29 results found
Vouriot CVM, Higton TD, Linden PF, et al., 2023, Uniformly distributed floor sources of buoyancy can give rise to significant spatial inhomogeneities within rooms, Flow: Applications of Fluid Mechanics, ISSN: 2633-4259
Displacement ventilation, where cool external air enters a room through low-level vents and warmer airleaves through high-level vents, is characterised by vertical gradients in pressure arising from the warmerindoor temperatures. Models usually assume that horizontal variations of temperature difference are smallin comparison and are, therefore, unimportant. Small-scale laboratory experiments and computational fluiddynamics were used to examine these flows, driven by a uniformly heated floor. These experiments andsimulations show that the horizontal variations of temperature difference can be neglected for predictions of the bulk ventilation rate; however, they also evidence that these horizontal variations can be significant andplay a critical role in establishing the pattern of flow within the room — this renders the horizontal position ofthe low- and high-level vents (relative to one another) important. We consider two cases: single-ended (whereinlet and outlet are at the same end of the room) and opposite-ended. In both cases the ventilation flow rateis the same. However, in the opposite-ended case a dead zone is established in the upper part of the roomwhich results in significant horizontal variations. We consider the formation of this dead zone by examiningthe streamline patterns and the age of air within the room. We discuss the implications for occupant exposureto pollutants and airborne disease.Impact Statement:Exposure to indoor air pollution and airborne diseases are major factors in human health and well being.Guidance on appropriate ventilation rates is typically based on bulk ventilation rates, either in terms of theamount supplied per individual or as air exchange rates for a space. Such bulk measures assume homogeneousconditions within a space while, in practice, there are often significant spatial variations in properties. Thispaper shows that in displacement ventilation, where it is commonly assumed that horizontal variations arenegligible
Huang J, Burridge HC, Reeuwijk MV, 2023, The internal structure of forced fountains, Journal of Fluid Mechanics, Vol: 961, Pages: 1-29, ISSN: 0022-1120
We study the mixing processes inside a forced fountain using data from directnumerical simulation. The outer boundary of the fountain with the ambient is aturbulent/non-turbulent interface. Inside the fountain, two internalboundaries, both turbulent/turbulent interfaces, are identified: 1) theclassical boundary between upflow and downflow which is composed of the loci ofpoints of zero mean vertical velocity; and 2) the streamline that separates themean flow emitted by the source from the entrained fluid from the ambient (theseparatrix). We show that entrainment due to turbulent fluxes across theinternal boundary is at least as important as that by the mean flow. However,entrainment by the turbulence behaves substantively differently from that bythe mean flow and cannot be modelled using the same assumptions. This presentsa challenge for existing models of turbulent fountains and other environmentalflows that evolve inside turbulent environments.
Burridge H, Bontitsopoulos S, Brown C, et al., 2023, Variations in classroom ventilation during the COVID-19 pandemic: Insights from monitoring 36 naturally ventilated classrooms in the UK during 2021, Journal of Building Engineering, Vol: 63, Pages: 1-15, ISSN: 2352-7102
Seasonal changes in the measured CO2 levels at four schools are herein presented through a set of indoor air quality metrics that were gathered during the height of the COVID-19 pandemic in the UK. Data from non-intrusive environmental monitoring units were remotely collected throughout2021 from 36 naturally ventilated classrooms at two primary schools and two secondary schools in England. Measurements were analysed to assess the indoor CO2 concentration and temperature. Relative to UK school air quality guidance, the CO2 levels within classrooms remained relatively lowduring periods of warmer weather, with elevated CO2 levels being evident during the colder seasons, indicating lower levels of per person ventilation during these colder periods. However, CO2 data from the cold period during the latter part of 2021, imply that the per person classroom ventilation levelswere significantly lower than those achieved during a similarly cold weather period during the early part of the year. Given that the classroom architecture and usage remained unchanged, this finding suggests that changes in the ventilation behaviours within the classrooms may have altered, and raisesquestions as to what may have given rise to such change, in a year when, messaging and public concerns regarding COVID-19 varied within the UK. Significant variations were observed when contrasting data, both between schools, and between classrooms within the same school building;suggesting that work is required to understand and catalogue the existing ventilation provisions and architecture within UK classrooms, and that more work is required to ascertain the effects of classroom ventilation behaviours.
