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Domenico Anfossi - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Wind Meandering in Low-Wind-Speed Conditions
Boundary-Layer Meteorology, 2016Co-Authors: Luca Mortarini, Gervasio Annes Degrazia, Michel Stefanello, Debora Roberti, Silvia Trini Castelli, Domenico AnfossiAbstract:Investigation of Low-Wind cases observed during the Urban Turbulent Project campaign (Torino, Italy) and at the Santa Maria meteorological station (Santa Maria, Brazil) provides insight into the Wind-meandering phenomenon, i.e. large, non-turbulent oscillations of horizontal Wind Speed and temperature. Meandering and non-meandering cases are identified through analysis of the Eulerian autocorrelation functions of the horizontal Wind-velocity components and temperature. When all three autocorrelation functions oscillate, meandering is present. As with weak turbulence, meandering shows no dependence on stability but is influenced by presence of buildings and depends on Wind Speed. We show that, while the standard deviation of the horizontal velocity is always large in Low-Wind conditions, the standard deviation of the vertical velocity shows very different behaviour in meandering and non-meandering conditions. In particular, the value of the ratio of the standard deviations of the vertical and horizontal velocities typifies the meandering condition.
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proposal of a new autocorrelation function in Low Wind Speed conditions
Physica A-statistical Mechanics and Its Applications, 2015Co-Authors: Lilian Moor, Gervasio Annes Degrazia, Michel Stefanello, Luca Mortarini, Otavio C Acevedo, Silvana Maldaner, Charles R P Szinvelski, Debora Regina Roberti, Lidiane Buligon, Domenico AnfossiAbstract:Abstract In this study a new mathematical expression to describe the observed meandering autocorrelation functions in Low-Wind Speed is proposed. The analysis utilizes a large number of best fit curves to show that the proposed theoretical function well reproduces the general form and the negative lobes characterizing the experimental meandering autocorrelation function. Further, the good agreement of the measured autocorrelation curves with the proposed algebraic autocorrelation function alLows to calculate the magnitudes of the meandering period and of the loop parameter. The results agree with the values presented and discussed in the literature. Therefore, the new formulation describing experimental meandering autocorrelation functions can be used to simulate the dispersion of contaminant during Low Wind episodes and to determine relevant meandering parameters.
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Assessment of dispersion parameterizations through Wind data measured by three sonic anemometers in a urban canopy
Advances in Science and Research, 2009Co-Authors: Luca Mortarini, Domenico Anfossi, Enrico Ferrero, R. Richiardone, S. Falabino, S. Trini Castelli, E. CarrettoAbstract:Abstract. One year of continuous Wind and turbulence measurements at three levels (5, 9 and 25 m) on a mast located in the suburb of the city of Turin were collected. Those recorded during April 2007 are analyzed and their main characteristics are presented and discussed. The analysis includes, at each level, mean, standard deviation, Skewness, Kurtosis for the 3-D Wind components and sonic temperature. The integral time scales for the 3-D Wind components are also computed and friction velocity and Monin-Obukhov length are determined as well. In particular, the Wind standard deviation profiles as a function of stability are compared to the literature predictions for flat undisturbed terrain. It is found that, while the vertical component agrees reasonably well, the horizontal components deviate from the prescribed values, as expected considering the buildings and other obstacles effects and the high percentage of Low-Wind conditions. Also the integral time scales, estimated by the autocorrelation functions, are compared to the literature predictions, finding significant differences, again attributed to the Low-Wind Speed occurrences.
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tracer dispersion simulation in Low Wind Speed conditions with a new 2d langevin equation system
Atmospheric Environment, 2006Co-Authors: Domenico Anfossi, Dietmar Oettl, Stefano Alessandrini, Trini S Castelli, E Ferrero, Gervasio Annes DegraziaAbstract:The simulation of atmospheric dispersion in Low Wind Speed conditions (LW) is still recognised as a challenge for modellers. Recently, a new system of two coupled Langevin equations that explicitly accounts for meandering has been proposed. It is based on the study of turbulence and dispersion properties in LW. The new system was implemented in the Lagrangian stochastic particle models LAMBDA and GRAL. In this paper we present simulations with this new approach applying it to the tracer experiments carried out in LW by Idaho National Engineering Laboratory (INEL, USA) in 1974 and by the Graz University of Technology and CNR-Torino near Graz in 2003. To assess the improvement obtained with the present model with respect to previous models not taking into account the meandering effect, the simulations for the INEL experiments were also performed with the old version of LAMBDA. The results of the comparisons clearly indicate that the new approach improves the simulation results.
