paper.bib

@article{Crimaldi2008,
   abstract = {Planar laser-induced fluorescence (PLIF) is a non-intrusive technique for measuring scalar concentrations in fluid flows. A fluorescent dye is used as a scalar proxy, and local fluorescence caused by excitation from a thin laser sheet can be related to dye concentration. This review covers quantitative PLIF in aqueous flows, with discussions of fluorescence theory, experimental methods and equipment, image processing and calibration, and applications of the technique. © 2008 Springer-Verlag.},
   author = {J. P. Crimaldi},
   doi = {10.1007/s00348-008-0496-2},
   issn = {07234864},
   issue = {6},
   journal = {Experiments in Fluids},
   month = {6},
   pages = {851-863},
   title = {Planar laser induced fluorescence in aqueous flows},
   volume = {44},
   year = {2008},
}

@article{Baj2016,
   abstract = {A new technique of planar laser-induced fluorescence calibration is presented in this work. It accounts for a nonlinear dye response at high concentrations, an illumination light attenuation and a secondary fluorescence’s influence in particular. An analytical approximation of a generic solution of the Beer–Lambert law is provided and utilized for effective concentration evaluation. These features make the technique particularly well suited for high concentration measurements, or those with a large range of concentration values, c, present (i.e. a high dynamic range of c). The method is applied to data gathered in a water flume experiment where a stream of a fluorescent dye (rhodamine 6G) was released into a grid-generated turbulent flow. Based on these results, it is shown that the illumination attenuation and the secondary fluorescence introduce a significant error into the data quantification (up to 15 and 80 %, respectively, for the case considered in this work) unless properly accounted for.},
   author = {P. Baj and P. J.K. Bruce and O. R.H. Buxton},
   doi = {10.1007/s00348-016-2190-0},
   issn = {07234864},
   issue = {6},
   journal = {Experiments in Fluids},
   pages = {1-19},
   publisher = {Springer Berlin Heidelberg},
   title = {On a PLIF quantification methodology in a nonlinear dye response regime},
   volume = {57},
   year = {2016},
}

@article{Vanderwel2014,
   abstract = {The purpose of this article was to assess the measurement uncertainty of the planar laser-induced fluorescence (PLIF) method and, as much as possible, to devise corrections for predictable biases. More specifically, we considered the measurement of concentration maps in cross sections parallel to and normal to the axis of a slender plume containing Rhodamine 6G as a passive scalar tracer and transported by a turbulent shear flow. In addition to previously examined sources of error related to PLIF, we also investigated several unexplored ones. First, we demonstrated that errors would arise if the laser sheet thickness was comparable to or larger than the thickness of the instantaneous plume. We then investigated the effect of secondary fluorescence, which was attributed to absorption and re-emission of primary fluorescence by dye both within and outside the laser sheet. We found that, if uncorrected, this effect would contaminate the calibration as well as the instantaneous concentration measurements of the plume, and proposed methods for the correction of these errors and for identifying the instantaneous boundaries of the in-sheet dye regions. © 2014 Springer-Verlag Berlin Heidelberg.},
   author = {Christina Vanderwel and Stavros Tavoularis},
   doi = {10.1007/s00348-014-1801-x},
   issn = {07234864},
   issue = {8},
   journal = {Experiments in Fluids},
   publisher = {Springer Verlag},
   title = {On the accuracy of PLIF measurements in slender plumes},
   volume = {55},
   year = {2014},
}

@article{Fellini2022,
   abstract = {Greening cities is a key solution to improve the urban microclimate and mitigate the impact of climate change. However, the effect of tree planting on pollutant dispersion in streets is still a debated topic. To shed light on this issue, we present a wind-tunnel experiment aimed at investigating the effect of trees on street canyon ventilation. An idealized urban district was simulated by an array of blocks, and two rows of model trees were arranged at the sides of a street canyon oriented perpendicularly with respect to the wind direction. Reduced scale trees were chosen to mimic a realistic shape and aerodynamic behaviour. Three different spacings between the trees were considered. A passive scalar was injected from a line source placed at ground level and concentration measurements were performed in the whole canyon. Results show that the presence of trees alters the concentration pattern in the street with a progressive shift from a nearly two-dimensional to a three-dimensional field depending on tree density. Despite the significant change of the concentration field induced by trees, the average level of pollution in the street, and thus the overall ventilation efficiency, does not show a specific trend with the density of trees.},
   author = {Sofia Fellini and Massimo Marro and Annika Vittoria Del Ponte and Marilina Barulli and Lionel Soulhac and Luca Ridolfi and Pietro Salizzoni},
   doi = {10.1016/j.buildenv.2022.109763},
   issn = {03601323},
   journal = {Building and Environment},
   keywords = {Air pollution,Street canyon ventilation,Street trees,Urban vegetation},
   month = {12},
   publisher = {Elsevier Ltd},
   title = {High resolution wind-tunnel investigation about the effect of street trees on pollutant concentration and street canyon ventilation},
   volume = {226},
   year = {2022},
}