Burridge HC, Fan S, Jones RL, et al., 2022, Predictive and retrospective modelling of airborne infection risk using monitored carbon dioxide, Indoor and Built Environment, Vol: 31, Pages: 1363-1380, ISSN: 1420-326X
The risk of long range, herein ‘airborne', infection needs to be better understood and is especially urgent during the COVID-19 pandemic. We present a method to determine the relative risk of airborne transmission that can be readily deployed with either modelled or monitored CO2 data and occupancy levels within an indoor space. For spaces regularly, or consistently, occupied by the same group of people, e.g. an open-plan office or a school classroom, we establish protocols to assess the absolute risk of airborne infection of this regular attendance at work or school. We present a methodology to easily calculate the expected number of secondary infections arising from a regular attendee becoming infectious and remaining pre/asymptomatic within these spaces. We demonstrate our model by calculating risks for both a modelled open-plan office and by using monitored data recorded within a small naturally ventilated office. In addition, by inferring ventilation rates from monitored CO2, we show that estimates of airborne infection can be accurately reconstructed, thereby offering scope for more informed retrospective modelling should outbreaks occur in spaces where CO2 is monitored. Well-ventilated spaces appear unlikely to contribute significantly to airborne infection. However, even moderate changes to the conditions within the office, or new variants of the disease, typically result in more troubling predictions.
- Open Access Link
- Citations: 16
Higton TD, Burridge HC, Hughes GO, 2021, Natural ventilation flows established by a localised heat source in a room with a doorway and a high-level vent, Building and Environment, Vol: 203, Pages: 1-9, ISSN: 0360-1323
Ventilation flows generated by a localised heat source within a room containing two openings to the ambient environment are examined. The openings are representative of a doorway and a high-level vent, and a steady two-layer stratification of well-mixed fluid is established within the room for all cases considered. Classical displacement ventilation flow is observed when the interface between the two layers is above the height of the doorway. Displacement ventilation flow can persist when the interface within the room is below the height of the doorway; in general, however, an unbalanced exchange flow forms across the doorway and the ventilating flow is found to be dependent on the doorway aspect ratio, the doorway height relative to the room height, the effective area of the high-level vent (relative to the square of the room height) and the rate of entrainment into the plume generated by the localised heat source. An analytical model is presented which predicts the ventilation rates and temperature structures within the room for these flows. Results from analogue experiments demonstrate good agreement with the model for a wide range of the parameter space relevant to the full-scale application.
Vouriot C, Burridge H, Noakes C, et al., 2021, Seasonal variation in airborne infection risk in schools due to changes in ventilation inferred from monitored carbon dioxide, Indoor Air: international journal of indoor air quality and climate, Vol: 31, Pages: 1154-1163, ISSN: 0905-6947
The year 2020 has seen the world gripped by the effects of the COVID‐19 pandemic. It is not the first time, nor will it be last, that our increasingly globalized world has been significantly affected by the emergence of a new disease. In much of the Northern Hemisphere, the academic year begins in September, and for many countries, September 2020 marked the return to full schooling after some period of enforced closure due to COVID‐19. In this paper, we focus on the airborne spread of disease and investigate the likelihood of transmission in school environments. It is crucial to understand the risk airborne infection from COVID‐19 might pose to pupils, teachers, and their wider social groups. We use monitored CO2 data from 45 classrooms in 11 different schools from within the UK to estimate the likelihood of infection occurring within classrooms regularly attended by the same staff and pupils. We determine estimates of the number of secondary infections arising via the airborne route over pre/asymptomatic periods on a rolling basis. Results show that, assuming relatively quiet desk‐based work, the number of secondary infections is likely to remain reassuringly below unity; however, it can vary widely between classrooms of the same school even when the same ventilation system is present. Crucially, the data highlight significant variation with the seasons with January being nearly twice as risky as July. We show that such seasonal variations in risk due to changes in ventilation rates are robust and our results hold for wide variations in disease parameterizations, suggesting our results may be applied to a number of different airborne diseases.
Burridge HC, Bhagat RK, Stettler MEJ, et al., 2021, The ventilation of buildings and other mitigating measures for COVID-19: a focus on wintertime, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 477, Pages: 1-31, ISSN: 1364-5021
The year 2020 has seen the emergence of a global pandemic as a result of the disease COVID-19. This report reviews knowledge of the transmission of COVID-19 indoors, examines the evidence for mitigating measures, and considers the implications for wintertime with a focus on ventilation.