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a new hypothesis on meandering atmospheric fLows in Low Wind Speed conditions
Atmospheric Environment, 2005Co-Authors: Dietmar Oettl, Gervasio Annes Degrazia, Antonio G Goulart, Domenico AnfossiAbstract:Abstract Low Wind Speeds are often associated with high pollutant concentrations in the atmosphere. Dispersion modelling in such conditions is still an important challenge for scientists due to phenomena associated with Low Wind Speeds, which are not well understood. One such phenomenon is the large horizontal oscillation of the atmosphere, which is called meandering. This study aims at providing a new hypothesis for the cause of meandering. Meandering is explained as an inherent property of atmospheric fLows in Low Wind Speed conditions, and generally no particular trigger mechanism is necessary to initiate meandering as discussed previously by several scientists (e.g. gravity waves). The hypothesis is verified by numerically and analytically solving the two-dimensional Reynolds averaged Navier–Stokes equations under the assumption of negligible Reynolds stress terms, Coriolis forces, and pressure gradients in Low Wind Speed conditions. Meandering is shown to arise when the 2-D fLow studied here is approaching or near approximate geostrophic balance, and is damped out and vanishes when the Reynolds stresses are larger. Further, the analytical solution provides an autocorrelation function for the horizontal velocity components, which was recently proposed by Anfossi et al. (Boundary Layer Meteorol. (2005), 114, 179–203) for use in Low Wind Speed conditions. In addition, a new set of Langevin equations is proposed for simulating dispersion in Low Wind Speed conditions.
Gervasio Annes Degrazia - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Wind Meandering in Low-Wind-Speed Conditions
Boundary-Layer Meteorology, 2016Co-Authors: Luca Mortarini, Gervasio Annes Degrazia, Michel Stefanello, Debora Roberti, Silvia Trini Castelli, Domenico AnfossiAbstract:Investigation of Low-Wind cases observed during the Urban Turbulent Project campaign (Torino, Italy) and at the Santa Maria meteorological station (Santa Maria, Brazil) provides insight into the Wind-meandering phenomenon, i.e. large, non-turbulent oscillations of horizontal Wind Speed and temperature. Meandering and non-meandering cases are identified through analysis of the Eulerian autocorrelation functions of the horizontal Wind-velocity components and temperature. When all three autocorrelation functions oscillate, meandering is present. As with weak turbulence, meandering shows no dependence on stability but is influenced by presence of buildings and depends on Wind Speed. We show that, while the standard deviation of the horizontal velocity is always large in Low-Wind conditions, the standard deviation of the vertical velocity shows very different behaviour in meandering and non-meandering conditions. In particular, the value of the ratio of the standard deviations of the vertical and horizontal velocities typifies the meandering condition.
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proposal of a new autocorrelation function in Low Wind Speed conditions
Physica A-statistical Mechanics and Its Applications, 2015Co-Authors: Lilian Moor, Gervasio Annes Degrazia, Michel Stefanello, Luca Mortarini, Otavio C Acevedo, Silvana Maldaner, Charles R P Szinvelski, Debora Regina Roberti, Lidiane Buligon, Domenico AnfossiAbstract:Abstract In this study a new mathematical expression to describe the observed meandering autocorrelation functions in Low-Wind Speed is proposed. The analysis utilizes a large number of best fit curves to show that the proposed theoretical function well reproduces the general form and the negative lobes characterizing the experimental meandering autocorrelation function. Further, the good agreement of the measured autocorrelation curves with the proposed algebraic autocorrelation function alLows to calculate the magnitudes of the meandering period and of the loop parameter. The results agree with the values presented and discussed in the literature. Therefore, the new formulation describing experimental meandering autocorrelation functions can be used to simulate the dispersion of contaminant during Low Wind episodes and to determine relevant meandering parameters.
