Paul Hayden

Dr Paul Hayden


Research Fellow
+44 (0)1483 689545
05 AB 02

Academic and research departments

Department of Mechanical Engineering Sciences.

My publications

Publications

Castro I, Vosper S, Paisley M, Hayden P (2001) Vortex shedding behind tapered obstacles in neutral & stratified flow, DYNAMICS OF ATMOSPHERES AND OCEANS 34 (2-4) pp. 145-163 ELSEVIER SCIENCE BV
Robins AG, Hayden P (2009) Wind tunnel measurements in support of the DAPPLE project, Proc. 8th Conference on the Urban Environment, The 89th American Meteorological Society Annual Meeting
Robins AG, Fuka V, Castro IP, Xie Z-T, Hayden P (2015) LES of flow and dispersion in an array of rectangular buildings,
Xie ZT, Hayden P, Wood CR (2013) Large-eddy simulation of approaching-flow stratification on dispersion over arrays of buildings, Atmospheric Environment 71 pp. 64-74
The study investigates thermal stratification effects of approach flows on dispersion in urban environments. This is in some ways analogous to a well-developed non-neutral flow (e.g. through a large urban area) approaching a neighbourhood-scale urban region, where the effect of the local heat transfer was assumed less important. A generic urban-type geometry, i.e. a group of staggered cubes, was taken as the first test case. The DAPPLE site, which was about a one-km2 region near the intersection of Marylebone Road and Gloucester Place in central London, was taken as the second test case. Only weakly unstable conditions (i.e. bulk Richardson number Rb e - 0.2) of approach flows were considered, with adiabatic boundary conditions at the ground and building surfaces. A number of numerical experiments were performed. The modelled mean concentration for Rb = -0.1 gave the best agreement with the field data at all DAPPLE stations. This suggests that stratification effects on dispersion in weakly unstable conditions (e.g. in London) are not negligible. © 2013 Elsevier Ltd.
Coceal O, Xie Z-T, Robins A, Bohnenstengel SI, Boppana B, Hayden P, Goulart E, Carpentieri M, Thomas TG, Castro IP, Belcher SE (2015) DIPLOS: Dispersion of Localised Releases in a Street Network,
Gallacher DJ, Robins AG, Hayden P (2016) Conversion of simulated radioactive pollutant gas concentrations for a complex building array into radiation dose, Journal of Radiological Protection 36 pp. 785-818 IOP Publishing
Methods used to convert wind tunnel and ADMS concentration feld data for a
complex building array into effective radiation dose were developed based on
simulations of a site in central London. Pollutant source terms were from positron
emitting gases released from a cyclotron and clinical PET radiotracer facility.
Five years of meteorological data were analysed to determine the probability
distribution of wind direction and speed. A hemispherical plume cloud model
(both static and moving) was developed which enabled an expression of
gamma-ray dose, taking into account build-up factors in air, in terms of analytic
functions in this geometry. The standard building wake model is presented, but
this is extended and developed in a new model to cover the concentration feld
in the vicinity of a roof top structure recirculation zone, which is then related
to the concentration in the main building wake zone. For all models presented
the effective dose was determined from inhalation, positron cloud immersion
and gamma ray plume contributions. Results of applying these models for
determination of radiation dose for a particular site are presented elsewhere.
Hill R, Arnott A, Hayden P, Lawton T, Robins A, Parker T (2011) Evaluation of CFD model predictions of local dispersion from an area source on a complex industrial site, International Journal of Environment and Pollution 44 (1-4) pp. 173-181
The CFD model Fluidyn-Panache was configured to model
atmospheric transport from an area source. Modelled flow and turbulence
were evaluated by comparison with on-site meteorological measurements,
whilst atmospheric dispersion was compared with wind tunnel measurements.
The results showed that higher rates of vertical and lateral dispersion were
modelled than were determined in the wind tunnel, though modelled and
measured ground-level centreline concentration data were within a factor
of two. Uncertainties in wind tunnel and numerical modelling were highest
close to the source. Consideration of fine-scale features was only necessary for
receptors in the immediate near-field.