Parker DA, Burridge HC, Partridge JL, et al., 2021, Vertically distributed wall sources of buoyancy. Part 2. Unventilated and ventilated confined spaces, Journal of Fluid Mechanics, Vol: 907, ISSN: 0022-1120
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Parker DA, Burridge HC, Partridge JL, et al., 2021, Vertically distributed wall sources of buoyancy. Part 1. Unconfined, Journal of Fluid Mechanics, Vol: 907, ISSN: 0022-1120
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Burridge HC, Pini R, Shah SMK, et al., 2021, Identifying efficient transport pathways in early-wood timber: insights from 3D X-ray CT imaging of softwood in the presence of flow, Transport in Porous Media, Vol: 136, Pages: 813-830, ISSN: 0169-3913
Wider use of timber has the potential to greatly reduce the embodied carbon of construction. Improved chemical treatment could help overcome some of the barriers to wider application of timber, by furthering the durability and/or mechanical properties of this natural material. Improving timber treatment by treating the whole volume of a piece of timber, or tailored sections thereof, requires sound understanding and validated modelling of the natural paths for fluid flow through wood. In this study we carry out a robust analysis of three-dimensional X-ray CT measurements on kiln-dried softwood in the presence of flow and identify small portions of early-wood which are uniquely capable of transporting fluids—herein ‘efficient transport pathways’. We successfully model the effects of these pathways on the liquid uptake by timber by introducing a spatial variability in the amount of aspiration of the bordered pits following kiln drying. The model demonstrates that fluid advances along these efficient transport paths between 10 and 30 times faster than in the remainder of the timber. Identifying these efficient transport pathways offers scope to improve and extend the degree to which timber properties are enhanced at an industrial scale through processes to impregnate timber.
Burridge H, Hallstadius O, 2020, Observing the Mpemba effect with minimal bias and the value of the Mpemba effect to scientific outreach and engagement, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 476, ISSN: 1364-5021
The Mpemba effect is the assertion that it is quicker to cool or freeze water when the initial temperature is high. We define the Mpemba effect to have been observed when two samples of water, one initially warmer than the other, are cooled and the initially hotter sample freezes or cools to a prescribed temperature in less time; this assumes that the samples are of the same mass, are at least as pure as drinking water, the cooling is delivered to both samples in the same manner and the same level of insulation is applied to both. Under this definition, we enable repeatable observations of the Mpemba effect by systematically introducing increased nucleation sites (in our case by roughening the container walls with sandpaper) within the cooling environment of the initially warmer sample. We remain able to observe the Mpemba effect when the enthalpy of cooling and freezing the initially warmer sample exceeds that of the initially cooler sample by over 50%, corresponding to a difference in the initial temperatures of around 50 °C. The context of this study, initiated by a high-school student who then carried out all of the experiments, highlights the value of the Mpemba effect as a tool for scientific learning and engagement.
Parker DA, Burridge HC, Partridge JL, et al., 2020, A comparison of entrainment in turbulent line plumes adjacent to and distant from a vertical wall, Journal of Fluid Mechanics, Vol: 882, Pages: 1-36, ISSN: 0022-1120
We present simultaneous two-dimensional measurements of the velocity and buoyancy fields on a central vertical plane in two-dimensional line plumes: a free plume distant from vertical boundaries and a wall plume, adjacent to a vertical wall. Data are presented in both an Eulerian and a plume coordinate system that follow the instantaneous turbulent/non-turbulent interface (TNTI) of the plume. We present measurements in both coordinate systems and compare the entrainment in the two flows. We find that the value of the entrainment coefficient in the wall plume is greater than half that of the free plume. The reduction in entrainment is investigated by considering a decomposition of the entrainment coefficient based on the mean kinetic energy where the relative contributions of turbulent production, buoyancy and viscous terms are calculated. The reduced entrainment is also investigated by considering the statistics of the TNTI and the conditional vertical transport of the ambient and engulfed fluid. We show that the wall shear stress is non-negligible and that the free plume exhibits significant meandering. The effect of the meandering on the entrainment process is quantified in terms of the stretching of the TNTI where it is shown that the length of the TNTI is greater in the free plume and, further, the relative vertical transport of the engulfed ambient fluid is observed to be 15 % greater in the free plume. Finally, the turbulent velocity and buoyancy fluctuations, Reynolds stresses and the turbulent buoyancy fluxes are presented in both coordinate systems.
