natural streak estimate. The output of the FB sensor was fed to a PI controller to correct for any remaining, uncancelled disturbance resulting from, for example, inaccuracies in the LSE model of streak growth. Results, such as notable changes in the mean and rms wall normal velocity profiles and energy spectra, for FF only, and FF + FB control, provide an evaluation of the viability of the control approach to weaken boundary layer streaks and delay transition.
Zhao X, Gouder K, Graham JMR, et al., 2016, Buffet loading, dynamic response and aerodynamic control of a suspension bridge in a turbulent wind, Journal of Fluids and Structures, Vol: 62, Pages: 384-412, ISSN: 1095-8622
This paper describes experiments relating to the buffet response and control of a section of a long-span suspension bridge deck elastically mounted as part of a wind tunnel experiment. The bridge section is subject to grid generated flow turbulence. Two grids are used — one is a standard biplanar grid, while the second is a new design that provides larger turbulence length scales. The buffet response results are compared with admittances calculated using unsteady, three-dimensional, lifting-surface theory that extends standard two-dimensional Sears׳ theory. The bridge deck heave and pitch responses are predicted with comparisons made with wind tunnel measurements. In order to suppress buffeting, and increase the deck׳s critical flutter speed, the deck model is fitted with controllable leading- and trailing-edge flaps. Two sets of passive controllers, which use the flap angles as the control inputs, are demonstrated and evaluated for their capability to suppress the buffet response of the deck and increase its critical flutter speed. The first set of controllers sense the deck׳s position (pitch angle and heave, or pitch angle alone), whilst the second set (which are mechanical controllers) sense the vertical velocity of the flap hinge points. The control system design problem is solved as a mixed H2/H∞ optimisation problem. The wind tunnel experiments show that these control systems can reduce considerably the deck׳s buffet response, whilst simultaneously increasing its critical flutter speed.
Gouder K, Zhao X, Limebeer DJN, et al., 2015, Experimental Aerodynamic Control of a Long-Span Suspension Bridge Section Using Leading- and Trailing-Edge Control Surfaces, IEEE Transactions on Control Systems Technology, Vol: 24, Pages: 1441-1453, ISSN: 1558-0865
We experimentally investigate the suppression of flutter in long-span suspension bridges. A rigid sectional model of a long-span suspension bridge is mounted in a wind tunnel on a suspension system. Control surfaces, which are used to suppress flutter, are movable flaps that are fitted to the bridge section's leading and trailing edges. The flaps are responsive to the deck's heave and pitch motions. In this paper, the aerodynamic force is modeled using a thin aerofoil theory, although other modeling techniques can be used. The controller has a second-order passive transfer function with inputs of a combination of the deck's pitch angle and heave position, and outputs of the flaps' angular positions. The control system design problem is solved as an H∞ optimization problem.
Zhao X, Gouder K, Limebeer DJN, et al., 2014, Experimental flutter and buffet suppression of a sectional suspended-bridge, 53rd IEEE Conference on Decision and Control
This paper conducts flutter and buffet suppression of a section of a long-span bridge deck mounted elastically across a wind tunnel working section. The incident streamturbulence for buffet tests is generated by a standard biplanar grid. The bridge deck response in its two major degrees of freedom, heave and pitch. A mechanical flutter control system is developed which senses the vertical velocity of flap pivots andadjusts the leading and trailing-edge flap angles accordingly. The wind tunnel experiments show that the mechanical flutter control system can not only increase the critical flutter speed of the bridge deck but also can suppress the buffeting greatly.