Robins A, Carpentieri M, Hayden P, Nathan P, Benson A (2016) MODITIC wind tunnel experiments,
Robins AG, Hayden P, Teasdale I (2000) Dispersion from elevated sources above obstacle arrays: modelling requirements, INTERNATIONAL JOURNAL OF ENVIRONMENT AND POLLUTION 14 (1-6) pp. 186-197 INDERSCIENCE ENTERPRISES LTD
Reynolds RT, Hayden P, Castro IP, Robins AG (2007) Spanwise variations in nominally two-dimensional rough-wall boundary layers, EXPERIMENTS IN FLUIDS 42 (2) pp. 311-320 SPRINGER
Hancock PE, Zhang S, Pascheke F, Hayden P (2014) Wind tunnel simulation of a wind turbine wake in neutral, stable and unstable wind flow, Journal of Physics: Conference Series 555 (1)
© Published under licence by IOP Publishing Ltd.Measurements of mean velocity, Reynolds stresses, temperature and heat flux have been made in the wake of a model wind turbine in the EnFlo meteorology wind tunnel, for three atmospheric boundary layer states: the base-line neutral case, stable and unstable. The full-to-model scale is approximately 300:1. Primary instrumentation is two-component LDA combine with cold-wire thermometry to measure heat flux. In terms of surface conditions, the stratified cases are weak, but there is a strong 'imposed' condition in the stable case. The measurements were made between 0.5D and 10D, where D is the turbine disk diameter. In the stable case the velocity deficit decreases more slowly; more quickly in the unstable case. Heights at which quantities are maximum or minimum are greater in the unstable case and smaller in the stable case. In the stable case the wake height is suppressed but the width is increased, while in the unstable case the height is increased and the width (at hub height) reaches a maximum and then decreases. The turbulence in the wake behaves in a complex way. Further work needs to be done, to cover stronger levels of surface condition, requiring more extensive measurements to properly capture the wake development.
Xie ZT, Hayden P, Voke PR, Robins AG (2004) Large-eddy simulation of dispersion: comparison between elevated and ground-level sources, JOURNAL OF TURBULENCE 5 PII S1468-5248(04)72587-X IOP PUBLISHING LTD
Contini D, Hayden P, Robins AG (2005) Wind tunnel measurements of the fluctuating concentration field during mixing of two identical plumes., Proceedings PHYSmod 2005
Robins A, Carpentieri M, Hayden P, Batten J, Benson J, Nunn A (2016) MODITIC wind tunnel experiments,
Cheng H, Hayden P, Robins AG, Castro IP (2007) Flow over cube arrays of different packing densities, JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 95 (8) pp. 715-740 ELSEVIER SCIENCE BV
Hertwig D, Fuka V, Hayden P, Carpentieri M, Goulart E, Thomas G, Castro I, Robins A, Xie Z-T, Coceal O (2016) A comparison of fast dispersion models for localised releases in a streen network,
Fuka V, Xie Z-T, Castro I, Hayden P, Carpentieri M, Robins A (2016) LES of scalar dispersion from localized sources in a regular array of buildings,
Robins AG, Hayden P (2009) Wind tunnel experiments in support of the DAPPLE project.,
Carpentieri M, Hayden P, Robins AG (2012) Wind tunnel measurements of pollutant turbulent fluxes in urban intersections, Atmospheric Environment
Carpentieri M, Hayden P, Robins A, Xie Z-T, Coceal O (2015) DIPLOS wind tunnel experiments,
Robins A, Hayden P, Carpentieri M, Nathan P, Benson J (2015) MODITIC wind tunnel experiments,
Marucci D, Hancock P, Carpentieri M, Hayden P (2016) Wind-tunnel simulation of stable atmospheric boundary layers for fundamental studies in dispersion and wind power,
Hancock PE, Hayden P, Zhang S (2013) A Wind-Tunnel Artificially-Thickened Simulated Weakly Unstable Atmospheric Boundary Layer, Boundary-Layer Meteorology pp. 1-26
A wind-tunnel simulation of an atmospheric boundary layer, artificially thickened as is often used in neutral flow wind-loading studies, has been investigated for weakly unstable stratification, including the effect of an overlying inversion. Rather than using a uniform inlet temperature profile, the inlet profile was adjusted iteratively by using measured downstream profiles. It was found that three cycles are sufficient for there to be no significant further change in profiles of temperature and other quantities. Development to nearly horizontally-homogeneous flow took a longer distance than in the neutral case because the simulated layer was deeper and therefore the length scales larger. Comparisons show first-order and second-order moments quantities are substantially larger than given by 'standard forms' in the mixed layer but are close in the surface layer. Modified functions, obtained by matching one to the other, are suggested that amount to an interpolation in the mixed layer between the strongly unstable and the weakly unstable cases. © 2013 Springer Science+Business Media Dordrecht.
