scholarly journals Validation of conventional Lagrangian stochastic footprint models against LES driven footprint estimates

2009 ◽  
Vol 9 (1) ◽  
pp. 4195-4230
Author(s):  
T. Markkanen ◽  
G. Steinfeld ◽  
N. Kljun ◽  
S. Raasch ◽  
T. Foken
Keyword(s):  
Flow Field ◽  
Model Comparison ◽  
Flux Footprint ◽  
Footprint Model ◽  
Lagrangian Trajectory ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Field Characteristics ◽  
Conventional Models ◽  
Neutral Conditions

Abstract. In this study we compare the performance of conventional Lagrangian stochastic (LS) footprint models that use parameterised flow field characteristics with results of a Lagrangian trajectory model embedded in a large eddy simulation (LES) framework. The two conventional models follow the particles backward and forward in time while the trajectories in LES only evolve forward in time. We assess their performance in unstably and neutrally stratified boundary layers at observation levels covering the whole depth of the atmospheric boundary layer. We present a concept for footprint model comparison that can be applied for 2-D footprints and demonstrate that comparison of only cross wind integrated footprints is not sufficient for purposes facilitating two dimensional footprint information. Because the flow field description among the three models is most realistic in LES we use those results as the reference in the comparison. We found that the agreement of the two conventional models against the LES is generally better for intermediate measurement heights and for the convective case, whereas the two conventional flux footprint models agree best under near neutral conditions.

scholarly journals Comparison of conventional Lagrangian stochastic footprint models against LES driven footprint estimates

2009 ◽  
Vol 9 (15) ◽  
pp. 5575-5586 ◽  
Author(s):  
T. Markkanen ◽  
G. Steinfeld ◽  
N. Kljun ◽  
S. Raasch ◽  
T. Foken
Keyword(s):  
Flow Field ◽  
Model Comparison ◽  
Comparison Method ◽  
Flux Footprint ◽  
Footprint Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Field Characteristics ◽  
Unstable Case ◽  
Conventional Models

Abstract. In this study we introduce a comparison method for footprint model results by evaluating the performance of conventional Lagrangian stochastic (LS) footprint models that use parameterised flow field characteristics with results of a Lagrangian trajectory model embedded in a large eddy simulation (LES) framework. The two conventional models follow the particles backward and forward in time while the trajectories in LES only evolve forward in time. We assess their performance in two unstably stratified boundary layers at observation levels covering the whole depth of the atmospheric boundary layer. We present a concept for footprint model comparison that can be applied for 2-D footprints and demonstrate that comparison of only cross wind integrated footprints is not sufficient for purposes facilitating two dimensional footprint information. Because the flow field description among the three models is most realistic in LES we use those results as the reference in the comparison. We found that the agreement of the two conventional models against the LES is generally better for intermediate measurement heights and for the more unstable case, whereas the two conventional flux footprint models agree best under less unstable conditions. The model comparison in 2-D was found quite sensitive to the grid resolution.

scholarly journals Large Eddy Simulation of Self-Excited Oscillation Pulsed Jet (SEOPJ) Induced by a Helmholtz Oscillator in Underground Mining

Energies ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 2161 ◽  
Author(s):  
Zhenlong Fang ◽  
Qiang Wu ◽  
Mengda Zhang ◽  
Haoyang Liu ◽  
Pan Jiang ◽  
...  
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Coherent Structure ◽  
Underground Mining ◽  
Operating Pressure ◽  
Mean Flow ◽  
The Core ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Field Characteristics