Burridge H, Wu G, Reynolds T, et al., 2019, The transport of liquids in softwood: timber as a model porous medium, Scientific Reports, Vol: 9, Pages: 1-14, ISSN: 2045-2322
Timber is the only widely used construction material we can grow. The wood from which it comeshas evolved to provide structural support for the tree and to act as a conduit for fluid flow. Theseflow paths are crucial for engineers to exploit the full potential of timber, by allowing impregnationwith liquids that modify the properties or resilience of this natural material. Accurately predictingthe transport of these liquids enables more efficient industrial timber treatment processes to be de-veloped, thereby extending the scope to use this sustainable construction material; moreover, it isof fundamental scientific value — as a fluid flow within a natural porous medium. Both structuraland transport properties of wood depend on its micro-structure but, while a substantial body ofresearch relates the structural performance of wood to its detailed architecture, no such knowledgeexists for the transport properties. We present a model, based on increasingly refined geometricparameters, that accurately predicts the time-dependent ingress of liquids within softwood timber,thereby addressing this long-standing scientific challenge. Moreover, we show that for the minimal-istic parameterisation the model predicts ingress with a square-root-of-time behaviour. However,experimental data show a potentially significant departure from this√tbehaviour — a departurewhich is successfully predicted by our more advanced parametrisation. Our parameterisation of thetimber microstructure was informed by computed tomographic measurements; model predictionswere validated by comparison with experimental data. We show that accurate predictions requirestatistical representation of the variability in the timber pore space. The collapse of our dimen-sionless experimental data demonstrates clear potential for our results to be up-scaled to industrialtreatment processes.
Reynolds TPS, Burridge HC, Johnston R, et al., 2018, Cell geometry across the ring structure of Sitka spruce, Journal of the Royal Society Interface, Vol: 15, ISSN: 1742-5662
For wood to be used to its full potential as an engineering material, it is necessary to quantify links between its cell geometry and the properties it exhibits at bulk scale. Doing so will make it possible to predict timber properties crucial to engineering, such as mechanical strength and stiffness, and the resistance to fluid flow, and to inform strategies to improve those properties as required, as well as to measure the effects of interventions such as genetic manipulation and chemical modification. Strength, stiffness and permeability of timber all derive from the geometry of its cells, and yet current practice is to predict them based on properties, such as bulk density, that do not directly describe the cell structure. This work explores links between micro-computed tomography data for structural-size pieces of wood, which show the variation of porosity across the wood's ring structure, and high-resolution tomography showing the geometry of the cells, from which we measure cell length, lumen area, porosity, cell wall thickness and the number density of cells. High-resolution scans, while informative, are time-consuming and expensive to run on a large number of samples at the scale of building components. By scanning the same volume of timber at both low and high resolutions (high-resolution scans over a near-continuous volume of timber of approx. 20 mm3 at 15 μm3 per voxel), we are able to demonstrate correlations between the measurements at the two different resolutions, reveal the physical basis for these correlations, and demonstrate that the data from the low-resolution scan can be used to estimate the variation in (small-scale) cell geometry throughout a structural-size piece of wood.
Burridge HC, Sehmbi G, Fiuza Dosil D, et al., 2017, Determining the venting efficiency of simple chimneys for buoyant plumes, 38th AIVC Conference
We present preliminary results from an examination of the capture and venting of a buoyant plume by a chimney. The aim is to enable improved management of indoor pollutant sources –for instance, the plume rising from a cooking pan in a kitchen or a cooking fire in a hut. Using the principle of dynamic similarity, we precisely and controllably model the behaviour of indoor plumes by using saline solutions ejected into an enclosure containing freshwater. These well-established laboratory analogue techniques enable the location and concentration of tracer in the plume to be easily tracked, reflecting the evolution of pollutants carried in the plume. Focusing on a plume within a room containing a quiescent ambient environment, we identify two physical mechanisms potentially responsible for driving the removal of pollutants. The first, we describe as the capture of the plume, a process driven by the direct interaction between the plume and the evacuation opening; the second, we describe as the draining flow driven by a buoyant layer of fluid which may accumulate at the ceiling and is then evacuated through the effects of buoyancy. We first demonstrate that the addition of a simple cylindrical chimney that hangs downwards from an opening in the (analogue) ceiling increases the venting efficiency of these potentially polluting plumes.We go on to examine how the capture efficiency of these simple chimneys varies as the relative size of the plume and the chimney are altered, and demonstrate that simple model can provide predictionsof the observed variation in capture efficiency.
