On the Impact of Trees on Ventilation in a Real Street in Pamplona, Spain

This paper is devoted to the quantification of changes in ventilation of a real neighborhood located in Pamplona, Spain, due to the presence of street trees Pollutant dispersion in this urban zone was previously studied by means of computational fluid dynamic (CFD) simulations. In the present work, that research is extended to analyze the ventilation in the whole neighborhood and in a tree-free street. Several scenarios are investigated including new trees in the tree-free street, and different leaf area density (LAD) in the whole neighborhood. Changes between the scenarios are evaluated through changes in average concentration, wind speed, flow rates and total pollutant fluxes. Additionally, wind flow patterns and the vertical profiles of flow properties (e.g., wind velocity, turbulent kinetic energy) and concentration, horizontally-averaged over one particular street, are analyzed. The approach-flow direction is almost perpendicular to the street under study (prevailing wind direction is only deviated 4º from the perpendicular direction). For these conditions, as LAD increases, average concentration in the whole neighborhood increases due to the decrease of wind speed. On the other hand, the inclusion of trees in the street produces an increase of averaged pollutant concentration only within this street, in particular for the scenario with the highest LAD value. In fact, the new trees in the street analyzed with the highest LAD value notably change the ventilation producing an increase of total pollutant fluxes inward the street. Additionally, pollutant dispersion within the street is also influenced by the reduction of the wind velocity along the street axis and the decrease of turbulent kinetic energy within the vegetation canopy caused by the new trees. Therefore, the inclusion of new trees in a tree-free street should be done by considering ventilation changes and traffic emissions should be consequently controlled in order to keep pollutant concentration within healthy levels.

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Mesoscale Influences of Wind Farms throughout a Diurnal Cycle

Monthly Weather Review ◽

10.1175/mwr-d-12-00185.1 ◽

2013 ◽

Vol 141 (7) ◽

pp. 2173-2198 ◽

Cited By ~ 71

Author(s):

Anna C. Fitch ◽

Julie K. Lundquist ◽

Joseph B. Olson

Keyword(s):

Boundary Layer ◽

Wind Speed ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Diurnal Cycle ◽

Wind Farm ◽

Wind Farms ◽

Temperature Perturbation ◽

Mean Temperature ◽

The Impact

Abstract Large wind farms are expected to influence local and regional atmospheric circulations. Using a mesoscale parameterization of the effects of wind farms that includes a momentum sink and a wind speed–dependent source of turbulent kinetic energy, simulations were carried out to quantify the impact of a wind farm on an atmospheric boundary layer throughout a diurnal cycle. The presence of a wind farm covering 10 km × 10 km is found to have a significant impact on the local atmospheric flow and on regions up to 60 km downwind at night. Daytime convective conditions show little impact of the wind farm on wind speeds, as the momentum deficits generated by the wind farm rapidly mix through the depth of the boundary layer. At night, the stable layer within the rotor area inhibits turbulent mixing of the momentum deficit, leading to a shallower wake and a greater reduction in the wind speed within the wake. Although a low-level jet forms at altitudes within the rotor area in the hours before dawn, it is completely eliminated within the wind farm. At night, a maximum warming of 1 K is seen at the bottom of the rotor area. Near the surface, there is less warming (0.5 K). Downwind, the surface temperature perturbation is small, with a cooling of up to 0.3 K. Over the simulation period, the mean temperature change over the wind farm area at 2 m is a very slight warming (0.2 K). Mean temperature changes downwind are negligible. Other influences on turbulent kinetic energy, surface heat fluxes, and boundary layer height, are discussed.

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Impact of Different Turbulence Models on Air Pollutant Flow and Distribution

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.439-440.1373 ◽

2010 ◽

Vol 439-440 ◽

pp. 1373-1378

Author(s):

Peng Wang ◽

Hai Lin Mu

Keyword(s):

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Street Canyon ◽

Calculated Data ◽

Turbulence Models ◽

Pollutant Dispersion ◽

Air Pollutant ◽

Turbulent Dissipation ◽

Boundary Velocity ◽

The Impact

The aim of this study is to provide a simulation of air pollutant in a street canyon and investigates the impact of different turbulence models on the flow structure and air pollutant dispersion. Three studied k-ε turbulence models are evaluated to determine the most optimum turbulence model and the most suitable parameters of inlet boundary velocity and turbulent kinetic energy for simulating the pollutant dispersion in the present street canyon. The calculated data of the numerical model are then validated by comparing the extensive experimental database obtained from Kastner-Klein and Plate. Compared with the measured results, it can be concluded that modified RNG model with the inlet velocity profile and turbulent kinetic energy and turbulent dissipation rate provides the best calculated results, while standard and RNG k-ε turbulence models under-predict the pollutant concentrations.