Xie Z, Voke PR, Hayden P, Robins AG (2004) Les and extreme value theory - Modelling the upper tail of the PDF of concentration in turbulent dispersion, Direct and Large-Eddy Simulation V, Proceedings 9 pp. 323-332 SPRINGER
Hertwig D, Coceal O, Fuka V, Xie ZT, Thomas TG, Castro I, Carpentieri M, Hayden P, Robins A (2016) Modeling dispersion in a street network for emergency response scenarios: the DIPLOS project,
Aubrun S, Espana G, Loyer S, Hayden P, hancock P (2010) Is the actuator disc concept sufficient to model the far-wake of a wind turbine?,
Robins AG, Hayden P, Carpentieri M DIPLOS 1, University of Surrey
Contini D, Robins AG, Hayden P (2013) Statistical properties of concentration fluctuations in two merging plumes, Environmental Fluid Mechanics pp. 1-24
The statistics of the fluctuating concentration field within a plume is important in the analysis of atmospheric dispersion of toxic, inflammable and odorous gases. Previous work has tended to focus on concentration fluctuations in single plumes released in the surface layer or at ground level and there is a general lack of information about the mixing of two adjacent plumes and how the statistical properties of the concentration fluctuations are modified in these circumstances. In this work, data from wind tunnel experiments are used to analyse the variance, skewness, kurtosis, intermittency, probability density function and power spectrum of the concentration field during the mixing of two identical plumes and results are compared with those obtained for an equivalent single plume. The normalised variance, skewness and kurtosis on the centre-lines of the combined plume increase with distance downwind of the stack and, in the two-source configuration, takes lower values than those found in the single plumes. The results reflect the merging process at short range, which is least protracted for cases in which the sources are in-line or up to 30 {Mathematical expression} off-line. At angles of 45 {Mathematical expression} and more, the plumes are effectively side-by-side during the merging process and the interaction between the vortex pairs in each plume is strong. Vertical asymmetry is observed between the upper and the lower parts of the plumes, with the upper part having greater intermittency (i.e. the probability that no plume material is present) and a more pronounced tail to the concentration probability distribution. This asymmetry tends to diminish at greater distances from the source but occurs in both buoyant and neutral plumes and is believed to be associated with the 'bending-over' of the emission in the cross-flow and the vortex pair that this generates. The results allowed us to identify three phases in plume development. The first, very near the stack, is dominated by turbulence generated within the plume and characterised by concentration spectra with distinct peaks corresponding to scales comparable with those of the counter-rotating vortex pair. A second phase follows at somewhat greater distances downwind, in which there are significant contributions to the concentration fluctuations from both the turbulence internal to the plume and the external turbulence. The third phase is one in which the concentration fluctuations appear to be contr
Carpentieri M, Hayden P, Robins A (2016) Wind tunnel experiments in the DIPLOS project,
Giambini P, Robins AG, Hayden P, Corti A (2009) Modelling traffic pollutant concentration fluctuations and dosages in urban area through wind tunnel experiments,
Aubrun S, Loyer S, Hancock PE, Hayden P (2013) Wind turbine wake properties: Comparison between a non-rotating simplified wind turbine model and a rotating model, Journal of Wind Engineering and Industrial Aerodynamics 120 pp. 1-8