Parker D, Burridge HC, Partridge J, et al., 2017, A comparison of line-sources of buoyancy placed near and far from a wall, 38th AIVC Conference: Ventilating healthy low-energy buildings
Experiments are presented on turbulent buoyant free-line and wall plumes,whereby the buoyancy source is emitted from a horizontal line source, in one case free of the presence ofa wall and in the other placed immediately adjacent to a wall. The dynamics of turbulent entrainment, whereby ambient fluid is mixed in to theplume, are explored. The velocity field and scalar edge of the plumes are measured. From this the time-averaged plume-width and volume flux are compared. The spreading rate, and therefore the entrainment, of the wall plume is found to be half that of the free-line plume, indicating that the wall has a significant effect on the entrainment process. Further, the volume flux of the wall plume is found to be half that of the free-line plume, indicating that larger maximum scalar concentrations are present in the wall plume. The effect that the reduced entrainment rate has on a typical heated room,via a line source of buoyancy, is demonstrated by comparing a numerical model of the developing temperature stratification within a sealed enclosure in the case of the line source near a wall and away from a wall, wherein particular it isfound that higher maximum temperatures are present for the case of the line source near a wall.
Burridge HC, Parker DA, Kruger ES, et al., 2017, Conditional sampling of a high Peclet number turbulent plume and the implications for entrainment, Journal of Fluid Mechanics, Vol: 823, Pages: 26-56, ISSN: 0022-1120
We present simultaneous two-dimensional velocity and scalar measurements on a central vertical plane in an axisymmetric pure turbulent plume. We use an edge-detection algorithm to determine the edge of the plume, and compare the data obtained in both a fixed Eulerian frame and a frame relative to local coordinates defined in terms of the instantaneous plume edge. In an Eulerian frame we observe that the time-averaged distributions of vertical and horizontal velocity are self-similar, the vertical velocity being well represented by a Gaussian distribution. We condition these measurements on whether fluid is inside or outside of the plume, and whether fluid inside is mixed plume fluid or engulfed ambient fluid. We find that, on average, 5 % of the total vertical volume transport occurs outside the plume and this figure rises to nearly 14 % at heights between large-scale coherent structures. We show that the fluxes of engulfed fluid within the plume envelope are slightly larger than the vertical transport outside the plume – indicating that ambient fluid is engulfed into the plume envelope before being nibbled across the turbulent/non-turbulent interface (TNTI) and then ultimately irreversibly mixed. Our new measurements in the plume coordinate (following the meandering fluctuating plume) show the flow within the plume and in the nearby ambient fluid is strongly influenced by whether an eddy is present locally within the plume, or absent. When an eddy is present and the plume is wide, the vertical velocities near the plume edge are small and hence all vertical transport is inside the plume. In regions where the plume is narrow and there is no eddy, large vertical velocities and hence transport are observed outside the plume suggesting that pressure forces associated with the eddies accelerate ambient fluid which is then engulfed into the plume. Finally, we show that observing significant vertical velocities beyond the scalar edge of the plume does not suggest tha
Wu G, Shah DU, Janeček E-R, et al., 2017, Predicting the pore-filling ratio in lumen-impregnated wood, Wood Science and Technology, Vol: 51, Pages: 1277-1290, ISSN: 0043-7719
Lumen impregnation, unlike most other wood modification methods, is typically assessed by the pore-filling ratio (PFR) (i.e. the fraction of luminal porosity filled) rather than by weight percentage gain (WPG). During lumen impregnation, the impregnants act on the voids in the wood rather than on the solid mass (e.g. cell walls), but the PFR cannot be measured as conveniently as the WPG during processing. Here, it is demonstrated how the PFR can be calculated directly from the WPG if the bulk density of the untreated wood is known. The relationship between the WPG and bulk density was examined experimentally by applying a pressured impregnation on knot-free specimens from Sitka spruce with a liquid mixture of methacrylate monomers. Based on the validated model, it was possible to further study the effect of different process-related parameters, such as hydraulic pressure, on lumen impregnation. Skeletal density is another key parameter in this model, which directly reflects the amount of inaccessible pores and closed lumens, and can be independently determined by helium pycnometry. The permeability can be qualitatively evaluated by PFR as well as skeletal density. For instance, poor permeability of knotty wood, due to the large extractives content around knots, was reflected by a lower skeletal density and inefficient lumen impregnation (low PFR). Although this model was examined on a laboratory scale, it provides guidance on the precise effect of different parameters on lumen impregnation, thereby improving the fundamental understanding of and enabling better control over the modification of wood by impregnation.