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A New Method to Determine the Impact of Individual Field Quantities on Cycle-to-Cycle Variations in a Spark-Ignited Gas Engine

Energies ◽

10.3390/en14144136 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4136

Author(s):

Clemens Gößnitzer ◽

Shawn Givler

Keyword(s):

Kinetic Energy ◽

Flow Field ◽

Turbulent Kinetic Energy ◽

Negative Impact ◽

Operating Conditions ◽

Engine Operation ◽

Gas Engine ◽

Cycle Simulation ◽

Simulation Results ◽

The Impact

Cycle-to-cycle variations (CCV) in spark-ignited (SI) engines impose performance limitations and in the extreme limit can lead to very strong, potentially damaging cycles. Thus, CCV force sub-optimal engine operating conditions. A deeper understanding of CCV is key to enabling control strategies, improving engine design and reducing the negative impact of CCV on engine operation. This paper presents a new simulation strategy which allows investigation of the impact of individual physical quantities (e.g., flow field or turbulence quantities) on CCV separately. As a first step, multi-cycle unsteady Reynolds-averaged Navier–Stokes (uRANS) computational fluid dynamics (CFD) simulations of a spark-ignited natural gas engine are performed. For each cycle, simulation results just prior to each spark timing are taken. Next, simulation results from different cycles are combined: one quantity, e.g., the flow field, is extracted from a snapshot of one given cycle, and all other quantities are taken from a snapshot from a different cycle. Such a combination yields a new snapshot. With the combined snapshot, the simulation is continued until the end of combustion. The results obtained with combined snapshots show that the velocity field seems to have the highest impact on CCV. Turbulence intensity, quantified by the turbulent kinetic energy and turbulent kinetic energy dissipation rate, has a similar value for all snapshots. Thus, their impact on CCV is small compared to the flow field. This novel methodology is very flexible and allows investigation of the sources of CCV which have been difficult to investigate in the past.

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A Simulation and Optimization Study of the Swirling Nozzle for Eccentric Flow Fields of Round Molds

Metals ◽

10.3390/met10050691 ◽

2020 ◽

Vol 10 (5) ◽

pp. 691

Author(s):

Peng Lin ◽

Yan Jin ◽

Fu Yang ◽

Ziyu Liu ◽

Rundong Jing ◽

...

Keyword(s):

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Rotation Angle ◽

Steel Slag ◽

Submerged Entry Nozzle ◽

Operating Conditions ◽

Gas Absorption ◽

Simulation And Optimization ◽

Bias Flow ◽

The Impact

In continuous casting, the nozzle position may deviate from the center under actual operating conditions, which may cause periodic fluctuation of the steel-slag interface and easily lead to slag entrapment and gas absorption. Swirling nozzles can reduce these negative effects. A mathematical simulation method based on a round mold of steel components with a 600 mm diameter is applied to study the flow field of molten steel in a mold. The swirling nozzle is optimized through the establishment of a fluid dynamics model. Meanwhile, a 1:2 hydraulic model is established for validation experiments. The results show that, when the submerged entry nozzle (SEN) is eccentric in the mold, it results in serious bias flow, increasing the drift index in the mold up to 0.46 at the eccentric distance of 50 mm. The impact depth of liquid steel and turbulent kinetic energy can be decreased by increasing the rotation angle of the nozzle. The nozzle with one bottom hole, which significantly decreases the bottom pressure and turbulent kinetic energy, greatly weakens the scour on nozzle and surface fluctuation. In the eccentric casting condition, using the optimized swirling nozzle that employs a 5-fractional structure, in which the rotation angle of 4 side holes is 30° and there is one bottom outlet, can effectively restrain bias flow and reduce the drift index to 0.28, a decline of more than 39%.

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Turbulent Kinetic Energy in Bolt Fishway

AgriEngineering ◽

10.3390/agriengineering1020020 ◽

2019 ◽

Vol 1 (2) ◽

pp. 265-282

Author(s):

Marta Puzdrowska ◽

Tomasz Heese

Keyword(s):

Spatial Distribution ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Laboratory Tests ◽

Flow Structures ◽

3D Flow ◽

Velocity Magnitude ◽

Biological Development ◽

The Impact ◽

Channel Development

The paper presents an analysis the spatial distribution of turbulent kinetic energy (TKE) for bolt fishways, including the impact of additional spillway slots and fixed channel development. The research was done for two models, each containing a different arrangement of slots. The presented results of research for bolt fishways were obtained as an effect of laboratory tests. The measurements were done for three components of instant flow velocity magnitude (speed). Analysis of the results was done for a 3D flow structure using Matlab software. In the case of bolt fishways, significant differences were noted for the method of velocity and TKE distribution, in reference to research comprising channels with biological development. It was stated that a reason for this is the flexible development of the channel. The occurrence of extreme TKE values in the chamber (pool) is strictly associated with the characteristics of interaction zones between various flow structures. It was also stated that the lower the parapet of the slot’s spillway shelf is in the fishway’s partition, the higher TKE could be expected just downstream of the section. These establishments may be important for the designing process in the case of fish passes of various types of construction.