Gouder K, Potter M, Morrison JF, 2013, Turbulent friction drag reduction using electroactive polymer and electromagnetically driven surfaces, EXPERIMENTS IN FLUIDS, Vol: 54, ISSN: 0723-4864
Rennie CE, Gouder K, Taylor DJ, et al., 2011, Characterisation of the temporal profile of nasal inspiration, British Rhinology Society meeting in Edinburgh
BackgroundThis study quantifies the time-varying flow rate during inspiration at rest and in sniffing, both predecongestion and postdecongestion. It aims to provide a better understanding of nasal airflow mechanics, for application to the physiological modeling of nasal respiration and to therapeutic drug delivery.MethodsThe temporal profiles of nasal inspiration were measured at high fidelity in 14 healthy individuals using simultaneous bilateral hot-wire anemometry. Peak nasal inspiratory flow (PNIF) rate, acoustic rhinometry (AR), and the sinonasal outcome test (SNOT) provided complementary clinical measurements. The impact of decongestion was also investigated.ResultsIn the initial phase of inspiration, a rapid rise in flow rate was observed. Flow first exceeded 150 mL/second in either passage within a median time of approximately 120 ms for inspiration at rest and approximately 60 ms in sniffing (∼20 ms in the fastest sniffs). The mean sustained flow rate attained and the overall period of each measured inspiratory profile were analyzed. AR showed a significant change in nasal volume with decongestion, although these change were not manifest in the temporal profiles of inspiratory flow (barring a weak effect associated with the most vigorous sniffs).ConclusionNovel methods were applied to investigate the temporal profiles of nasal inspiration. Characteristic features of the profile were identified and found to be significantly different between inspiration at rest and sniffing. Decongestion was found to have little effect on the temporal profiles for the flow regimes studied.
Potter M, Gouder K, Morrison JF, 2010, A numerical model for electro-active polymer actuators with experimental validation, Sensors and Actuators A-Physical, Vol: 170, Pages: 121-130
This paper presents a theoretical model for predicting the behavior of electro-active polymer actuators. This model takes the form of an array of masses with the interconnecting forces derived using Hooke's law coupled with an electrostatic force, and is solved using time-marching integration. Forming the model in this way allows the response of actuators of various sizes and pre-strains to be simulated with a range of electrode designs and mechanically stiffened sections. To validate the response of the model a series of Nusil MED4905 polydimethylsiloxane actuators were built and tested with differing electrode designs and with additional mechanical stiffening of the membrane. Through a comparison of maximum electrode displacement, with applied electrode voltage, tracking of a grid on the membrane surface and dynamic testing, the model was found to show excellent agreement with the experimental results.
Gouder K, Morrison JF, 2009, The Effects of Periodic Surface Forcing on a Turbulent Boundary Layer, European Turbulence Conference
Gouder K, Morrison JF, 2009, Turbulent friction drag reduction over electroactive polymer smart surfaces, KATnet Conference on Key Aerodynamic Technologies
Both experiments and numerical simulations have provided evidence that an initially fully developed two-dimensional boundary layer, subjected to a sudden spanwise forcing, exhibits a decrease in turbulent friction drag as well as turbulent quantities such as the Reynolds shear stress and turbulent kinetic energy. In past experiments, such forcing has traditionally been in the form of cam-shaft driven spanwise wall oscillations and spanwise travelling Lorentz forcing. Computationally the forcing has been in the form of superimposed spanwise pressure gradients, spanwise travelling waves of an in-plane ﬂexible wall and spanwise travelling Lorentz forcing. The aim of this work is to take the idea a step further and develop an active surface which locally executes the motions described above and making such a system more easy to manufacture. The material chosen to build the active surface texture is electroactive polymer (EAP) which is able to undergo large deﬂections at high frequencies. This work reports the development and testing of one version of these active walls, namely one executing in-plane local oscillations with an amplitude close to the mean streak spacing in a turbulent ﬂow. The eﬀect of this surface was conﬁned to wallnormal heights on the order of the viscous sub-layer of the turbulent boundary layer, and frequency and wavelength similar to those reported in literature. Direct measurement of friction drag using a purposely-developed drag balance and extensive hot-wire measurements are presented for the systematic variation of the relevant parameters for turbulent friction drag reduction.
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