Burridge HC, Hunt GR, 2017, From free jets to clinging wall jets: the influence of a horizontal boundary on a horizontally forced buoyant jet, Physical Review Fluids, Vol: 2, Pages: 1-20, ISSN: 2469-990X
We investigate the incompressible turbulent jet formed when buoyant fluid is steadily ejected horizontally from a circular source into an otherwise quiescent uniform environment. As our primary focus, we introduce a horizontal boundary beneath the source. For sufficiently small separations, the jet attaches and clings to the boundary, herein the “clinging jet,” before, farther downstream, the jet is pulled away from the boundary by the buoyancy force. For larger source-boundary separations, the buoyant jet is free to rise under the action of the buoyancy force, herein the “free jet.” Based on measurements of saline jets in freshwater surroundings we deduce the conditions required for a jet to cling. We present a data set that spans a broad range of source conditions for the variation in volume flux (indicative of entrainment), jet perimeter, and jet centerline for both “clinging” and “free” jets. For source Froude numbers Fr0≥12 the data collapse when scaled, displaying universal behaviors for both clinging and free jets. Our results for the variation in the volume flux across horizontal planes, πQjet, show that within a few jet lengths of the source, πQjet for the clinging jet exceeds that of a free jet with identical source conditions. However, when examined in a coordinate following the jet centerline πQjet for free jets is greater. Finally, we propose a new parametrization for an existing integral model which agrees well with our experimental data as well as with data from other studies. Our findings offer the potential to tailor the dilution of horizontal buoyant jets by altering the distance at which they are released from a boundary.
Burridge HC, Linden PF, 2016, Questioning the Mpemba effect: hot water does not cool more quickly than cold, Scientific Reports, Vol: 6, ISSN: 2045-2322
The Mpemba effect is the name given to the assertion that it is quicker to cool water to a given temperature when the initial temperature is higher. This assertion seems counter-intuitive and yet references to the effect go back at least to the writings of Aristotle. Indeed, at first thought one might consider the effect to breach fundamental thermodynamic laws, but we show that this is not the case. We go on to examine the available evidence for the Mpemba effect and carry out our own experiments by cooling water in carefully controlled conditions. We conclude, somewhat sadly, that there is no evidence to support meaningful observations of the Mpemba effect.
Ramage MH, Burridge H, Busse-Wicher M, et al., 2016, The wood from the trees: the use of timber in construction, Renewable and Sustainable Energy Reviews, Vol: 68, Pages: 333-359, ISSN: 1879-0690
Trees, and their derivative products, have been used by societies around the world for thousands of years. Contemporary construction of tall buildings from timber, in whole or in part, suggests a growing interest in the potential for building with wood at a scale not previously attainable. As wood is the only significant building material that is grown, we have a natural inclination that building in wood is good for the environment. But under what conditions is this really the case? The environmental benefits of using timber are not straightforward; although it is a natural product, a large amount of energy is used to dry and process it. Much of this can come from the biomass of the tree itself, but that requires investment in plant, which is not always possible in an industry that is widely distributed among many small producers. And what should we build with wood? Are skyscrapers in timber a good use of this natural resource, or are there other aspects of civil and structural engineering, or large-scale infrastructure, that would be a better use of wood? Here, we consider a holistic picture ranging in scale from the science of the cell wall to the engineering and global policies that could maximise forestry and timber construction as a boon to both people and the planet.