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tracer dispersion simulation in Low Wind Speed conditions with a new 2d langevin equation system
Atmospheric Environment, 2006Co-Authors: Domenico Anfossi, Dietmar Oettl, Stefano Alessandrini, Trini S Castelli, E Ferrero, Gervasio Annes DegraziaAbstract:The simulation of atmospheric dispersion in Low Wind Speed conditions (LW) is still recognised as a challenge for modellers. Recently, a new system of two coupled Langevin equations that explicitly accounts for meandering has been proposed. It is based on the study of turbulence and dispersion properties in LW. The new system was implemented in the Lagrangian stochastic particle models LAMBDA and GRAL. In this paper we present simulations with this new approach applying it to the tracer experiments carried out in LW by Idaho National Engineering Laboratory (INEL, USA) in 1974 and by the Graz University of Technology and CNR-Torino near Graz in 2003. To assess the improvement obtained with the present model with respect to previous models not taking into account the meandering effect, the simulations for the INEL experiments were also performed with the old version of LAMBDA. The results of the comparisons clearly indicate that the new approach improves the simulation results.
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a new hypothesis on meandering atmospheric fLows in Low Wind Speed conditions
Atmospheric Environment, 2005Co-Authors: Dietmar Oettl, Gervasio Annes Degrazia, Antonio G Goulart, Domenico AnfossiAbstract:Abstract Low Wind Speeds are often associated with high pollutant concentrations in the atmosphere. Dispersion modelling in such conditions is still an important challenge for scientists due to phenomena associated with Low Wind Speeds, which are not well understood. One such phenomenon is the large horizontal oscillation of the atmosphere, which is called meandering. This study aims at providing a new hypothesis for the cause of meandering. Meandering is explained as an inherent property of atmospheric fLows in Low Wind Speed conditions, and generally no particular trigger mechanism is necessary to initiate meandering as discussed previously by several scientists (e.g. gravity waves). The hypothesis is verified by numerically and analytically solving the two-dimensional Reynolds averaged Navier–Stokes equations under the assumption of negligible Reynolds stress terms, Coriolis forces, and pressure gradients in Low Wind Speed conditions. Meandering is shown to arise when the 2-D fLow studied here is approaching or near approximate geostrophic balance, and is damped out and vanishes when the Reynolds stresses are larger. Further, the analytical solution provides an autocorrelation function for the horizontal velocity components, which was recently proposed by Anfossi et al. (Boundary Layer Meteorol. (2005), 114, 179–203) for use in Low Wind Speed conditions. In addition, a new set of Langevin equations is proposed for simulating dispersion in Low Wind Speed conditions.
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an analysis of sonic anemometer observations in Low Wind Speed conditions
Boundary-Layer Meteorology, 2005Co-Authors: Domenico Anfossi, Dietmar Oettl, Gervasio Annes Degrazia, Antonio G GoulartAbstract:When the Wind Speed decreases beLow a certain value (1–2 m s-1) meandering (Low frequency horizontal Wind oscillations) starts to prevail. In these conditions it becomes difficult to define a precise mean Wind direction and to estimate the airborne dispersion. To study the Wind and turbulence characteristics during meandering, two sonic anemometer datasets, containing hourly Wind observations, were analysed: the first one, lasting 1 year, was recorded in complex terrain (Graz, Austria) and the second one, lasting about 1month, was recorded in a rather flat area (Tisby, Sweden). It was found that meandering seems to exist under all meteorological conditions regardless of the stability or Wind Speed and it was confirmed that meandering sets a Lower limit for the horizontal Wind component variances. Further, it was found that the autocorrelation functions of the horizontal Wind components, computed for the Low Wind cases, show an oscillating behaviour with the presence of large negative lobes. Two different relationships from the literature, and relevant to these oscillatory aspects, were fitted to the data. They contain two parameters: one associated and relevant to the classical integral time scale and the second with meandering occurrence. Based on these relationships, expressions for the mean square displacement of particles σy2(t) were also derived.
Masoud Mirzaei - One of the best experts on this subject based on the ideXlab platform.