@article{Lim2022,
   abstract = {Pollutant dispersion by a tall-building cluster within a low-rise neighbourhood of Beijing is investigated using both full-scale Large-Eddy Simulation and water flume experiments at 1:2400 model-to-full scale with Particle Image Velocimetry and Planar Laser-Induced Fluorescence. The Large-Eddy Simulation and flume results of this realistic test case agree remarkably well despite differences in the inflow conditions and scale. Tall buildings have strong influence on the local flow and the development of the rooftop shear layer which dominates vertical momentum and scalar fluxes. Additional measurements using tall-buildings-only models at both 1:2400 and 1:4800 scales indicates the rooftop shear layer is insensitive to the scale. The relatively thicker incoming boundary layer affects the Reynolds stresses, the relative size of the pollutant source affects the concentration statistics and the relative laser-sheet thickness affects the spatially averaged results of the measured flow field. Low-rise buildings around the tall building cluster cause minor but non-negligible offsets in the peak magnitude and vertical location, and have a similar influence on the velocity and concentration statistics as the scale choice. These observations are generally applicable to pollutant dispersion of realistic tall building clusters in cities. The consistency between simulations and water tunnel experiments indicates the suitability of both methodologies.},
   author = {H. D. Lim and Denise Hertwig and Tom Grylls and Hannah Gough and Maarten van Reeuwijk and Sue Grimmond and Christina Vanderwel},
   doi = {10.1007/s00348-022-03439-0},
   issn = {0723-4864},
   issue = {6},
   journal = {Experiments in Fluids},
   month = {6},
   publisher = {Springer Science and Business Media LLC},
   title = {Pollutant dispersion by tall buildings: laboratory experiments and Large-Eddy Simulation},
   volume = {63},
   year = {2022},
}

@article{Karra2017,
   abstract = {In this work we investigate the influence of real world conditions, including heterogeneity and natural variability of background wind, on the air flow and pollutant concentrations in a heterogeneous urban street canyon using both a series of field measurements and controlled laboratory experiments. Field measurements of wind velocities and Carbon Monoxide (CO) concentrations were taken under field conditions in a heterogeneous street in a city centre at several cross-sections along the length of the street (each cross-section being of different aspect ratio). The real field background wind was in fact observed to be highly variable and thus different Intensive Observation Periods (IOPs) represented by a different mean wind velocity and different wind variability were defined. Observed pollution concentrations reveal high sensitivity to local parameters: there is a bias towards the side closer to the traffic lane; higher concentrations are found in the centre of the street as compared to cross-sections closer to the junctions; higher concentrations are found at 1.5 height from the ground than at 2.5 m height, all of which are of concern regarding pedestrian exposure to traffic-related pollution. A physical model of the same street was produced for the purpose of laboratory experiments, making some geometrical simplifications of complex volumes and extrusions. The physical model was tested in an Atmospheric Boundary Layer water channel, using simultaneously Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF), for flow visualisation as well as for quantitative measurement of concentrations and flow velocities. The wind field conditions were represented by a steady mean approach velocity in the laboratory simulation (essentially representing periods of near-zero wind variability). The laboratory investigations showed a clear sensitivity of the resulting flow field to the local geometry and substantial three-dimensional flow patterns were observed throughout the modelled street. The real-field observations and the laboratory measurements were compared. Overall, we found that lower variability in the background wind does not necessarily ensure a better agreement between the airflow velocity measured in the field and in the lab. In fact, it was observed that in certain cross sections, the airflow was more affected by the particular complex architectural features such as building extrusions and balconies, which were not represented in the simplified physical model tested in the laboratory, than by the real wind field variability. For wind speed comparisons the most favourable agreement (36.6% of the compared values were within a factor of 2) was found in the case of lowest wind variability and in the section with the most simple geometry where the physical lab model was most similar to the real street. For wind direction comparisons the most favourable agreement (45.5% of the compared values was within ±45°) was found in the case with higher wind variability but in the cross-sections with more homogeneous geometrical features. Street canyons are often simplified in research and are often modelled as homogenous symmetrical canyons under steady flow, for practical purposes; our study as a whole demonstrates that natural variability and heterogeneity play a large role in how pollution disperses throughout the street, and therefore further detail in models is vital to understand real world conditions.},
   author = {Styliani Karra and Liora Malki-Epshtein and Marina K.A. Neophytou},
   doi = {10.1016/J.ATMOSENV.2017.06.035},
   issn = {1352-2310},
   journal = {Atmospheric Environment},
   keywords = {Field measurements,PIV,PLIF,Street canyon,Urban air pollution},
   month = {9},
   pages = {370-384},
   publisher = {Pergamon},
   title = {Air flow and pollution in a real, heterogeneous urban street canyon: A field and laboratory study},
   volume = {165},
   year = {2017},
}