Burridge HC, Parker D, Kruger E, et al., 2016, The significance of engulfment in the process of turbulent entrainment by plumes, VIIIth Int. Symp. on Stratified Flows, Publisher: University of California
We present simultaneous two-dimensional velocity and scalar concentrations measuredon a central vertical plane in a turbulent plume. We use an edge-detection algorithm todetermine the scalar plume edge, and compare the data obtained in both a fixed Eulerianframe and relative to local plume coordinates defined in terms of the instantaneous plumeedge. We observe that the time-averaged distributions of vertical and horizontal velocityare self-similar. Measurements in the plume coordinate show that there is significantvertical flow outside the edge of the plume, contrary to the classical notion of purelyhorizontal velocities at the plume edge. We observe large variations in the plume widthand reason these to be due to the passage of large coherent eddies. The flow within theplume and in the nearby ambient fluid depends on whether an eddy is present or absent.When an eddy is present and the plume is wide, the vertical velocities near the plume edgeare small, but in regions where the plume is narrow and there is no eddy, large verticalvelocities are observed outside the plume.
Burridge HC, Partridge JL, Linden PF, 2016, The fluxes and behaviour of plumes inferred from measurements of coherent structures within images of the bulk flow, Atmosphere-Ocean, Vol: 54, Pages: 403-417, ISSN: 0705-5900
This paper describes how measurements of the movement of identifiable features at the edge of a turbulent plume can be interpreted to determine the properties of the mean flow and consequently, using plume theory, can be used to make estimates of the fluxes of volume (mass), momentum, and buoyancy in a plume. This means that video recordings of smoke rising from a chimney or buoyant material from a source on the sea bed can be used to make accurate estimates of the source conditions for the plume. At best we can estimate the volume flux and buoyancy flux to within about 5% and 15% of the actual values, respectively. Although this is restricted to the case of a plume rising in a stationary and unstratified environment, we show that the results may be of practical use in other more complex situations. In addition, we demonstrate that large-scale (turbulent) coherent structures at the plume edge form on a scale approximately 40% of the local (mean) plume half-width and travel at almost 60% of the average local (mean) velocity in the plume.
Burridge HC, Hunt GR, 2016, Entrainment by turbulent fountains, Journal of Fluid Mechanics, Vol: 790, Pages: 407-418, ISSN: 1469-7645
Experimental measurements of entrainment by turbulent fountains from circular sources in quiescent uniform environments are presented. Our results span almost four orders of magnitude in the source Froude number (0.004⩽Fr0⩽250.004⩽Fr0⩽25) and thereby encompass the entrainment across all classes of fountain behaviour identified to date. We identify scalings for the entrained volume flux QEQE, in terms of Fr0Fr0 and the source volume flux Q0Q0, within a number of distinct Froude-number bands corresponding to each class of fountain. Additionally we identify a distinct class of new behaviour, as yet unreported, for Fr0≲0.1Fr0≲0.1.
Burridge HC, Mistry A, Hunt GR, 2015, The effect of source Reynolds number on the rise height of a fountain, PHYSICS OF FLUIDS, Vol: 27, ISSN: 1070-6631
- Author Web Link
- Citations: 15
Hunt GR, Burridge HC, 2015, Fountains in Industry and Nature, ANNUAL REVIEW OF FLUID MECHANICS, VOL 47, Vol: 47, Pages: 195-220, ISSN: 0066-4189
- Author Web Link
- Citations: 54
Burridge HC, Hunt GR, 2014, Scaling arguments for the fluxes in turbulent miscible fountains, JOURNAL OF FLUID MECHANICS, Vol: 744, Pages: 273-285, ISSN: 0022-1120
- Author Web Link
- Citations: 10
Burridge HC, Hunt GR, 2013, The rhythm of fountains: the length and time scales of rise height fluctuations at low and high Froude numbers, JOURNAL OF FLUID MECHANICS, Vol: 728, Pages: 91-119, ISSN: 0022-1120
- Author Web Link
- Citations: 34
Burridge HC, Hunt GR, 2012, The rise heights of low- and high-Froude-number turbulent axisymmetric fountains, JOURNAL OF FLUID MECHANICS, Vol: 691, Pages: 392-416, ISSN: 0022-1120
- Author Web Link
- Citations: 49
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