Experimental results on the wake properties of a non-rotating simplified wind turbine model, based on the actuator disc concept, and a rotating model, a three-blade wind turbine, are presented. Tests were performed in two different test sections, one providing a nominally decaying isotropic turbulent inflow (turbulence intensity of 4% at rotor disc location) and one providing a neutral atmospheric boundary layer above a moderately rough terrain at a geometric scale of 1:300 (determined from the combination of several indicators), with 13% of turbulence intensity at hub height. The objective is to determine the limits of the simplified wind turbine model to reproduce a realistic wind turbine wake. Pressure and high-order velocity statistics are therefore compared in the wake of both rotor discs for two different inflow conditions in order to quantify the influence of the ambient turbulence. It has been shown that wakes of rotating model and porous disc developing in the modeled atmospheric boundary layer are indistinguishable after 3 rotor diameters downstream of the rotor discs, whereas few discrepancies are still visible at the same distance with the decaying isotropic turbulent inflow. copy; 2013 Elsevier Ltd.
Carpentieri M, Hayden P, Robins AG (2012) Wind tunnel measurements of pollutant turbulent fluxes in urban intersections, Atmospheric Environment 46 pp. 669-674 Elsevier
Wind tunnel experiments have been carried out at the EnFlo laboratory to measure mean and turbulent
tracer fluxes in geometries of real street canyon intersections. The work was part of the major DAPPLE
project, focussing on the area surrounding the intersection between Marylebone Road and Gloucester
Place in Central London, UK. Understanding flow and dispersion in urban streets is a very important issue
for air quality management and planning, and turbulent mass exchange processes are important
phenomena that are very often neglected in urban modelling studies. The adopted methodology involved
the combined use of laser Doppler anemometry and tracer concentration measurements. This methodology
was applied to quantify the mean and turbulent flow and dispersion fields within several street
canyon intersections. Vertical profiles of turbulent tracer flux were also measured. The technique, despite
a number of limitations, proved reliable and allowed tracer balance calculations to be undertaken in the
selected street canyon intersections. The experience gained in this work will enable much more precise
studies in the future as issues affecting the accuracy of the experimental technique have been identified
and resolved.
Hancock PE, Zhang S, Hayden P (2013) A Wind-Tunnel Artificially-Thickened Simulated Weakly Unstable Atmospheric Boundary Layer, Boundary-Layer Meteorology 149 (3) pp. 355-380
A wind-tunnel simulation of an atmospheric boundary layer, artificially thickened as is often used in neutral flow wind-loading studies, has been investigated for weakly unstable stratification, including the effect of an overlying inversion. Rather than using a uniform inlet temperature profile, the inlet profile was adjusted iteratively by using measured downstream profiles. It was found that three cycles are sufficient for there to be no significant further change in profiles of temperature and other quantities. Development to nearly horizontally-homogeneous flow took a longer distance than in the neutral case because the simulated layer was deeper and therefore the length scales larger. Comparisons show first-order and second-order moments quantities are substantially larger than given by 'standard forms' in the mixed layer but are close in the surface layer. Modified functions, obtained by matching one to the other, are suggested that amount to an interpolation in the mixed layer between the strongly unstable and the weakly unstable cases. © 2013 Springer Science+Business Media Dordrecht.