Pulsed waterjet can break rocks effectively by taking advantage of the water hammer effect, and is thus widely used in mining, petroleum, and natural gas fields. With the aim to further clarify the flow field characteristics of pulsed jets induced by a Helmholtz oscillator, large eddy simulation was conducted under different operating pressures. The velocity distribution, mean flow field, and the coherent structure were examined using the oscillators of different cavity lengths and diameters. The results clearly showed that the major frequency of jet pulsation gradually increased with the increase of operating pressure. A stable periodic velocity core was formed at the outlet of the Helmholtz oscillator, while the external flow field was subjected to periodic impact. As a result, the ambient fluid was strongly entrained into the jet beam. With the increase of the cavity length, the length of the core segment decreased while the energy loss caused by the cavity increased, which was also accompanied by a rapid attenuation of the axial velocity at the jet outlet. The coherent structure of the jet in the oscillator with small cavity diameter was more disordered near the nozzle outlet, and the vortex scale was larger. The effect of cavity diameter can be reflected in the feedback modulation of the jet in the cavity. Compared with the conical nozzle, the length of the core section of the jet was shorter, but the jet had better bunching, a smaller diffusion angle, and better mixing performance. These results provide a further understanding of the characteristics of pulsed water jet for better utilizations in the fields of energy exploitation.

scholarly journals Large Eddy Simulation and Flow Field Analysis of Car on the Bridge under Turbulent Crosswind

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Juyue Ding ◽  
Weitan Yin ◽  
Yongqi Ma
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Wind Tunnel Test ◽  
Simulation Method ◽  
Field Analysis ◽  
Long Span Bridges ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Field Characteristics

As more long-span bridges continue to be completed and opened to traffic, the safety of cars driving across the bridge has attracted more and more attention, especially when the car is suddenly affected by the crosswind, the car is likely to have direction deviation or even a rollover accident. In this paper, the large eddy simulation method is used to study the flow field characteristics and safety of the car on the bridge under the turbulent crosswind. The numerical simulation model is established by referring to the Donghai Bridge, and the correctness of the car model is validated by combining with the data of wind tunnel test. The influence of factors such as the porosity and height of the bridge guardrail and the Reynolds number of airflow on the flow field characteristics is analyzed. The study shows that, in order to ensure the safety of cars on the bridge, the bridge guardrail porosity should be small, 35.8% is more suitable, the guardrail height should be more suitable within the range of 1.5–1.625 meters, and the Reynolds number should not be 3.51e + 5. The research results of this paper will provide reference for the optimal design of bridge guardrail.

Modeling Wind Flow and Particulate Pollutant Dispersion Around a Realistic Model of a Building Using Large-Eddy Simulation

2012 ◽  
Author(s):  
Behtash Tavakoli ◽  
Goodarz Ahmadi
Keyword(s):  
Air Pollution ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Model Comparison ◽  
Urban Air Pollution ◽  
Urban Air ◽  
Wind Flow ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Urban air pollution has been of concern due to its adverse effect on human health. A major portion of urban air pollution is attributed to vehicle emissions. Center of Excellence (CoE) Building was built in Syracuse NY at the intersection of two major highways. The building is fully instrumented for assessing outdoor and indoor air pollutions. In this study the airflow and the dispersion of particulate air pollutants emitted from the highways surrounding the CoE building were analyzed. The wind flow around the model of the CoE building was first simulated using the RANS model. Comparison of the numerical simulations with the available PIV experimental data showed that the RANS turbulence model was not able to capture all features of the flow field due to the complexity of the building’s geometry. While the pressure field on the walls of the building model matched with those measured by the pressure taps, some aspects of the airflow velocity profile were not in agreement with the PIV data. The computational modeling of the wind flow around the building was then performed using the Large-Eddy Simulation (LES) approach. The mean velocity magnitude predicted by the LES showed good agreement with the experimental PIV measurements. The simulated flow field was used to predict the dispersion of the particulate pollutant around the building and the deposition fraction of particles on the walls of the building is studied.