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applying micro scales of horizontal axis Wind turbines for operation in Low Wind Speed regions
Energy Conversion and Management, 2014Co-Authors: Abolfazl Pourrajabian, Reza Ebrahimi, Masoud MirzaeiAbstract:Abstract Utilizing the micro scales of Wind turbines could noticeably supply the demand for the electricity in Low Wind Speed regions. Aerodynamic design and optimization of the blade, as a main part of a Wind turbine, were addressed in the study. Three micro scales of horizontal axis Wind turbines with output power of 0.5, 0.75 and 1 kW were considered and the geometric optimization of the blades in terms of the two involved parameters, chord and twist, was undertaken. In order to improve the performance of the turbines at Low Wind Speeds, starting time was included in an objective function in addition to the output power – the main and desirable goal of the Wind turbine blade design. A purpose-built genetic algorithm was employed to maximize both the output power and the starting performance which were calculated by the blade-element momentum theory. The results emphasize that the larger values of the chord and twist at the root part of the blades are indispensable for the better performance when the Wind Speed is Low. However, the noticeable value of the generator resistive torque could largely delay the starting of the micro-turbines especially for the considered smaller size, 0.5 kW, where the starting aerodynamic torque could not overcome the generator resistive torque. For that size, an increase in the number of blades improved both the starting performance and also output power.
Dietmar Oettl - One of the best experts on this subject based on the ideXlab platform.
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tracer dispersion simulation in Low Wind Speed conditions with a new 2d langevin equation system
Atmospheric Environment, 2006Co-Authors: Domenico Anfossi, Dietmar Oettl, Stefano Alessandrini, Trini S Castelli, E Ferrero, Gervasio Annes DegraziaAbstract:The simulation of atmospheric dispersion in Low Wind Speed conditions (LW) is still recognised as a challenge for modellers. Recently, a new system of two coupled Langevin equations that explicitly accounts for meandering has been proposed. It is based on the study of turbulence and dispersion properties in LW. The new system was implemented in the Lagrangian stochastic particle models LAMBDA and GRAL. In this paper we present simulations with this new approach applying it to the tracer experiments carried out in LW by Idaho National Engineering Laboratory (INEL, USA) in 1974 and by the Graz University of Technology and CNR-Torino near Graz in 2003. To assess the improvement obtained with the present model with respect to previous models not taking into account the meandering effect, the simulations for the INEL experiments were also performed with the old version of LAMBDA. The results of the comparisons clearly indicate that the new approach improves the simulation results.
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a new hypothesis on meandering atmospheric fLows in Low Wind Speed conditions
Atmospheric Environment, 2005Co-Authors: Dietmar Oettl, Gervasio Annes Degrazia, Antonio G Goulart, Domenico AnfossiAbstract:Abstract Low Wind Speeds are often associated with high pollutant concentrations in the atmosphere. Dispersion modelling in such conditions is still an important challenge for scientists due to phenomena associated with Low Wind Speeds, which are not well understood. One such phenomenon is the large horizontal oscillation of the atmosphere, which is called meandering. This study aims at providing a new hypothesis for the cause of meandering. Meandering is explained as an inherent property of atmospheric fLows in Low Wind Speed conditions, and generally no particular trigger mechanism is necessary to initiate meandering as discussed previously by several scientists (e.g. gravity waves). The hypothesis is verified by numerically and analytically solving the two-dimensional Reynolds averaged Navier–Stokes equations under the assumption of negligible Reynolds stress terms, Coriolis forces, and pressure gradients in Low Wind Speed conditions. Meandering is shown to arise when the 2-D fLow studied here is approaching or near approximate geostrophic balance, and is damped out and vanishes when the Reynolds stresses are larger. Further, the analytical solution provides an autocorrelation function for the horizontal velocity components, which was recently proposed by Anfossi et al. (Boundary Layer Meteorol. (2005), 114, 179–203) for use in Low Wind Speed conditions. In addition, a new set of Langevin equations is proposed for simulating dispersion in Low Wind Speed conditions.