Xie Z-T, Hayden P, Robins AG, Voke PR (2007) Modelling extreme concentrations from a source in a turbulent flow over a rough wall, ATMOSPHERIC ENVIRONMENT 41 (16) pp. 3395-3406 PERGAMON-ELSEVIER SCIENCE LTD
Robins A, Castro I, Hayden P, Steggel N, Contini D, Heist D, Taylor TJ (2001) A wind tunnel study of dense gas dispersion in a stable boundary layer over a rough surface, ATMOSPHERIC ENVIRONMENT 35 (13) pp. 2253-2263 PERGAMON-ELSEVIER SCIENCE LTD
Contini D, Hayden P, Robins A (2006) Concentration field and turbulent fluxes during the mixing of two buoyant plumes, ATMOSPHERIC ENVIRONMENT 40 (40) pp. 7842-7857 PERGAMON-ELSEVIER SCIENCE LTD
Smethurst A, Hayden P, Robins A, Carpentieri M (2013) Urban dispersion and the streen network concept,
Robins A, Castro I, Hayden P, Steggel N, Contini D, Heist D (2001) A wind tunnel study of dense gas dispersion in a neutral boundary layer over a rough surface, ATMOSPHERIC ENVIRONMENT 35 (13) pp. 2243-2252 PERGAMON-ELSEVIER SCIENCE LTD
Castro I, Xie Z, Fuka V, Robins A, Carpentieri M, Hayden P, Hertwig D, Coceal O (2017) Measurements and computations of ?ow in an urban street system, Boundary-Layer Meteorology: an international journal of physical and biological processes in the atmospheric boundary layer 162 (2) pp. 207-230 Springer-Verlag
We present results from laboratory and computational experiments on the turbulent flow over an array of rectangular blocks modelling a typical, asymmetric urban canopy at various orientations to the approach flow. The work forms part of a larger study on dispersion within such arrays (project DIPLOS) and concentrates on the nature of the mean flow and turbulence fields within the canopy region, recognis- ing that unless the flow field is adequately represented in computational models there is no reason to expect realistic simulations of the nature of the dispersion of pollutants emitted within the canopy. Comparisons between the experimental data and those ob- tained from both large-eddy simulation (LES) and direct numerical simulation (DNS) are shown and it is concluded that careful use of LES can produce generally excellent agreement with laboratory and DNS results, lending further confidence in the use of LES for such situations. Various crucial issues are discussed and advice offered to both experimentalists and those seeking to compute canopy flows with turbulence resolving models
Xie Z, Voke P, Hayden P, Robins AG (2004) Large-eddy simulation of turbulent flow over a rough surface, BOUNDARY-LAYER METEOROLOGY 111 (3) pp. 417-440 Springer Verlag
A family of wall models is proposed that exhibits more satisfactory performance than
previous models for the large-eddy simulation (LES) of the turbulent boundary layer over a rough
surface. The time and horizontally averaged statistics such as mean vertical profiles of wind velocity,
Reynolds stress, turbulent intensities, turbulent kinetic energy and also spectra are compared with
wind-tunnel experimental data. The purpose of the present study is to obtain simulated turbulent
flows that are comparable with wind-tunnel measurements for use as the wind environment for the
numerical prediction by LES of source dispersion in the neutral atmospheric boundary layer.
Contini D, Robins AG, Hayden P (2014) Statistical properties of concentration fluctuations in two merging plumes, Environmental Fluid Mechanics 14 (4) pp. 919-942 Springer International
The statistics of the fluctuating concentration field within a plume is important in the analysis of atmospheric dispersion of toxic, inflammable and odorous gases. Previous work has tended to focus on concentration fluctuations in single plumes released in the surface layer or at ground level and there is a general lack of information about the mixing of two adjacent plumes and how the statistical properties of the concentration fluctuations are modified in these circumstances. In this work, data from wind tunnel experiments are used to analyse the variance, skewness, kurtosis, intermittency, probability density function and power spectrum of the concentration field during the mixing of two identical plumes and results are compared with those obtained for an equivalent single plume. The normalised variance, skewness and kurtosis on the centre-lines of the combined plume increase with distance downwind of the stack and, in the two-source configuration, takes lower values than those found in the single plumes. The results reflect the merging process at short range, which is least protracted for cases in which the sources are in-line or up to 30° and more, the plumes are effectively side-by-side during the merging process and the interaction between the vortex pairs in each plume is strong. Vertical asymmetry is observed between the upper and the lower parts of the plumes, with the upper part having greater intermittency (i.e. the probability that no plume material is present) and a more pronounced tail to the concentration probability distribution. This asymmetry tends to diminish at greater distances from the source but occurs in both buoyant and neutral plumes and is believed to be associated with the 'bending-over' of the emission in the cross-flow and the vortex pair that this generates. The results allowed us to identify three phases in plume development. The first, very near the stack, is dominated by turbulence generated within the plume and characterised by concentration spectra with distinct peaks corresponding to scales comparable with those of the counter-rotating vortex pair. A second phase follows at somewhat greater distances downwind, in which there are significant contributions to the concentration fluctuations from both the turbulence internal to the plume and the external turbulence. The third phase is one in which the concentration fluctuations appear to be controlled by the external turbulence present in the ambient flow. © 2013 Springer