@article{Milton-McGurk2020,
   abstract = {Turbulent negatively buoyant jets occur when the buoyancy of a jet opposes its source momentum. In these flows, the fluid will rise until it reaches a stagnation point and a return flow is established, forming a fountain (Hunt and Burridge, 2015). This study looks at both the initial negatively buoyant jet stage of this flow, before the return flow has established, and the fully developed fountain stage. Two-dimensional particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) are used to simultaneously measure the velocity and scalar concentration fields. An experimental and image processing procedure for the PLIF is introduced that accounts for pulse-to-pulse variations in laser power and beam profile for an Nd:YAG laser, which has been demonstrated to reduce the error in scalar concentration measurements. The flow is investigated experimentally using a 1m3 tank of salt-water ambient with freshwater + ethanol negatively buoyant jets, allowing for measurements to be taken at Fro=30 and Reo=5900. The entrainment coefficient for a negatively buoyant jet has been estimated as α ≅ 0.054, lower than a neutral jet at α ≅ 0.058. A finding consistent with existing literature (Bloomfield and Kerr, 2000; McDougall, 1981).},
   author = {L. Milton-McGurk and N. Williamson and S. W. Armfield and M. P. Kirkpatrick},
   doi = {10.1016/j.ijheatfluidflow.2020.108561},
   issn = {0142727X},
   journal = {International Journal of Heat and Fluid Flow},
   keywords = {Fountain,LIF,Negatively buoyant jet,PIV},
   month = {4},
   publisher = {Elsevier B.V.},
   title = {Experimental investigation into turbulent negatively buoyant jets using combined PIV and PLIF measurements},
   volume = {82},
   year = {2020},
}

@article{Djenidi2008,
   abstract = {Particle image velocimetry (PIV) measurements and planar laser induced fluorescence (PLIF) visualizations have been made in a turbulent boundary layer over a rough wall. The wall roughness consisted of square bars placed transversely to the flow at a pitch to height ratio of λ/k = 11 for the PLIF experiments and λ/k = 8 and 16 for the PIV measurements. The ratio between the boundary layer thickness and the roughness height k/δ was about 20 for the PLIF and 38 for the PIV. Both the PLIF and PIV data showed that the near-wall region of the flow was populated by unstable quasi-coherent structures which could be associated to shear layers originating at the trailing edge of the roughness elements. The streamwise mean velocity profile presented a downward shift which varied marginally between the two cases of λ/k, in agreement with previous measurements and DNS results. The data indicated that the Reynolds stresses normalized by the wall units are higher for the case λ/k = 16 than those for λ/k = 8 in the outer region of the flow, suggesting that the roughness density effects could be felt well beyond the near-wall region of the flow. As expected the roughness disturbed dramatically the sublayer which in turn altered the turbulence production mechanism. The turbulence production is maximum at a distance of about 0.5k above the roughness elements. When normalized by the wall units, the turbulence production is found to be smaller than that of a smooth wall. It is argued that the production of turbulence is correlated with the form drag. © 2007 Springer-Verlag.},
   author = {Lyazid Djenidi and Robert A. Antonia and Muriel Amielh and Fabien Anselmet},
   doi = {10.1007/s00348-007-0372-5},
   issn = {07234864},
   issue = {1},
   journal = {Experiments in Fluids},
   month = {1},
   pages = {37-47},
   title = {A turbulent boundary layer over a two-dimensional rough wall},
   volume = {44},
   year = {2008},
}

@article{Tomas2017,
   abstract = {Both large-eddy simulations (LES) and water-tunnel experiments, using simultaneous stereoscopic particle image velocimetry and laser-induced fluorescence, have been used to investigate pollutant dispersion mechanisms in regions where the surface changes from rural to urban roughness. The urban roughness was characterized by an array of rectangular obstacles in an in-line arrangement. The streamwise length scale of the roughness was kept constant, while the spanwise length scale was varied by varying the obstacle aspect ratio l / h between 1 and 8, where l is the spanwise dimension of the obstacles and h is the height of the obstacles. Additionally, the case of two-dimensional roughness (riblets) was considered in LES. A smooth-wall turbulent boundary layer of depth 10h was used as the approaching flow, and a line source of passive tracer was placed 2h upstream of the urban canopy. The experimental and numerical results show good agreement, while minor discrepancies are readily explained. It is found that for l/ h= 2 the drag induced by the urban canopy is largest of all considered cases, and is caused by a large-scale secondary flow. In addition, due to the roughness transition the vertical advective pollutant flux is the main ventilation mechanism in the first three streets. Furthermore, by means of linear stochastic estimation the mean flow structure is identified that is responsible for street-canyon ventilation for the sixth street and onwards. Moreover, it is shown that the vertical length scale of this structure increases with increasing aspect ratio of the obstacles in the canopy, while the streamwise length scale does not show a similar trend.},
   author = {J. M. Tomas and H. E. Eisma and M. J.B.M. Pourquie and G. E. Elsinga and H. J.J. Jonker and J. Westerweel},
   doi = {10.1007/s10546-016-0226-x},
   issn = {15731472},
   issue = {2},
   journal = {Boundary-Layer Meteorology},
   keywords = {Large-eddy simulation,Laser-induced fluorescence,Pollutant dispersion,Roughness transition,Stereoscopic particle image velocimetry},
   note = {Good base line for tests.},
   pages = {225-251},
   publisher = {Springer Netherlands},
   title = {Pollutant Dispersion in Boundary Layers Exposed to Rural-to-Urban Transitions: Varying the Spanwise Length Scale of the Roughness},
   volume = {163},
   year = {2017},
}