Large Eddy Simulation of Flow and Heat Transfer Mechanism in Matrix Cooling Channel

2017 ◽  
Author(s):  
Yigang Luan ◽  
Lianfeng Yang ◽  
Bo Wan ◽  
Tao Sun
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Gas Turbine ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism ◽  
Longitudinal Vortices ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy

Gas turbine engines have been widely used in modern industry especially in the aviation, marine and energy fields. The efficiency of gas turbines directly affects the economy and emissions. It’s acknowledged that the higher turbine inlet temperatures contribute to the overall gas turbine engine efficiency. Since the components are subject to the heat load, the internal cooling technology of turbine blades is of vital importance to ensure the safe and normal operation. This paper is focused on exploring the flow and heat transfer mechanism in matrix cooling channels. In order to analyze the internal flow field characteristics of this cooling configuration at a Reynolds number of 30000 accurately, large eddy simulation method is carried out. Methods of vortex identification and field synergy are employed to study its flow field. Cross-sectional views of velocity in three subchannels at different positions have been presented. The results show that the airflow is strongly disturbed by the bending part. It’s concluded that due to the bending structure, the airflow becomes complex and disordered. When the airflow goes from the inlet to the turning, some small-sized and discontinuous vortices are formed. Behind the bending structure, the size of the vortices becomes big and the vortices fill the subchannels. Because of the structure of latticework, the airflow is affected by each other. Airflow in one subchannel can exert a shear force on another airflow in the opposite subchannel. It’s the force whose direction is the same as the vortex that enhances the longitudinal vortices. And the longitudinal vortices contribute to the energy exchange of the internal airflow and the heat transfer between airflow and walls. Besides, a comparison of the CFD results and the experimental data is made to prove that the numerical simulation methods are reasonable and acceptable.

scholarly journals Investigation of the velocity field downstream of a benchmark vent using numerical simulation and hot-wire anemometry

2019 ◽  
Vol 213 ◽  
pp. 02076
Author(s):  
Jan Sip ◽  
Frantisek Lizal ◽  
Jakub Elcner ◽  
Jan Pokorny ◽  
Miroslav Jicha
Keyword(s):  
Fluid Dynamics ◽  
Numerical Simulation ◽  
Velocity Field ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Turbulence Models ◽  
Hot Wire ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Precise Prediction

The velocity field in the area behind the automotive vent was measured by hot-wire anenemometry in detail and intensity of turbulence was calculated. Numerical simulation of the same flow field was performed using Computational fluid dynamics in commecial software STAR-CCM+. Several turbulence models were tested and compared with Large Eddy Simulation. The influence of turbulence model on the results of air flow from the vent was investigated. The comparison of simulations and experimental results showed that most precise prediction of flow field was provided by Spalart-Allmaras model. Large eddy simulation did not provide results in quality that would compensate for the increased computing cost.

scholarly journals Large eddy simulation of turbulent channel flow using differential equation wall model

2018 ◽  
Vol 15 (2) ◽  
pp. 75-89
Author(s):  
Muhammad Saiful Islam Mallik ◽  
Md. Ashraf Uddin
Keyword(s):  
Differential Equation ◽  
Flow Field ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Wall Region ◽  
Computational Domain ◽  
Wall Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Near Wall

A large eddy simulation (LES) of a plane turbulent channel flow is performed at a Reynolds number Re? = 590 based on the channel half width, ? and wall shear velocity, u? by approximating the near wall region using differential equation wall model (DEWM). The simulation is performed in a computational domain of 2?? x 2? x ??. The computational domain is discretized by staggered grid system with 32 x 30 x 32 grid points. In this domain the governing equations of LES are discretized spatially by second order finite difference formulation, and for temporal discretization the third order low-storage Runge-Kutta method is used. Essential turbulence statistics of the computed flow field based on this LES approach are calculated and compared with the available Direct Numerical Simulation (DNS) and LES data where no wall model was used. Comparing the results throughout the calculation domain we have found that the LES results based on DEWM show closer agreement with the DNS data, especially at the near wall region. That is, the LES approach based on DEWM can capture the effects of near wall structures more accurately. Flow structures in the computed flow field in the 3D turbulent channel have also been discussed and compared with LES data using no wall model.

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