Fuka V, Xie Z-T, Castro P, Hayden Paul, Carpentieri Matteo, Robins Alan (2018) Scalar fluxes near a tall building in an aligned array of rectangular buildings, Boundary Layer Meteorology 167 (1) pp. 53-76 Springer Verlag
Scalar dispersion from ground-level sources in arrays of buildings is investigated using wind-tunnel measurements and large-eddy simulation (LES). An array of uniform-height buildings of equal dimensions and an array with an additional single tall building (wind tunnel) or a periodically repeated tall building (LES) are considered. The buildings in the array are aligned and form long streets. The sensitivity of the dispersion pattern to small changes in wind direction is demonstrated. Vertical scalar fluxes are decomposed into the advective and turbulent parts and the influences of wind direction and of the presence of the tall building on the scalar flux components are evaluated. In the uniform-height array turbulent scalar fluxes were dominant, whereas the tall building causes an increase of the magnitude of advective scalar fluxes which become the largest component. The presence of the tall building causes either an increase or a decrease to the total vertical scalar flux depending on the position of the source with respect to the tall building. The results of the simulations can be used to develop parametrizations for street canyon dispersion models and enhance their capabilities in areas with tall buildings.
Carpentieri Matteo, Robins Alan, Hayden Paul, Santi Edoardo (2018) Mean and turbulent mass flux measurements in an idealised street network, Environmental Pollution 234 pp. 356-367 Elsevier
Pollutant mass fluxes are rarely measured in the laboratory, especially their turbulent
component. They play a major role in the dispersion of gases in urban
areas and modern mathematical models often attempt some sort of parametrisation.
An experimental technique to measure mean and turbulent fluxes in an
idealised urban array was developed and applied to improve our understanding
of how the fluxes are distributed in a dense street canyon network. As expected,
horizontal advective scalar fluxes were found to be dominant compared with the
turbulent components. This is an important result because it reduces the complexity
in developing parametrisations for street network models. On the other
hand, vertical mean and turbulent fluxes appear to be approximately of the
same order of magnitude. Building height variability does not appear to affect
the exchange process significantly, while the presence of isolated taller buildings
upwind of the area of interest does. One of the most interesting results, again,
is the fact that even very simple and regular geometries lead to complex advective
patterns at intersections: parametrisations derived from measurements
in simpler geometries are unlikely to capture the full complexity of a real urban
area.
Hancock Philip, Hayden Paul (2018) Wind-Tunnel Simulation of Weakly and Moderately Stable Atmospheric Boundary Layers, Boundary-Layer Meteorology 168 (1) pp. 29-57 Springer Verlag
The simulation of horizontally homogeneous boundary layers that have characteristics of weakly and moderately stable atmospheric flow is investigated, where the well-established wind engineering practice of using ?flow generators? to provide a deep boundary layer is employed. Primary attention is given to the flow above the surface layer, in the absence of an overlying inversion, as assessed from first- and second-order moments of velocity and temperature. A uniform inlet temperature profile ahead of a deep layer, allowing initially neutral flow, results in the upper part of the boundary layer remaining neutral. A non-uniform inlet temperature profile is required but needs careful specification if odd characteristics are to be avoided, attributed to long-lasting effects inherent of stability, and to a reduced level of turbulent mixing. The first part of the wind-tunnel floor must not be cooled if turbulence quantities are to vary smoothly with height. Closely horizontally homogeneous flow is demonstrated, where profiles are comparable or closely comparable with atmospheric data in terms of local similarity and functions of normalized height. The ratio of boundary-layer height to surface Obukhov length, and the surface heat flux, are functions of the bulk Richardson number, independent of horizontal homogeneity. Surface heat flux rises to a maximum and then decreases.