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Effect of Tip Clearance Size on Tubular Turbine Leakage Characteristics

Processes ◽

10.3390/pr9091481 ◽

2021 ◽

Vol 9 (9) ◽

pp. 1481

Author(s):

Xinrui Li ◽

Zhenggui Li ◽

Baoshan Zhu ◽

Weijun Wang

Keyword(s):

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Flow Instability ◽

Flow Direction ◽

Flow Characteristics ◽

Tip Clearance ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage Vortex ◽

Tip Leakage

To study the effect of tip clearance on unsteady flow in a tubular turbine, a full-channel numerical calculation was carried out based on the SST k–ω turbulence model using a power-plant prototype as the research object. Tip leakage flow characteristics of three clearance δ schemes were compared. The results show that the clearance value is directly proportional to the axial velocity, momentum, and flow sum of the leakage flow but inversely proportional to turbulent kinetic energy. At approximately 35–50% of the flow direction, velocity and turbulent kinetic energy of the leakage flow show the trough and peak variation law, respectively. The leakage vortex includes a primary tip leakage vortex (PTLV) and a secondary tip leakage vortex (STLV). Increasing clearance increases the vortex strength of both parts, as the STLV vortex core overlaps Core A of PTLV, and Core B of PTLV becomes the main part of the tip leakage vortex. A “right angle effect” causes flow separation on the pressure side of the tip, and a local low-pressure area subsequently generates a separation vortex. Increasing the gap strengthens the separation vortex, intensifying the flow instability. Tip clearance should therefore be maximally reduced in tubular turbines, barring other considerations.

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A Statistical Evaluation of WRF-LES Trace Gas Dispersion Using Project Prairie Grass Measurements

Monthly Weather Review ◽

10.1175/mwr-d-20-0233.1 ◽

2021 ◽

Author(s):

Alex Rybchuk ◽

Caroline B. Alden ◽

Julie K. Lundquist ◽

Gregory B. Rieker

Keyword(s):

Kinetic Energy ◽

Natural Gas ◽

Turbulent Kinetic Energy ◽

Similarity Theory ◽

Trace Gas ◽

Near Surface ◽

Gas Dispersion ◽

Prairie Grass ◽

Strong Convection ◽

The Impact

AbstractIn recent years, new measurement systems have been deployed to monitor and quantify methane emissions from the natural gas sector. Large-eddy simulation (LES) has complemented measurement campaigns by serving as a controlled environment in which to study plume dynamics and sampling strategies. However, with few comparisons to controlled-release experiments, the accuracy of LES for modeling natural gas emissions is poorly characterized. In this paper, we evaluate LES from the Weather Research and Forecasting (WRF) model against Project Prairie Grass campaign measurements and surface layer similarity theory. Using WRF-LES, we simulate continuous emissions from 30 near-surface trace gas sources in two stability regimes: strong and weak convection. We examine the impact of grid resolutions ranging from 6.25 m to 52 m in the horizontal dimension on model results. We evaluate performance in a statistical framework, calculating fractional bias and conducting Welch’s t-tests. WRF-LES accurately simulates observed surface concentrations at 100 m and beyond under strong convection; simulated concentrations pass t-tests in this region irrespective of grid resolution. However, in weakly convective conditions with strong winds, WRF-LES substantially overpredicts concentrations – the magnitude of fractional bias often exceeds 30%, and all but one C-test fails. The good performance of WRF-LES under strong convection correlates with agreement with local free convection theory and a minimal amount of parameterized turbulent kinetic energy. The poor performance under weak convection corresponds to misalignment with Monin-Obukhov similarity theory and a significant amount of parameterized turbulent kinetic energy.

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The Microscale Obstacle Resolving Meteorological Model MITRAS: Model Theory

10.5194/gmd-2017-250 ◽

2017 ◽

Cited By ~ 1

Author(s):

Mohamed H. Salim ◽

K. Heinke Schlünzen ◽

David Grawe ◽

Marita Boettcher ◽

Andrea M. U. Gierisch ◽

...