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an analysis of sonic anemometer observations in Low Wind Speed conditions
Boundary-Layer Meteorology, 2005Co-Authors: Domenico Anfossi, Dietmar Oettl, Gervasio Annes Degrazia, Antonio G GoulartAbstract:When the Wind Speed decreases beLow a certain value (1–2 m s-1) meandering (Low frequency horizontal Wind oscillations) starts to prevail. In these conditions it becomes difficult to define a precise mean Wind direction and to estimate the airborne dispersion. To study the Wind and turbulence characteristics during meandering, two sonic anemometer datasets, containing hourly Wind observations, were analysed: the first one, lasting 1 year, was recorded in complex terrain (Graz, Austria) and the second one, lasting about 1month, was recorded in a rather flat area (Tisby, Sweden). It was found that meandering seems to exist under all meteorological conditions regardless of the stability or Wind Speed and it was confirmed that meandering sets a Lower limit for the horizontal Wind component variances. Further, it was found that the autocorrelation functions of the horizontal Wind components, computed for the Low Wind cases, show an oscillating behaviour with the presence of large negative lobes. Two different relationships from the literature, and relevant to these oscillatory aspects, were fitted to the data. They contain two parameters: one associated and relevant to the classical integral time scale and the second with meandering occurrence. Based on these relationships, expressions for the mean square displacement of particles σy2(t) were also derived.
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evaluation of a gaussian and a lagrangian model against a roadside data set with emphasis on Low Wind Speed conditions
Atmospheric Environment, 2001Co-Authors: Dietmar Oettl, Jaakko Kukkonen, Raimund Almbauer, Peterjohann Sturm, Mia Pohjola, Jari HarkonenAbstract:The evaluation of the high percentiles of concentration distributions is required by most national air quality guidelines, as well as the EU directives. However, it is problematic to compute such high percentiles in stable, Low Wind Speed or calm conditions. This study utilizes the results of a previous measurement campaign near a major road at ElimaK ki in southern Finland in 1995, a campaign speci"cally designed for model evaluation purposes. In this study, numerical simulations were performed with a Gaussian "nite line source dispersion model CAR-FMI and a Lagrangian dispersion model GRAL, and model predictions were compared with the "eld measurements. In comparison with corresponding results presented previously in the literature, the agreement of measured and predicted data sets was good for both models considered, as measured using various statistical parameters. For instance, considering all NO data (N"587), the so-called index of agreement values varied from 0.76 to 0.87 and from 0.81 to 1.00 for the CAR-FMI and GRAL models, respectively. The CAR-FMI model tends to slightly overestimate the NO concentrations (fractional bias FB"#14%), while the GRAL model has a tendency to underestimate NO concentrations (FB"!16%). The GRAL model provides special treatment to account for enhanced horizontal dispersion in Low Wind Speed conditions; while such adjustments have not been included in the CAR-FMI model. This type of Lagrangian model therefore predicts Lower concentrations, in conditions of Low Wind Speeds and stable strati"cation, in comparison with a standard Lagrangian model. In Low Wind Speed conditions the meandering of the #ow can be quite signi"cant, leading to enhanced horizontal dispersion. We also analyzed the di!erence between the model predictions and measured data in terms of the Wind Speed and direction. The performance of the CAR-FMI model deteriorated as the Wind direction approached a direction parallel to the road, and for the Lowest Wind Speeds. However, the performance of the GRAL model varied less with Wind Speed and direction; the model simulated better the cases of Low Wind Speed and those with the Wind nearly parallel to the road. 2001 Elsevier Science Ltd. All rights reserved.
Kamel Ali Khalil - One of the best experts on this subject based on the ideXlab platform.
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Experimental and theoretical investigation of micro Wind turbine for Low Wind Speed regions
Renewable Energy, 2018Co-Authors: Salih N. Akour, Mohammed Al-heymari, Talha Ahmed, Kamel Ali KhalilAbstract:Micro Wind turbine blades for Low average Wind Speed regions like the Arabian Peninsula, Jordan Desert and United Arab Emirates are designed and implemented. Wind profiles for two locations in UAE are investigated and utilized in the design and the economic analysis. Airfoils BW3, A18 and SG6043 are selected and utilized as candidates for designing micro turbine blades. Blade element momentum theory is used to design the blade 3D geometry. A methodology to optimize the blade geometry for average Wind Speed 5 m/s based on operational Reynolds number is developed and utilized. To account for the aerodynamic behavior over the 3D blade geometry, the power coefficient for the blades of each airfoil is obtained using the simulation software QBlade. Blades developed using airfoil BW3 showed the highest performance. A prototype is built using 3D printer and tested in open air environment (natural environment) to validate the simulation results. Comparison with existing commercial Wind turbines according to cost and output power is carried out based on the concept of replacing Wind turbines swept area with the equivalent array of micro Wind turbines. The results show that the new design is more cost-effective and more Wind energy is harnessed using equivalent swept area.