Hertwig D, Soulhac L, Fuka V, Auerswald T, Carpentieri Matteo, Hayden Paul, Robins Alan, Xie Z-T, Coceal O (2018) Evaluation of fast atmospheric dispersion models in a regular
street network,
Environmental Fluid Mechanics 18 (4) pp. 1007-1044 Springer Verlag
The need to balance computational speed and simulation accuracy is a key challenge in designing atmospheric dispersion models that can be used in scenarios where near
real-time hazard predictions are needed. This challenge is aggravated in cities, where models need to have some degree of building-awareness, alongside the ability to capture effects
of dominant urban flow processes. We use a combination of high-resolution large-eddy simulation (LES) and wind-tunnel data of flow and dispersion in an idealised, equal-height
urban canopy to highlight important dispersion processes and evaluate how these are reproduced by representatives of the most prevalent modelling approaches: (i) a Gaussian plume model, (ii) a Lagrangian stochastic model and (iii) street-network dispersion models. Concentration data from the LES, validated against the wind-tunnel data, were averaged over
the volumes of streets in order to provide a high-fidelity reference suitable for evaluating
the different models on the same footing. For the particular combination of forcing wind direction and source location studied here, the strongest deviations from the LES reference
were associated with mean over-predictions of concentrations by approximately a factor of
2 and with a relative scatter larger than a factor of 4 of the mean, corresponding to cases
where the mean plume centreline also deviated significantly from the LES. This was linked
to low accuracy of the underlying flow models/parameters that resulted in a misrepresentation of pollutant channelling along streets and of the uneven plume branching observed in
intersections. The agreement of model predictions with the LES (which explicitly resolves
the turbulent flow and dispersion processes) greatly improved by increasing the accuracy
of building-induced modifications of the driving flow field. When provided with a limited
set of representative velocity parameters, the comparatively simple street-network models
performed equally well or better compared to the Lagrangian model run on full 3D wind
fields. The study showed that street-network models capture the dominant building-induced
dispersion processes in the canopy layer through parametrisations of horizontal advection
and vertical exchange processes at scales of practical interest. At the same time, computational costs and computing times associated with the network approach are ideally suited
for emergency-response applications.
Marucci Davide, Carpentieri Matteo, Hayden Paul (2018) On the simulation of thick non-neutral boundary layers
for urban studies in a wind tunnel,
International Journal of Heat and Fluid Flow 72 pp. 37-51 Elsevier
Stable and convective boundary layers over a very rough surface have been studied
in a thermally-stratified wind tunnel. Artificial thickening by means of spires
was used to accelerate the formation of a sufficiently deep boundary layer, suitable
for urban-like boundary layer flow and dispersion studies. For the stable
boundary layer, the methodology presented in Hancock and Hayden (2018) for
low-roughness offshore surface conditions has been successfully applied to cases
with higher-roughness. Different levels of stratification and roughness produced
modifications in the turbulence profiles of the lower half of the boundary layer,
but little or no change in the region above. Data for a stronger stability case
suggested that the employed spires may not be suitable to simulate such extreme
condition, though further studies are needed. The results were in reasonably
good agreement with field measurements. For the convective boundary layer,
great attention was given to the flow uniformity inside the test section. The
selection of a non-uniform inlet temperature profile was in this case found not
as determinant as for the stable boundary layer to improve the longitudinal
uniformity, while the application of a calibrated capping inversion considerably
improved the lateral uniformity. The non-dimensional vertical profiles of turbulent
quantities and heat fluxes, did not seem to be influenced by roughness.