Keyword(s):

Wind Speed ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Radiation Absorption ◽

Grid Cells ◽

Meteorological Model ◽

Production Term ◽

Wall Functions ◽

Radiative Processes ◽

Microscale Model

Abstract. This paper describes the developing theory and the underlying processes of the microscale obstacle resolving model MITRAS Version 2. MITRAS calculates wind, temperature, humidity and precipitation fields as well as transport within the obstacles layer using Reynolds averaging. It explicitly resolves obstacles, including buildings and overhanging obstacles, to consider their aerodynamic and thermodynamic effects. Buildings are represented by impermeable grid cells at the building positions so that the wind speed vanishes and zero turbulent kinetic energy is assumed in these grid cells. Wall functions are used to calculate appropriate turbulent fluxes. Most exchange processes at the obstacle surfaces are considered in MITRAS, including convective and radiative processes in order to obtain an accurate surface temperature. MITRAS is also able to simulate the effect of wind turbines. They are parameterized using the actuator-disk concept to account for the reduction in wind speed. The turbulence generation in the wake of a wind turbine is parameterized by adding an additional part to the turbulence mechanical production term in the turbulent kinetic energy equation. Effects of trees are considered explicitly, including the wind speed reduction, turbulence production, and dissipation due to drag forces from plant foliage elements as well as the radiation absorption and shading. The paper is providing not only a documentation of the model dynamics and numerical framework but also a solid foundation for future microscale model extensions.

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Analysis of Turbulent Flow Structure with Its Fluvial Processes around Mid-Channel Bar

Sustainability ◽

10.3390/su14010392 ◽

2021 ◽

Vol 14 (1) ◽

pp. 392

Author(s):

Md. Amir Khan ◽

Nayan Sharma ◽

Jaan Pu ◽

Faisal M. Alfaisal ◽

Shamshad Alam ◽

...

Keyword(s):

Kinetic Energy ◽

Turbulent Flow ◽

Flow Velocity ◽

Turbulent Kinetic Energy ◽

Production Rate ◽

Energy Transport ◽

Vertical Distance ◽

Scour Hole ◽

The Impact ◽

Channel Bar

Researchers have recognized that the successive growth of mid-channel bar deposits can be entertained as the raison d’être for the initiation of the braiding process, which is closely interlinked with the growth, decay, and vertical distribution of fluvial turbulent kinetic energy (TKE). Thus, focused analysis on the underlying mechanics of turbulent flow structures in the proximity of a bar deposit occurring in the middle of the channel can afford crucial scientific clues for insight into the initiating fluvial processes that give rise to braiding. In the study reported herein, a physical model of a mid-channel bar is constructed in an experimental flume to analyze the turbulence parameters in a region close to the bar. Notably, the flow velocity plays an important role in understanding the flow behavior in the scour-hole location in the upstream flow divergence zone as well as near the downstream zone of flow convergence in a mid-channel bar. Therefore, the fluctuating components of turbulent flow velocity are herein discussed and analyzed for the regions located close to the bar. In the present study, the impact of the mid-channel bar, as well as its growth in turbulent flow, on higher-order velocity fluctuation moments are investigated. For near-bed locations, the results show the dominance of ejection events in upstream zones and the dominance of sweep events at locations downstream of the mid-channel bar. In scour-hole sections, the negative value of the stream-wise flux of turbulent kinetic energy and the positive value of the vertical flux of turbulent kinetic energy indicate energy transport in downward and forward directions, respectively. The downward and forward energy transport processes lead to scouring at these locations. The maximum turbulent production rate occurs in the wake region of the bar. The high rate of turbulence production has occurred in that region, which can be ascribed to the process of shedding turbulent vortices. The results show that the impact of the presence of the bar is mainly restricted to the lower layers of flow. The turbulent dissipation rate monotonically decreases with an increase in the vertical distance from the bed. The turbulent production rate first increases and then decreases with successive increases in the vertical distance from the bed. The paper concludes with suggestions for the future potential use of the present research for the practical purpose of examining braid bar occurrences in alluvial rivers to develop an appropriate response through training measures.

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Windtech – A Sensory Device for ‘Cold’ Sensation Measurements

10.20944/preprints202112.0345.v1 ◽

2021 ◽

Author(s):

Amir Leyli ◽

Hassan Khawaja ◽

Ståle Antonsen ◽

Daniel Swart

Keyword(s):

Wind Speed ◽

Ambient Temperature ◽

Wind Velocity ◽

Environmental Parameters ◽

Cold Sensation ◽

Wind Chill ◽

Industrial Operations ◽

Combined Indices ◽

Industrial Standards ◽

The Impact

Abstract: Windtech device is a novel tool for measuring the sensation of the ‘cold’. Cold poses numerous challenges for industrial operations, human survival, and living convenience. The impact of the cold is not possible to be quantified just based on temperatures; however other factors such as wind speed, humidity, irradiance have to be taken into consideration. Efforts have been made to develop combined indices such as wind chill temperature (WCT), AccuWeather RealFeel®, and others. The presented article discusses these along with the industrial standards that emphasize on the quantification of the ‘cold’. The following article introduces the Windtech device and its operating principle involving ‘heated temperature’, where the ‘heated temperature’ is affected by environmental parameters including ambient temperature, humidity, wind velocity, and irradiance. The discussed Windtech device is calibrated for operation according to the ISO 11079:2007 standard.

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